Determination of Isomeric Dibenzo[ a, l]pyrene-Adenine Adducts by Six Different Tandem Mass Spectrometric Experiments

Six different tandem-mass-spectrometric experiments were evaluated to assess their ability to distinguish four isomeric, carcinogen-modified adenines. Metastable-ion dissociations and high-energy collisional activated decompositions (HE CAD) of fast-atom bombardment (FAB)-produced ions were followed on a four-sector tandem mass spectrometer. Precursor ions were also produced by electrospray on the four-sector instrument, and they were submitted to both high-energy and electrospray ionization (ESI)-source CAD. We contrasted these means of activation with low-energy (LE) CAD of electrospray-produced ions on a triple quadrupole instrument and with post-source decompositions (PSD) of ions produced by matrix-assisted laser desorption ionization (MALDI). The latter experiment was conducted with a time-of-flight mass spectrometer. The four subject molecules were isomeric dibenzo[ a, l]pyrene (DB[ a, l]P) adenine adducts, in which N1, N3, N7, and N 6 positions were substituted. We used similarity indicies (SI), which were calculated from the relative abundances of common fragment ions for the isomers, to confirm quantitatively that HE CAD of FAB and ESI-produced ions can distinguish two of three, and that LE CAD and MALDI-PSD can distinguish three of the three isomers that give qualitatively identical product-ion spectra. The results also show that LE CAD and MALDI-PSD have comparable discriminating capability for these three DBP adducts.