Quantitative analysis of solid samples using modified specular reflectance accessory.

Diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) is a fast, reliable and cost effective analytical method, requiring minimal or no sample preparation. It is commonly used in the course of qualitative and quantitative analysis of pharmaceutical ingredients and food. We demonstrate that simpler and cheaper specular reflectance (SR) accessory working in a DRIFTS like mode (SR-DL) can be an alternative for DIRFTS attachment. An application of a modified SR accessory for quantitative analysis of solids samples is presented. As a case study the concentration of cinnarizine in commercial tablets has been determined from DRIFTS and SR-DL infrared (IR) and near-infrared (NIR) spectra recorded using DTGS (deuterated triglicine sulphate) detector in the IR and NIR regions and InGaAs (indium-gallium arsenide) detector in the NIR range. Based on these spectra Partial Least Squares (PLS) models were constructed and relative standard errors of prediction (RSEP) were calculated for the calibration, validation and analysed data sets. They amounted to 2.4-2.5%, 2.1-2.7% and 2.0-2.6% for the DRIFTS attachment while 2.1-2.2%, 2.0-2.3% and 1.9-2.6%, respectively, for the modified SR accessory. Obtained error values indicate that modified SR accessory can be effectively used for quantification of solid pharmaceutical samples in the mid- and near-infrared regions.