analysis of carcinogen - dna adducts has been regarded as a useful means of assessing human exposure to chemical carcinogens . 
 we have established a method for quantitation of 4-aminobiphenyl ( 4-abp)-dna adducts by alkaline hydrolysis and gas chromatography with negative ion chemical ionization mass spectrometry ( gc - nici - ms ) . 
 aliquots of dna ( typically 100 micrograms / ml ) were spiked with an internal standard , d9 - 4-abp , and were hydrolyzed in 0.05 n naoh at 130 degrees c overnight . the liberated 4-abp 
 was extracted with hexane and derivatized using pentafluoropropionic anhydride in trimethylamine for 30 min at room temperature prior to gc - nici - ms . with in vitro [ 3h]n - hydroxy-4-abp modified dna standards , we observed 59 + /- 
 7% ( n = 9 ) recovery of the 4-abp and a linear correlation between hydrolyzed 4-abp and the adduct levels ranging from about 1 in 10(8 ) to 1 in 10(4 ) nucleotides ( r = 0.999 , n = 9 ) . 
 the method was further validated by comparison of the results with that obtained by the 32p - postlabeling method . 
 there was excellent agreement ( r = 0.994 , p < 0.001 ) between the two methods for quantitation of the adduct in eight samples of salmonella typhimurium dna treated with 4-abp and rat liver s9 , although the 32p - postlabeling method gave slightly higher values . 
 the dna adducts in 11 human lung and 8 urinary bladder mucosa specimens were then determined by our gc - nici - ms method . 
 the adduct levels were found to be < 0.32 to 49.5 adducts per 10(8 ) nucleotides in the lungs and < 0.32 to 3.94 adducts per 10(8 ) nucleotides in the bladder samples.(abstract truncated at 250 words)imagesfigure 4 . 
 afigure 4 . 
 b