General unknown screening of xenobiotics: the contribution of an acidic extraction

摘要

Although general unknown screening (GUS) is often used to detect and identify exogenous compounds in biological matrices, some compounds are not detected for two main reasons: first the method carried out for the extraction, secondly, the lack of sensitivity in the detection of the unknown molecules. The aim of this study was to improve the detection, using an acidic extraction procedure and a MRM mode (ES~-+ or ES~-). Methods: Blank sera were spiked with 42 substances, not detected in GUS. 1 mL was extracted after addition of internal standards and 500 μL of acetate buffer by 3 mL of organic extraction solution (dichloromethane: ether: hexane: isoamyl alcohol; 30:50:20:0.5, v/v). Basic extraction was also carried out by substituting the sodium acetate buffer with saturated borate buffer. The extracts were analysed by UPLC-MS-MS, using MRM mode (ES~+ or ES~-). Results: All the non detected substances by the GUS method were indentified in this study, 25 in ES~+ mode and 17 in ES~- mode. Extraction yield was between 9 and 104%, and upper, compared to that after basic extraction. Conclusion: A rapid, sensitive and selective method using positive or negative MRM mode, with a triple quadrupole mass spectrometer and a simple acidic liquid-liquid extraction allows to identify, confirm and quantify 42 substances (drugs and pesticides) not detected by a routine GUS method.