Simultaneous and co-located dual polarity ion confinement and mobility separation in traveling wave-based structures for lossless ion manipulations (SLIM) (ASMS 2017)

Ion mobility (IM) coupled with mass spectrometry has gained prominence as a powerful analytical tool. To advance IM technology performance to higher levels SLIM technology has recently been developed in our laboratory, and has provided the basis for large gains in IM resolution as well as sensitivity. In many applications both positive and negative ion separations provide complementary information. In this work we explore the use of traveling waves in SLIM to simultaneously confine and separate by IM co-located cations and anions. SIMION ion trajectory software was used to simulate ion confinement in SLIM, as well as ion transport. Ion-neutral collisions during ion transport simulations were modelled using the SDS collision model, which employs statistical methods to account for ion collision with buffer gas. The simulations were used to optimize the SLIM design process as well as predict possible experimental performance. MATLAB software package was also used to obtain and analyze the ion confinement potentials. Static voltages applied to guard electrodes in traditional SLIM configurations provide good lateral confinement for single ion polarity experiments, but such conditions lead to the loss of opposite polarity ions. It is well recognized that rf ion traps can simultaneously confine ions of both polarities. In this work we have explored the potential for developing instrumentation allowing the simultaneous introduction, and manipulation (including IM separation) of both positive and negative ions in a new SLIM design. Preliminary data obtained from ion trajectory simulations have shown the possibility to simultaneously confine and transport both positively and negatively charged ions. Simultaneous confinement for ions of both polarities was achieved by replacing the guard electrodes in the traditional SLIM configuration which employed static voltages (typically 5V above the travelling wave (TW) voltage) for lateral confinement of ions between the SLIM boards with RF “guards” which use dynamic voltages for the lateral confinement of the ions. Concurrent ion transport is also achieved due to the nature of the dynamic voltage profile of the TW which presents a potential minima at opposite ends of the voltage wave for each ion polarity as the wave transverses the segmented TW electrodes, and thus subsequently provide efficient ion transport. We have also shown using ion trajectory simulations, the capability to manipulate the spatial separation of ion populations in SLIM based on their polarities, by biasing the RF guards on each side of the ion conduit so as to limit the interactions between the two ion polarity populations if ion-ion interactions could lead to ion loss during transmission. This presentation will also describe our progress in experimental implementation.<p></p

Structures for Lossless Ion Manipulations Device as an Ion Mobility Filter (ASMS 2017)

Structures for Lossless Ion Manipulations (SLIM) allow confining and manipulating ions utilizing a combination of radio frequency (RF) and direct current (DC) fields or traveling waves (TW). TW can be employed in SLIM devices to separate ions based on their mobility. We have been exploring concepts for the continuous filtering of ions for the selection of specific and narrow mobility ranges. Such a device would be an IM analog of a e.g. quadruple mass filter. In this presentation we show the supporting simulations and the experiments to demonstrating the filtering capability of the SLIM device.The SLIM filter module (30.5 cm) was designed having two parallel arrays of electrodes, namely the rung and guard electrodes. Ions are confined laterally by the applied DC voltage to the guard electrodes, while confined between the surfaces by effective potentials created by applying alternating 1800 out of phase RF voltages. In the current design, ions are guided by a combination of TW and opposing DC drift fields. The SLIM was segmented into two mirror-image sections where the TW and opposing DC are applied. By choosing the suitable combination of DC gradient and TW parameters for the two sections, it is possible to transmit ions of certain mobility while filtering out other ions.In this presentation, we demonstrate a SLIM ion mobility filter allowing ions of specific mobility to be efficiently transmitted. Ion trajectories simulations showed the SLIM devices can filter ions according to their mobilities when opposing TW and DC drift fields are combined. By choosing the suitable combination of DC gradient and TW parameters for the two sections, we found it is possible to transmit ions of certain mobility while filtering out other ions. The SLIM filter is operated by combining a positive DC gradient in the first half and a negative DC gradient in the second half of the SLIM. Two TW were used, one moving forward in the first section, while with the other is moving in the reverse direction in the second section of the SLIM module. The filtering is determined by DC gradient and the TW parameters, such as frequency, amplitude and the sequence (or in other words, the duty cycle of the travelling waveTW). Experiments show that filtering with minor loss of ions could can be achieved by adjusting proper selection of TW frequencies. The difference in frequency, frequency window, determines the range of mobilities transmitted through the filter, which can be explained by the relative ion velocity obtained from the applied DC and TW potentials. The sequence of the TW was found to affect the sensitivity of the device. The velocity of the ions due to TW and that due to the DC field were extracted from the simulations. The filtering is due to the opposing effects of the TW and the DC gradient. Those ions whose mobility due to TW is higher than that due to the DC gradient will successfully pass the first section. While in the second section ions having a higher mobility due to DC gradient will be transmitted

Towards Serpentine Ultra long ion Path with Extended Routing (SUPER) Ion Mobility using Traveling Waves in Structures for Lossless Ion Manipulations (SLIM) (ASMS 2017)

The applicability and benefits of Ion mobility (IM) techniques increase with their separation power, which can be enhanced by increasing the applied field or ion path length. Here, we present a new compact multilevel Structures for Lossless Ion Manipulations (SLIM) module that is capable of achieving very high resolution by using extremely long ion path for traveling wave ion mobility (TWIM) separations. This presentation will describe the novel approaches of using “escalators” and “elevators” to guide ions across multiple SLIM levels with no loss to the achieved sensitivity and resolution. Moreover, the ability to efficiently move ions between different levels of multilevel SLIM devices will greatly expand the range of potential applications and enable more complex ion manipulations. SLIM long serpentine path length multilevel modules have been developed which use the new TW escalators or TW elevators to transport ion packets between SLIM levels. SLIM relies on three arrays of electrodes to which RF, TW and guard potentials are applied to confine and manipulate ions. The arrays of electrodes are deposited on two planar nonconductive surfaces utilizing printed-circuit board technology. To create a compact design, the electrodes are patterned on both sides of the SLIM surfaces, enabling the eventual extension of the ion path length to ~1 km hosted in a 17”x17”x10” chamber. The SLIM devices have been evaluated at a pressure of ~4 torr N₂. We have previously demonstrated SLIM TW ion mobility separation modules with short as well as long serpentine paths by moving ions in a single plane. However, in order to expand the use of these high resolution, highly flexible SLIM devices for a range of applications, they would benefit from being more compact. Therefore, efficient use of the available space is crucial. Therefore, expanding the ion path into three dimensions is expected to lead to much higher resolution without increasing the footprint of the TWIM instrument.<br> In this work we evaluated an ion escalator in a short SLIM module (~31 cm). Ion current measurements confirmed the lossless nature of the ion transmission. We also show that the TWIM resolution was conserved in the TW escalator, allowing the separation of ions with very similar structural features. The ion mobility resolution was optimized by adjusting the TW speed, amplitude, RF amplitude, guard bias and the gap between the SLIM surfaces. Moreover, in order to increase the TWIM resolution using the same instrumentation profile, we investigated a new “TW elevator” approach using theoretical and experimental approaches. Ion trajectory simulations using TW were performed using SIMION 8.1 on an elevator module and which showed that the efficient operation of an elevator based TW-SLIM device is feasible in the context of a double-sided surface design that has one TW electrode at the edge of the orifice to transfer ions between two SLIM levels. In addition, negligible ion loss was indicated from the ion trajectory simulations for the elevators.<br