Laser mass spectrometric analysis of polycyclic aromatic hydrocarbons with wide wavelength range laser multiphoton ionization spectroscopy

In many analytical techniques, 1+1 resonance-enhanced multiphoton ionization (1+1 REMPI) is used because it is an efficient and optically selective soft ionization method. While 1+1 REMPI of jet-cooled molecules has been extensively studied, little has been reported so far about this mechanism as it is used in analytical techniques, that is, in the cases where the molecules are not jet-cooled and where widely varying ionization wavelengths are employed. We used two-step laser mass spectrometry (L2MS) to study the wavelength (238-310 nm) dependence and the laser pulse energy dependence of the ion yield for 17 polycyclic aromatic hydrocarbons (PAHs). We discuss how these data allow prediction of the efficiency of 1+1 REMPI for a given compound. These advances open new perspectives for better understanding the L2MS spectra obtained directly from complex mixtures such as environmental samples.