EXTERNAL-STANDARD HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHIC METHOD FOR QUANTITATIVE-DETERMINATION OF FUROSEMIDE IN PLASMA BY USING SOLID-PHASE EXTRACTION AND ONLINE ELUTION

A rapid and simple external-standard high-performance liquid chromatographic (HPLC) method has been developed for the determination of the concentration of furosemide in plasma. The analyte is extracted with a C-2 ethyl sorbent. On-line elution of the analyte into the HPLC system is accomplished with an advanced automated sample processor (Varian). Furosemide is quantified by fluorescence detection within a linear range of 25 to 1000 ng/mL (average correlation coefficient, 0.9998), with a limit of detection of 1.8 ng/mL. Both internal- and external-standard procedures were evaluated, and the external-standard procedure demonstrated superior characteristics. The external-standard procedure was precise to within a relative standard deviation of 8% and accurate with < 3% error throughout the concentration range studied. The external-standard HPLC method was used to analyze the concentration of furosemide in > 1000 plasma samples obtained from patients with either normal kidney function or renal failure who had received furosemide either orally or intravenously in an experimental setting.