Evaluating the Impact of an Octopole for a Portable Trapped Ion Mobility Spectrometry Device

Ion Mobility spectrometry (IMS) rapidly separates ions on a millisecond timescale based on their mobility through a buffer gas, reflecting their size-to-charge ratio. When detecting hazardous materials, explosives, narcotics, and chemical warfare agents, portable IMS devices have demonstrated promise. Achieving sufficient resolving power is essential to mitigate false positives. In a portable device, achieving high resolving power is a challenging feat, as typically this is accomplished by increasing the length of the analysis region to allow for a greater number of collisions with the drift gas. However, this would enlarge the instrument footprint, compromising portability, thus leading to an examination of alternative methodologies to improve resolution. Trapped ion mobility attains improved resolution through gas flow, upholding a small analysis region. Here, we investigate the outcome of altering a quadrupole geometry to an octopole analysis region on both gas flow and ion containment. Utilizing computational fluid dynamics, gas flow is assessed within the device based on the portable pumping capabilities. SIMION software is used to simulate ion trajectories under a gas flow, demonstrating the operating conditions needed for ion analysis (i.e., direct current, RF frequency, ion elution drop time, etc.). These results are compared to the prior designs to assess the viability and potential advantages of an octopole analysis region.