Simultaneous direct determination of amiloride and triamterene in urine using isopotential fluorometry

A method for the simultaneous fluorometric determination of two diuretics i n urine is proposed. The combination of matrix isopotential synchroronous f luorescence (MISF) and first derivative techniques provides good analytical results. MISF spectra are obtained by calculating the isopotential traject ory in the three dimensional fluorescence spectrum for a urine solution. In the spectral contour, the trajectory is taken to be the portion of the lin e that passes by the fluorescence maxima of both diuretics (lambda (ex) = 3 65 and lambda (em) = 413 nm for amiloride and lambda (ex) = 365 and lambda (em) = 437 nm for triamterene). Because contour lines connect points of ide ntical intensity and the trajectory is part of a contour line, it is called "isopotential." Analyses was carried out in a 1/1 (v/v) ethanol/water mixt ure, using an apparent pH of 6.3 provided by 0.01 M sodium/citrate citric a cid buffer. Urine samples are diluted 50 times and provide linear calibrati on plots at amiloride and triamterene concentrations up to 320 and 100 ng m L(-1), respectively. The goodness of the analytical signal was checked by u sing variance analysis. Signals recorded throughout the calibration range w ere subjected to three calibrations per each analyte, both in the absence a nd in the presence of variable amounts of the other analyte. Differences be tween individual calibrations and slopes were compared with those within in dividual calibrations. Based on the results, triamterene and amiloride can be accurately quantified in the presence of each other. The limit of detect ion calculated according to Clayton who uses error propagation throughout t he calibration curve and a noncentralized security factor was 16.8 and 2.4 ng mL(-1) for amiloride and triamterene, respectively. (C) 2001 Academic Pr ess.