Fourier transform-Raman spectroscopy for the qualitative and quantitative characterization of sulfasalazine-containing polymeric microspheres

FT-Raman spectroscopy (FTRS) has been used to characterize microspheres produced from the pharmaceutical polymer Eudragit RS containing a range of concentrations of the drug sulfasalazine. While pure sulfasalazine produced an intense and complex Raman spectrum, the spectrum of drug-free Eudragit RS microspheres was considerably weaker in intensity and contained only a few prominent Raman scattering peaks. In spectra of the drug-polymer microspheres, peaks arising from the individual components could be identified. This enabled a quantitative analysis to be undertaken by calculating the ratio between the area of a sulfasalazine peak and the area of a Eudragit RS peak for each microsphere spectrum. A correlation was shown between the peak area ratio and the microsphere sulfasalazine content. FTRS was then applied to a series of microsphere samples which had been dissoluted into pH 7 buffer for 1, 3, 6, 9, 12, or 24 hr. For each spectrum, the drug-polymer peak area ratio was determined and this in turn enabled calculation of the residual drug content of the microsphere sample. FTRS-calculated data showed good agreement with microsphere drug content values determined spectrophotometrically.