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Ion-selective poly(vinyl chloride)(PVC) membrane electrodes for the determination of the calcium antagonist verapamil and its pharmaceutical preparations were described. Verapamil-superchrome garnet Y(SGY), lumogallion(LG), acid red 97(AR97), Dragendorff(DD) and Meyer reagent ion pairs were inverstigated as an electroactive compound for membrane electrode. Stable potentiometric response was obtained with azo dye at pH 6.5-4.0 and with DD, and Meyer reagent at pH 6.5-3.0. The best plasticizer was 49w/w% 2-nitrophenyl octyl ether for azo dye, and 65.3w/w% tri(n-butyl) citrate for DD and Meyer reagent. Potentiometric response slopes of optimized membrane electrodes based on SGY, LG, AR97, DD, and Meyer complex for verapamil were 52.49, 54.88, 50.81, 54.13 and 49.31 mV/dec., respectively. Lower limits of linear range were 1.0X106M for SGY, LG, and AR97, while those for DD and Meyer reagent were 4X10-6M. Detection limits for all these electrodes were 1X10-5M, 4X10-6M, 1.8X10-6M, 8X10-7M, and 1X10-6M with relative standard deviation of 2.56, 3.6, 3.96, 2.56, 3.20%, respectively.
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