Parametric Sensitivity in a Generalized Model for Atmospheric Pressure Chemical Ionization Reactions

• Published in: Journal of the American Society for Mass Spectrometry 2021-08, Vol.32 (8), p.2218-2226
• Main Authors: Lattouf, Elie, Anttalainen, Osmo, Kotiaho, Tapio, Hakulinen, Hanna, Vanninen, Paula, Eiceman, Gary
• Format: Article
• Language: English
• ISSN: 1044-0305; 1879-1123
• DOI: 10.1021/jasms.1c00158

Gas phase reactions between hydrated protons H+(H2O) n and a substance M, as seen in atmospheric pressure chemical ionization (APCI) with mass spectrometry (MS) and ion mobility spectrometry (IMS), were modeled computationally using initial amounts of [M] and [H+(H2O) n ], rate constants k 1 to form protonated monomer (MH+(H2O) x ) and k 2 to form proton bound dimer (M2H+(H2O) z ), and diffusion constants. At 1 × 1010 cm–3 (0.4 ppb) for [H+(H2O) n ] and vapor concentrations for M from 10 ppb to 10 ppm, a maximum signal was reached at 4.5 μs to 4.6 ms for MH+(H2O) x and 7.8 μs to 46 ms for M2H+(H2O) z . Maximum yield for protonated monomer for a reaction time of 1 ms was ∼40% for k 1 from 10–11 to 10–8 cm3·s–1, for k 2/k 1 = 0.8, and specific values of [M]. This model demonstrates that ion distributions could be shifted from [M2H+(H2O) z ] to [MH+(H2O) x ] using excessive levels of [H+(H2O) n ], even for [M] > 10 ppb, as commonly found in APCI MS and IMS measurements. Ion losses by collisions on surfaces were insignificant with losses of