Tetracycline-selective electrode for content determination and dissolutionstudies of pharmaceuticals by flow-injection analysis (FIA)

The present work describes the construction and evaluation of different tet racycline (TC)-selective electrodes without inner reference solution and wi th polymer membranes. The several electrodes were prepared with poly(vinyl chloride) or ethylene(vinyl acetate) membranes comprising o-nitrophenyl oct yl ether or bis(2-ethylhexyl)sebacate as mediator solvents and tetracycline tetrakis(4-clorophenyl)borate as ion exchanger. The best performance was r ecorded for the poly(vinyl chloride) membranes with bis(2-ethylhexyl)sebaca te. Using solutions with adjusted ionic strength, this type of electrode pr esented a slope of 57.4 mV decade(-1) and a reproducibility of +/-0.3 mV da y(-1), for an analytical range from 1.2 x 10(-4) to 10 x 10(-2) M. The pH w orking range was 2.0-3.8. Tubular-shaped potentiometric detectors based on the same selective membrane were also constructed. When TC solutions with a djusted ionic strength of concentrations ranging from 1.0 x 10(-4) to 1.0 x 10(-2) M were injected into a single-channel flow manifold, the detectors presented a slope of 56.6 mV decade(-1) and a reproducibility of +/-0.5 mV day(-1). The pH working range was 1.9-3.9. Both batch and flow procedures w ere applied to the potentiometric analysis of oral dosage forms. Average re coveries were within 98.6 to 100.3% and the t test indicated the accuracy o f these results in comparison to an independent methodology. The flow syste m with the potentiometric detector was employed in dissolution studies as w ell. (C) 2001 Wiley-Liss, Inc. and the American Pharmaceutical Association.