Liquid chromatography-tandem mass spectrometry analysis of cocaine and itsmetabolites from blood, amniotic fluid, placental and fetal tissues: studyof the metabolism and distribution of cocaine in pregnant rats

The ability to simultaneously quantitate cocaine and its 12 metabolites fro m pregnant rat blood, amniotic fluid, placental and fetal tissue homogenate s aids in elucidating the metabolism and distribution of cocaine. An effici ent extraction method was developed to simultaneously recover these 13 comp onents using underivatized silica solid-phase extraction (SPE) cartridges. The overall recoveries for cocaine and its metabolites were studied from pr egnant rat blood (47-100%), amniotic fluid (61-100%), placental homogenate (31-83%), and fetal homogenate (39-87%). Extraction of the samples using si lica is not classical SPE, but rather allows for the concentration of the s ample into a small volume prior to injection and the removal of the protein s due to their strong interaction with the active silica surface. A positiv e ion mode electrospray ionization liquid chromatography-tandem mass spectr ometry (LC-MS-MS) method was used and validated to simultaneously quantitat e cocaine and 12 metabolites from these four biological matrices. A gradien t elution method with a Zorbax XDB C-8 reversed-phase column was used to se parate the components. Multiple reaction monitoring (MRM) of a product ion arising from the corresponding precursor ion was used in order to enhance t he selectivity and sensitivity of the method Low background noise was obser ved from the complex biological matrices due to efficient SPE and the selec tivity of the MRM mode. Linear calibration curves were generated from 0.01 to 2.50 ppm. The method also showed high intra-day (n=3) and inter-day (n=9 ) precision (% RSD) and accuracy (% error) for all components. The limits o f detection (LODs) for the method ranged from 0.15 to 10 ppb. The LODs of c ocaine and its major metabolites were less than I ppb from all four biologi cal matrices. This method was applied to the study of the metabolism and di stribution of cocaine in pregnant rats following intravenous infusion to a steady state plasma drug concentration. The following results were observed in the pregnant rat study: (1) the observations correlated strongly with t he previous literature data on cocaine metabolism and distribution, (2) coc aine and norcocaine accumulated in the placenta, (3) arylhydroxylation of c ocaine was a major metabolic pathway, (4) para-arylhydroxylation of cocaine was favored over meta-arylhydroxylation in rats and (5) accumulation of co caine and its major metabolites was observed in the amniotic fluid. (C) 200 0 Elsevier Science B.V. All rights reserved.