Published: Journal of Analytical Toxicology, ISSN 0146-4760, Volume 25, Number 5, July/August, pp. 339-343

Importance of Vacutainer Selection in Forensic Toxicological Analysis of Drugs of Abuse
Stefan W. Toennes* and Gerold F. Kauert
Institute of Forensic Toxicology, University of Frankfurt, Kennedyallee 104, D-60596 Frankfurt/Main, Germany

The enzymatic degradation of cocaine in blood samples, even during transport to a forensic laboratory, is a common problem in toxicological analysis. This can be avoided by the use of blood-sampling devices such as gray-top Vacutainers containing the cholinesterase inhibitor sodium fluoride. In the present study, which included 147 authentic cases, blood samples were collected into two different tubes, one containing fluoride/oxalate and one without stabilizing agents. In all cases, both samples were analyzed for drugs of abuse using Abbott FPIA immunoassays after precipitation and gas chromatography–mass spectrometry (GC–MS) for quantitative analysis. The cannabinoid immunoassay showed markedly lower values in the fluoride-containing samples; this was investigated further and could be explained by hemolysis of these samples. In addition, the concentrations of 11-nor-­9-tetrahydrocannabinol-9-carboxylic acid (THCCOOH) were lower in these samples. A stability study with the THCCOOH acyl glucuronide showed that it is unstable in unpreserved serum, which could explain our observation. GC–MS quantitative data for amphetamine and derivatives, opiates, ­9-tetrahydrocannabinol, and 11-hydroxy-­9-tetrahydrocannabinol were essentially identical; however, they also differed substantially for cocaine, cocaethylene, ecgonine methylester, and benzoylecgonine. Unexpectedly, the concentrations of benzoylecgonine in unpreserved serum were almost half as high as in the fluoride-containing samples.

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