Experimental design approach for the optimisation of a HPLC-fluorimetric method for the quantitation of the angiotensin II receptor antagonist telmisartan in urine.

A high performance liquid chromatographic method with fluorimetric detection has been developed for the quantitation of the angiotensin II receptor antagonist (ARA II) 4-((2-n-propyl-4-methyl-6-(1-methylbenzimidazol-2-yl)-benzimidazol-1-yl)methyl)biphenyl-2-carboxylic acid (telmisartan) in urine, using a Novapak C18 column 3.9 x 150 mm, 4 microm. The mobile phase consisted of a mixture acetonitrile-phosphate buffer (pH 6.0, 5 mM) (45:55, v/v) pumped at a flow rate of 0.5 ml min(-1). Effluent was monitored at excitation and emission wavelengths of 305 and 365 nm, respectively. Separation was carried out at room temperature. Chromatographic variables were optimised by means of experimental design. A clean-up step was used for urine samples consisting of a solid-phase extraction procedure with C8 cartridges and methanol as eluent. This method proved to be accurate (RE from -12 to 6%), precise (intra- and inter-day coefficients of variation (CV) were lower than 8%) and sensitive enough (limit of quantitation (LOQ), ca. 1 microg l(-1)) to be applied to the determination of the active drug in urine samples obtained from hypertensive patients. Concentration levels of telmisartan at different time intervals (from 0 up to 36 h after oral intake) were monitored.