Isomer Composition Assessment of Synthetic Phosphatidylethanol by Collision-Induced and Ozone-Induced Dissociation Mass Spectrometry.

The direct blood-alcohol biomarker phosphatidylethanol (PEth), especially its most abundant analogue 1-palmitoyl-2-oleoyl-sn-phosphatidylethanol (PEth 16:0/18:1) has gained increasing relevance in clinical and forensic applications for assessing alcohol consumption. Accurate quantification of PEth is essential to reliably differentiate between abstinence, moderate alcohol consumption and excessive alcohol intake. Measurement accuracy of PEth 16:0/18:1 by well-established liquid chromatography-tandem mass spectrometry (LC-MS/MS) approaches such as multiple reaction monitoring (MRM) can be confounded by the presence of the regioisomer 1-oleoyl-2-palmitoyl-sn-phosphatidylethanol (PEth 18:1/16:0) in samples and synthetic reference standards. To address this measurement uncertainty, we conducted a new assessment of the isomeric composition of six currently available reference materials from four suppliers using collision-induced dissociation/ozone-induced dissociation (CID/OzID). Examination of these synthetic compounds found a high degree of regioisomeric purity of > 95%. Thus verified, the relative abundance of two key LC-MS/MS transitions were compared across a range of collision energies for both reference materials and an exemplary set of 10 dried blood spot case samples. These findings suggest a significantly wider range of natural isomer distributions spanning both higher and lower regiochemical composition (88.8%-98.85%) than the reference materials but within a range that would not significantly impact clinical classification.