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?

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.

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!

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

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.

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 .

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.