NIR spectroscopy as a process analytical technology (PAT) tool for on-line and real-time monitoring of an extraction process

The application of near-infrared (NIR) spectroscopy for on-line monitoring of the extraction process of red paeony root was investigated. For NIR measurements, two fiber optic probes designed to transmit NIR radiation through a 2 mm pathlength flow cell were employed to collect spectra in real-time. Partial least squares regression (PLSR) calibration models were developed for the parameters of interest: total solid, paeoniflorin, and benzoic acid. The influences of flow rate and air bubble on the NIR spectra and calibration models were also investigated. The established models were used for on-line and real-time monitoring of extraction process, and a model updating method was proposed for the long-term usage of the developed models. Furthermore, both the moving block of standard deviation (MBSD) and relative concentration changing rate (RCCR) methods were used to identify the end point of extraction process. The results of this particular application of implementing NIR spectroscopy to monitor extraction process are very encouraging. Successful models have been built and applied on-line, which proffers real-time data and instant feedback about the extraction course, and in turn, provides improved control.