Evaluation of ultrahigh resolution ion mobility spectrometry as an analytical separation device in chromatographic terms

An ion mobility spectrometer (IMS) that routinely achieves separation efficiencies in line with the theoretical diffusion limited maximum has been constructed. The theoretical maximum efficiency is a function of the total voltage drop, the temperature, the number of charges on the ion, the initial pulse width, the length of the spectrometer, and the mobility (K) of the ion of interest. Despite the fact that our current instrumental setup uses modest voltages and fairly high temperatures, we were able to achieve over 130,000 theoretical plates for a singly charged ion in less than 25 ms. In addition, selectivity can be altered in IMS by changing the drift gas or by increasing the electric field (>1000 V/cm) such that the mobility of ions is no longer a linear function of the electric field. Separation factors (α) can be altered by as much as 20% by changing the drift gas in the spectrometer. Finally leucine and isoleucine were separated in less than 23 ms with a resolution of 0.668 demonstrating the separation power of the instrument.