Identifying Unknowns Using Infrared Light By Mark E. Weiss

FT-IR (Fourier Transform Infrared) Spectroscopy is a technique used to extract chemical information from a sample, using infrared energy.  Some molecules, when exposed to infrared energy, absorb some of it.  Measuring the amount of energy absorbed over a range of infrared light can indicate the types of chemistry present in an unknown sample.  Some of the areas where this technique may be useful are in the identification of foreign particles in food products; verification of various types of plastics; and analysis of oils, gasoline and diesel fuel in potential vandalism cases.

Crane Engineering has recently installed a Cary 670 FTIR Spectrometer and 620 FT-IR microscope with a Focal Plane Array (FPA) detector.  This instrument gives us a significant increase in resolution over our previous single point measurement system. The FPA detector captures a chemical image of the sample, much like a camera but instead of recording colors of visible light, it records infrared light.  The system can resolve targets as small as one to two microns.  Not only does this allow us to analyze smaller particles, but it allows us to do it in less time, with less sample preparation.

In applications such as medical devices and electronics, small particles and contaminants must be identified so the source can be eliminated.  In short, even if you can only see your particle at 200X magnification we can very likely analyze it. 

The images below are of a collection of polymer flakes with a possible defect in the substrate under the flakes. The overall visual image (gold background) is roughly 500 x 500 microns. The chemical image of the same area is to the right.

Analysis of the above data indicates that the suspect area is a very thin flake of polymer as shown in the oval below and not a defect in the substrate.

Applications for this technique are endless:  from identification of unknown particles, fibers, and oils to deconstruction of multilayer films, and mapping of biological components to aid in disease research—the uses are vast.

If you have a challenging sample, contact me and we can discuss the analysis options available.