Raman spectroscopy has become a workhorse [1-3] technology in the pharmaceutical industry, and new applications are emerging rapidly. Many of these applications involve the use of Raman libraries for material identification and verification. Raman spectroscopy differs in several important respects from absorbance spectrometry. First, absorbance spectra are always normalized to the transmitted intensity of the excitation source spectrum, so source intensity fluctuations do not alter the measured absorbance. Raman signal levels, on the other hand, depend directly on the source intensity. More importantly, any emission that can be excited by the Raman source will contribute to the measured Raman spectra. For example, fluorescence is a common interference in Raman spectra that can arise from trace level impurities in the material under study, resulting in a broad background signal. Many Raman spectrometers in use today utilize 785 nm excitation sources to minimize the effect of fluorescence, but it can be difficult to completely eliminate this background contribution.
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