Rapid preparation of human urine and plasma samples for analysis of F2-isoprostanes by gas chromatography-mass spectrometry

Reliable MS-based methods have been developed for the measurement of free and esterified F-2-isoprostanes. However, prior to sample analysis several steps of purification, including solid-phase extraction followed by TLC or HPLC, are usually required, making it tedious to analyze large sample numbers, e.g., for population studies. We report a quick sample purification method using anion exchange solid phase extraction (SPE), which is highly selective for acidic compounds. Urine and hydrolyzed plasma of healthy individuals were acidified before SPE extraction, washed with 4 different solvent mixtures and finally eluted with ethyl acetate. The eluted samples were first derivatized with pentafluorobenzyl bromide followed by a second derivatization with bis(trimethylsilyl)trifluoroacetamide. F-2-isoprostanes were analyzed by GGMS-NCI. The method was highly sensitive; the limit of detection at 5:1 signal-to-noise ratio was 0.037 ng/ml and 0.007 ng/mg creatinine for plasma and urine, respectively. Anion exchange SPE extraction for F-2-isoprostane showed recovery of 55-65% and high linearity for concentration 0-1.0 ng/ml for urine (CV = 4.08%, r(2) = 0.990) and 0-0.5 ng/ml for plasma (CV = 4.07%, r(2) = 0.998). Fasting for 6 h significantly increased plasma F-2-isoprostanes levels, which has implications for the design of intervention studies using this biomarker. (C) 2004 Elsevier Inc. All rights reserved.