Interlaboratory studies on the analysis of hair for drugs of abuse: results from the fourth exercise.

Fourteen laboratories interested in the analysis of human hair for drugs of abuse participated in a fourth interlaboratory study to determine how well drugs could be detected and quantitated in hair. The drugs of abuse included cocaine, benzoylecgonine, cocaethylene, codeine, morphine, and 6-monoacetylmorphine. The hair samples analyzed were in the form of short segments and included hair from drug users, soaked hair (drug-free hair into which drugs had been soaked), and drug-free hair. Results from the study show that the laboratories performed well qualitatively, but that there was a large amount of scatter in quantitative results. Various methods were used to extract the drugs from the hair, and the most commonly used approaches, HCl extractions, methanol extractions, and enzyme digestions, all gave comparable results. Gas chromatography-mass spectrometry (GC-MS) was the most commonly used analytical technique. Of the laboratories using GC-MS, some produced consistently good results, whereas others produced results of poorer quality. Two laboratories using liquid chromatography-mass spectrometry produced good results, but the one laboratory using liquid chromatography without mass spectrometric detection produced less accurate results. Laboratories that reported good results on control material sent with the unknowns generally performed better on the unknowns than did laboratories whose results on the control were less accurate.