To improve the quality of the analy

To improve the quality of the analysis, two multivariate methods, namely PLS and principal component regression (PCR) were applied. The following spectral ranges 2897–2864, 1625–1558, 1497–741 and 564–422 cm−1 were chosen for diclofenac sodium solutions. Results obtained were evidently better than those for univariate models. The calibration curves for API and additives were characterised by R2 values in the range of 0.992–0.997. This is depicted in Fig. 4 for API. In Table 1 the RSEP values found for the calibration, validation and testing samples using PLS and PCR models are quoted.