Acidic mobile phases are commonly used in reversed phase liquid chromatography tandem mass spectrometry (LC-MS/MS) bioanalysis. However, increased sensitivity, improved peak symmetry, and increased retention, especially for basic hydrophilic drugs have been observed using basic mobile phases. In our previous acidic mobile phase LC-MS/MS method we needed two injections (0.4 and 2.0μL) of each sample for this task, which is inefficient. The aim of this study was to investigate if basic mobile phase LC-MS/MS could be used to determine phosphatidylethanol 16:0/18:1 and 20 other drugs and metabolites with satisfactory sensitivity in one single run. Whole blood was prepared by 96-well supported-liquid extraction using heptane/ethyl acetate/2-propanol (16:64:20, v:v:v). Chromatographic separation was achieved on an Acquity BEH C18 column (50×2.1mm I.D.), using a mobile phase with 0.025% ammonia, pH 10.7 (Solvent A) and methanol (Solvent B). All compounds had isotope-labelled internal standards. The method was fully validated. Recovery was between 63 and 91% for 20 compounds and 10% for benzoylecgonine. Matrix effects were low, except for ion enhancement of buprenorphine and ion suppression for THC. However, internal standards compensated for these effects. Inter-assay precision and accuracy were < ± 20% for all compounds at five tested concentrations, except for methamphetamine at the highest concentration. An LC-MS/MS method for simultaneous determination of PEth 16:0/18:1 and 20 drugs and metabolites in whole blood were for the first time developed and validated. Retention of PEth 16:0/18:1 was, in contrast to the other 20 compounds, largely affected by mobile phase buffer concentration. The buffer free basic mobile phase ensured that phosphatidylethanol 16:0/18:1 eluted before most of the unwanted phospholipids.
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