Laser ionization of H2S and ion-molecule reactions of H3S+ in laser-based ion mobility spectrometry and drift cell time-of-flight mass spectrometry

The detection of hydrogen sulfide (H₂S) by 2?+?1 resonance-enhanced multi-photon ionization (REMPI) and the application of H₂S as a laser dopant for the detection of polar compounds in laser ion mobility (IM) spectrometry at atmospheric pressure were investigated. Underlying ionization mechanisms were elucidated by additional studies employing a drift cell interfaced to a time-of-flight mass spectrometer. Depending on the pressure, the primary ions H₂S⁺, HS⁺, S⁺, and secondary ions, such as H₃S⁺, were observed. The 2?+?1 REMPI spectrum of H₂S near λ?=?302.5 nm was recorded at atmospheric pressure. Furthermore, the limit of detection and the linear range were established. In the second part of the work, H₂S was investigated as an H₂O analogous laser dopant for the ionization of polar substances by proton transfer. H₂S exhibits a proton affinity (PA) similar to that of H₂O, but a significantly lower ionization energy facilitating laser ionization. Ion-molecule reactions (IMR) of H₃S⁺ with a variety of polar substances with PA between 754.6 and 841.6 kJ/mol were investigated. Representatives of different compound classes, including alcohols, ketones, esters, and nitroaromatics were analyzed. The IM spectra resulting from IMR of H₃S⁺ and H₃O⁺ with these substances are similar in structure, i.e., protonated monomer and dimer ion peaks are found depending on the analyte concentration.