|SOFT - TIAFT 1998||Poster Session 4||Friday October 9, 1998|
A GAS CHROMATOGRAPHIC POSITIVE ION CHEMICAL IONIZATION MASS SPECTROMETRIC METHOD THAT USES SOLID PHASE EXTRACTION FOR DETERMINATION OF COCAINE, BENZOYLECGONINE, ECGONINE METHYL ESTER AND NORCOCAINE|
Alan C. Spanbauer, David E. Moody and Rodger L. Foltz
Center for Human Toxicology, University of Utah, Salt Lake City, UT 84112, USA
|The gas chromatographic-mass spectrometric method to determine cocaine, benzoyl-ecgonine (BZE), ecgonine methyl ester (EME) previously described by Crouch et al. (J. Anal. Toxicol. 19: 352, 1995) has been modified to also allow determination of norcocaine. Analytes were isolated from human plasma utilizing a modification of the previously described solid-phase extraction. Hexafluoroisopropanol and pentafluoroproprionic anhydride replaced N-methyl-N-(tert-butyldimethylsilyl)-trifluoroacetamide as derivatizing reagents. Quantitation of cocaine and its metabolites using deuterium labeled internal standards was determined after separation of the compounds by capillary chromatography. Analysis was performed by positive ion chemical ionization mass spectrometry using methane and ammonia as the reagent gases. The ions monitored for the analytes and respective internal standards were: cocaine (d0/d3), m/z 304/307; BZE (d0/d3), m/z 440/443; EME (d0/d3), m/z 346/349; and norcocaine (d0/d5), m/z 453/458.
Linearity of the method was established from 1.0 to 1000 ng/mL with r2 for 6 runs of 0.992-0.997. Recovery of cocaine and each of its metabolites was approximately 80%. Intra-run precision and accuracy were determined for the limit of quantitation (LOQ) calibrators at 1 ng/mL and quality control samples (QCs) at 25, 100 and 250 ng/mL. At the LOQ accuracy was within 10% of target for all analytes and % CVs ranged from 9 to 18%. QCs had accuracy within 15% of target and CVs were also within 15%. Inter-run precision and accuracy were also determined with the accuracy at the LOQ ranged from 100 to 120%, and the CVs for the LOQ ranged from 0 to 10%. The inter-run accuracy for the QCs were within 12% and the CVs ranged from 4 to 15%. Stability data suggest the analytes are stable for 24 hours at room temperature and following 2 freeze-thaw cycles.