Spectrophotometric Determination of Chloroquine, Pyrimethamine and Trimethoprim by Ion Pair Extraction in Pharmaceutical Formulation and Urine

A simple and accurate method lot the determination of chloroquine diphosphate (CQ), pyrimethamine (PYM) and trimethoprim (TMP) in pure, pharmaceutical and urine samples is described The method involved an ion pair extraction procedure with chloroform using an acid base indicator, bromocresol purple (BCP), as a counter ion The ion pair extracted in organic phase was yellow, and the absorbance was measured at lambda(max) = 420 nm Beer's law was obeyed over the concentration range of I 25-8 75, 0 62-7 5, and 1 25-10 71 mu g/mL, respectively The Sandell's sensitivity was 0 01258. 0 01102 and 0 01464 mu g/cm(2) The Ringbom optimum concentration range, which was 2 5-7 5, 1 25-7 5 and 2 5-10.7 mu g/mL for CQ. PYM, and TMP, respectively, exhibited reliability of the method Stoichiometry and thermodynamic of the complexes were evaluated by Job's method and Benesi-Hildebrand plot The statistical results of intra- and inter-day estimation of drugs and comparison with the reported methods demonstrated high precision and accuracy of the method The procedure was tapid, simple and suitable for quality control purpose