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

The present work describes the construction and evaluation of different tetracycline (TC)-selective electrodes without inner reference solution and with polymer membranes. The several electrodes were prepared with poly(vinyl chloride) or ethylene(vinyl acetate) membranes comprising o-nitrophenyl octyl ether or bis(2-ethylhexyl)sebacate as mediator solvents and tetracycline tetrakis(4-clorophenyl)borate as ion exchanger. The best performance was recorded for the poly(vinyl chloride) membranes with bis(2-ethylhexyl)sebacate. Using solutions with adjusted ionic strength, this type of electrode presented a slope of 57.4 mV decade(-1) and a reproducibility of +/-0.3 mV day(-1), for an analytical range from 1.2 x 10(-4) to 1.0 x 10(-2) M. The pH working range was 2.0-3.8. Tubular-shaped potentiometric detectors based on the same selective membrane were also constructed. When TC solutions with adjusted 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 were applied to the potentiometric analysis of oral dosage forms. Average recoveries were within 98.6 to 100.3% and the t test indicated the accuracy of these results in comparison to an independent methodology. The flow system with the potentiometric detector was employed in dissolution studies as well.