Study of Coulombic broadening in stand-alone ion mobility spectrometry

This paper proposes a method for investigating the Coulombic broadening, tcou, in an ambient pressure ion mobility spectrometer based on the analysis of peaks originating from O2−(H2O)n and electrons. It showed that the full width at half maximum (FWHM) of electrons was independent of electron density and remained at a constant contribution from the initial width of ion packets, tg, and amplifier broadening, tamp; in contrast, the FWHM of O2−(H2O)n increased with the rise of O2−(H2O)n density due to additional contributions from tcou and diffusion broadening tdiff. The tcou of O2−(H2O)n was extracted from the FWHM by subtracting tg, tamp, and tdiff. The tcou of O2−(H2O)n was found to increase from 0.14 ms to 0.24 ms as the O2−(H2O)n density increased from 7.35 × 105 to 1.22 × 107 cm−3. The percentage of tcou in the FWHM was in the range of 45%–80%, and the Coulomb-limited resolving power decreased from 70 to 40 as the ion density increased, which indicated that the Coulomb effect was dramatic.This paper proposes a method for investigating the Coulombic broadening, tcou, in an ambient pressure ion mobility spectrometer based on the analysis of peaks originating from O2−(H2O)n and electrons. It showed that the full width at half maximum (FWHM) of electrons was independent of electron density and remained at a constant contribution from the initial width of ion packets, tg, and amplifier broadening, tamp; in contrast, the FWHM of O2−(H2O)n increased with the rise of O2−(H2O)n density due to additional contributions from tcou and diffusion broadening tdiff. The tcou of O2−(H2O)n was extracted from the FWHM by subtracting tg, tamp, and tdiff. The tcou of O2−(H2O)n was found to increase from 0.14 ms to 0.24 ms as the O2−(H2O)n density increased from 7.35 × 105 to 1.22 × 107 cm−3. The percentage of tcou in the FWHM was in the range of 45%–80%, and the Coulomb-limited resolving power decreased from 70 to 40 as the ion density increased, which indicated that the Coulomb effect was dramatic.