Determination of hydroxy metabolites of cocaine in hair samples for proof of consumption.

Although hair is widely used to identify drug use, there is a risk of false positives due to environmental contamination. This especially applies to cocaine (COC). Several strategies such as detection of norcocaine (NCOC) or cocaethylene, metabolite concentration ratios or intricate washing procedures have been proposed to differentiate actual use from contamination. The aim of the present study was to identify hydroxy metabolites of COC in hair specimens, thus enabling unambiguous prove of ingestion. A suspect screening of 41 COC-positive samples for these compounds was performed by liquid chromatography-quadrupole time of flight-mass spectrometry (LC-QTOF-MS). Once identified, mass transitions for o-, p- and m-isomers of hydroxy COC as well as p- and m-isomers of hydroxy benzoylecgonine (BE) and hydroxy NCOC were introduced into a routine procedure for testing drugs of abuse in hair by liquid chromatography-tandem mass spectrometry (LC-MS/MS) which was applied to 576 hair samples. Hydroxy metabolites were present in 92.2% of COC-positive hair samples; their detection rate exceeded that of cocaethylene and NCOC. Moreover, p-OH-BE, m-OH-BE as well as p-OH-NCOC and m-OH-NCOC have been identified for the first time in COC-positive hair specimens. Hydroxy cocainics could be detected in samples having a negative conclusion on drug use applying hitherto established criteria. We suggest a more conclusive interpretation outcome including detection of hydroxy metabolites into the evaluation of COC-positive hair samples.