Evaluation of carrier gases for use in high-field asymmetric waveform ion mobility spectrometry

Effects of carrier gas type (N-2, O-2, CO2, N2O, and SF6) on changes in the ratio of high- to low-field ion mobility, K-h/K, of cesium, gramicidin S, tetrahexylammonium, heptadecanoic acid, and aspartic acid in fields of up t o 67 Td are presented. The theory of the mobility of ions at high E/N in di fferent gases is discussed. Plots of K-h/K as a function of the ionic energ y parameter, E/N, for the five ions in each of the gases were derived from experimental data collected using a high-held asymmetric waveform ion mobil ity spectrometer. The change in the ratio of high- to low-field ion mobilit y of cesium in carrier gases of O-2 and N-2 showed excellent agreement with literature values. The behavior of cesium in O-2 and N-2 is used to illust rate that the ratio K-h/K as a function of effective temperature is invaria nt with gas type as long as the well depth of the interaction potential sig nificantly exceeds thermal energy. From these results, it appears that the well depth of the interaction potential of the heavier ions studied here, i ncluding gramicidin S, tetrahexylammonium, and heptadecanoic acid, with bat h gases such as N-2 and O-2 is shallow relative to thermal energy. (J Am So c Mass Spectrom 2000, 11, 1125-1133) (C) 2000 American Society for Mass Spe ctrometry.