Liquid chromatography-electrospray ionization mass spectrometry determination of methylphenidate and ritalinic acid in conventional and non-conventional biological matrices

A procedure based on liquid chromatography-electrospray ionization mass spectrometry is described for determination of methylphenidate (MPH) and its principal metabolite ritalinic acid (RA) in plasma, urine, oral fluid and sweat using 3,4-methylendioxypropylamphetamine (MDPA) as internal standard. Aliquots of 100 mu L biological fluids and sweat patch were initially treated with acetonitrile, centrifuged, and clear supernatants evaporated and redissolved in 10 mM ammonium acetate. Chromatography was performed on a reversed-phase column using a gradient of 10 mM ammonium acetate and acetonitrile as a mobile phase at a flow rate of 1 mL/min. Separated analytes were confirmed and quantified by positive electrospray ionization mass spectrometry and selected ion monitoring acquisition mode. Limits of quantifications were 1 ng/mL plasma, 1 ng/sweat patch, 0.5 ng/mL oral fluid and urine for MHF; 1 ng/mL plasma and oral fluid, 1 ng/sweat patch, 0.5 ng/mL urine for RA using 100 mu L biological fluids or one sweat-patch per assay. Calibration curves were linear over the calibration ranges for both MPH and RA, with r(2) > 0.99. At three concentrations spanning the linear dynamic range of the assay, mean recoveries ranged between 67.9-90.3% for MPH and 36.3-92.4% for RA in the different biological matrices. This method was applied to therapeutic monitoring of MHP and RA in conventional and non-conventional biological matrices from individuals in drug treatment. (C) 2008 Elsevier B.V. All rights reserved.