Simultaneous determination of folic acid photolysis products and oxidized guanine derivatives in plasma by liquid chromatography‐tandem mass spectrometry

Folic acid (FA) is easily photodegraded to yield 6‐formylpterin and pterin‐6‐carboxylic acid, which can generate reactive oxygen species and result in the formation of oxidized guanine derivatives such as 8‐hydroxy‐2′‐deoxyguanosine and 8‐hydroxy‐guanosine. In this study, we developed a simple, rapid, and sensitive liquid chromatography‐tandem mass spectrometry strategy for the simultaneous determination of FA photolysis products and oxidized guanine derivatives in plasma samples. Chromatographic separation was performed on a Waters HSS T3 column (2.1 × 100 mm, 5.0 μm) with gradient elution at a flow rate of 0.25 mL/min. Plasma samples were first pretreated with 1% formic acid, followed by protein precipitation with methanol. The developed method showed good linear relationships between 1 and 2000 ng/mL ( r 2 > 0.99). The intra‐ and inter‐day precisions ranged from 2.6% to 7.5% and from 2.5% to 6.5%, respectively. Recoveries of the analytes were between 75.4% and 112.4% with the relative standard deviation < 9.1%. Finally, the method was applied to quantify FA photolysis products and oxidized guanine derivatives in rats with light and non‐light conditions.