Abstract
A highly sensitive and selective method for the direct determination of buprenorphine (BUP), norbuprenorphine (NBUB), buprenorphine-3-glucuronide, and norbuprenorphine-3-glucuronide in urine was developed and validated. Analytes of interest were extracted by solid-phase extraction on Bond Elut C18, followed by liquid chromatography-electrospray ionization tandem mass spectrometry analysis using a Synergy Polar RP column. Gradient elution was based on a mobile phase consisting of 10 mM ammonium formate adjusted to pH 3 and acetonitrile. Acceptance criteria for linearity, precision, and recovery were achieved for all analytes. Intraday and interday precisions were better than 12% and 14%, respectively. Calibration curves were linear for BUP and its metabolites over the concentration range of 5-250 ng/mL, and correlation coefficients (R(2)) were better than 0.999. Limits of detection and lower limits of quantification were 0.2-0.4 and 0.7-1.2 ng/mL, respectively. Recoveries were in the range of 76-96%. No interference was detected with other common drugs. The described method was compared with an in-house hydrolysis method using 21 real urine case samples. BUP and NBUP were detected using both methods, with higher concentrations obtained using the direct method. Both methods were linear with correlation coefficients of 0.994 and 0.986 for total BUP and total NBUP, respectively. The comparison between the direct detection of BUP and its metabolites with the analysis of total BUP and total NBUP using the hydrolysis method is reported for the first time in this work.