Determination of cocaine and its derivatives in hair samples by liquid phase microextraction (LPME) and gas chromatography–mass spectrometry (GC–MS)

Abstract

Hair testing is a recognized approach when it comes to accessing historical drug use. According to the World Drug Report of United Nations Office on Drugs and Crime (UNODC) 2015, Brazil is the largest cocaine (COC) market in South America. New analytical methodologies to detect crack/cocaine analytes in hair samples are highly desirable. Here, a method consisting of a liquid-phase microextraction (LPME) as a clean-up step, followed by gas chromatography–mass spectrometry (GC–MS) analysis has been proposed. The new validated method consisted of a washing step; an overnight incubation with methanol and a quick derivatization with butylchloroformate. Once derivatized, the samples were then submitted to the LPME procedure. Limits of detection (LoD) and quantitation (LoQ) obtained were of 0.1 and 0.5ng/mg for COC 0.4 and 0.5ng/mg for anhydroecgonine methyl ester (AEME); 0.03 and 0.05 for cocaethylene (CE), respectively and 0.05ng/mg for both LoD and LoQ for benzoylecgonine (BZE). All calibration curves were linear over the scope applied, from LoQ up to 20ng/mg, with a r2>0.99. Precision and accuracy assays showed acceptable %RSD values, according to international guidelines. Twelve postmortem head hair samples stemming from the Institute of Legal Medicine of Sao Paulo (IML-SP) have been analyzed, from which seven have shown to be positive for COC (0.75–>20ng/mg) and BZE (0.1–>20ng/mg). Apart from COC’s main metabolite, four samples were also positive for CE (0.1–3.9ng/mg) and three samples for AEME (0.5–4.9ng/mg). To conclude, the LPME technique together with GC–MS analysis have shown promising results and were able to meet the demand of the laboratory of analyzing postmortem hair samples to look for all four analytes.