Atmospheric\nPressure Laser Ionization Mass Spectrometry\nwith Tunable UV Wavelength Utilizing an Optical Parametric Oscillator

To our knowledge, this study presents the first implementation\nof wavelength-resolved resonance-enhanced multiphoton ionization (REMPI)\nspectroscopy under atmospheric pressure ionization conditions using\na high-resolution mass spectrometric system. Atmospheric pressure\nlaser ionization MS spectroscopic measurements were conducted on over\n70 different polycyclic aromatic hydrocarbons (PAHs) and hetero-PAHs\n(N, S, and O) in standard solutions, as well as three complex PAH-containing\nsamples. The results demonstrate the successful transfer of REMPI\nspectroscopy from vacuum to atmospheric pressure conditions, maintaining\nspectral integrity without significant band broadening. The obtained\nspectral data add an orthogonal dimension to mass spectrometry, providing\nstructural insights into aromatic core motifs and enabling isomeric\ndifferentiation. This differentiation is further enhanced by linear\nregression algorithms, which allow for the semiquantitative analysis\nof isomer mixtures. Comparison between standard spectra and complex\nsample spectra reveals high correlation values for certain peaks,\nstrongly indicating the presence of specific PAHs and distinguishing\nbetween phenanthrene and anthracene in fossil- and biobased samples.