Isomer differentiation in 7, 12-dimethylbenz[a]anthracene-pyridine adducts by fast atom bombardment tandem mass spectrometry.

Three isomeric 7,12-dL-nethylbenz[α]anthracene-pyridine adduct salts, namely.. the 5-N-pyridinium-7,12-dimethylbenz[α]anthracene perchlorate, the 7-N-pyridiniummethylene-12methylbenz[ α]anthracene picrate, and the 7-methyl-12-N-pyridiniummethylenebenz[ α]anthracene picrate, were studied by fast atom bombardment tandem mass spectrometry using high energy collisional-activated dissociation (CAD). The CAD mass spectra of the molecular cations and the (M - pyridine)(+) ions allow one to distinguish positional isomers on the basis of daughter ion peak height ratios. The differences in the CAD mass spectra of the (M - pyridine)(+) ions are probably due in part to formation of isomer-specific fused-ring tropyliumions.