Statistical optimization of a reversed-phase liquid chromatographic method for the analysis of amiloride and hydrochlorothiazide in tablets.

A method has been developed for the separation of hydrochlorothiazide and amiloride by high-performance liquid chromatographic (HPLC) method on a C18 column with detection at 280 nm. The optimal conditions of separation were determined with the aid of 'window diagram' technique of Laub and Purnell. The effect of simultaneously varying the pH, proportion aqueous acetic acid and methanol in the mobile phase were studied to optimize the separation. A response surface diagram was used to optimize the experimental conditions for the separation. The mobile phase composition that provides an acceptable resolution hydrochlorothiazide and amiloride in a short elution time is water:methanol (60:40) and pH 3.2 (pH adjusted to 3.2 with CH3COOH). A method is applied for the quantitative analysis of Moduretic tablets (Merck Sharp & Dokme International). The powdered tablets are extracted with methanol, containing caffeine as the internal standard, and assayed by comparison of peak areas after liquid chromatography.