An automated sample preparation approach for routine liquid chromatography tandem-mass spectrometry measurement of the alcohol biomarkers phosphatidylethanol 16:0/18:1, 16:0/16:0 and 18:1/18:1

Background Phosphatidylethanols (PEths) are currently under investigation as highly sensitive and specific direct biomarkers of long-term alcohol abuse. PEths belong to a group of aberrant phospholipids formed in erythrocyte membranes in presence of ethanol by the catalytic action of the enzyme phospholipase D on phosphatidylcholine. Compared to other alcohol biomarkers, a higher sensitivity (94.5–100%) and specificity (100%) characterizes PEth species. Method Prior to detection, an important practical aspect in the work-flow of PEths analysis is the sample preparation step. To date, traditional techniques such as liquid-liquid extraction (LLE) and solid phase extraction (SPE) require multiple steps to remove blood interferences. Due to the simplicity of use and the possibility of automation, sample filtration is also a widespread technique in biomedical laboratories. In this work, a reliable sample preparation method based on an automated filtration with Phree™ Phospholipid Removal Plates (Phenomenex, California, USA) was developed to extract PEths from human whole blood. Surface characteristics of Phospholipids Removal material allow phospholipids retention on the filter and a suitable PEths recovery after elution. The blood samples were added with internal standard (IS) and purified in acetonitrile (1 mL). After centrifugation, supernatants were applied to the Phospholipids Removal Plates in an automated workstation. After washing, the phospholipids retained on the filter were eluted with 1-mL 2-propanol 1% ammonia. PEth 16:0/18:1, PEth 16:0/16:0 and PEth 18:1/18:1 were extracted using the proposed method and detected by LC–MS/MS operated in electron spray ionization (ESI). The detection of all compounds was based on multiple reaction monitoring (MRM) transitions. This method was validated for the quantitative profiling of PEth molecular species in human blood collected from heavy and social drinkers. Results The method was validated according to Food and Drug Administration (FDA) guidelines. Linearity was observed in the 25 – 1250 (PEth 16:0/18:1) and 5 – 250 (PEth 16:0/16:0 and PEth 18:1/18:1) ng/mL range with a correlation coefficient (r²) between 0.997 and 0.999 for all three compounds. Moreover, the nominal concentrations of non-zero calibrators were ±15%. Variation coefficient (%CV) was < 10 % for all the analytes, while lowest limit of quantitation (LLOQ) was found to be 1.25 ng/mL for PEth 16:0/18:1, 0.50 ng/mL for PEth 16:0/16:0 and 0.50 ng/mL for PEth 18:1/18:1. Intra- and inter-day precision and accuracy were always lower than 14% and 11%, respectively. Analytical recovery was higher than 68.8 % for all analytes. Sample stability at 4 °C and– 20 °C showed a concentration drop ≤ 20 % up to 4 weeks. Extracts were stable for 7 days in the autosampler and 30 days at – 20 °C and 4 °C in a closed vial. The procedure was successfully applied to blood samples collected from heavy drinkers (n = 8), social drinkers (n = 5), and teetotalers (n = 7). Conclusions Due to the simplicity of application and the possibility of automation, sample filtration is well suited for a clinical and forensic laboratory. To monitor alcohol consumption, an analytical method based on liquid chromatography–tandem mass spectrometry (LC–MS/MS) with novel and automated sample preparation was developed and validated for the simultaneous quantification of PEth 16:0/18:1, PEth 16:0/16:0 and PEth 18:1/18:1 in whole blood samples, characterized by a fast sample preparation and lower pre-analysis costs than other extraction procedures.