Detection of nitrated and oxygenated polycyclic aromatic hydrocarbons using atmospheric pressure chemical ionization high resolution mass spectrometry

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are common pollutants in the atmosphere and have long been recognized to be toxic to humans. These PAHs can be oxidized into more toxic products in both the gas and condensed (on the surface of suspended particulate matter) phases. In this work, we report fragmentation patterns observed using atmospheric pressure chemical ionization with high resolution mass spectrometry (APCI–HRMS) of PAH oxidation products. A representative group of 18 PAH derivatives containing carbonyl (oxo-PAHs), hydroxyl (hydroxy-PAHs), carboxyl (carboxy-PAHs), and/or nitro (nitro-PAHs) groups were studied. Ionization of carboxy-PAHs in negative mode yielded common fragments of [M−H]−, [M−H−CO]−, and [M−H−CO2]−. Oxo-PAHs provided common fragments of [M+H]+, [M+H−CO]+ and [M+H−2CO]+ in positive mode and [M+e−]− in negative mode. Mass spectra of aldehydes exhibited common fragments of [M+H]+, [M+H−CO]+, and [M+H−O]+ in positive mode and [M+e−]− and [M−H+O]− in negative mode. For all nitro-PAHs, [M+H]+, [M+H−O]+ and [M+3H−O2]+ ions were observed in positive mode. On the basis of the APCI–HRMS analysis of standards, eight reaction products of pyrene oxidation under heterogeneous conditions were characterized. HRMS data, specific fragments and common ions such as that of 205m/z, characteristic for carbonyl phenanthrene, enabled the identification of the oxidation products.