Drift Time Corrections Based on a Practical Measurement of the Depletion Zone to Allow Accurate and Reproducible Determination of the Reduced Mobility of Ions in DT-IMS.

Abstract

The reduced mobility of an ion is a key parameter for identifying ions and comparing spectra in drift time ion mobility spectrometry. As the resolution of spectrometers improves, accurate determination of the reduced mobility is increasingly important. The drift time, used to calculate the reduced mobility, is affected by the ion gate, and this effect has previously been compensated with a linear correction. These corrections, however, do not allow for changes in the distances that the ions must drift to reach the detector caused by the electric field around the ion gate. As these corrections are a linear correction, nonlinearity in the influence of the ion gate may also lead to greater errors. By measuring the length of the depletion zone in front of the ion gate the extra distance traveled by the ions may be corrected for. This measurement also provides the boundary conditions for when a correction to the drift time may be accurately applied. This work shows that the length of the depletion zone can be experimentally measured and that it is consistent for a particular geometry of ion gate.