Spectrophotometric method for the determination of telmisartan with congo red

In pH 2.50 HCl-NaAc buffer solution, the reaction between telmisartan and congo red could form ionassociation complex, which has the maximum absorbance at 593 nm in the spectrophotometric experiment. Under this wavelength, the Beer's law was obeyed within the concentration range of 1.08 x 10(-6)-2.24 x 10(-5) M. The linear regression equation was A = -0.1913 x 10(5) c + 0.0286 (C: M). The regression coefficient r was 0.9986. The apparent molar coefficient E >(593) was 1.63 x 10(4) L mol(-1) cm(-1) and the detection limit was 5.66 x 10(-7) M. The established method having high sensitivity and good selectivity could be applied to the determination of telmisartan in pharmaceutical, urine and blood plasma samples with satisfactory results. The reaction mechanism was also discussed by using density functional theory methods. The result obtained was consilient with experimental data.