Interlaboratory comparison studies on the analysis of hair for drugs of abuse

Eleven laboratories interested in the analysis of human hair for drugs of abuse participated in a study to determine how well drugs could be detected and quantified in hair. For the two exercises completed to date, substances to be determined were limited to cocaine, benzoylecgonine, and morphine. Samples sent to the participating laboratories included hair from drug users, drug-free hair, and hair into which drugs had been soaked. For the first exercise, the hair samples were sent as powders; for the second, they were in the form of short segments. Results from these studies have shown that the laboratories, with a few exceptions, have performed very well qualitatively. However, scatter in quantitative results was high. Various approaches were used to liberate drugs from the hair, with the most commonly used, acid extractions and enzyme digestions, producing similar results. Laboratories using GC/MS generally performed well and reported no false positives. In contrast, one laboratory analyzing hair directly using MS/MS without extractions produced three of the four false positives and the worst quantitative results.