A double-membrane ephedrine selective electrode based on ephedrine-tetraphenylborate in poly (vinyl chloride) resin.

The construction and performance characteristics of a double-membrane ephedrine selective electrode are described. The electrode is based on the use of an internal conducting membrane made of tetrabutylammonium bromide and another external electroactive membrane containing the ionic pair ephedrine-tetraphenylborate in a poly (vinyl chloride) resin (with some plasticizers incorporated) as an inert matrix. The ephedrine electrode exhibits linear Nernstian response within the range 10(-2)-5 x 10(-5)M of ephedrine, with a slope of 58.2 +/- 0.5 mV decade(-1) at 25 +/- 0.2 degrees . The detection limit is 10(-4.5)M. The reproducibility (coefficient of variation) was 0.54% (n = 10 determinations) and the stability of its potential is 2.3 mV/24 h. The selectivity coefficients for 15 ions were calculated. The electrode was applied to the determination of ephedrine in some pharmaceutical preparations with satisfactory results.