Samples were centrifuged at approximately 3000 rpm for 5 minutes at approximately 4°C within 30 minutes of collection. Plasma samples were acidified with 1% (v/v) formic acid (FA) to avoid degradation of PG and metabolites in plasma within 20 minutes of the start of centrifugation and then stored frozen (≤-60 °C). Acidified plasma was extracted using internal standard-spiked solution (100 mM ammonium bicarbonate : acetonitrile = 1:4). Samples were then centrifuged to collect supernatant, followed by drying to completion. The dried samples were reconstituted with 200 uL of 0.1% (v/v) formic acid in water. Samples were vortexed and centrifuged before injection. In order to assess potential impact of hemolysis on qualification of PG and its metabolites, hemolyzed plasma was prepared by spiking fully hemolyzed whole blood at indicated percentage into plasma.