High-performance liquid chromatography versus solid-phase extraction for post-derivatization cleanup prior to gas chromatography-electron-capture negative-ion mass spectrometry of N1,N3-bis-(pentafluorobenzyl)-N7- (2-[pentafluorobenzyloxy]ethyl)xanthine, a product derived from an ethylene oxide DNA adduct.

N7-(2-Hydroxyethyl)xanthine (N7-HEX), as a standard, has been measured at the low picomole level by the following sequence of steps: (1) derivatization with pentafluorobenzyl bromide; (2) post-derivatization sample cleanup by reversed-phase high-performance liquid chromatography (HPLC) or silica solid-phase extraction; and (3) separation/detection by gas chromatography electron-capture negative-ion mass spectrometry (GC-ECNI-MS). The average yield of product from the two sample cleanup procedures applied to 95 pg (0.48 pmol) of N7-HEX was comparable: 60% for HPLC; 56% for solid-phase extraction. The reaction blanks (0 pg N7-HEX) showed an interfering GC-ECNI-MS peak after HPLC cleanup. This problem was not encountered with solid-phase extraction, which, along with its greater convenience, made it the preferred technique for post-derivatization sample cleanup.