In many industries there is a need to identify raw materials as they come in the door, and the process is called “performing an identity” or “identity testing”. Because of its molecular fingerprinting abilities, FTIR is well suited for this type of work. Performing an identity normally entails comparing the sample spectrum to the reference spectrum of a known material.
Recently there have been moves afoot, particularly within the pharmaceutical industry, to use near infrared (NIR) spectroscopy or Raman scattering in place of FTIR for identity testing. Any identity testing technique should ideally be fast and easy, specific, and widely accepted in industry. Obtaining NIR spectra can be fast and easy, but this technique fails the specificity test. The features in NIR spectra are broad and diffuse, few in number, and difficult to interpret. Also, in general only functional groups containing O-H, N-H, and C-H bonds are observed in the NIR. These spectra simply lack the specificity we need in an identity testing method.
Recently developed handheld Raman scattering spectrometers (www.ahurascientific.com) make obtaining Raman spectra fast and easy. Raman spectra contain many sharp peaks and give much of the same information as infrared spectra, so they have the specificity needed for identity testing. However, the use of Raman spectra for identity testing is in its infancy, there are few libraries of Raman spectra available, and the technique certainly is not yet widely accepted in industry.
If two molecules have different chemical structures they have different infrared spectra…you can’t get more specific than that. From my own observation FTIRs are already used for identity testing in thousands of companies in dozens of industries, so the technique is widely accepted. In the past the main criticism of FTIR for identity testing was that the sample preparation is not fast and easy. The development of diamond ATRs has solved this problem (see previous blog posts). An FTIR equipped with a diamond ATR accessory can obtain spectra on powders, solids, liquids, and polymers in a matter of seconds. If one desires to take the instrument out of the lab to the loading dock where the sample is, some lab FTIRs such as the Bruker ALPHA that I use (http://www.brukeroptics.com/alpha.html ) are portable enough and rugged enough to be put on a cart and wheeled up to the vessel containing the sample. If one wants to take portability to its extreme, hand held FTIRs do now exist (see previous blog posts and http://www.a2technologies.com/index.html ). FTIR now satisfies all criteria for a perfect identity testing tool. Why would you bother using any other technique?