Detection and Determination of Minor Components in Nominally Pure Solids by Raman Spectroscopy

Abstract

The problems encountered in applying Raman spectroscopy to direct qualitative and quantitative analysis for minor impurities in nominally pure, colorless solids have been examined. Samples of sulfamethoxazole spiked with 0.5 to 5% of sulfanilamide and sulfanilic acid were used as test materials. A procedure is described which permits detection of spectral features of the specified impurities at the 0.5% level. Least-squares fitting and cross-correlation data treatment procedures for the determination of sulfanilamide in sulfamethoxazole, with limits of detection of about 0.1% for either approach, are described. Computer simulations have been used to examine detection of impurity peaks for a variety of conditions, including the worst-case scenario in which the impurity features coincide with the strongest features of the spectrum of the host material. A least-squares fitting approach is described which permits detection of the impurity peak at the 0.5% level, even under worst case conditions.