Liquid-phase microextration combined with liquid chromatography–electrospray tandem mass spectrometry for detecting diuretics in urine

Trace amounts of diuretics were determined in human urine by hollow fiber liquid-phase microextraction (LPME) combined with liquid chromatography–electrospray ionization–tandem mass spectrometry (LC–ESI–MS/MS) in this study. Chromatography was performed on a C8 reversed-phase column. A 25 μL n-octanol was used to extract analytes in urine. Extraction was optimized using a pH 2 solution spiked with 0.15 g/mL NaCl for 40 min at 40 °C with 1010 rpm stirring. The limits of detection of diuretics in urine were 0.3–6.8 ng/mL, and linearity range was 1–1000 ng/mL. Recoveries of spiked 50 ng/mL diuretics were 97.7–102.5%. The intra-day precision and inter-day precision were 3–18% and 4–21%, respectively. The diuretics concentration profiles in patient urine were also determined. The results of this study reveal the adequacy of LPME–LC–MS/MS method for analyzing diuretics in urine and quantification limits exceed World Anti-Doping Agency requirements.