Ultrafast laser analysis of nitro-PAHs using laser desorption/femtosecond ionization mass spectrometry

Abstract

Analytical interest in nitrated polycyclic aromatic hydrocarbons (nitro-PAHs) is related to their high mutagenicity and potential presence in a variety of environmental media such as diesel exhaust and urban air particulate matter. Furthermore, fundamental interest in these molecular systems stems from the photophysics of the labile NO₂ functional group, which has been investigated using mass spectrometry. The nitro-PAHs, 1-nitronaphthalene, 9-nitroanthracene, and 1-nitropyrene, have been studied using both femtosecond (λ = 395 and 790 nm) and nanosecond (λ = 266 nm) lasers coupled to a reflectron time of flight mass spectrometer. Analysis of mass spectra taken over a range of intensities (10¹⁴–10¹⁵ W/cm²) has demonstrated that structurally specific ions can be observed for each molecule, with little or no fragmentation at lower intensities. It has also been found that an intact parent ion can be detected using femtosecond ionization at 395 nm in each case. This work demonstrates the potential use of laser desorption/femtosecond laser mass spectrometry (LD/FLMS) as an analytical technique for the detection of nitro-PAHs and other environmental pollutants and as a means of studying the photodynamics of labile molecular systems.