Development of Vanadometric System for Spectrophotometric Determination of Timolol in Pure and Dosage Forms

Purpose: To develop a simple vanadometric spectrophotometric method for the assay of timolol.
Methods: The oxidation reactions were performed at optimum conditions of 3 mL 20 % v/v H₂SO₄, 6.5 % w/v ammonium metavanadate, 40 - 60 ºC and 5 min for full colour (blue) development. The proposed method was validated in accordance with International Council on Harmonization (ICH) guidelines Q2 (R1) and applied to assay commercial timolol.
Results: Oxidation of timolol occurred at 504 nm wavelength. The developed method recovered 99.25 - 102.00 % of timolol in pre-analyzed formulations and 99.85 - 102.00 % of the manufacturers’ claim in commercial samples with RSD < 2 %. Linearity of 2 - 20 ppm (R² = 0.9995),as well as accuracy, 98 - 101 %; precision, 0.98 % (intraday) and 1.25 % (interday); robustness, 0.95 %; LOD, 0.256 ppm; LOQ, 0.425 ppm; and robustness, 0.95 - 1.10 %, were obtained.
Conclusion: The developed method is simple, sensitive, low-cost, accurate, reproducible, robust and rugged, and compares well with some complex methods for assay of timolol maleate in pure and dosage forms.