Analysis of methylated and oxidized purines in urine by capillary gas chromatography-mass spectrometry.

Methylated purine bases from urine can be quantitated by capillary gas chromatography-mass spectrometry with selected ion monitoring. The method is based on a separation of the purines in urine using XAD-2 column chromatography and bonded-phase extraction methods. The extracted samples are derivatized with N-(tert-butyldimethylsilyl)-N-methyltrifluoroacetamide and analyzed by capillary gas chromatography-mass spectrometry. The tert-butyldimethylsilyl derivatives of the purines showed excellent GC and GC/MS properties suitable for low-level detection in extracts of human urine as well as in urine extracts from animals treated with the methylating carcinogen N-nitrosodimethylamine. The oxidized purine bases 7-methyl-8-hydroxyguanine, 8-hydroxyadenine, and 8-hydroxyguanine were also detected in urine. To our knowledge, the latter two modified bases have not been previously reported in normal urine.