Debunking FTIR Myths I: "FTIR Can't Identify Things in Mixtures"

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.

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 .