Sensitive method for detection of cocaine and associated analytes by liquid chromatography-tandem mass spectrometry in urine

Abstract

Cocaine (COC) is a potent CNS stimulant that is metabolized to benzoylecgonine (BE) and further metabolized to minor metabolites such as m-hydroxybenzoylecgonine (m-HOBE). COC is also metabolized to norcocaine (NC). Cocaethylene (CE) is formed when cocaine and ethyl alcohol are used simultaneously. Anhydroecgonine methyl ester (AEME) is a unique marker following smoked cocaine, and anhydroecgonine ethyl ester (AEEE) is found in cocaine smokers who also use ethyl alcohol. We developed a liquid chromatography-tandem mass spectrometry (LC-MS-MS) method for the detection and quantitation of COC, BE, NC, CE, m-HOBE, AEME, and AEEE in urine. Two hundred samples previously analyzed by gas chromatography (GC) coupled with MS were extracted using solidphase extraction. Chromatographic separation was achieved using a gradient consisting of mobile phase A [20 mM ammonium formate (pH 2.7)] and mobile phase B (methanol/acetonitrile, 50:50), an XDB-C8 (50 × 2.1 mm, 1.8 μ m) column and a flow rate of 270 μ L/min. Concentrations were calculated by comparing the peak-area with the internal standard and plotted against a standard curve. The assay displayed linearity from 1.0 to 100 ng/mL. Within- and between-run coefficients of variation were < 10% throughout the linear range. A method comparison between GC-MS and LC-MS-MS showed good correlation for COC (r2 = 0.982) and BE (r2 = 0.955). We report here on a sensitive method to identify clinically and forensically relevant cocaine and associated analytes at concentrations as low as 1.0 ng/mL.