Scattering orthogonalization of near-infrared spectra for analysis of pharmaceutical tablets

The paper explores scattering orthogonalization as a preprocessing technique to reduce physical interference and maintain chemical information in near-infrared (NIR) spectra of pharmaceutical tablets. Samples used in this study were tablets compressed at five compression forces; they were composed of theophylline, lactose, and microcrystalline cellulose (PH200). The NIR spectra were orthogonalized against the reduced scattering coefficients (representative of physical interference of scattering), and concentrations of all constituents were predicted. The robustness of predictions was compared to the widely employed standard normal variate (SNV) for the specificity of removing interference representative of physical parameter (such as tablet density). Group-wise cross-validation (groups were based upon similar chemical composition) and prediction demonstrated the enhanced robustness on prediction of chemical information via scattering orthogonalization in comparison to SNV. When compared to the SNV, scattering orthogonalization demonstrated an improved capacity to reduce physical interference while maintaining spectral variance attributable to chemical information. The improved capacity is expected to be useful for spectroscopy-based multivariate model calibration and continuous model update.