CONSTRUCTION AND EVALUATION OF ATROPINE SELECTIVE ELECTRODES - THEIR APPLICATION TO OPHTHALMIC FORMULATIONS

Atropine selective electrodes with PVC membranes and without inner reference solutions were prepared, characterized and used in the analysis of pharmaceutical products. Their sensor system incorporates atropine-tetrakis(4-chlorophenyl)borate as an ionic exchanger and 2-nitrophenyloctylether (Type I) or dibutylphthalate (Type II) as solvent mediator. The electrodes showed stable and rapid responses (about 6 s) for 1.2X10(-5)-10(-1) M (Type I) and 1.4X10(-4)-10(-1) M (Type II) atropine (ATR). A slope of about 58 mV/log[ATR] was obtained in a 2.5-9.0 pH range. Both type of electrodes showed good selectivity. Their reproducibility was +/-1.5 mV throughout the working day. Electrodes with 2-nitrophenyloctylether as solvent mediator showed both wider linear response zone and better selectivity to sodium. Therefore they were used in direct potentiometric determinations of atropine in ophthalmic products. The results obtained showed an average recovery of 102% and a relative standard deviation of +/-3%.