A Direct Immersion Solid-Phase Microextraction Gas Chromatography/Mass Spectrometry Method for the Simultaneous Detection of Levamisole and Minor Cocaine Congeners in Hair Samples From Chronic Abusers

Background: Because levamisole has been increasingly found as a component of illicit drugs, a robust method to detect its presence in hair samples is needed. However, no systematic research on the detection of levamisole in hair samples has been published. The method presented here uses direct immersion solid-phase micro-extraction coupled with gas chromatography and mass spectrometry (DI-SPME-GC/MS) to detect levamisole and minor cocaine congeners in hair samples using a single-extraction method. Methods: Fifty hair samples taken in the last 4 years were obtained from cocaine abusers, along with controls taken from drug-free volunteers. Sampling was performed using direct immersion with a 30-mm polydimethylsiloxane fused silica/stainless steel fiber. Calibration curves were prepared by adding known amounts of analytes and deuterated internal standards to the hair samples taken from drug-free volunteers. This study focused on the adulterant levamisole and some minor cocaine congeners (tropococaine, norcocaine, and cocaethylene). Results: Levamisole was detected in 38% of the hair samples analyzed; its concentration ranged from 0.2 to 0.8 ng/mg. The limit of quantification and limit of detection for levamisole, tropococaine, norcocaine, and cocaine were 0.2 and 0.1 ng/mg, respectively. Conclusions: DI-SPME-GC/MS is a sensitive and specific method to detect the presence of levamisole and cocaine congeners in hair samples.