GENERAL-METHOD FOR DETERMINING ETHYLENE-OXIDE AND RELATED N-7-GUANINEDNA-ADDUCTS BY GAS CHROMATOGRAPHY-ELECTRON CAPTURE MASS-SPECTROMETRY

A 112-mu g sample of DNA was spiked with 103 pg of N-7-(2'-hydroxyethy l)guanine and 100 pg of N-7-(2'-hydroxyethyl-d4)guanine, the internal standard. The sample was subjected to the following sequence of steps: heating at 100 degrees C, precipitation of the DNA with HCl, reaction with nitrous acid to form the corresponding xanthines, reaction twice with pentafluorobenzyl bromide (first to derivatize NH, then OH), sol id-phase extraction on silica and detection by gas chromatography-elec tron capture mass spectrometry. The absolute, overall yield of final p roduct for both the analyte and internal standard was 9.7%. Convenient ly, the three chemical reactions are conducted sequentially in the sam e vial and, aside from a washing step, are separated only by evaporati ons. Corresponding N-7-guanine methyl, phenyl and styrene oxide adduct s were detected at about the 50-ng level by the procedure, to indicate the generality of the method.