Enhanced spectrophotometric determination of Losartan potassium based on its physicochemical interaction with cationic surfactant

In this study, a simple and sensitive spectrophotometric method was developed for determination of Losartan potassium (LST K), an angiotensin-II receptor (type AT₁) antagonist, in presence of cationic surfactant cetyltrimethylammonium bromide (CTAB). The physicochemical interaction of LST K with CTAB was investigated. The effect of cationic micelles on the spectroscopic and acid-base properties of LST K was studied at pH 7.4. The binding constant (K_b) and the partition coefficient (K_x) of LST K-CTAB were 1.62 × 10⁵ M^-1 and 1.38 × 10⁵; respectively. The binding of LST K to CTAB micelles implied a shift in drug acidity constant (ΔpK_a = 0.422).

The developed method is linear over the range 0.5-28 μg mL^-1. The accuracy was evaluated and was found to be 99.79 ± 0.509% and the relative standard deviation for intraday and interday precision was 0.821 and 0.963; respectively. The method was successfully applied to determine LST K in pharmaceutical formulations.