Liquid chromatography/tandem mass spectrometry method for simultaneous determination of cocaine and its metabolite (−)ecgonine methyl ester in human acidified stabilized plasma samples

Two simple, sensitive and rapid liquid chromatography/electrospray ionization tandem mass spectrometry (LC–ESI-MS/MS) methods (low range and high range) were developed and validated for the quantification of cocaine and its metabolite (−)ecgonine methyl ester (EME) in human acidified stabilized plasma samples. In the low range assay, cocaine and the internal standard, cocaine-D3, were extracted using a single step liquid–liquid extraction from human acidified stabilized plasma. For the high range assay, human acidified stabilized plasma containing cocaine, EME, and the internal standards, cocaine-D3 and EME-D3, was mixed with acetonitrile, and the protein precipitate was separated by centrifugation. Both cocaine and EME extracted from both assays were separated on a HILIC column and detected in positive ion mode using multiple reaction monitoring (MRM). Both methods were validated and the specificity, linearity, lower limit of quantitation (LLOQ), precision, accuracy, recoveries and stability were determined. The linear range for the low range assay was 0.01–5 ng/mL for cocaine; in the high range assay values were 5–1000 ng/mL for cocaine and 1–200 ng/mL for EME. The correlation coefficient (R2) values for both assays were 0.993 or greater. The precision and accuracy for intra-day and inter-day were better than 13.0%. The recovery was above 85% and matrix effects were low with the matrix factor ranging from 0.817 to 1.10 for both analytes in both assays. The validated methods were successfully used to quantify the plasma concentrations of cocaine and EME in clinical pharmacokinetic and pharmacodynamic studies.