Potentiometric PVC membrane sensor for the determination of scopolamine in some pharmaceutical formulations.

A novel PVC membrane electrode for the determination of scopolamine ion based on the formation of an ion-association complex of scopolamine with the phosphotungstate counter anion as an electroactive material dispersed in a PVC matrix is described. The sensor shows a fast, stable, near-Nenstian response for 1 x 10(-2) mol dm(-3) to 1 x 10(-6) mol dm(-3) scopolamine at 25 degrees C over the pH range of 3 - 7 with a cationic slope of 54.5 +/- 0.5 mV/decade. The lower detection limit is 8 x 10(-7) mol dm(-3) and the response time is 15 -45 s. The selectivity coefficients for scopolamine relative to the number of interfering substances were investigated. There was negligible interference from the studied cations, anions, and pharmaceutical excipients. The determination of scopolamine in aqueous solution shows an average recovery of 100.0% and a mean relative standard deviation (RSD) of 1.5% at 500 microg/cm3. The direct determination of scopolamine in some formulations (scopolamine injection and eye drops) gave results that compare favorably with those obtained by the United State of Pharmacopoeia method. Potentiometric titration of scopolamine with sodium tetraphenylborate and phosphotungstic acid as a titrant was monitored with the developed scopolamine electrode as an end point indicator electrode.