Derivative and Derivative Ratio Spectrophotometric Analysis of Antihypertensive Ternary Mixture of Amiloride Hydrochloride, Hydrochlorothiazide and Timolol Maleate

Two simple, rapid and reliable spectrophotometric methods are described for the resolution of the three‐component mixture of amiloride hydrochloride (AMD), hydrochlorothiazide (HCT) and timolol maleate (TIM). The first method involves the use of derivative spectrophotometry with the zero‐crossing technique where AMD was easily determined using its 0 D and 1 D(Δλ = 6) amplitudes at 365 and 385 nm, respectively, while HCT and TIM were determined by measuring the 3 D(Δλ = 6) amplitude at 265 nm and the 1 D(Δλ = 8) amplitude at 315.4 nm, respectively. The second method involves the application of the ratio‐spectra zero‐crossing first and second derivative spectrophotometry where two points have been used for the quantification of each compound. For the determination of AMD, HCT was used as divisor and the 1 DD (Δλ = 4) and 2 DD (Δλ = 6) values at 299.4 and 311 nm, respectively, were plotted against AMD concentration; while — by using TIM as divisor — the 2 DD (Δλ = 6) amplitudes at 264.2 and 290 nm were found to be proportional to HCT concentration. TIM was assayed in the mixture using its 1 DD (Δλ = 6) amplitudes at 289.8 nm (Divisor was AMD) and 314.8 nm (Divisor was HCT). Synthetic mixtures of different proportions and laboratory‐made tablets were assayed by the proposed methods and the results revealed good accuracy and repeatability of the developed methods.