Although meconium is more easily collectable from a newborn as compared to urine, its analysis is considerably more difficult. Before analysis, it is important that the sample be homogenized, as meconium is a non-homogenous and is a gelatinous material. The methods of analysis include immunoassays for screening and GC-MS for confirmation. Although there is no FDA-approved immunoassay for drugs of abuse testing for meconium, the laboratories generally modify commercially available urine assays for drugs of abuse. The commonly used immunoassays are RIA, enzyme multiplied immunoassay technique (EMIT), kinetic interactions of microparticles in solution, cloned enzyme donor immunoassay and fluorescence polarization immunoassay.
Unlike urine or serum or plasma, drugs need to be extracted from meconium before analysis by immunoassays. Several methods have been described for extraction of drugs from meconium. Common methods include using 100-500 mg of meconium and extraction of drugs with 1-2 mL of organic solvents such as acetonitrile and methanol by vigorous agitation of the sample with a vortex mixer. The specimen is then centrifuged at high speed (~10, 000 x g), and supernatant is used for analysis using immunoassays (97,105). Some laboratories evaporate the organic solvent extract and reconstitute the residue into a buffer prior to analysis (106).
Moore et al. (107) compared several methods of drug detection from meconium. The authors compared extraction efficiency, false-positive and false-negative rates using hydrochloric acid, phosphate buffer/methanol and glacial acetic acid/ dipheny-lamine/acetone as extraction solvents. The study found that extraction performed with hydrochloric acid was poorest while glacial acetic acid/diphenylamine/acetone extraction protocol was the best. The confirmation method for this study was GC-MS, and the drugs studied were cocaine, THC-COOH, amphetamines, PCP and opiates.
ElSohly et al. (100) described a GC-MS method for confirmation of cannabinoids, cocaine, opiates, amphetamines and PCP in meconium. EMIT and TDx immunoassays were used as screening methods, and cut-off levels were 20 ng/g for THC-COOH and PCP, and 200ng/g for benzoylecgonine, morphine and amphetamines. The GC-MS confirmation rate for the immunoassay-positive specimens was low, ranging from 0% for amphetamines to 75% for opiates. The lowest rate of confirmed positives was found with the cannabinoids, suggesting that THC metabolites other than free THC-COOH may be major contributors to the immunoassay response in meconium.
Pichini et al. (108) described an atmospheric pressure ionization-electrospray LC-MS method for determination of amphetamine, methamphetamine and methylenedioxy derivatives in meconium. The drugs were extracted in methanolic hydrochloric acid and cleaned by a solid-phase extraction. Chromatography involved C18 reversed-phase column and a mobile phase consisting of 10 mM ammonium bicarbonate (pH 9.0) and methanol. The method demonstrated excellent sensitivity with LOQ of 0.005 ^g/g meconium for amphetamine, methamphetamine and 4-hydroxy-3-methoxymethamphetamine. The LOQ was 0.004 ^g/g meconium for MDA, MDMA and MDEA.
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