Determination of losartan, telmisartan, and valsartan by direct injection of human urine into a column-switching liquid chromatographic system with fluorescence detection

Column-switching high-performance liquid chromatographic (HPLC) method has been developed and validated for quantification of losartan, telmisartan, and valsartan in human urine. Urine samples were diluted on the extraction mobile phase (1:4, v/v) and a volume of 20 μL of this mixture were directly injected onto the HPLC system. The analytes were extracted from the matrix using an on-line solid-phase extraction procedure involving a precolumn packed with 25 μm C 18 alkyl-diol support (ADS), and a solution 2% methanol in 5 mM phosphate buffer (pH 3.8) at a flow-rate of 0.8 mL/min for isolation and preconcentration of losartan, telmisartan, and valsartan. The enriched analytes were back-flushed after, onto the analytical column with a mixture of 5 mM phosphate buffer (pH 3.8)–acetonitrile–methanol (65:20:15, v/v/v) at a flow-rate of 3.0 mL/min and detected by fluorescence at 259 and 399 nm as excitation and emission wavelength respectively. The separation of losartan, telmisartan, and valsartan was achieved on a Chromolith RP-18e monolithic column. The method provides extraction recoveries from spiked urine samples greater than 93%. Intra-day and inter-day precision were generally acceptable; the intra-day-assay C.V. was