Immunoassay and GCÐMS Procedures for the Analysis of Drugs of Abuse in Meconium

Published: Journal of Analytical Toxicology, Volume 23, Number 6, October 1999, pp.436-445

Immunoassay and GC–MS Procedures for the Analysis of Drugs of Abuse in Meconium
Mahmoud A. ElSohly, Donald F. Stanford, Timothy P. Murphy, Barry M. Lester, Linda L. Wright, Vincent L. Smeriglio, Joel Verter, Charles R. Bauer, Seetha Shankaran, Henrietta S. Bada, and H. Chip Walls

The analysis of meconium specimens for metabolites of substances of abuse is a relatively accurate method for the detection of fetal exposure to drugs. Most of the methods reported in the literature before the early 1990s relied on radioimmunoassays. The purpose of this study was to develop and validate methods for meconium sample preparation for the screening and gas chromatography–mass spectrometry (GC–MS) confirmation of meconium extracts for cannabinoids, cocaine, opiates, amphetamines, and phencyclidine. EMIT™ and TDx™ immunoassays were evaluated as screening methods. The sample preparation method developed for screening included extraction and purification prior to analysis. Cutoff levels were administratively set at 20 ng/g for 11-nor-D9-THC-9-COOH (THCCOOH) and phencyclidine and at 200 ng/g for benzoylecgonine, morphine, and amphetamines, although lower levels could be detected in meconium using the EMIT-ETS™ system. Ninety-five meconium specimens were subjected to the screening procedure with GC–MS confirmation of presumptive positives. In addition, 30 (40 for cocaine) meconium specimens were subjected to GC–MS analysis for all analytes regardless of the screening results to determine the false-negative rate, if any, of the immunoassay. Although there were no false negatives detected, the GC–MS confirmation rate for the immunoassay-positive specimens was generally low, ranging from 0% for amphetamines to 75% for opiates. The lowest rate of confirmed positives was found with the cannabinoids, suggesting that tetrahydrocannabinol (THC) metabolites other than free 11-nor-9-carboxy-D9-THC may be major contributors to the immunoassay response in meconium.

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