Determination of total organic carbon and soluble solids contents in Tanreqing injection intermediates with NIR spectroscopy and chemometrics

Near infrared spectroscopy combined with chemometrics was investigated for the fast determination of total organic carbon (TOC) and soluble solids contents (SSC) of Tanreqing injection intermediates. The NIR spectra were collected in transflective mode, and the TOC and SSC reference values were determined with Multi N/C UV HS analyzer and loss on drying method. The samples were divided into calibration sets and validation sets using the Kennard–Stone (KS) algorithm. The Dixon test, leverage and studentized residual test were studied for the sample outlier analysis. The selection of wavebands, spectra pretreated method and the number of latent variables were optimized to obtain better results. The quantitative calibration models were established with 3 different PLS regression algorithms, named linear PLS, non-linear PLS and concentration weighted PLS, and the net result was defined as the average of the predicted values of the different calibration models. The overall results indicated that the presented method is more powerful than single multivariable regression method, characterized by higher mean recovery rate (MRR) of the validation set, and can be used for the rapid determination of TOC and SSC values of Tanreqing injection intermediates, which are two important quality indicators for the process monitoring.