Structural Characterization of Polycyclic Aromatic Hydrocarbon Dihydrodiol Epoxide DNA Adducts Using Matrix-Assisted Laser Desorption/Ionization Fourier Transform Mass Spectrometry

Matrix-assisted laser desorption/ionization (MALDI) Fourier transform ion cyclotron resonance mass spectrometry (FTMS) has been applied for the structural characterization of four polycyclic aromatic hydrocarbon dihydrodiol epoxide (PAH-DE) adducts, including the 5,6-dimethylchrysene DE adduct of 2′-deoxyadenosine, the 5-methyl- and 5,6-dimethylchrysene DE adducts of 2′-deoxyguanosine, and the benzo[a]pyrene-DE adduct of 2′-deoxyguanosyl 3′-phosphate. Measurement of positive and negative ion mass spectra, accurate mass determinations, and CID experiments were carried out using 10–40 ng (20–70 pmol) of sample. An evaluation of five MALDI matrices showed that matrix selection can be used to control the degree of analyte fragmentation. Three MALDI matrices commonly used for the analysis of proteins (sinapinic acid, ferulic acid, 2,5-dihydroxybenzoic acid) gave positive ion adduct mass spectra showing protonated or sodiated molecular ions accompanied by abundant, structurally informative fragment ions. Fragmentation was significantly reduced when working with two matrices used for oligonucleotide analysis (an anthranilic-nicotinic acid mixture and 3-hydroxypicolinic acid). Using the CID capabilities of FTMS, isolation and activation of the MALDI-produced ions was used to provide additional structural information. While characteristic negative ions were not detected for the adenosyl adduct, the guanosyl and guanosyl 3′-phosphate adducts gave [M-H]⁻ ions when the anthranilic-nicotinic acid matrix mixture was used. The guanosyl adducts also showed [M-H-2H₂O]⁻ fragments. Compared with FAB or FAB-MS/MS for the analysis of underivatized PAH-DE adducts, MALDI-FTMS signals are long-lived, the direct MALDI-FT mass spectra show more structurally informative fragments, and accurate mass and CID experiments require lower sample quantities.