Liquid chromatography electrospray ionization mass spectrometry (MS) with a triplequadrupole MS was used to identify known and novel heterocyclic aromatic amines (HAAs) inhuman urine. The identities of 2-amino-3,8-dimethylimidazo[4,5-
f]quinoxaline (8-MeIQx) and2-amino-1-methyl-6-phenylimidazo[4,5-
b]pyridine (PhIP) were confirmed by their product ionspectra. The constant neutral loss scan mode was employed to probe for other analytes inurine that display the transition [M + H]
+ [M + H - CH
3]
+, which is common to HAAscontaining an
N-methylimidazo moiety, and led to the detection of a previously unreportedisomer of 8-MeIQx [Holland, R., et al. (2004)
Chem. Res. Toxicol. 17, 1121-1136]. We nowreport the identification of another novel HAA, 2-amino-1-methylimidazo[4,5-
b]quinoline(IQ[4,5-
b]), an isomer of the powerful animal carcinogen 2-amino-3-methylimidazo[4,5-
f]quinoline (IQ). The amounts of IQ[4,5-
b] measured in the urine of human volunteers whoconsumed grilled beef ranged from 15 to 135% of the ingested dose, while the amounts of8-MeIQx and PhIP excreted in urine were on average <2% of the ingested dose. Base treatmentof urine at 70
C increased the concentrations of 8-MeIQx and PhIP by as much as 6-fold,indicating the presence of phase II conjugates; however, the amount of IQ[4,5-
b] increased bymore than 100-fold. IQ[4,5-
b] was also detected in the urine of
vegetarians following basehydrolysis. The formation of IQ[4,5-
b], but not IQ, 8-MeIQx, or PhIP, also occurred in urineincubated at 37
C. Creatinine and 2-aminobenzaldehyde are likely precursors of IQ[4,5-
b].The detection of IQ[4,5-
b] in the urine of both meat eaters and
vegetarians suggests that thisHAA may be present in nonmeat staples or that IQ[4,5-
b] formation may occur endogenouslywithin the urinary bladder or other biological fluids.