False‐Positive EtG Immunoassay Screening After Exposure to Aliphatic Alcohols. LC‐HRAM‐Orbitrap‐MS Detection of C1–C6 EtG Homologs in Urine, Chest, and Pubic Hair Samples

A subject, admitted to an addiction treatment unit, was occupationally exposed to solvent mixtures and paint thinners containing aliphatic alcohols, while being a coachbuilder. He repeatedly tested positive for ethyl glucuronide (EtG) in weekly urine immunoassays performed in a hospital laboratory. However, he denied any alcohol consumption. Therefore, presumptive positive urine samples, as well as chest and pubic hair samples, were submitted to targeted liquid chromatography-high-resolution accurate mass-Orbitrap-mass spectrometry (LC-HRAM-Orbitrap-MS) analysis, after derivatization of analytes with N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide (EDC). MS acquisition was carried out in full scan positive-ion mode, followed by data-dependent MS² and parallel reaction monitoring confirmation modes, according to an inclusion list of accurate mass values calculated from the elemental composition of MH⁺ ion species of several derivatized EtG homologs. All urine samples turned out to be EtG negative. Instead, methyl, propyl, butyl, and hexyl glucuronides were detected at varying levels depending on the exposure and/or inhalation conditions (product types, amounts, etc.), and urine sampling times. As expected, chest hair and pubic hair were EtG negative too, whereas the same other alcohol glucuronides were detected in both matrices, with higher abundances in pubic hair. Cross-reaction of EtG homologs, in this case due to exposure to chemicals containing several aliphatic alcohols, explains the false-positive urine immunoassay results. Furthermore, LC-HRAM-Orbitrap-MS analyses show that EtG homologs, like EtG, can be incorporated and detected in a variety of hair samples.