Abstract Alcohol consumption can lead to serious health repercussions, including motor impairments and organ failure. Testing for short-term alcohol use is routinely conducted using blood ethanol tests in clinical laboratories. However, there is an emergent need to identify heavy alcohol users, especially crucial for patients undergoing organ transplant evaluations. With the advent of various biomarkers to detect heavy alcohol use, phosphatidyl ethanol (PEth), a group of abnormal phospholipids formed in cell membranes due to alcohol consumption, has gained prominence. PEth has been analyzed in whole blood with liquid chromatography-tandem mass spectrometry (LC-MS/MS) as two isomers: 18:1 (fatty acid:double bond) and 18:2 (fatty acid:double bond). We have developed an LC-MS/MS method that can detect these isomers in 4.5 minutes at concentrations of 10-500 ng/mL with excellent linearity and precision. In contrast to most LC-MS/MS methods where phospholipids are removed to minimize ion suppression, this method requires retaining phospholipids because the analyte, PEth, is a type of phospholipid. This was achieved through a ‘reverse extraction’ approach using phospholipid removal cartridges. Subsequently, the extracted samples were separated in an Agilent Protoshell 120 HPLC column on a Vanquish UHPLC instrument using 1 mM ammonium formate with 0.2% formic acid in water as Solution A and 50/50 isopropanol/acetonitrile as Solution B. The separation is performed starting at 80% Solution B (rest is Solution A) followed by a gradient elution where Solution B was increased to 95% over 2.3 minutes. Ions were analyzed using a ThermoFisher TSQ Endura MS/MS instrument in the negative mode. Additionally, commercially available whole blood was found to contain detectable levels of PEth in random lots, rendering them unsuitable for use as blank blood in the preparation of calibrators and quality controls. Instead, synthetic was used for this purpose. Ion suppression was observed, and various strategies were attempted to minimize it, including adjusting additives in the mobile phase, extending LC separation times, among others. More details on the impact of these adjustments and their effectiveness in improving the method’s performance will be presented.
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