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

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) ion mobility (IMS), were modeled computationally using initial amounts of [M] [H+(H2O)n], rate constants k1 to form protonated monomer (MH+(H2O)x) k2 proton bound dimer (M2H+(H2O)z), diffusion constants. At 1 × 1010 cm–3 (0.4 ppb) for [H+(H2O)n] vapor concentrations M from 10 ppb ppm, maximum signal was reached at 4.5 μs 4.6 ms MH+(H2O)x 7.8 46 M2H+(H2O)z. Maximum yield reaction time ∼40% 10–11 10–8 cm3·s–1, k2/k1 = 0.8, specific values [M]. This model demonstrates that distributions could be shifted [M2H+(H2O)z] [MH+(H2O)x] excessive levels even > ppb, commonly found APCI MS IMS measurements. Ion losses by collisions on surfaces insignificant <0.5% <0.1% dimethyl methylphosphonate (DMMP) 5 ms. In this model, production an environment is treated over ranges parameters important spectrometric The models establish foundation detailed computations response mixtures neutral substances.