Liquid-liquid extraction using 96-well plate format in conjunction with liquid chromatography/tandem mass spectrometry for quantitative determination of methylphenidate (Ritalin®) in human plasma

Methylphenidate (MPH; Ritalin®: methyl‐α‐phenyl‐2‐piperidinacetate hydrochloride) is utilized for the treatment of attention deficit hyperactivity disorder (ADHD) and narcolepsy. Recently, we described a rapid enantioselective liquid chromatography/tandem mass spectrometry (LC/MS/MS) method for the determination of the enantiomers of MPH (Rapid Commun. Mass Spectrom. 1999; 13: 2054). A lower limit of quantification (LLOQ) of 87 pg/mL was attained for the human plasma assay. The present paper describes a high‐throughput sample preparation procedure in conjunction with racemic LC/MS/MS analysis for MPH with a LLOQ of 50 pg/mL. A semi‐automated robotics method using liquid‐liquid extraction (LLE) in a 96‐well plate format was developed and validated. The correlation coefficients were ≥0.998 for MPH indicating good fits of the regression models over the range of the calibration curve. The accuracy and precision of the semi‐automated approach were comparable to those obtained using the manual sample preparation technique reported previously (vide supra). The current method can easily be adapted to the enantioselective LC/MS/MS assay of MPH. The assay was simple, fast, specific, and exhibited excellent ruggedness. Copyright © 2000 John Wiley & Sons, Ltd.