Liquid membrane electrode for selective determination of salicylate in pharmaceutical preparations

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Abstract
A salicylate-selective liquid membrane electrode with a nitron-salicylate ion-pair complex in nitrobenzene as the electroactive species is described. At pH 4.5–9.5, the electrode provides a rapid and near-Nernstian response to salicylate ion in the concentration range 10–1–10–4 M. The selectivity coefficients obtained for 40 different carboxylate, phenolate and inorganic anions showed that there was negligible interference by most of these ions. In general, the proposed electrode has significantly better performance characteristics than many of the previously described salicylate electrodes. The results obtained for the direct potentiometric determination of salicylate in the range 10 µg ml–1–10 mg ml–1 show an average recovery of 98.9% and a mean standard deviation of 1.8%. Procedures for the determination of salicylate in some keratolytic solutions, ointments, powders and tablet dosage forms containing salicylic acid, methyl salicylate and acetylsalicylic acid are described. The average recovery is 98.3% of the nominal values (standard deviation, 2.1%), which compares favourably with results given by the British Pharmacopoeia method.

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