Combination of flow injection with capillary electrophoresis: Part 4. Automated multicomponent monitoring of drug dissolution Original Research Article

The combined flow injection–capillary electrophoresis (FI–CE) system, described previously in this series, was used in connection with a drug dissolution testing system to automatically monitor the dissolution process of multicomponents. Samples from the dissolution medium were withdrawn at fixed intervals through an on-line membrane filter to load the sample loop of an injection valve, from which 25 μl samples were injected into a carrier buffer and transported into a split–flow interface coupling the FI and CE systems. Trimethoprim (TMP) and sulphamethoxazole (SMZ), the two active components in a sulphatrim tablet formulation dissolved in 0.1 mol l−1 HCl, were introduced into a short silica separation capillary of 14.5 cm effective length by electrokinetic means, separated at a constant voltage of 1.0 kV by capillary zone electrophoresis, using a phosphate running buffer (pH 6.5), and the separated constituents recorded continuously, using an UV detector at 224 nm. The signals were recorded within a testing period of 65 min. By partially overlapping the separation zones of neighboring samples, a high sample throughput of 60 h−1 was achieved with single-vessel dissolution and 48 (24 duplicates) h−1 with dual-vessel dissolution. The reproducibility of the FI–CE system, obtained using TMP and SMZ standards within the testing period was 1.6 and 0.8% relative standard deviation (RSD) with peak height evaluation, and 2.0 and 1.1% RSD (n=72), respectively, for peak area. Good agreement of results was obtained between those using the reported method and a standard liquid chromatography method.