Spectrophotometric determination of the antihistamines, carbinoxamine maleate and doxylamine succinate, in an N-cetylpyridinium chloride micellar medium

The pyridine antihistamines carbinoxamine maleate and doxylamine succinate were derivatized by hydrolysis with cyanogen bromide and coupling with aniline to form a polymethine dye, and determined by colorimetry. In a micellar cationic medium of N-cetylpyridinium chloride (NCPC), the reaction times were reduced and the sensitivities improved. In 0.1 M NCPC the apparent molar absorptivities of the derivatives were 5,900 and 3,500 M(-1) cm(-1), and the limits of detection (as 3s) were 8.6 x 10(-7) M and 1.7 x 10(6) M, for carbinoxamine and doxylamine, respectively. The sensitivity was enhanced in a three- to six-fold factor with respect to a nonmicellar medium. The reproducibility was 0.8% for 1.6 x 10(-4) M carbinoxamine, and 1.8% for 1.3 x 10(-4) M doxylamine. The procedure was applied to the evaluation of the drugs in pharmaceutical preparations.