Minimum proton affinity for efficient ionization with atmospheric pressure desorption/ionization on silicon mass spectrometry

We performed a systematic study using a set of compounds with different proton affinities (PAs) on the ionization in atmospheric pressure desorption/ionization on silicon mass spectrometry (AP‐DIOS‐MS). The compounds studied included various aromatic molecules of different sizes. The PAs of these compounds were calculated using ab initio and hybrid density functional theory calculations at the B3LYP/6‐31G(d) level of theory. We observed that only compounds with relatively high PAs above a threshold value of 920–950 kJ/mol were efficiently ionized as protonated molecules under AP‐DIOS conditions and produced very clean mass spectra. Copyright © 2006 John Wiley & Sons, Ltd.