Flow-based fluorimetric determination of furosemide in pharmaceutical formulations and biological samples:: Use of micelar media to improve sensitivity

Two fast flow injection procedures with fluorimetric detection based on the furosemide emission are presented. The first configuration used a phosphate buffer solution pH 3.00, 0.2 ionic strength (mu) solution flowing at 3.0mlmin-1 as carrier, a 80cm sample loop (400 mu l total sample injection), and a 40cm long reactor coil, which was kept at room temperature; the second has a unique difference: the introduction of a new channel of surfactant solution with reduction of flow rate. The excitation and emission were carried out at 270 and 410nm, respectively; both systems presented linear dynamic range from 1.0 x 10(-7) to 1.0 x 10(-5) mol 1(-1). The limit of detection (3 sigma/slope) was 3.0 x 10(-8) mol 1(-1), to the first system, and 10(-8) mol 1(-1) for the second one. Both proposed methods were applied to three commercial samples from different suppliers, as tablets and ampoules, and a synthetic urine sample spiked with the analyte. They presented an analytical frequency of 90 and 60 measurements per hour, respectively to phosphate and micelar media. The results agreed with those from the label and determined by a UV-Vis spectrophotometric comparative procedure. Recoveries around 101% were found in the commercial formulations and synthetic urine matrixes.