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# .
Sunday, March 29, 2009
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.
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