Spectrophotometric determination of salicylic acid in pharmaceutical formulations using copper(II) acetate as a colour developer

TLDR: A simple and rapid spectrophotometric method based on the complexation of salicylic acid with copper(II) acetate to form a stable yellowish green complex based on Beer's law is obeyed over the range 0.2–4.0 mg ml–1 of salcylic acid and the complex is stable for 30 h.

Abstract: A simple and rapid spectrophotometric method for the determination of salicylic acid alone or in pharmaceutical preparations has been developed based on the complexation of salicylic acid with copper(II) acetate to form a stable yellowish green complex at pH 5.5–6. The yellowish green species has an absorption maximum at 730 nm with a molar absorptivity of 0.02 × 103 l mol–1 cm–1. Beer's law is obeyed over the range 0.2–4.0 mg ml–1 of salicylic acid and the complex is stable for 30 h. The precision of the method is 1.42%. Benzoic acid and boric acid interfere in the normal procedure but interference from boric acid can be removed by extraction with diethyl ether.