Effect of Space Charge on Resolving Power and Ion Loss in Ion Mobility Spectrometry

Abstract

The effect of space charge on the performance of an Ion Mobility Spectrometry (IMS) system becomes more important as the system is made smaller. We use the SIMION software package with the Statistical Diffusion Simulation (SDS) module and SIMION's new capability to solve the Poisson equation to study the effect of space charge on ion loss and resolving power in IMS systems. We consider IMS systems ranging in length from 50 mm to 150 mm and in diameter from 8.33 mm to 50 mm with a fixed electric field of 50 V/mm. We also examine a system with a length of 50 mm, a diameter of 16.7 mm, and an electric field of 16.7 V/mm. We assume that any charge density can be injected into the IMS system, and we have obtained expressions that predict the ion loss and resolving power of IMS systems as a function of input charge density and drift tube aspect ratio (length/diameter).

Review on Ion Mobility Spectrometry. Part 2: hyphenated methods and effects of experimental parameters

“…112 obtained a R p /L of 3.4 cm −1 (for a length L of 3.50cm and a R p of 12). As the length L of an IMS is reduced, the primary limitation to resolving power is the limit on producing effective ion pulses to inject into the IMS As the length of a DTIMS cell is reduced, the optimal resolving power voltage on the cell decreases, and therefore decreasing the maximum resolving power possible 87, 108, 115 .…”

A comparison of SIMION and LORENTZ for IMS simulation

“…We have previously discussed the role of space-charge effects in IMS using SIMION [26]; several other researchers have discussed space-charge effects in IMS [15,23,30,33,34,37,43]. Both SIMION and LORENTZ solve the Poisson equation to determine the electric field in the drift region subject to boundary conditions of voltage specified on the electrodes and Faraday plate.…”

“…In [26] we set the parameter PIC_refine_period to 6, which causes SIMION to update the electric field solution only every six time steps. We have discovered that this can introduce some anomalies in the solution.…”

“…Note that previous work in IMS simulation includes work with SIMION [19,26,42] as well as COMSOL [3,6,22], a program we do not consider in this paper. LORENTZ is a program that has not previously been used for simulation of IMS with space charge or a diffusion model.…”

Ionization, Transport, Separation, and Detection of Ions in Non-Electrolyte Containing Liquids

“…Note that this expression, often cited as conditional resolving power, ignores broadening of the ion pulse due to the spacecharge effects as discussed earlier. 15,17,18 On the basis of R d in eq 1, a parametric study was made. Shown in Figure 7 is a set of constant R d mapped on a 2-D plot of pulse width and drift cell length for different voltages across the drift cell.…”