Characterization of Toad Skin for Traditional Chinese Medicine by Near-Infrared Spectroscopy and Chemometrics

Extraction is a widely used manufacturing protocol for medicinal materials. Near-infrared spectroscopy was implemented to simultaneously and nondestructively monitor toad skin extraction and to determine the ideal end point. A fiber optic probe was coupled to the extraction setup to collect real-time spectra. Four mathematical algorithms, including spectra dissimilarity, moving block standard deviation, mean square, and principal component analysis, were investigated to find a suitable method to determine the end point of extraction. The moving block standard deviation was the most effective method to evaluate the end point. Multivariate models based on partial least square regression were established to monitor changes. Four quantitative models for the indole alkaloid concentration and total solids in two extraction processes provided favorable statistics, and the determination coefficients of the calibration models exceeded 0.95. For indole alkaloids and total solids in the first and second extractions, the latent variables were 8, 5, 5, and 4, respectively; the root mean square error of cross-validation values were 8.26?mg?mL^?1, 0.18%, 7.50?mg?mL^?1, and 0.16%; and the root mean square error of prediction results were 11.10?mg?mL^?1, 0.27%, 4.89?mg?mL^?1, and 0.14%. The extraction monitoring system was able to ensure product quality and batch consistency while providing lower cost and faster analysis for pharmaceutical applications.