Spectrophotometric methods for determination of enalapril and timolol in bulk and in drug formulations

摘要

Two simple and accurate spectrophotometric methods for determination of timolol and enalapril maleate are described. The first method is based on chelate formation with palladium(II) chloride in buffered medium. The second method is based on the formation of the colored complex between palladium(II), eosin, and the two cited drugs using methylcellulose as surfactant to increase the solubility and intensity of the formed complexes. Under optimum conditions the complexes showed maximum absorption at 369.4 nm and 362.8 nm for timolol and enalapril maleate, respectively, in the first method and 552.2 and 550.6 nm for the second method. Apparent molar absorptivities were 1.8 * 10~3 and 1.3 * 10~3 and Sandell's sensitivities were 5.9 * 10~(-4) and 2.7 * 10~(-4) for timolol and enalapril maleate in the first method; in the second method molar absorptivities were 2.8 * 10~4 and 1.1 * 10~4 while Sandell's constants were 9.1 * 10~(-3) and 2.3 * 10~(-3) for timolol and enalapril maleate. The solutions of the complexes obeyed Beer's law in the concentration ranges 20-200 μg mL~(-1) and 50-300 μg mL~(-1) for timolol and enalapril maleate, respectively. In the second method, because the reaction was more sensitive the ranges were reduced to 1.6-16 μg mL~(-1) for timolol 8-56 μg mL~(-1) for enalapril maleate. The proposed methods were applied to the determination of the two drugs in their pharmaceutical formulation.