Automated continuous monitoring of drug dissolution process using a flow injection on-line dialysis sampling - solvent extraction separation spectrophotometric system

A flow injection (FI) system was developed incorporating on-line solvent extraction separation and stopped-flow dialysis systems for automated continuous monitoring of multi-vessel drug dissolution processes. The system employed PTFE pump tubes for solvent delivery, and combined a coaxial phase segmentor, conical cavity gravitational phase separator with a microdialysis sampling system to produce a reliable extraction system capable of stable non-stop operation over extended period of time. The system was evaluated for continuous monitoring in multi-vessel drug dissolution testing of ethambutol hydrochloride tablets using bromocresol green as reagent and chloroform as extractant. With the six-vessel dissolution system used, a sampling frequency of 15/h for each dissolution vessel was achieved with a total of 90 determinations per hour, giving an average precision of 3.6% RSD (n = 11). Results showed good agreement with those obtained using the Chinese Pharmacopoeia standard method.