Tetracycline-Selective Electrode for Content Determination and Dissolution Studies of Pharmaceuticals by Flow-Injection Analysis (FIA)

Abstract

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 × 10−4 to 1.0 × 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 × 10−4 to 1.0 × 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. © 2001 Wiley‐Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 90:1125–1133, 2001