Disopyramide ion-selective plastic membrane sensors and their pharmaceutical applications

Disopyramide ion-selective poly(vinyl chloride) membrane electrodes contain an ion-pair complex of disopyramide tetrakis (4-chlorophenyl)borate as the electroactive material with 2-nitrophenyl octyl ether (electrode I) or bis (2-ethylhexyl)sebacate (electrode II) as the solvent mediators. The electro des (I and II) show a linear response for the disopyramide concentration ra nge 3.0 x 10(-4)-10(-2) and 8.5 x 10(-5)-10(-2) mol.l(-1) over a pH range o f 3.75-8.30 with a cationic slope of 57.3 and 58.5 mV decade(-1), respectiv ely, The response time varied from 20 s to 1 min depending on the disopyram ide concentration. Electrode II was used for the potentiometric determinati on of the disopyramide phosphate substance and the content of capsules with average recovery and mean standard deviation (+/- SD) of 100.8 +/- 0.34 an d 100.1 +/- 0.68 of the nominal values, which are comparable with those obt ained by the U.S. Pharmacopoeia method.