Non-extractive spectrophotometric estimation of indomethacin in pharmaceuticals and biological fluids via ion-pair complexes

Abstract

Two simple, rapid and inexpensive spectrophotometric methods were proposed for the determination of indomethacin in its pure form, pharmaceutical formulations and in the biological fluids. The two suggested approaches were based on the formation of a wine-red ion-pair complex between indomethacin and chrome azurol S in presence of cetylpyridinium chloride at pH4.8 (in method A) and a pinkish-red complex with methyl red in presence of cetyltrimethylammonium bromide at pH 4.3 (in method B). The two ion-pair complexes formed exhibit two maximum absorption peaks at the wavelengths of 513 and 527 nm in methods A and B, respectively. For both methods, optimal spectrophotometric conditions were established. The calibration graph of the two methods is linear and Beer's law was valid within the concentration ranges of 0.4–28 and 0.4–24 μg/mL with molar absorptivity values 2.6369 × 10⁴ and 3.0198 × 10⁴ L/mol.cm in method A and B, correspondingly. The precision (RSD%) value is better than ≤1.57 % for both methods depending on the concentration level. Both recommended methods A and B have low detection limit (LOD) values of 0.0281 and 0.0327, respectively. Results of the two suggested methods compare favorably with the published method and offer the virtues of stability and sensitivity. The two suggested methods have been employed successfully to estimate indomethacin in its pharmaceutical forms (capsules, suppositories and spray) and in the spiked human urine and serum samples with mean recoveries of 95.41–101.64 %, and no intrusions were noticed from the shared excipients additives present in the commercial pharmaceutical forms.