Figure 4. (a ) Raman spectra for Beifalast after different durations of heat treatment; (b ) plot of Qr versus Tr2 for a principal component analysis (PCA) model developed using the spectra in (a ); (c ) Raman spectra for Beifalast after different durations of light treatment; (d ) plot of Qr versus Tr2 for a PCA model developed using the spectra in (c ).
Two principal components were selected (cumulative variance: 78.18%; 95% confidence level). Decision criterion: Qr ≤ 1.5, pass; Qr > 1.5, fail. Figure 1b plots the reduced Q-residuals (Qr) and Hotelling’s T2 (Tr2) for the resulting model after optimization. The spectra after 12 h of heat treatment were rejected by the model because of high residuals (Qr), which were superior to the Q limit. Therefore, Raman can easily differentiate samples after 12 h of heat treatment from the intact samples. As a result, samples show distinct changes after 12 h of heat treatment, which is in agreement with the results of the HPLC/activity. In line with this, the Qr versus Tr2 plot in Figure 4d shows a separation between samples after 96 h and before 48 h of light treatment. The sample is relatively stable within 48 h of light treatment, which is in accordance with the results of the HPLC/activity.