Calf thymus DNA was incubated with [8-14C]styrene oxide in vitro, and six covalent xenobiotic-DNA adducts were detected using the [32P]-postlabeling procedure. Adducts 1-3 were purified by HPLC and identified as bis-substituted-2'-deoxyguanosine 3'-phosphate derivatives using four-sector tandem mass spectrometry. These adducts represented less than 2% of the total adducts detected by [14C]-radioactivity. Adducts 1-3 were also detected when styrene oxide was allowed to react with the mononucleotide, 2'-deoxyguanosine 3'-phosphate only. The elemental compositions of these adducts (C26H30N5O9P) were determined by measurement of their accurate masses by high-resolution mass spectrometry and revealed the unusual incorporation of 2 mol of hydroxyphenylethyl moieties. The structures of these bis(phenylethyl) adducts were established by interpretation of high-energy collision-induced dissociation (CID) mass spectra, together with UV/visible and fluorescence spectrophotometry as N2-(2-hydroxy-1-phenylethyl)-O6-(2-hydroxy-2-phenylethyl)-2'-deoxygua nos ine 3'-phosphate (adduct 1), N2-(2-hydroxy-1-phenylethyl)-O6-(2-hydroxy-1-phenylethyl)-2'-deoxygua nos ine 3'-phosphate (adduct 2), and N1,N2-bis(2-hydroxy-1-phenylethyl)-2'-deoxyguanosine 3'-phosphate (adduct 3). The other most abundant adducts were detected only by [14C]-radioactivity and represented approximately 65% of the total covalent binding. These were identified as depurinated N7-substituted guanines by tandem mass spectrometry and UV/visible spectroscopy. The combination of advanced techniques of mass spectrometry with the [32P]-postlabeling assay and spectroscopic techniques is a comprehensive strategy to assure complete structural identification of all xenobiotic-DNA adducts.(ABSTRACT TRUNCATED AT 250 WORDS)