RESUMEN
Simple, selective and highly sensitive spectrophotometric methods are proposed for the rapid and accurate determination of anti-hypertensive drugs namely telmisartan (TEL), propranolol (PRO), bisoprolol (BIS) and carvedilol (CRV) in tablets and biological fluids using bromocressol green (BCG) and bromothymol blue (BTB). The developed methods involve formation of stable yellow colored dichloromethane extractable ion-pair complexes of the amino derivative of four antihypertensive drugs such as TEL, PRO, BIS and CRV with two sulphonphthalein acid dyes, namely; BCG and BTB in acidic buffer. The effect of optimum conditions via pH on the ion-pair formation, reagent concentration, time and temperature and solvent was studied. The composition of the ion-pairs was found 1: 1 by Job’s method. The established methods having high sensitivity and good selectivity could be applied to the determination of the studied drugs in pharmaceutical, urine and blood serum samples with satisfactory results. The results obtained are good agreement with experimental data. The reaction mechanism was also discussed.