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Fourier Transform Infrared Analysis of Contamination by Searching Difference Spectra Against Libraries of Difference Spectra

Volume 62, Number 2 (Feb. 2008) Page 176-181

Laughlin, Kenneth B.


A method is presented for quickly identifying contaminants in a material. Fourier transform infrared (FT-IR) spectra are collected for anomalous and normal material using a method that gives highly reproducible absolute intensity, such as attenuated total reflection (ATR) spectroscopy of liquids or solids that contact the crystal perfectly. The difference spectrum is calculated as the point-by-point subtraction of absorbance values without the use of a variable subtraction factor, giving a spectrum with positive and negative spectral features. This spectrum is then searched against libraries of difference spectra, such as spectra of possible contaminants minus the spectrum of normal material. The key advantage of the method is that it removes subjective judgment in choosing the subtraction factor. It also provides information about the material that is depleted along with identifying the contaminant.