Improvement of hair testing for Ethylglucuronide by supported liquid extraction and ultra-high performance liquid chromatography tandem mass spectrometry

To improve the reproducibility, suitability and speed of hair testing for Ethylglucuronide (EtG), an ultra-high performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS) method was developed and validated together with a supported liquid extraction (SLE) EtG from the keratin matrix. EtG was analyzed using reversed phase chromatography with gradient elution and detection with tandem mass spectrometry operated in multiple reaction monitoring (MRM) mode via negative electrospray ionization (ESI). The method showed good linearity from limit of quantification (LOQ) to 100 pg/mg hair (r2 0.996 ± 0.004). Recovery of the analyte was always higher than 80%, whereas intra- and inter-assay precision were always better than 15%. The developed method was applied to the analysis of more than 200 samples with medico-legal and epidemiological purposes ranging from non-detection of the analyte to 88.1 pg/mg and its robustness was proved by reanalysis of six different proficiency testing samples from the Society of hair testing obtaining a Z-score always less than 2.