I am not normally one to trash other chemical analysis techniques. But when people mouth untruths about FTIR it raises my dander and I feel compelled to respond. I have talked to several people lately who have said, “FTIR can’t be used to identify things in mixtures. It’s easier to shoot the sample into the GC-MS instead.” I am fully aware, and I always teach in my courses, that FTIR has difficulty with mixtures. However, as I also always teach, there are strategies for getting around the mixture analysis problem, some of which I have talked about in previous blog posts. These techniques include purifying the sample, mixture analysis software, subtraction, library searching, and the “process of elimination”. These techniques make analyzing mixtures doable, and frequently some of the components in a mixture can be identified from the infrared spectrum of a sample as a result. I have identified components in mixtures hundreds of times during my career using these tools. FTIR can be used to identify things in mixtures if the analysis if performed properly.
GC-MS stands for Gas Chromatography-Mass Spectrometry. In this technique the GC purifies mixtures into their components, and then the mass spectrometer identifies each component. Thus, it appears GC-MS does not suffer from a mixture problem like FTIR. Additionally, GC-MS is more sensitive than FTIR and does a better job of handling aqueous solutions. I have in fairness sung the praises of GC-MS.
Here is why the phrase “It’s easier to shoot the sample through the GC-MS” raises my ire. A GC-MS is always more expensive, more time consuming, and more difficult to use than an FTIR. This is why so many more labs have an FTIR than a GC-MS. Also, GC-MS does suffer from a mixture problem. The retention time of a peak in a gas chromatograph is not unique to that molecule. Molecules with different chemical structures can, by coincidence, elute at the same time. Thus, there is always the possibility that what we think is a pure component coming off a GC column may in fact contain two or more components. The other dirty little secret about a mass spectrum is that it does not provide a completely unique fingerprint of a molecule. Mass spectrometry does not distinguish between structural isomers. These are molecules that have the same chemical formula but different chemical structures. For example, a mass spectrometer normally can’t distinguish ortho-, meta-, and para- xylene from each other. These three molecules are easy to distinguish by FTIR. Infrared spectroscopy can distinguish between structural isomers, and provides a unique fingerprint for a given molecule. A mixture of structural isomers would be difficult to distinguish by MS. It could thus be argued that you can’t identify things in mixtures by GC-MS either.
There is really is no victor in the FTIR/GC-MS smackdown except hopefully the truth. Both techniques have their strengths and weaknesses, and you need to have an understanding of both of these to pick the right technique for the right sample. Since FTIR is faster, simpler, and cheaper than GC-MS I believe it should the first choice for analyzing unknown mixtures.
Tuesday, November 24, 2009
Tuesday, November 10, 2009
A Certification Program for FTIR Users
FTIRs have been used for decades to perform chemical analyses including in such critical applications as the analysis of drugs, criminal evidence, and in homeland defense. The user of an FTIR must prepare the sample appropriately, choose the correct scanning parameters, and interpret the data correctly to achieve a successful analysis. In short, a properly trained human being is key to achieving accurate FTIR results. However, there are no formal proficiency guidelines or certification programs that insure the competency of FTIR users and hence the quality of FTIR results…until now.
Starting in 2010 my company, Spectros Associates, will be offering a Certified FTIR User(CFU) program. To earn the CFU certificate FTIR users will be required to take a 5 day sequence of FTIR training courses consisting of my Fundamentals of FTIR, Hands-On FTIR Sample Preparation, and Infrared Spectral Interpretation I, II and III courses. Then, you must pass a written exam consisting of multiple choice questions and several unknown spectra that must be interpreted. Only upon completing the coursework and successfully passing the exam will the CFU certificate be awarded.
The advantage of this program to FTIR users is that it will be your proof to the world that you know how to do your job well. The knowledge you obtain in earning the CFU will make your FTIR analyses faster, better, and cheaper. This will make you more valuable to your employer and enhance your career. The certificate can be held up at review time as an accomplishment, perhaps to be rewarded with a higher salary. Your certification can be put on your resume as proof to potential employers that you possess an important skill set, and might make you more employable than those who are not certified. The CFU can also be used towards the continuing education requirement that some professional societies require of their members.
There are also advantages to employers of the CFU program. By certifying their workers they can rest assured they are getting the best FTIR analyses possible. If regulatory bodies ever question the quality of spectra, employers can point out that the data were measured by certified workers following best practices. Finally, employers hiring FTIR workers can rest assured that job applicants who have earned the CFU possess the skills needed to do the job well.
Please let me know what you think of thie Certified FTIR User idea by leaving a post below or e-mailing me at bcsmith@spectros1.com .
Starting in 2010 my company, Spectros Associates, will be offering a Certified FTIR User(CFU) program. To earn the CFU certificate FTIR users will be required to take a 5 day sequence of FTIR training courses consisting of my Fundamentals of FTIR, Hands-On FTIR Sample Preparation, and Infrared Spectral Interpretation I, II and III courses. Then, you must pass a written exam consisting of multiple choice questions and several unknown spectra that must be interpreted. Only upon completing the coursework and successfully passing the exam will the CFU certificate be awarded.
The advantage of this program to FTIR users is that it will be your proof to the world that you know how to do your job well. The knowledge you obtain in earning the CFU will make your FTIR analyses faster, better, and cheaper. This will make you more valuable to your employer and enhance your career. The certificate can be held up at review time as an accomplishment, perhaps to be rewarded with a higher salary. Your certification can be put on your resume as proof to potential employers that you possess an important skill set, and might make you more employable than those who are not certified. The CFU can also be used towards the continuing education requirement that some professional societies require of their members.
There are also advantages to employers of the CFU program. By certifying their workers they can rest assured they are getting the best FTIR analyses possible. If regulatory bodies ever question the quality of spectra, employers can point out that the data were measured by certified workers following best practices. Finally, employers hiring FTIR workers can rest assured that job applicants who have earned the CFU possess the skills needed to do the job well.
Please let me know what you think of thie Certified FTIR User idea by leaving a post below or e-mailing me at bcsmith@spectros1.com .
Thursday, October 22, 2009
Infrared Spectroscopy in Outer Space!
Last month NASA announced the presence of a thin layer of water and hydroxyl ions on the surface of the moon. Not one, not two, but three different satellites recorded data to support this conclusion. And guess what technology the three satellites used to detect the water? Infrared Spectroscopy of course! As many of you know from looking at the spectra of liquid water or water vapor, this molecule absorbs strongly around 3500 cm-1, or since astronomers like to use wavelength, around 3 microns. The first evidence that there was water on the moon came from the analysis of the moon rocks brought back by the Apollo missions back in the 1970s (it was watching these missions as a kid that inspired me to become a scientist). Water was found in the rocks, but it was assumed that they had been contaminated with terrestrial moisture.
In 1999 NASA’s Cassini satellite flew past the moon on its way to Saturn and detected water as well. However, at the time the data were thought to be erroneous and were not published until this year. More recently, the Moon Mineralogy Mapper aboard the Indian Space Agencies’ Chandrayaan-1 spacecraft found evidence for water on the moon. In June of this year NASA’s Epoxi spacecraft, flying past the moon on its way to a comet encounter in 2010, also detected water on the moon. For all three of these spacecraft the spectrum of the moon was measured in infrared reflectance. A dispersive grating spectrometer was used rather than an FTIR, perhaps because FTIRs have moving parts and are hard to fix billions of miles from home. The spectra are measured in single beam mode since there is not an identical twin moon available devoid of water to provide a background spectrum. However, the spectra from equatorial regions, where it is known to be drier, can be subtracted from the spectra of polar regions to hopefully remove any contribution from the moon’s surface other than OH and water. Examples of the types of spectra measured are seen above.
Now, it’s not time to pack your swim trunks and head to the moon for a dip. The water and hydroxyl are estimated to be present in concentrations of about 1000 ppm. You would have to wring dry a ton of lunar soil to obtain a quart of lunar water. The water is thought to form when energetic protons in the solar wind collide with oxygen bearing minerals on the moon’s surface. More details at these NASA websites.
(cut and paste these URLs into your browser...blogger won't let me post links!).
http://science.nasa.gov/headlines/y2009/24sep_moonwater.htm
http://www.nasa.gov/topics/moonmars/features/moonm3-images.html
Wednesday, September 30, 2009
Abrasive Sampling: Spectra of Intractable Samples
There is a sampling technique used on powders and solids called Diffuse Reflectance Infrared Fourier Transform Spectroscopy, or DRIFTS for short. I think some graduate student spent several months thinking up that acronym. At any rate, the technique involves using a special sampling accessory that fits into your FTIR sample compartment to bounce the light off the sample. The light is then collected and sent to the IR detector (more on DRIFTS in a later blog post). Abrasive sampling is an interesting application of DRIFTS. Some FTIR accessory manufacturers make flat metal posts that fit into their DRIFTS accessories and SiC disks with an adhesive backing. The SiC disk is adhered to the metal post, and then the disk is rubbed against the sample to abrade off sample particles. The SiC disk with particles is then placed at the focal point of a DRIFTS accessory, the light is reflected off of the sample particles, and is collected and sent to the detector to obtain the sample spectrum. The background spectrum is run on a clean SiC disk.
The attached spectrum is of the white paint on a light fixture obtained by abrasive sampling using an Alpha spectrometer from Bruker Optics (http://www.brukeroptics.com/). This spectrum would have been difficult to obtain any other way. The light fixture was firmly attached to the ceiling and so could not be taken down. In theory, one could scrape a lot of the paint off and make a KBr pellet or cast a film of the paint. However, this would damage the light fixture, involve time consuming trial and error, and may still not work. With abrasive sampling, only a small hidden part of the light fixture was scratched, and the entire measurement process took about 2 minutes. Abrasive sampling is useful for spectra of large, intractable objects such as furniture, large pieces of plastic, or anything that is simply too big to be analyzed by normal FTIR sampling techniques. The beauty of abrasive sampling is that it is fast and easy. However, the SiC scatters the IR beam a lot, so abrasive sampling spectra can be noisy. This can sometimes be dealt with by increasing the number of scans, perhaps to as many as 256.
A note on the SiC disks. I have seen labs try to save a little money by going to the hardware store, buying SiC paper, and then using a cork borer to punch out SiC disks of the proper size. As long as these disks fit into the sample cup that came with your DRIFTS accessory this should at least in theory allow you to obtain abrasive sampling spectra.
Use your imagination…what type of applications might abrasive sampling have at your company?
The attached spectrum is of the white paint on a light fixture obtained by abrasive sampling using an Alpha spectrometer from Bruker Optics (http://www.brukeroptics.com/). This spectrum would have been difficult to obtain any other way. The light fixture was firmly attached to the ceiling and so could not be taken down. In theory, one could scrape a lot of the paint off and make a KBr pellet or cast a film of the paint. However, this would damage the light fixture, involve time consuming trial and error, and may still not work. With abrasive sampling, only a small hidden part of the light fixture was scratched, and the entire measurement process took about 2 minutes. Abrasive sampling is useful for spectra of large, intractable objects such as furniture, large pieces of plastic, or anything that is simply too big to be analyzed by normal FTIR sampling techniques. The beauty of abrasive sampling is that it is fast and easy. However, the SiC scatters the IR beam a lot, so abrasive sampling spectra can be noisy. This can sometimes be dealt with by increasing the number of scans, perhaps to as many as 256.
A note on the SiC disks. I have seen labs try to save a little money by going to the hardware store, buying SiC paper, and then using a cork borer to punch out SiC disks of the proper size. As long as these disks fit into the sample cup that came with your DRIFTS accessory this should at least in theory allow you to obtain abrasive sampling spectra.
Use your imagination…what type of applications might abrasive sampling have at your company?
Wednesday, September 9, 2009
ATR V: Depth Profiling Redux
This is the fifth in my intermittent installment series on Attenuated Total Reflectance (ATR), the sampling technique of choice for many FTIR samples. The second post in the series introduced an equation that determines the depth of penetration (DP) in the ATR experiment, a measure of how far the infrared beam penetrates into the sample. The most recent post in this series discussed how changing the refractive index of the ATR crystal can change the DP and allow spectra to be taken at different depths in samples non-destructively, which is called “Depth Profiling”. This blog post is subtitled “Depth Profiling Redux” because altering the angle of incidence of the infrared beam to the sample, called theta, can also alter DP. Examination of the DP equation shows that theta is in the denominator, so as theta goes up DP goes down. If we had some means of varying theta we could take spectra at different depths in a sample non-destructively i.e. perform depth profiling.
Fortunately, varying theta is not difficult. By adjusting the position of the mirror(s) involved in focusing the IR beam onto the ATR crystal, the angle of incidence of the beam at the sample can be adjusted. There exist ATR accessories where changing theta is simply a matter of moving one or more mirrors. The variable angle ATR accessory I use, the VeeMax from PIKE Technologies (details here: http://www.piketech.com/products/atr.html) allows theta to be adjusted by simply moving a knob up or down. This allows you to easily fine tune theta and hence easily fine tune the DP of your spectrum. This is, I feel, superior to adjusting the refractive index to change DP because in this case only certain fixed DPs are available to us depending upon the refractive indices of the ATR crystals mother nature provides us.
The attached figure shows the spectrum of a sample of polyethylene taken using 9 different angles of incidence varying between 42 and 70 degrees. Note how the peaks stack on top of each other; the absorbances are different sizes for the same sample because the DP for each spectrum is different. Adjusting theta to perform depth profiling will be useful for any sample where you would like to know how composition changes with depth. For example, this technique can be used on polymer laminates that consist of layers of different polymers. For example, a low DP scan can measure the spectrum of first layer. A high DP scan can measure the spectrum of the first and second layers. Subtracting this top layer spectrum from this spectrum will yield the spectrum of layer two non-destructively.
Fortunately, varying theta is not difficult. By adjusting the position of the mirror(s) involved in focusing the IR beam onto the ATR crystal, the angle of incidence of the beam at the sample can be adjusted. There exist ATR accessories where changing theta is simply a matter of moving one or more mirrors. The variable angle ATR accessory I use, the VeeMax from PIKE Technologies (details here: http://www.piketech.com/products/atr.html) allows theta to be adjusted by simply moving a knob up or down. This allows you to easily fine tune theta and hence easily fine tune the DP of your spectrum. This is, I feel, superior to adjusting the refractive index to change DP because in this case only certain fixed DPs are available to us depending upon the refractive indices of the ATR crystals mother nature provides us.
The attached figure shows the spectrum of a sample of polyethylene taken using 9 different angles of incidence varying between 42 and 70 degrees. Note how the peaks stack on top of each other; the absorbances are different sizes for the same sample because the DP for each spectrum is different. Adjusting theta to perform depth profiling will be useful for any sample where you would like to know how composition changes with depth. For example, this technique can be used on polymer laminates that consist of layers of different polymers. For example, a low DP scan can measure the spectrum of first layer. A high DP scan can measure the spectrum of the first and second layers. Subtracting this top layer spectrum from this spectrum will yield the spectrum of layer two non-destructively.
Thursday, August 27, 2009
Fall 2009 Training Course Offerings
The purpose of this blog is to offer my readers advice on how to improve their chemical analyses. One of the best ways to improve your analyses is to take a training course. The purpose of this blog post is to alert you to upcoming training courses I will be teaching that you can take this year. These are mostly FTIR courses, along with some offerings of my Principles of Analytical Chemistry and Principles of Organic Chemistry courses.
There are a number of training course delivery options available to you here, including public and online training courses. Please see previous blog posts for the relative advantages and disadvantages of these course delivery options. For more info about Spectros Associates FTIR courses go here: http://www.spectros1.com/2009 .
Public FTIR Training Course Series Sponsored by Spectros Associates
Sept. 21-25 2009, Minneapolis MN
This is my 5-day series of FTIR courses. You can register for as many days as you wish. For more info or to register click here: http://www.spectros1.com/2009 .
Fundamentals of FTIR Sept. 21
Hands-On FTIR Sample Preparation Sept. 22
Infrared Spectral Interpretation I Sept. 23
Infrared Spectral Interpretation II Sept. 24
Infrared Spectral Interpretation III Sept. 25
Oct. 5-9, 2009, Cleveland OH
This is my 5-day series of FTIR courses. You can register for as many days as you wish. For more info or to register click here: http://www.spectros1.com/2009 .
Fundamentals of FTIR Oct. 5
Hands-On FTIR Sample Preparation Oct. 6
Infrared Spectral Interpretation I Oct. 7
Infrared Spectral Interpretation II Oct. 8
Infrared Spectral Interpretation III Oct. 9
FTIR Courses I Will be Teaching at Scientific Meetings
Federation of Analytical Chemistry and Spectroscopy Societies (FACSS) Meeting, Louisville KY. Oct. 19-20
I will be teaching IR Spectral interpretation I&II as a single two-day course. Details here: https://facss.org/contentmgr/showdetails.php/id/1450 .
Eastern Analytical Symposium (EAS) Meeting, Nov. 18-19, Somerset NJ.
I will be teaching IR Spectral Interpretation I on Nov. 18 and IR Spectral Interpretation II on Nov. 19. You can take each course by itself or take the pair. More info here: http://www.eas.org/education/ .
Online Courses I teach Sponsored by the American Chemical Society
For more info on these courses click here:
http://www.proed.acs.org/online_courses/online_courses.cfm .
Fourier Transform Infrared Spectroscopy: Three 2.5 hour online sessions, Sept. 14, 16, &18, 11:00 AM to 1:30 PM EDT. This is similar to the Fundamentals of FTIR course I teach.
Infrared Spectral Interpretation Basic: two 3.5 hour online sessions, Sept. 29 & 30, Noon to 3:30 PM EDT. This is similar to the Infrared Spectral Interpretation I course I teach.
Infrared Spectral Interpretation Intermediate: two 3.5 hour online sessions, Oct. 27 & 28, Noon to 3:30 PM EDT. This is similar to the Infrared Spectral Interpretation II course I teach.
Principles of Analytical Chemistry: three 2.5 hour online sessions. Sept. 28, Oct. 1 &2, Noon to 2:30 PM EDT.
Principles of Analytical Chemistry II: Three 2.5 hour online sessions, Nov.30, Dec. 2 &4. 11:00 AM to 1:30 PM EDT.
Public Principles of Chemistry Course Offerings
I teach these exclusively through the Center for Professional Innovation & Education: www.cfpie.com.
Principles of Organic Chemistry: Malvern PA, Nov. 10-11, 2009. More info here: http://www.cfpie.com/showitem.aspx?productid=108 .
Principles of Analytical Chemistry: Malvern PA, Nov. 12-13, 2009. More info here: http://www.cfpie.com/showitem.aspx?productid=107 .
I hope to see you at one or more of these courses soon!
There are a number of training course delivery options available to you here, including public and online training courses. Please see previous blog posts for the relative advantages and disadvantages of these course delivery options. For more info about Spectros Associates FTIR courses go here: http://www.spectros1.com/2009 .
Public FTIR Training Course Series Sponsored by Spectros Associates
Sept. 21-25 2009, Minneapolis MN
This is my 5-day series of FTIR courses. You can register for as many days as you wish. For more info or to register click here: http://www.spectros1.com/2009 .
Fundamentals of FTIR Sept. 21
Hands-On FTIR Sample Preparation Sept. 22
Infrared Spectral Interpretation I Sept. 23
Infrared Spectral Interpretation II Sept. 24
Infrared Spectral Interpretation III Sept. 25
Oct. 5-9, 2009, Cleveland OH
This is my 5-day series of FTIR courses. You can register for as many days as you wish. For more info or to register click here: http://www.spectros1.com/2009 .
Fundamentals of FTIR Oct. 5
Hands-On FTIR Sample Preparation Oct. 6
Infrared Spectral Interpretation I Oct. 7
Infrared Spectral Interpretation II Oct. 8
Infrared Spectral Interpretation III Oct. 9
FTIR Courses I Will be Teaching at Scientific Meetings
Federation of Analytical Chemistry and Spectroscopy Societies (FACSS) Meeting, Louisville KY. Oct. 19-20
I will be teaching IR Spectral interpretation I&II as a single two-day course. Details here: https://facss.org/contentmgr/showdetails.php/id/1450 .
Eastern Analytical Symposium (EAS) Meeting, Nov. 18-19, Somerset NJ.
I will be teaching IR Spectral Interpretation I on Nov. 18 and IR Spectral Interpretation II on Nov. 19. You can take each course by itself or take the pair. More info here: http://www.eas.org/education/ .
Online Courses I teach Sponsored by the American Chemical Society
For more info on these courses click here:
http://www.proed.acs.org/online_courses/online_courses.cfm .
Fourier Transform Infrared Spectroscopy: Three 2.5 hour online sessions, Sept. 14, 16, &18, 11:00 AM to 1:30 PM EDT. This is similar to the Fundamentals of FTIR course I teach.
Infrared Spectral Interpretation Basic: two 3.5 hour online sessions, Sept. 29 & 30, Noon to 3:30 PM EDT. This is similar to the Infrared Spectral Interpretation I course I teach.
Infrared Spectral Interpretation Intermediate: two 3.5 hour online sessions, Oct. 27 & 28, Noon to 3:30 PM EDT. This is similar to the Infrared Spectral Interpretation II course I teach.
Principles of Analytical Chemistry: three 2.5 hour online sessions. Sept. 28, Oct. 1 &2, Noon to 2:30 PM EDT.
Principles of Analytical Chemistry II: Three 2.5 hour online sessions, Nov.30, Dec. 2 &4. 11:00 AM to 1:30 PM EDT.
Public Principles of Chemistry Course Offerings
I teach these exclusively through the Center for Professional Innovation & Education: www.cfpie.com.
Principles of Organic Chemistry: Malvern PA, Nov. 10-11, 2009. More info here: http://www.cfpie.com/showitem.aspx?productid=108 .
Principles of Analytical Chemistry: Malvern PA, Nov. 12-13, 2009. More info here: http://www.cfpie.com/showitem.aspx?productid=107 .
I hope to see you at one or more of these courses soon!
Wednesday, August 12, 2009
R.I.P. Norm Colthup (1924-2009)
It might seem odd for me to be posting an obituary in a blog about infrared spectroscopy, but the passing of Norm Colthup is worth noting by anyone who has ever measured or interpreted an infrared spectrum. Norm spent most of his career working for American Cyanamid, now known as Cytec Industries. In the 1940s Norm was involved in designing and building one of the first infrared spectrometers used in industry. Subsequent to this he measured a number of spectra and saw a need for summarizing the peak positions of functional groups. He then invented the now well known Colthup Chart, which summarizes the wavenumber regions where different functional groups absorb in an easy-to-read format. It is safe to say that thousands of people around the world have used the Colthup chart since Norm developed it over 50 years ago.
Norm also co-authored two seminal books on infrared spectroscopy. I have learned a great deal from his books. Norm was the 1979 recipient of the Williams-Wright Award of the Coblentz Society, presented annually to an industrial spectroscopist who has made significant contributions to vibrational spectroscopy while working in industry (I am the current chair of Coblentz Society’s Williams-Wright committee. More on the 2010 winner in a later post). Norm also received the Maurice F. Hasler Award, presented by the Spectroscopy Society of Pittsburgh to a scientist having notable achievements in spectroscopy that have resulted in significant applications of broad utility. Norm also shared his knowledge and love of infrared spectroscopy by teaching short courses, which in part was an inspiration for my career as an FTIR short course instructor. Norm will be sorely missed by a large community of colleagues, family, and friends
Norm also co-authored two seminal books on infrared spectroscopy. I have learned a great deal from his books. Norm was the 1979 recipient of the Williams-Wright Award of the Coblentz Society, presented annually to an industrial spectroscopist who has made significant contributions to vibrational spectroscopy while working in industry (I am the current chair of Coblentz Society’s Williams-Wright committee. More on the 2010 winner in a later post). Norm also received the Maurice F. Hasler Award, presented by the Spectroscopy Society of Pittsburgh to a scientist having notable achievements in spectroscopy that have resulted in significant applications of broad utility. Norm also shared his knowledge and love of infrared spectroscopy by teaching short courses, which in part was an inspiration for my career as an FTIR short course instructor. Norm will be sorely missed by a large community of colleagues, family, and friends
Wednesday, July 29, 2009
ATR IV: Depth Profiling and Analyzing Filled Polymers
It is finally time to resume our ongoing discussion of the Attenuated Total Reflectance (ATR) sample preparation technique. Recall from my earlier posts that the depth of penetration (DP) in an ATR experiment is a measure of how far the infrared beam penetrates into a sample. The equation that allows us to calculate the DP has a number of variables in it, each of which will be the subject of a separate blog post. The subject of this post will be the refractive index of the ATR crystal, nc. This parameter appears in the denominator of the DP equation, so as nc goes up depth of penetration goes down.
There are a number of materials that can be used as ATR crystals that have different refractive indices. For example, diamond has an nc of 2.4 while germanium (Ge) has an nc of 4.0. Depths of penetration from less than 1 micron to up to 10 microns are possible depending upon the crystal used. This means that if these two crystals are used to measure spectra of the same sample, spectra from different depths in the sample are obtained without having to take the sample apart. This ability of ATR is called “depth profiling”. Many ATR accessories allow the ATR crystal to be changed easily, making taking spectra of the same sample with different crystals straightforward. Now to be clear, the spectra are taken from the outside in; spectra of “slices” or layers internal to the sample by themselves are not obtained. For example, to analyze different layers in a polymer laminate non-destructively, spectra at a shallow DP using a germanium crystal and at a greater DP using a diamond crystal are obtained. The Ge spectrum is then subtracted from the diamond spectrum to reveal the spectrum below the surface of the sample. The depth profiling ability of ATR can be used on any sample where you need to know how composition changes with depth.
An excellent example of how the change of DP with nc can be put to good use is the analysis of filled polymers. A filled polymer consists of an organic resin, such as a rubber, and a filler such as carbon black, silica, or limestone. One of the purposes of the filler is to add bulk to the material and reduce cost; fillers are cheaper than resins. When FTIR spectra are obtained of filled polymers it is generally the spectrum of the resin that is desired. The problem is that many types of filler, particularly carbon black, have broad, intense absorbances that can mask the spectrum of the resin. This is illustrated in the bottom spectrum, which is the spectrum of an O-ring filled with carbon black. Note the strong absorbances, sloping baseline and distorted peak shapes caused by the presence of the carbon black. It is very difficult to identify the resin from such a low quality spectrum.
The top spectrum shows the spectrum of the same O-ring obtained using a Ge ATR crystal. Note that although the spectrum is not perfect the absorbances have been reduced, there is less baseline slope, and the peak shapes are no longer distorted. This spectrum is interpretable, and gives reasonable library matches when searched. The Ge ATR crystal, having a higher refractive index than diamond, has a lower DP. In the diamond spectrum the DP is great enough that the carbon black contributes significantly to the spectrum. With Ge the carbon black contribution is reduced and the spectrum of the resin is easier to see. These results indicate that Ge ATR is the method of choice for obtaining FTIR spectra of filled polymers. This is also a neat illustration of how the dependence of DP on nc allows a normally difficult sample to yield a usable spectrum.
Wednesday, July 22, 2009
Training Delivery Options Part III: Public Training Courses
My definition of a public training course is one that is open to anyone who can pay the admission fee and features good old fashioned in-person training. This type of training is offered by private companies such as Spectros Associates, by professional groups such as the American Chemical Society, and at scientific meetings such as the Pittsburgh Conference. These courses are frequently held in hotel meeting rooms or at conference centers. No doubt many of you have taken this type of training before.
One of the advantages of public training courses is the ability to interact with the instructor fostering the transfer of information from lecturer to attendee. Another advantage of public courses is it allows attendees to receive hands-on training. A nice thing about public courses is that it gets people away from the distractions of their offices and the need to “put out fires”; allowing attendees to focus more fully on learning. A unique advantage of public training courses is the opportunity to interact with people from different companies. It has been my experience after teaching hundreds of these courses that attendees not only learn from me, but from each other as well. Public courses also give people the opportunity to socialize and make new friends.
The disadvantages of public courses revolve around money and convenience. Since these courses are held at a central location attendees typically have to travel to them to attend. This involves travel time and costs and means one’s work and personal lives are put on hold to attend the training. Cost wise public training courses are the most expensive on a per-head basis since there are travel costs in addition to the cost to attend the seminar.
It’s time to pull together the three blog posts on training delivery options. Public training courses make the most sense if there are one or a few people who need training. For groups of 4 or more onsite training is more cost efficient with the advantage the training is in-person and can be customized. Online training works well for groups scattered at different locations, for people who cannot travel for some reason, or at companies looking to slash their travel budgets.
Spectros Associates offers FTIR training courses via all three of these delivery methods. For more info click here: www.spectros1.com .
One of the advantages of public training courses is the ability to interact with the instructor fostering the transfer of information from lecturer to attendee. Another advantage of public courses is it allows attendees to receive hands-on training. A nice thing about public courses is that it gets people away from the distractions of their offices and the need to “put out fires”; allowing attendees to focus more fully on learning. A unique advantage of public training courses is the opportunity to interact with people from different companies. It has been my experience after teaching hundreds of these courses that attendees not only learn from me, but from each other as well. Public courses also give people the opportunity to socialize and make new friends.
The disadvantages of public courses revolve around money and convenience. Since these courses are held at a central location attendees typically have to travel to them to attend. This involves travel time and costs and means one’s work and personal lives are put on hold to attend the training. Cost wise public training courses are the most expensive on a per-head basis since there are travel costs in addition to the cost to attend the seminar.
It’s time to pull together the three blog posts on training delivery options. Public training courses make the most sense if there are one or a few people who need training. For groups of 4 or more onsite training is more cost efficient with the advantage the training is in-person and can be customized. Online training works well for groups scattered at different locations, for people who cannot travel for some reason, or at companies looking to slash their travel budgets.
Spectros Associates offers FTIR training courses via all three of these delivery methods. For more info click here: www.spectros1.com .
Tuesday, July 14, 2009
Training Course Delivery Options II: Online Training
Online training is a relatively new development in the training world. You may here it called a webinar, internet training, remote training etc. In general, attendees log into a website where the instructor shows PowerPoint slides and talks in real time. All you need is high speed internet access and a phone line to participate. The presenter and trainees speak to teach other using either a traditional telephone line or the internet. Depending on the platform the instructor can annotate and illustrate the slides, engage in chat sessions with students, and show other websites or applications to attendees. A web camera can be used to allow attendees to see each other, and allow the presenter to engage in “show and tell”. Students can chat with the instructor, each other, ask questions by “raising their hand” and so on. Online training courses are typically held in sessions of a few hours or less. It is not practical to do all day sessions like traditional training because it is uncomfortable for people to sit for many hours in front of their computers.
There are number of advantages of online training over traditional training methods, which is why it is an increasingly popular training delivery option. Online training is cheaper than in-person training because it eliminates travel costs. There is no need to transport the trainer to the class or the class to the trainer. Another advantage of online training is that it saves on travel time. The hours that would normally be spent travelling to a seminar can now be spent productively at work. Online training is also convenient, allowing people to participate in a training course from the comfort of their own office. Also, If you have employees scattered at multiple locations it is much easier and cheaper to gather them together in a virtual meeting room for a course rather than gathering them in an actual meeting room. Lastly, by spreading shorter sessions over multiple days, attendees have more opportunity to review what they have learned and do homework, much like a college lecture course.
However, online training has its drawbacks. My great frustration as an instructor of online training courses is the lack of human interaction. No matter how hard I try it seems people are less likely to ask questions and participate in discussions online than they are in person. With in-person training I can tell by an audience’s facial expressions and posture whether I am effectively lecturing or not. This type of feedback is not available with online training making it more difficult for me to customize the course to people’s needs. The lack of human interaction also prevents attendees from talking to me outside of class about specific questions and problems they have, which means a learning opportunity is missed. Another thing attendees miss with online training is interaction with classmates. My experience is that attendees at my training courses learn from me and from each other. So, with online training opportunities to learn from the instructor and classmates are limited compared to in-person training. It is possible then that attendees will learn less in an online setting than they would in person.
Ultimately, because of the cost advantages of online training I believe it will become increasingly popular compared to in-person training.
There are number of advantages of online training over traditional training methods, which is why it is an increasingly popular training delivery option. Online training is cheaper than in-person training because it eliminates travel costs. There is no need to transport the trainer to the class or the class to the trainer. Another advantage of online training is that it saves on travel time. The hours that would normally be spent travelling to a seminar can now be spent productively at work. Online training is also convenient, allowing people to participate in a training course from the comfort of their own office. Also, If you have employees scattered at multiple locations it is much easier and cheaper to gather them together in a virtual meeting room for a course rather than gathering them in an actual meeting room. Lastly, by spreading shorter sessions over multiple days, attendees have more opportunity to review what they have learned and do homework, much like a college lecture course.
However, online training has its drawbacks. My great frustration as an instructor of online training courses is the lack of human interaction. No matter how hard I try it seems people are less likely to ask questions and participate in discussions online than they are in person. With in-person training I can tell by an audience’s facial expressions and posture whether I am effectively lecturing or not. This type of feedback is not available with online training making it more difficult for me to customize the course to people’s needs. The lack of human interaction also prevents attendees from talking to me outside of class about specific questions and problems they have, which means a learning opportunity is missed. Another thing attendees miss with online training is interaction with classmates. My experience is that attendees at my training courses learn from me and from each other. So, with online training opportunities to learn from the instructor and classmates are limited compared to in-person training. It is possible then that attendees will learn less in an online setting than they would in person.
Ultimately, because of the cost advantages of online training I believe it will become increasingly popular compared to in-person training.
Tuesday, July 7, 2009
Training Course Delivery Options I: Onsite Training
As you have probably figured out by now, I teach FTIR training courses for a living. There are a number of ways training courses can be delivered including public courses, onsite training, and online over the internet. This post will be the first in a series discussing training course delivery options, and their relative advantages and disadvantages.
Onsite training refers to training held at a company site. It is “we will come to you” training. Typically, the company provides the training room, facilities, and gathers people from around the company in that room. Sometimes these people all work at the same physical location, other times I have seen a company fly people in from several locations to attend a class at a given site. Then, all the trainer has to do is show up with a PowerPoint presentation, training materials, and impart wisdom to the assembled group.
I feel the most important advantage of onsite training is it gives the instructor the chance to customize the course for you. A good trainer will tailor the content and length of an onsite course to match your experience level, instrumentation, applications, and budget. If the trainer you have hired does not offer course customization or refuses to do it, hire yourself another trainer. It is the customization aspect of onsite training that many companies cite as the main reason they hold such courses in the first place because it gives them the most relevant information per dollar than any other training course delivery option. Another of the beauties of onsite training is convenience; you and your co-workers don’t have to travel anywhere, except perhaps down the hall to your department’s meeting room.
The other advantages of onsite training come from having the instructor “captive” at your facility. This means hands-on training, live demonstrations, and one-on-one consultations are possible. Many people learn better by seeing and doing rather than sitting and listening, which is why hands-on training is such a good idea. Speaking for myself, since I am being paid to be at a company and provide advice, I am happy to answer questions at onsite courses outside of class, particularly over a beer or dinner (hint hint).
The way I and some other trainers charge for onsite training is as a flat rate per day plus a small charge per head for training materials. Travel costs are normally paid for by the client as well. The beauty of this pricing scheme is that it minimizes the cost per head of training. The price for teaching 5 people is almost the same as it is for 15 people. Thus, onsite training is ideal when there is a group of people at a given company that need training. In my experience if there are 5 or more people in a company that need training it is cheaper for the trainer to come them rather than vice versa.
Now, to be fair there are some disadvantages to onsite training. First, I find if attendees have access to their office, phones, and e-mail during the course the frequently get distracted, or worse yet are pulled out of the course to “fight fires”. This is wasteful of company money. It costs thousands of dollars to bring a trainer in for a course, and companies should maximize the transfer of information from the trainer to their employees by making sure each attendee is present for the entire course. To pull people away on other business is short sighted. What leaves me shaking my head is that too frequently the manager who approved the money for the training is the one pulling people out of class to deal with perceived emergencies. To combat this problem, some companies hold “onsite” training at an off-site facility such as a hotel. Without the distractions of work people will learn more, spend more time in class and will be more comfortable. The final disadvantage of onsite training is that it is not cost effective for small groups. If you have only two or three people that need training, training delivery options other than onsite courses should be explored.
In summary then, onsite training is a cost effective way of obtaining customized training for a group of people at a given company. For more on Spectros Associates’ onsite training courses click here: http://www.spectros1.com/course_custom.html .
Onsite training refers to training held at a company site. It is “we will come to you” training. Typically, the company provides the training room, facilities, and gathers people from around the company in that room. Sometimes these people all work at the same physical location, other times I have seen a company fly people in from several locations to attend a class at a given site. Then, all the trainer has to do is show up with a PowerPoint presentation, training materials, and impart wisdom to the assembled group.
I feel the most important advantage of onsite training is it gives the instructor the chance to customize the course for you. A good trainer will tailor the content and length of an onsite course to match your experience level, instrumentation, applications, and budget. If the trainer you have hired does not offer course customization or refuses to do it, hire yourself another trainer. It is the customization aspect of onsite training that many companies cite as the main reason they hold such courses in the first place because it gives them the most relevant information per dollar than any other training course delivery option. Another of the beauties of onsite training is convenience; you and your co-workers don’t have to travel anywhere, except perhaps down the hall to your department’s meeting room.
The other advantages of onsite training come from having the instructor “captive” at your facility. This means hands-on training, live demonstrations, and one-on-one consultations are possible. Many people learn better by seeing and doing rather than sitting and listening, which is why hands-on training is such a good idea. Speaking for myself, since I am being paid to be at a company and provide advice, I am happy to answer questions at onsite courses outside of class, particularly over a beer or dinner (hint hint).
The way I and some other trainers charge for onsite training is as a flat rate per day plus a small charge per head for training materials. Travel costs are normally paid for by the client as well. The beauty of this pricing scheme is that it minimizes the cost per head of training. The price for teaching 5 people is almost the same as it is for 15 people. Thus, onsite training is ideal when there is a group of people at a given company that need training. In my experience if there are 5 or more people in a company that need training it is cheaper for the trainer to come them rather than vice versa.
Now, to be fair there are some disadvantages to onsite training. First, I find if attendees have access to their office, phones, and e-mail during the course the frequently get distracted, or worse yet are pulled out of the course to “fight fires”. This is wasteful of company money. It costs thousands of dollars to bring a trainer in for a course, and companies should maximize the transfer of information from the trainer to their employees by making sure each attendee is present for the entire course. To pull people away on other business is short sighted. What leaves me shaking my head is that too frequently the manager who approved the money for the training is the one pulling people out of class to deal with perceived emergencies. To combat this problem, some companies hold “onsite” training at an off-site facility such as a hotel. Without the distractions of work people will learn more, spend more time in class and will be more comfortable. The final disadvantage of onsite training is that it is not cost effective for small groups. If you have only two or three people that need training, training delivery options other than onsite courses should be explored.
In summary then, onsite training is a cost effective way of obtaining customized training for a group of people at a given company. For more on Spectros Associates’ onsite training courses click here: http://www.spectros1.com/course_custom.html .
Wednesday, June 24, 2009
Training is Back!
Training is back in budgets, at least that’s how it looks from my perspective. In my 17 years in business I have seen training budgets ebb and flow in sync with the economy. Spectros Associates training business has returned to pre-recession levels, and this may mean an overall economic upswing is in progress. I actually have more than one acquaintance, including my stock broker, who uses the level of my business as an economic indicator.
Training is often one of the first budget items cut during hard economic times. In reality, the time right after a recession has bottomed out is an excellent time to invest in training. With the turnover in the labor market in the last 12 months it is common at many companies for people to “inherit” the responsibility for running an FTIR. In fact, of the thousands of people I have trained over the last 17 years this is the most common story as to why they need training. These people frequently have little or no experience with FTIR and so cannot possibly do their jobs efficiently. A company can’t realize the efficiencies gained by reducing head count if the people left behind don’t know how to do the jobs of those let go. This is why training is so important now. Only by investing in the employees they still have will companies realize any increase in profit from this year’s job cutting.
Training also makes sense when money is tight because it saves money. For example, after hosting one of my onsite courses a lab learned how to change their FTIR sampling procedures and saved hundreds of hours of analysis time per month. Training can pay for itself in improved worker performance and fewer mistakes made. Remember, if putting out fires is a problem in your lab, training is your fire extinguisher!
Lastly, investing in training now will give you a leg up on your competitors. By being the first to spend money on training during this economic cycle you will realize the increase in analysis quality and efficiencies before your competitors do, who are probably waiting for a full economic recovery before unfreezing their training budgets. Your bottom will recover faster than your competitors as a result.
Spectros Associates FTIR courses can be delivered in public sessions (schedule here: http://www.spectros1.com/schedule.html), over the internet, or at as customized courses at your facility. Go to our website for more information on your training options: www.spectros1.com .
Training is often one of the first budget items cut during hard economic times. In reality, the time right after a recession has bottomed out is an excellent time to invest in training. With the turnover in the labor market in the last 12 months it is common at many companies for people to “inherit” the responsibility for running an FTIR. In fact, of the thousands of people I have trained over the last 17 years this is the most common story as to why they need training. These people frequently have little or no experience with FTIR and so cannot possibly do their jobs efficiently. A company can’t realize the efficiencies gained by reducing head count if the people left behind don’t know how to do the jobs of those let go. This is why training is so important now. Only by investing in the employees they still have will companies realize any increase in profit from this year’s job cutting.
Training also makes sense when money is tight because it saves money. For example, after hosting one of my onsite courses a lab learned how to change their FTIR sampling procedures and saved hundreds of hours of analysis time per month. Training can pay for itself in improved worker performance and fewer mistakes made. Remember, if putting out fires is a problem in your lab, training is your fire extinguisher!
Lastly, investing in training now will give you a leg up on your competitors. By being the first to spend money on training during this economic cycle you will realize the increase in analysis quality and efficiencies before your competitors do, who are probably waiting for a full economic recovery before unfreezing their training budgets. Your bottom will recover faster than your competitors as a result.
Spectros Associates FTIR courses can be delivered in public sessions (schedule here: http://www.spectros1.com/schedule.html), over the internet, or at as customized courses at your facility. Go to our website for more information on your training options: www.spectros1.com .
Monday, June 15, 2009
Mixture Analysis: The Importance of Reference Spectra
Mixture Analysis: The Importance of Reference Spectra
I’ve been struggling the last few weeks analyzing complex mixture samples sent to me by clients (performing FTIR sample analyses is part of my business…call for details). My challenges with these samples have me musing yet again on mixture analysis. As I teach in my Fundamentals of FTIR course, perhaps the biggest practical disadvantage of FTIR is mixtures. The problem is that the more molecules there are in a sample the more difficult it becomes to figure out what peaks are due to what molecules. FTIR is frequently sold as a great technique for identifying molecules in samples. It is-if the sample is pure or relatively simple in composition. However, my recent struggles with complex mixture spectra have shown me yet again the limitations of FTIR as a mixture analysis technique. My infrared spectral interpretation skills by themselves have not been enough to make any firm conclusions about the composition of these samples. I have found reference spectra to an invaluable aid in handling this type of problem.
By comparing the spectrum of your unknown mixture to spectra of known molecules you think are present, it is sometimes possible to identify the presence of molecules in a mixture. However, one needs to be careful. When comparing sample and reference spectra you can only conclude with 100% certainty if a molecule is present in a sample if all its peaks are present in the reference and the sample. Unfortunately, overlapping peaks and signal to noise problems can prevent you from clearly seeing all the peaks for a given molecule in a mixture spectrum. In these cases you have to find as many matching peaks as you can and use your judgment as to what to conclude. Frequently, phrases such as “suggest the presence of”, “are consistent with”, or “infer” should be used in these circumstances.
Serious consideration needs to be given to the reference spectrum to use. As I teach in my Infrared Spectral Interpretation course, when comparing sample and reference spectra it is a requirement that they be measured at the same resolution and important they be measured on the same instrument using the same sample preparation technique. You also need to consider the chemical matrix of the sample and reference. If, for example, the unknown is a solution of things dissolved in water it would be best to compare it to a water solution of the molecules suspected of being in the unknown. An appropriate reference spectrum gives you additional information along with your own interpretation of the spectrum when tackling mixture spectra.
I’ve been struggling the last few weeks analyzing complex mixture samples sent to me by clients (performing FTIR sample analyses is part of my business…call for details). My challenges with these samples have me musing yet again on mixture analysis. As I teach in my Fundamentals of FTIR course, perhaps the biggest practical disadvantage of FTIR is mixtures. The problem is that the more molecules there are in a sample the more difficult it becomes to figure out what peaks are due to what molecules. FTIR is frequently sold as a great technique for identifying molecules in samples. It is-if the sample is pure or relatively simple in composition. However, my recent struggles with complex mixture spectra have shown me yet again the limitations of FTIR as a mixture analysis technique. My infrared spectral interpretation skills by themselves have not been enough to make any firm conclusions about the composition of these samples. I have found reference spectra to an invaluable aid in handling this type of problem.
By comparing the spectrum of your unknown mixture to spectra of known molecules you think are present, it is sometimes possible to identify the presence of molecules in a mixture. However, one needs to be careful. When comparing sample and reference spectra you can only conclude with 100% certainty if a molecule is present in a sample if all its peaks are present in the reference and the sample. Unfortunately, overlapping peaks and signal to noise problems can prevent you from clearly seeing all the peaks for a given molecule in a mixture spectrum. In these cases you have to find as many matching peaks as you can and use your judgment as to what to conclude. Frequently, phrases such as “suggest the presence of”, “are consistent with”, or “infer” should be used in these circumstances.
Serious consideration needs to be given to the reference spectrum to use. As I teach in my Infrared Spectral Interpretation course, when comparing sample and reference spectra it is a requirement that they be measured at the same resolution and important they be measured on the same instrument using the same sample preparation technique. You also need to consider the chemical matrix of the sample and reference. If, for example, the unknown is a solution of things dissolved in water it would be best to compare it to a water solution of the molecules suspected of being in the unknown. An appropriate reference spectrum gives you additional information along with your own interpretation of the spectrum when tackling mixture spectra.
Tuesday, June 2, 2009
The Little FTIR That Could
The Little FTIR That Could
I seem to have an obsession with pint-size FTIRs lately given my recent blog posts about handheld FTIRs. The folks at Bruker Optics (Billerica MA) were recently kind enough to loan me one of their Alpha FTIRs. It has by far the smallest footprint of any laboratory FTIR I have ever seen. According to the Bruker website the instrument’s footprint is about 8” by 11”; smaller than a lab notebook, and it is only 5” tall. The instrument contains a small version of Bruker’s “RockSolid™” interferometer. This design has two gold coated cube corner mirrors that straddle the beamsplitter and are attached to a single rocker arm. A flex pivot causes the arm to tilt alternately to the left and right to generate an optical path difference. My version of the instrument has an air cooled silicon carbide source and DTGS detector.
My understanding is that part of the reason they were able to make this FTIR so small is by getting rid of the He-Ne laser that has been such an important part of FTIRs for decades. This laser and its power supply, as you may know if you have ever looked inside of an FTIR, takes up a good bit of space. Instead, the Bruker Alpha has a small diode laser that gives off light at 11734 cm-1. This may seem sacrilegious to some spectroscopists, but remember we only need to know the wavenumber of the laser we use to measure the optical path difference of the interferometer. It does not matter all that much what wavenumber that laser gives off.
I am teaching my series of 5 public FTIR courses in the Philadelphia area this week (it’s not too late to attend, details here: http://www.spectros1.com/schedule.html ). When I teach these courses I always bring an FTIR with me, which is particularly important for the hands-on sample prep. course where students learn to prepare and run their own samples. My previous instrument was a “full sized” FTIR which worked fine but was cumbersome to move around and ship. It weighed over 40 lbs. and got damaged so frequently during shipping that I had a special padded case designed and built for it. The shipping costs for this were getting out of control, and had me wondering if there was not a smaller, lighter instrument I could find that would be easier and cheaper to ship.
The Bruker Alpha FTIR has solved this problem for me. The way I got it to Philadelphia was by wrapping it in bubble wrap, putting it in my suitcase, and bringing it with me. When I got to my destination I unwrapped the bubble wrap, plugged it in, and it is working fine. It did an excellent job today measuring spectra of a variety of samples in the FTIR sample prep. course. So my shipping costs are reduced from hundreds of dollars per seminar series to zero! For more information on the Alpha, click here: http://www.brukeroptics.com/alpha.html .
I seem to have an obsession with pint-size FTIRs lately given my recent blog posts about handheld FTIRs. The folks at Bruker Optics (Billerica MA) were recently kind enough to loan me one of their Alpha FTIRs. It has by far the smallest footprint of any laboratory FTIR I have ever seen. According to the Bruker website the instrument’s footprint is about 8” by 11”; smaller than a lab notebook, and it is only 5” tall. The instrument contains a small version of Bruker’s “RockSolid™” interferometer. This design has two gold coated cube corner mirrors that straddle the beamsplitter and are attached to a single rocker arm. A flex pivot causes the arm to tilt alternately to the left and right to generate an optical path difference. My version of the instrument has an air cooled silicon carbide source and DTGS detector.
My understanding is that part of the reason they were able to make this FTIR so small is by getting rid of the He-Ne laser that has been such an important part of FTIRs for decades. This laser and its power supply, as you may know if you have ever looked inside of an FTIR, takes up a good bit of space. Instead, the Bruker Alpha has a small diode laser that gives off light at 11734 cm-1. This may seem sacrilegious to some spectroscopists, but remember we only need to know the wavenumber of the laser we use to measure the optical path difference of the interferometer. It does not matter all that much what wavenumber that laser gives off.
I am teaching my series of 5 public FTIR courses in the Philadelphia area this week (it’s not too late to attend, details here: http://www.spectros1.com/schedule.html ). When I teach these courses I always bring an FTIR with me, which is particularly important for the hands-on sample prep. course where students learn to prepare and run their own samples. My previous instrument was a “full sized” FTIR which worked fine but was cumbersome to move around and ship. It weighed over 40 lbs. and got damaged so frequently during shipping that I had a special padded case designed and built for it. The shipping costs for this were getting out of control, and had me wondering if there was not a smaller, lighter instrument I could find that would be easier and cheaper to ship.
The Bruker Alpha FTIR has solved this problem for me. The way I got it to Philadelphia was by wrapping it in bubble wrap, putting it in my suitcase, and bringing it with me. When I got to my destination I unwrapped the bubble wrap, plugged it in, and it is working fine. It did an excellent job today measuring spectra of a variety of samples in the FTIR sample prep. course. So my shipping costs are reduced from hundreds of dollars per seminar series to zero! For more information on the Alpha, click here: http://www.brukeroptics.com/alpha.html .
Monday, May 11, 2009
Hand Held FTIRs Part II
Hand Held FTIRs Part II
Way back in March as part of my post-Pittcon blogging I wrote a piece about one of the hand held FTIRs I saw at the meeting, the TruDefender FT from Ahura Scientific (see March 29 post). At that time I promised a follow-up article on the second brand of hand held FTIR I saw at the show. Here it is as promised.
The second company I found that makes a portable hand held FTIR is A2 Technologies of Danbury CT. Their product is called the ExoscanTM. The Exoscan is 6.75" x 4.68" x 8.81" and weighs 7 pounds. This spectrometer scans from 4000 to 650 cm-1, and the Exoscan website states that it uses a ZnSe beamsplitter. The machine is capable of 4 cm-1 resolution. It has a diamond ATR sampling head and two different external reflection sampling heads, one capable of what they call "grazing angle specular reflectance". The manufacturer claims a battery life of greater than 8 hours using re-chargeable lithium ion batteries.
The website and literature on the Exoscan emphasize its use in measuring spectra of surfaces, such as contamination on metal and damage to carbon fiber composite parts used in aircraft. I found the staff at their Pittcon booth knowledgeable and helpful, and they sent me home with an armload of applications literature. According to their literature the Exoscan has software that allows it to be calibrated so it can perform quantitative analyses.
I would imagine the Exoscan is small enough and rugged enough to be used in the same applications as the TruDefender FT, that is hazardous materials identification and homeland security. But in what I consider a strange business decision, A2 Technologies has handed over the sales, marketing, and support functions for this application to Smith's Detection. This is such a potentially lucrative market that I would think the company would want it all to itself.
An interesting aspect of the Exoscan is that you can buy a "docking station" for it which turns it into lab instrument. In this case, it would work like a lab FTIR with a diamond ATR or specular reflectance accessory in it. What's neat about this option is that it gives users the flexibility to develop methods, perform routine lab analyses, and engage in field work with the same instrument. For more information on the Exoscan go here:
http://www.a2technologies.com/exoscan_home_page.html .
Way back in March as part of my post-Pittcon blogging I wrote a piece about one of the hand held FTIRs I saw at the meeting, the TruDefender FT from Ahura Scientific (see March 29 post). At that time I promised a follow-up article on the second brand of hand held FTIR I saw at the show. Here it is as promised.
The second company I found that makes a portable hand held FTIR is A2 Technologies of Danbury CT. Their product is called the ExoscanTM. The Exoscan is 6.75" x 4.68" x 8.81" and weighs 7 pounds. This spectrometer scans from 4000 to 650 cm-1, and the Exoscan website states that it uses a ZnSe beamsplitter. The machine is capable of 4 cm-1 resolution. It has a diamond ATR sampling head and two different external reflection sampling heads, one capable of what they call "grazing angle specular reflectance". The manufacturer claims a battery life of greater than 8 hours using re-chargeable lithium ion batteries.
The website and literature on the Exoscan emphasize its use in measuring spectra of surfaces, such as contamination on metal and damage to carbon fiber composite parts used in aircraft. I found the staff at their Pittcon booth knowledgeable and helpful, and they sent me home with an armload of applications literature. According to their literature the Exoscan has software that allows it to be calibrated so it can perform quantitative analyses.
I would imagine the Exoscan is small enough and rugged enough to be used in the same applications as the TruDefender FT, that is hazardous materials identification and homeland security. But in what I consider a strange business decision, A2 Technologies has handed over the sales, marketing, and support functions for this application to Smith's Detection. This is such a potentially lucrative market that I would think the company would want it all to itself.
An interesting aspect of the Exoscan is that you can buy a "docking station" for it which turns it into lab instrument. In this case, it would work like a lab FTIR with a diamond ATR or specular reflectance accessory in it. What's neat about this option is that it gives users the flexibility to develop methods, perform routine lab analyses, and engage in field work with the same instrument. For more information on the Exoscan go here:
http://www.a2technologies.com/exoscan_home_page.html .
Monday, April 20, 2009
Getting Unknown Mixture Spectra to Yield Their Secrets
I was recently tasked with an interesting challenge by a client and it had me exercising spectral interpretation muscles I have not used in a long time. They sent me a dozen unknown mixture spectra to analyze prior to my teaching an on-site course on the topic at their facility (for the advantages of on-site FTIR training, including free customization, click here http://www.spectros1.com/course_custom.html ). These spectra are perhaps the most difficult to interpret because they are unknowns and because in mixture spectra it can be difficult to figure out what functional groups give rise to what peaks. As I was wading through these spectra I became conscious of the process I was following, and since I had some success I thought I would share that process with my readers.
In my Infrared Spectral Interpretation I course (outline here: http://www.spectros1.com/c-spectral-i.html ) I teach attendees a 12-step program for successfully interpreting spectra. I followed the 12 steps for each spectrum, but in several cases I got to the end of the process without having made much progress. This is when Step 12, "Get Help", comes into play. I found the first thing I did after completing my analysis of a difficult unknown mixture spectrum was to do a library search. In one case the search was of high quality and allowed me to identify the main component in an unknown.
In a few other cases the library search was inconclusive. This is when I hit the literature. I have published a book on Infrared Spectral Interpretation (more info here: http://www.spectros1.com/books.html) and I also have on my bookshelf a number of IR spectral interpretation books by other authors, some of which are more far ranging than my introductory text. Between these books I was able to narrow down some of the unknowns to categories of molecules. For instance, that several of the samples contained carboxylates.
After this I looked up reference spectra of possibilities in a specific chemical class in an infrared spectral atlas. Such an atlas is a collection of infrared spectra organized by functional group. My favorite infrared spectral atlas is the comprehensive 3-volume collection published by Aldrich Chemical (more info here: http://www.sigmaaldrich.com/catalog/ProductDetail.do?N4=Z286001ALDRICH&N5=SEARCH_CONCAT_PNOBRAND_KEY&F=SPEC). This compendium contains over 18,500 spectra organized into 53 functional groups. The beauty of this atlas is that you can look at many spectra of the same type of molecule together and quickly learn the pattern of peaks that is diagnostic for that functional group. I did this with a few of the unknowns to become more familiar with the spectra of functional groups that the library search suggested were present in a sample. If I wanted to look up a specific reference spectrum the Aldrich Spectral Atlas could be used for that. However, Aldrich also sells the Aldrich Spectral Viewer (details here: http://www.sigmaaldrich.com/labware/learning-center/spectral-viewer.html). This is an electronic collection of 11,000 infrared spectra that can be searched by compound name or functional group. I find that if I have to look up the spectrum of a specific compound the Spectral Viewer is faster than the Spectral Atlas. The spectral viewer is nice because the spectra are in color, the display limits can be altered, and peaks can be picked and marked. By looking up spectra of functional groups I made progress, and in a few cases by looking up specific spectra I was able to identify specific compounds in a mixture. In the end, I was able to identify specific molecules in a number of the unknowns. However, in a few cases I was only able to suggest what functional groups might be present in a sample.
So, the key then to analyzing unknown mixture spectra is to execute the first 11 steps of the 12-Step interpretation strategy I have discovered. Then exercise the "Get Help" step by using library searches, spectral atlases, and the spectroscopy literature. Using these techniques unknown mixture spectra can be convinced to yield some of their secrets.
In my Infrared Spectral Interpretation I course (outline here: http://www.spectros1.com/c-spectral-i.html ) I teach attendees a 12-step program for successfully interpreting spectra. I followed the 12 steps for each spectrum, but in several cases I got to the end of the process without having made much progress. This is when Step 12, "Get Help", comes into play. I found the first thing I did after completing my analysis of a difficult unknown mixture spectrum was to do a library search. In one case the search was of high quality and allowed me to identify the main component in an unknown.
In a few other cases the library search was inconclusive. This is when I hit the literature. I have published a book on Infrared Spectral Interpretation (more info here: http://www.spectros1.com/books.html) and I also have on my bookshelf a number of IR spectral interpretation books by other authors, some of which are more far ranging than my introductory text. Between these books I was able to narrow down some of the unknowns to categories of molecules. For instance, that several of the samples contained carboxylates.
After this I looked up reference spectra of possibilities in a specific chemical class in an infrared spectral atlas. Such an atlas is a collection of infrared spectra organized by functional group. My favorite infrared spectral atlas is the comprehensive 3-volume collection published by Aldrich Chemical (more info here: http://www.sigmaaldrich.com/catalog/ProductDetail.do?N4=Z286001ALDRICH&N5=SEARCH_CONCAT_PNOBRAND_KEY&F=SPEC). This compendium contains over 18,500 spectra organized into 53 functional groups. The beauty of this atlas is that you can look at many spectra of the same type of molecule together and quickly learn the pattern of peaks that is diagnostic for that functional group. I did this with a few of the unknowns to become more familiar with the spectra of functional groups that the library search suggested were present in a sample. If I wanted to look up a specific reference spectrum the Aldrich Spectral Atlas could be used for that. However, Aldrich also sells the Aldrich Spectral Viewer (details here: http://www.sigmaaldrich.com/labware/learning-center/spectral-viewer.html). This is an electronic collection of 11,000 infrared spectra that can be searched by compound name or functional group. I find that if I have to look up the spectrum of a specific compound the Spectral Viewer is faster than the Spectral Atlas. The spectral viewer is nice because the spectra are in color, the display limits can be altered, and peaks can be picked and marked. By looking up spectra of functional groups I made progress, and in a few cases by looking up specific spectra I was able to identify specific compounds in a mixture. In the end, I was able to identify specific molecules in a number of the unknowns. However, in a few cases I was only able to suggest what functional groups might be present in a sample.
So, the key then to analyzing unknown mixture spectra is to execute the first 11 steps of the 12-Step interpretation strategy I have discovered. Then exercise the "Get Help" step by using library searches, spectral atlases, and the spectroscopy literature. Using these techniques unknown mixture spectra can be convinced to yield some of their secrets.
Monday, April 13, 2009
Where CSI Gets it Wrong
Where CSI Gets it Wrong
I recently had the privilege of teaching my FTIR Analysis of Controlled Substances course at a well known forensics lab; one of the ones they make TV shows about (course outline is here: http://www.spectros1.com/c-forensic.html). The simple act of writing the letters "CSI" on the board elicited a chorus of groans and laughter from the roomful of forensic scientists taking the course. For those of you who don't watch much TV, the letters "CSI" stand for "Crime Scene Investigation", a series of shows about how forensic scientists help solve crimes. The chorus of groans and laughter is based on the fact that the science on these shows is so inaccurate as to be laughable.
The first thing CSI gets wrong is the role of forensic scientists in crime fighting. They portray lab workers donning bullet proof vests, carrying guns, and chasing down and arresting bad guys. Now in some states forensic scientists may go to the occasional crime scene, but there are no forensic lab workers that I am aware of that carry a gun and arrest people. In many forensics labs there is a strict division of labor between the police, who arrest the bad guys and collect evidence at crime scenes, and the civilian scientists who analyze crime scene evidence and testify about it in court.
Another thing CSI gets wrong is the speed of the analyses performed in a forensics lab. In the world of CSI it apparently only takes a few minutes to run a DNA analysis and identify the bad guy. In the real world it usually takes days or weeks to get DNA results back, and although DNA is a powerful forensics tool it may not be definitive because you can not identify someone who is not in your DNA database.
It is true of CSI, and most movies and TV shows, that the actors and actresses are exceedingly good looking. Now, I have great respect and admiration for the professionalism of forensic scientists and the important role they play in promoting public safety. However, I can tell you that they all don't look like supermodels :-).
But what CSI really gets wrong is the way it portrays the use of FTIR in forensic labs. If you watch the show closely you may have noticed there is a Thermo Nicolet FTIR on the set of one of the CSI shows. Several years ago a Nicolet salesman told me the story of how this came to be. The producers of the show approached Nicolet and asked them for a free FTIR in return for the free publicity Nicolet would enjoy by having the instrument appear on TV. The folks at Nicolet were a little leery of handing over an instrument worth tens of thousands of dollars for free. They had the intelligence to ask the producers of CSI, "Will you ever use the FTIR to perform an analysis?". The answer was no. So, instead of giving the show a complete instrument Nicolet proposed giving them the plastic shell that covers the instrument but with nothing inside of it. This was acceptable to the producers, and that is how a Nicolet "FTIR" came to be featured on a TV show.
Several years ago an episode of CSI featured the use of the FTIR in one of their shows, and they got it terribly wrong. On TV they showed a red visible light laser, apparently a He-Ne laser, as the light source of the FTIR As I teach in my Fundamentals of FTIR course all FTIRs contain a visible light laser that is used to measure the optical path difference of the interferometer. However, this laser is NOT the infrared source because you can't measure an infrared spectrum with visible light. Also, because a laser gives off only one wavelength of light it is impossible to use it to measure a spectrum, which requires many wavelengths of light. Another thing I teach in my Fundamentals of FTIR course is that FTIR is a form of molecular spectroscopy. Individual atoms are not chemically bonded to anything, do not possess vibrations, and hence generally don't have a mid-infrared spectrum. This makes FTIR inappropriate for elemental analysis. On the same show mentioned above they were using the FTIR to perform an atomic analysis on a sample. This is more than I could take, and I have not watched an episode of the show since.
These scientific inaccuracies may seem amusing, but they can have a negative effect upon the public safety of our country. A number of forensic scientists and police officers that I have talked to have said there exists a "CSI effect". Potential jurors, defense attorneys, and even some prosecutors have been so swept up into the imaginary world of the TV show that they have totally unrealistic expectations of what a crime lab can do. Prosecutors expect DNA test results back in hours and get cranky when they do not get what they want. But the scariest story I heard involved a juror. This person had watched so much CSI that he fancied himself an expert in the field. When the police did not run the tests that this juror thought they should have run, he assumed the police were hiding something and as a result voted to acquit a person who may very well have been guilty. So, as entertaining as these shows may be, there is always a cost to portraying things that are not true.
I recently had the privilege of teaching my FTIR Analysis of Controlled Substances course at a well known forensics lab; one of the ones they make TV shows about (course outline is here: http://www.spectros1.com/c-forensic.html). The simple act of writing the letters "CSI" on the board elicited a chorus of groans and laughter from the roomful of forensic scientists taking the course. For those of you who don't watch much TV, the letters "CSI" stand for "Crime Scene Investigation", a series of shows about how forensic scientists help solve crimes. The chorus of groans and laughter is based on the fact that the science on these shows is so inaccurate as to be laughable.
The first thing CSI gets wrong is the role of forensic scientists in crime fighting. They portray lab workers donning bullet proof vests, carrying guns, and chasing down and arresting bad guys. Now in some states forensic scientists may go to the occasional crime scene, but there are no forensic lab workers that I am aware of that carry a gun and arrest people. In many forensics labs there is a strict division of labor between the police, who arrest the bad guys and collect evidence at crime scenes, and the civilian scientists who analyze crime scene evidence and testify about it in court.
Another thing CSI gets wrong is the speed of the analyses performed in a forensics lab. In the world of CSI it apparently only takes a few minutes to run a DNA analysis and identify the bad guy. In the real world it usually takes days or weeks to get DNA results back, and although DNA is a powerful forensics tool it may not be definitive because you can not identify someone who is not in your DNA database.
It is true of CSI, and most movies and TV shows, that the actors and actresses are exceedingly good looking. Now, I have great respect and admiration for the professionalism of forensic scientists and the important role they play in promoting public safety. However, I can tell you that they all don't look like supermodels :-).
But what CSI really gets wrong is the way it portrays the use of FTIR in forensic labs. If you watch the show closely you may have noticed there is a Thermo Nicolet FTIR on the set of one of the CSI shows. Several years ago a Nicolet salesman told me the story of how this came to be. The producers of the show approached Nicolet and asked them for a free FTIR in return for the free publicity Nicolet would enjoy by having the instrument appear on TV. The folks at Nicolet were a little leery of handing over an instrument worth tens of thousands of dollars for free. They had the intelligence to ask the producers of CSI, "Will you ever use the FTIR to perform an analysis?". The answer was no. So, instead of giving the show a complete instrument Nicolet proposed giving them the plastic shell that covers the instrument but with nothing inside of it. This was acceptable to the producers, and that is how a Nicolet "FTIR" came to be featured on a TV show.
Several years ago an episode of CSI featured the use of the FTIR in one of their shows, and they got it terribly wrong. On TV they showed a red visible light laser, apparently a He-Ne laser, as the light source of the FTIR As I teach in my Fundamentals of FTIR course all FTIRs contain a visible light laser that is used to measure the optical path difference of the interferometer. However, this laser is NOT the infrared source because you can't measure an infrared spectrum with visible light. Also, because a laser gives off only one wavelength of light it is impossible to use it to measure a spectrum, which requires many wavelengths of light. Another thing I teach in my Fundamentals of FTIR course is that FTIR is a form of molecular spectroscopy. Individual atoms are not chemically bonded to anything, do not possess vibrations, and hence generally don't have a mid-infrared spectrum. This makes FTIR inappropriate for elemental analysis. On the same show mentioned above they were using the FTIR to perform an atomic analysis on a sample. This is more than I could take, and I have not watched an episode of the show since.
These scientific inaccuracies may seem amusing, but they can have a negative effect upon the public safety of our country. A number of forensic scientists and police officers that I have talked to have said there exists a "CSI effect". Potential jurors, defense attorneys, and even some prosecutors have been so swept up into the imaginary world of the TV show that they have totally unrealistic expectations of what a crime lab can do. Prosecutors expect DNA test results back in hours and get cranky when they do not get what they want. But the scariest story I heard involved a juror. This person had watched so much CSI that he fancied himself an expert in the field. When the police did not run the tests that this juror thought they should have run, he assumed the police were hiding something and as a result voted to acquit a person who may very well have been guilty. So, as entertaining as these shows may be, there is always a cost to portraying things that are not true.
Sunday, March 29, 2009
Pittcon Follow-Up:Portable Hand Held FTIRs Really Exist!
Pittcon Follow-Up: Portable Hand Held FTIRs Really Exist!
In my last post I was bemoaning the head cold I had while trying to navigate the grand halls of Pittcon. The head cold turned into a sinus infection, but thanks to the modern miracle of antibiotics I am now back in writing form.
One of the neatest things I saw at the Pittsburgh Conference in Chicago (it really sounds like the meeting planners don't know their geography) were hand held FTIRs. These are portable FTIR systems that are light enough to be held in one hand, are battery powered, and have enough on-board computing power to allow you to take spectra, identify unknowns, perform quantitative analyses, and diagnose instrument problems. These systems are a true miracle to me. I am old enough to have worked with some of the first commercial FTIR systems built in the 1970s. These were huge machines that weighed hundreds of pounds, were very sensitive to vibration, and were complex to run. Today we have FTIR systems that are rugged enough to be taken out into the field, weigh only several pounds, and can be operated by anyone with a little bit of training. I will review one instrument here, and another in a few days.
The first system I saw at Pittcon is made by Ahura Scientific of Wilmington, MA. It is called the TruDefender FT, although that moniker sounds like it could also be applied to a super hero. The system is 7.8" x 4.4" x 2.1 and weighs under 3 pounds. It uses a diamond ATR sensing head and can run on batteries for more than two hours. The spectrometer scans from 4000 to 650 cm-1, which indicates to me it probably has a ZnSe beamsplitter, and is capable of 4 cm-1 resolution. The unit seems to be designed for hazardous materials and homeland security applications. The area around a hazardous waste spill or bio-terrorism event is called the "hot zone". Ahura says their instrument is small enough and rugged enough to be taken right into the hot zone to examine the suspect material in-situ. There is no need to carry the material out of the hot zone to the instrument risking further contamination and wasting precious time.
Ahura Scientific claims their software can identify compounds from their infrared spectrum and provides, " definitive results that don’t require user interpretation or judgment" (this quote is from their website). I approached the people at the Ahura booth at Pittcon to ask them to explain how their identification software system works. They said "it's a trade secret" which I did not find helpful. More information on the TruDefender FT can be found here
http://www.ahurascientific.com/chemical-explosives-id/products/trudefenderft/index.php# .
In my last post I was bemoaning the head cold I had while trying to navigate the grand halls of Pittcon. The head cold turned into a sinus infection, but thanks to the modern miracle of antibiotics I am now back in writing form.
One of the neatest things I saw at the Pittsburgh Conference in Chicago (it really sounds like the meeting planners don't know their geography) were hand held FTIRs. These are portable FTIR systems that are light enough to be held in one hand, are battery powered, and have enough on-board computing power to allow you to take spectra, identify unknowns, perform quantitative analyses, and diagnose instrument problems. These systems are a true miracle to me. I am old enough to have worked with some of the first commercial FTIR systems built in the 1970s. These were huge machines that weighed hundreds of pounds, were very sensitive to vibration, and were complex to run. Today we have FTIR systems that are rugged enough to be taken out into the field, weigh only several pounds, and can be operated by anyone with a little bit of training. I will review one instrument here, and another in a few days.
The first system I saw at Pittcon is made by Ahura Scientific of Wilmington, MA. It is called the TruDefender FT, although that moniker sounds like it could also be applied to a super hero. The system is 7.8" x 4.4" x 2.1 and weighs under 3 pounds. It uses a diamond ATR sensing head and can run on batteries for more than two hours. The spectrometer scans from 4000 to 650 cm-1, which indicates to me it probably has a ZnSe beamsplitter, and is capable of 4 cm-1 resolution. The unit seems to be designed for hazardous materials and homeland security applications. The area around a hazardous waste spill or bio-terrorism event is called the "hot zone". Ahura says their instrument is small enough and rugged enough to be taken right into the hot zone to examine the suspect material in-situ. There is no need to carry the material out of the hot zone to the instrument risking further contamination and wasting precious time.
Ahura Scientific claims their software can identify compounds from their infrared spectrum and provides, " definitive results that don’t require user interpretation or judgment" (this quote is from their website). I approached the people at the Ahura booth at Pittcon to ask them to explain how their identification software system works. They said "it's a trade secret" which I did not find helpful. More information on the TruDefender FT can be found here
http://www.ahurascientific.com/chemical-explosives-id/products/trudefenderft/index.php# .
Tuesday, March 10, 2009
Pittcon 2009 Day 1: FTIR Mixture Analysis Software Packages
The first day of Pittcon was exciting for me, for the wrong reasons. I have come down with a nasty cold which has made standing and talking, the most common activity at Pittcon, a little more interesting than I would like. I hope I have not inadvertently infected any of my colleagues.
I visited a number of FTIR instrument company booths on Monday. There is much new and interesting to talk about, but one thing that really excites me are new software programs that assist the FTIR user in mixture analysis. As I mention in my Fundamentals of FTIR and IR Spectral Interpretation I courses, mixture analysis is the biggest practical disadvantage of FTIR. The problem is that the more chemically complex a mixture becomes the more complex the infrared spectrum becomes, making it harder to figure out what peaks are from what molecules. In my training courses I teach attendees the 4 ways of tackling mixtures. These mixture analysis software packages may represent a fifth way.
Time for a disclaimer. Two vendors, the Bio-Rad Informatics division and Thermo-Nicolet are demonstrating mixture analysis software here at Pittcon. My discussion of their offerings is in no way an endorsement of their products. If I find other companies showing mixture analysis software I will talk about them in a later post.
These mixture analysis software packages work like library searching, which is a technique many FTIR users are familiar with. In this case the mixture spectrum is selected, one or more spectral libraries are selected, and then the mixture search is performed. The algorithms on both systems are trade secret, but my hunch is that they use some sort of chemometric modeling, perhaps principle components or partial least squares analysis. For the results to work out well you have to tell the software how many different chemical components you think there are in the sample. Knowing this information greatly improves the quality of the results. However, as those of us who work in the real world know, we don't always know the exact number of components in a sample. I also noticed that for the most part you are limited to mixtures with 2, 3, or 4 components. Not surprisingly, the calculation time increases for each added component.
My hunch then is if you tell the software you have a two component mixture it will take spectra from the selected libraries two at a time, calculate mixture spectra from them, and compare them to your sample spectrum. This comparison gives a number similar to the hit quality index (HQI) in a normal library search. The pair of library spectra that when added together give the best match to your sample spectrum should give the best HQI. You can visually compare the calculated and sample spectra. Other tools, including the spectral residual, which is the result of subtracting the calculated spectrum from the sample spectrum, are available to judge the quality of the results. I think certain FTIR users, particularly those unfamiliar with IR Spectral Interpretation, may find this type of software package useful.
I am sure many of you are wondering whether these mixture analysis programs can provide quantitative information i.e.the percentage of different compounds in a sample. There was much careful talk about this issue from which I was not able to draw a conclusion. This is something I would like to see an unbiased third party put to the test (hint hint).
A blurb about the Bio-Rad software is here: http://collateral.knowitall.com/collateral/95372-Mixture_Analysis_Datasheet.pdf#zoom=75%
A blurb about the Nicolet software is here: http://www.thermo.com/com/cda/product/detail/1,,10137344,00.html
I visited a number of FTIR instrument company booths on Monday. There is much new and interesting to talk about, but one thing that really excites me are new software programs that assist the FTIR user in mixture analysis. As I mention in my Fundamentals of FTIR and IR Spectral Interpretation I courses, mixture analysis is the biggest practical disadvantage of FTIR. The problem is that the more chemically complex a mixture becomes the more complex the infrared spectrum becomes, making it harder to figure out what peaks are from what molecules. In my training courses I teach attendees the 4 ways of tackling mixtures. These mixture analysis software packages may represent a fifth way.
Time for a disclaimer. Two vendors, the Bio-Rad Informatics division and Thermo-Nicolet are demonstrating mixture analysis software here at Pittcon. My discussion of their offerings is in no way an endorsement of their products. If I find other companies showing mixture analysis software I will talk about them in a later post.
These mixture analysis software packages work like library searching, which is a technique many FTIR users are familiar with. In this case the mixture spectrum is selected, one or more spectral libraries are selected, and then the mixture search is performed. The algorithms on both systems are trade secret, but my hunch is that they use some sort of chemometric modeling, perhaps principle components or partial least squares analysis. For the results to work out well you have to tell the software how many different chemical components you think there are in the sample. Knowing this information greatly improves the quality of the results. However, as those of us who work in the real world know, we don't always know the exact number of components in a sample. I also noticed that for the most part you are limited to mixtures with 2, 3, or 4 components. Not surprisingly, the calculation time increases for each added component.
My hunch then is if you tell the software you have a two component mixture it will take spectra from the selected libraries two at a time, calculate mixture spectra from them, and compare them to your sample spectrum. This comparison gives a number similar to the hit quality index (HQI) in a normal library search. The pair of library spectra that when added together give the best match to your sample spectrum should give the best HQI. You can visually compare the calculated and sample spectra. Other tools, including the spectral residual, which is the result of subtracting the calculated spectrum from the sample spectrum, are available to judge the quality of the results. I think certain FTIR users, particularly those unfamiliar with IR Spectral Interpretation, may find this type of software package useful.
I am sure many of you are wondering whether these mixture analysis programs can provide quantitative information i.e.the percentage of different compounds in a sample. There was much careful talk about this issue from which I was not able to draw a conclusion. This is something I would like to see an unbiased third party put to the test (hint hint).
A blurb about the Bio-Rad software is here: http://collateral.knowitall.com/collateral/95372-Mixture_Analysis_Datasheet.pdf#zoom=75%
A blurb about the Nicolet software is here: http://www.thermo.com/com/cda/product/detail/1,,10137344,00.html
Thursday, March 5, 2009
I'm Off to Pittcon
I will be gone from March 9-12 to attend the Pittsburgh Conference on Analytical Chemistry & Applied Spectroscopy, which is being held in Chicago strangely enough. This is the show where FTIR manufacturers trot out their new products. As a service to you, dear reader, I will gather information on the latest and greatest FTIR instrumentation and report it to you here once I return from my trip. So make sure to come back soon.
ATR III: How Wavenumber Impacts DP
The first parameter to consider in the ATR depth of penetration (DP) equation is W, the wavenumber. At first glance the presence of this parameter in the equation should strike you as bizarre. In a transmission sampling experiment the infrared beam passes through a thin film of sample and all wavenumbers of light see the same sample thickness. Since wavenumber appears in the denominator of the DP equation, as W goes up DP goes down. This means, for example, that in an ATR experiment 1000 cm-1 light penetrates further into samples than 3000 cm-1 light does. Since peak size is proportional to pathlength, the relative intensities in ATR spectra are different than in spectra taken via other sampling techniques. In general in ATR spectra the peaks at high wavenumber are smaller than the peaks at low wavenumber.
This point is illustrated in the figure pasted into this blog post which shows the ATR and non-ATR spectra of sucrose (table sugar). Note in the ATR spectrum (top) the peaks at low wavenumber are much bigger than the peaks at high wavenumber, whereas in the non-ATR spectrum (bottom) the peaks at low and high wavenumber are about the same size.
This phenomenon has important implications for how we use ATR spectra. Since ATR spectra look different than non-ATR spectra it is best to only compare ATR spectra to each other. This also means you will get better library searching results by only searching ATR spectra against ATR libraries. If you own an ATR I strongly suggest you to build ATR libraries of your own samples and/or buy a commercial ATR library.
This point is illustrated in the figure pasted into this blog post which shows the ATR and non-ATR spectra of sucrose (table sugar). Note in the ATR spectrum (top) the peaks at low wavenumber are much bigger than the peaks at high wavenumber, whereas in the non-ATR spectrum (bottom) the peaks at low and high wavenumber are about the same size.
This phenomenon has important implications for how we use ATR spectra. Since ATR spectra look different than non-ATR spectra it is best to only compare ATR spectra to each other. This also means you will get better library searching results by only searching ATR spectra against ATR libraries. If you own an ATR I strongly suggest you to build ATR libraries of your own samples and/or buy a commercial ATR library.
Thursday, February 26, 2009
ATR II : Depth of Penetration
The depth of penetration (DP) in an ATR experiment is a measure of how far the evanescent wave penetrates into a sample. Understanding the variables that determine DP tell us a lot about how the technique works, why ATR spectra look the way they do, and the sorts of interesting applications that can be pursued via ATR. The equation for depth of penetration in an ATR experiment is (the envelope please):
DP = 1/2πWnc(sin2θ – n2sc)1/2
(please pardon the appearance of the equation, it had a rough night...and blogger does not allow subscripts and superscripts. Red is for superscripts, blue is for subscripts.)
Where
DP = Depth of Penetration (in cm)
W = Wavenumber in cm-1
nc = Refractive index of ATR crystal
θ = Angle of incidence of IR beam with crystal surface
nsc = refractive index of sample divided by refractive index of crystal
Note that all the paramaters in the DP equation are in the denominator, so when any of them goes up, DP goes down. The next several blog posts will cover the different parameters in this equation and what they teach us about the ATR experiment.
DP = 1/2πWnc(sin2θ – n2sc)1/2
(please pardon the appearance of the equation, it had a rough night...and blogger does not allow subscripts and superscripts. Red is for superscripts, blue is for subscripts.)
Where
DP = Depth of Penetration (in cm)
W = Wavenumber in cm-1
nc = Refractive index of ATR crystal
θ = Angle of incidence of IR beam with crystal surface
nsc = refractive index of sample divided by refractive index of crystal
Note that all the paramaters in the DP equation are in the denominator, so when any of them goes up, DP goes down. The next several blog posts will cover the different parameters in this equation and what they teach us about the ATR experiment.
Monday, February 9, 2009
FTIR Sample Preparation for the 21st Century: ATR
The holy trinity of FTIR sample analyses is speed, accuracy, and cost. Ideally an analysis will be carried out quickly, accurately, and as fast as possible. Sample preparation has long been the Achilles' heal of FTIR, too frequently involving long, tedious, manual operations. For example, even in the hands of a skilled analyst it can sometimes take over 1 hour to prepare a KBr pellet. This is unacceptable in a 21st century lab where time is money and speed is of the essence. Fortunately, there exists a sample preparation technique that is up to the challenge of giving us accurate, fast, and inexpensive analyses, it is called Attenuated Total Reflectance (ATR). This blog post will be the first in a series exploring how ATR works, what applications it is suited for, and why it is such an advantageous technique.
In the ATR technique the infrared beam is brought to a focus on the face of a prism-shaped crystal made of a material that is infrared transparent and has a high refractive index. Common examples of ATR crystals include diamond, Zinc Selenide (ZnSe), and Germanium. The infrared light is refracted by the crystal and travels towards the top surface of the crystal as illustrated above. The magic ocurrs when the infrared beam reaches the top surface of the crystal. Because of a phenonenon too complicated to explain, here a small portion of the infrared beam sticks up above the surface of the crystal. I call this region of space a "hot spot" but it is more properly called the "evanescent wave". Infrared spectra are obtained by bringing samples into contact with the evanescent wave so they can absorb some of the infrared radiation. More to follow...
In the ATR technique the infrared beam is brought to a focus on the face of a prism-shaped crystal made of a material that is infrared transparent and has a high refractive index. Common examples of ATR crystals include diamond, Zinc Selenide (ZnSe), and Germanium. The infrared light is refracted by the crystal and travels towards the top surface of the crystal as illustrated above. The magic ocurrs when the infrared beam reaches the top surface of the crystal. Because of a phenonenon too complicated to explain, here a small portion of the infrared beam sticks up above the surface of the crystal. I call this region of space a "hot spot" but it is more properly called the "evanescent wave". Infrared spectra are obtained by bringing samples into contact with the evanescent wave so they can absorb some of the infrared radiation. More to follow...
For more on the topic of ATR you can consult my book Fundamentals of FTIR, available for purchase here: FTIR Books , or take my Hands-On FTIR Sample Preparation Course as outlined here: FTIR Sample Prep. Course Outline.
Friday, January 30, 2009
Introduction and Welcome
Dear FTIR Community:
It's about time the FTIR world had a source of unbiased, relevant, and timely information. This blog, "FTIR: Applications & Advice", will be that source of information. I will post tidbits of useful information about how to improve your FTIR analyses on a regular basis. I encourage you, the FTIR user, to share your successful applications of FTIR with the rest of us. Don't be afraid to ask questions, myself and the rest of the community will try to answer them for you. Feel free to post comments on anything you see here. Our goal is to be the nexus of FTIR information on the internet.
It's about time the FTIR world had a source of unbiased, relevant, and timely information. This blog, "FTIR: Applications & Advice", will be that source of information. I will post tidbits of useful information about how to improve your FTIR analyses on a regular basis. I encourage you, the FTIR user, to share your successful applications of FTIR with the rest of us. Don't be afraid to ask questions, myself and the rest of the community will try to answer them for you. Feel free to post comments on anything you see here. Our goal is to be the nexus of FTIR information on the internet.
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