Optimizing NIR FT-Raman for quality control applications

NIR FT-Raman spectroscopy offers rapid measurements with very convenient sampling, especially for solids. However, for quality control applications an even more important consideration is the repeatability of the measurements. In this paper we examine how varying the measurement conditions can affect repeatability. Problems arise because the Raman spectrum is usually obtained from a fairly small volume of material. For solids such as pharmaceutical tablets both the homogeneity of the sample and its positioning in the instrument may affect the appearance of the spectrum. The spectrum is usually recorded from a small volume in order to maximize the collection angle and hence the signal-to-noise ratio in the spectra. Our results show that inhomogeneity can be the largest source of variation in the spectra of tablets. In this situation it is better to measure a larger volume, the increase in noise being offset by the more representative sampling.