Abstract: 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 Samples from the dissolution medium were withdrawn at fixed intervals through an online membrane filter to load the sample loop of an injection valve, from which 25 µL samples were injected into a carrier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 sulfamethoxazole (SMZ), the two active components in a sulfatrim 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.

Abstract: Trimethoprim (TMP) in four pharmaceutical preparations (compound sulfamethoxazol tablets, compound tetracycline tablets, compound trimethoprim and sulfamethoxazol tablets; and compound berberine injection) is determined by solvent extraction-flow injection spectrophotometry. It can be extracted into chloroform directly, and the absorbance at a wavelength of 280 nm of the organic phase is measured after phase separation. The manifold comprises two streams. The sample is injected into a 0.2 mol/L NaOH carrier stream, and extracted with chloroform in a 200-cm coil (ID 0.7 mm) after a 50 cm reaction tube (ID 1.0 mm). Calibration graph is linear in the range of 25-150 µg/ml. The average recovery is 101.4% with a relative standard deviation of 1.1%. The proposed system permits the analysis of about 50 samples per hour. Precise results in agreement with those obtained with official methods are achieved. Trimethoprim (I) in four pharmaceutical preparations, viz., (i) compound sulfamethoxazol (II) tablets, (ii) compound tetracycline tablets, (iii) compound I and II tablets, and (iv) compound berberine injection, was determined by the cited method. The solvent extraction - flow injection spectrophotometric system and its principle were described and illustrated. The sample was injected into a carrier stream of 0.2 M NaOH and extracted with CHCl3 on a coil (200 cm x 0.7 mm), and then passed through a reaction tube (50 cm x 1 mm). The absorbance of I in CHCl3 phase was measured at 280 nm. Calibration graph was rectilinear for 25 to 150 µg mL-1 of I. The mean recovery was 101.4%, with coefficient of variation (n = 4) of 1.1%. Results agreed with those obtained by the official methods.

Abstract: A simple, rapid microfluidic capillary electrophoresis system with a continuous sample introduction interface is described in the present paper. The interface with an H-channel structure was produced using a non-lithographic approach. The H-channel structure fixed on a planar plastic base utilized a horizontal 6.5-centimeter-long separation capillary with two vertical sidearm tubes on each end that served as inlet and outlet flow-through electrode reservoirs. The inlet reservoir also functioned as interface for coupling to the FI system. The performance of the system was demonstrated in the separation and determination of trimethoprim (TMP), sulfadiazine (SDZ), and sulfamethoxazole (SMZ) with UV detection at 214 nm, achieving baseline separation within 2.5 min. The sample throughput rate can reach up to 30 samples h-1. The repeatability (defined as relative standard deviation, RSD) was 2.23%, 1.19%, 2.64% with peak height evaluation and 2.43%, 1.46%, 3.58% for peak area evaluation, respectively. The limits of detection (S/N = 3) were 0.17 g/mL, 1.05 g/mL, and 1.28 g/mL for TMP, SDZ, and SMZ, respectively. This technique has been applied to the analysis of two commercial pharmaceutical preparations containing TMP, SDZ, and SMZ for the first time and has achieved satisfactory results.