Over the past few years, structures for lossless ion manipulations (SLIM) have used traveling waves (TWs) to move ions over long serpentine paths that can be further lengthened by routing the ions through multiple passages of the same path. Such SLIM “multipass” separations provide unprecedentedly high ion mobility resolving powers but are ultimately limited in their ion mobility range because of the range of mobilities spanned in a single pass; that is, higher mobility ions ultimately “overtake” and “lap” lower mobility ions that have experienced fewer passes, convoluting their arrival time distribution at the detector. To achieve ultrahigh resolution separations over broader mobility ranges, we have developed a new multilevel SLIM possessing multiple stacked serpentine paths. Ions are transferred between SLIM levels through apertures (or ion escalators) in the SLIM surfaces. The initial multilevel SLIM module incorporates four levels and three interlevel ion escalator passages, providing a total path length of 43.2 m. Using the full path length and helium buffer gas, high resolution separations were achieved for Agilent tuning mixture phosphazene ions over a broad mobility range (K 0 ≈ 3.0 to 1.2 cm2/(V*s)). High sensitivity was achieved using “in-SLIM” ion accumulation over an extended trapping region of the first SLIM level. High transmission efficiency of ions over a broad mobility range (e.g., K 0 ≈ 3.0 to 1.67 cm2/(V*s)) was achieved, with transmission efficiency rolling off for the lower mobility ions (e.g., K 0 ≈ 1.2 cm2/(V*s)). Resolving powers of up to ∼560 were achieved using all four ion levels to separate reverse peptides (SDGRG1+ and GRGDS1+). A complex mixture of phosphopeptides showed similar coverage could be achieved using one or all four SLIM levels, and doubly charged phosphosite isomers not significantly separated using one SLIM level were well resolved when four levels were used. The new multilevel SLIM technology thus enables wider mobility range ultrahigh-resolution ion mobility separations and expands on the ability of SLIM to obtain improved separations of complex mixtures with high sensitivity.

We determined absolute rate coefficients for the recurrent fluorescence (RF) process in C 6 − anions at excitation energies above the adiabatic electron attachment energy of 4.18 eV. The experiment was performed by extracting C 6 − ions from a sputter ion source and storing them in a bent electrostatic ion beam trap. After 1 s of storage, during which the anions cooled down to temperatures close to room temperature, they were excited by a short laser pulse and the neutralization rate due to vibrational autodetachment (VAD) was measured as a function of time at several wavelengths. Due to the different energy dependence of the two competing decays via the RF and the VAD process, their contributions to the measured total decay rate coefficients could be disentangled. For excitation energies ≲4.6 eV, the decay is found to be dominated by the RF process with decay rate coefficients on the order of 5 × 10 4 s −1 . The result clearly demonstrates the presence of the RF process in C 6 − and illustrates the importance of this process in the production and cooling of isolated molecules of astrophysical interest.

This article compares the experimental results obtained in metal-assisted secondary ion mass spectrometry of polymers, with molecular dynamics simulations involving hybrid metal-organic surfaces. The theoretical sputtering yields are in agreement with the trends highlighted in recent experiments, in which different projectiles (Ga + , C + 60 ) were used to bombard pristine and Au-covered polymer samples. In the experiments, the link between the organic ion yield enhancement/decrease and the fraction of the surface covered by the metal is clearly established. On the other hand, the simulations show that the position of the impact point on the metal-covered surface critically influences the calculated yields of metal and organic material, in a manner that depends on the projectile. The discussion analyzes the information obtained from the simulations and the experiments to propose a mechanism of yield enhancement.

No abstract

Here we describe instrumental approaches for performing dual polarity ion confinement, transport, ion mobility separations and reactions in Structures for Lossless Ion Manipulations (SLIM). Previous means of ion confinement in SLIM based upon rf- generated pseudopotentials and dc fields for lateral confinement cannot trap ions of opposite polarity simultaneously. Here we explore alternative approaches to provide lateral confinement of both ion polarities. Traveling wave ion mobility (IM) separations experienced by both polarities in such SLIM cause ions of both polarities to migrate in the same directions and exhibit similar separations. The ion motion (and relative motion of the two polarities) under both surfing and IM separation conditions are discussed. In surfing conditions, where the traveling wave speed is less than the ion velocity, the two polarities are transported losslessly and non-reactively in their respective potential minima (higher absolute voltage regions confines negative polarities and lower absolute potential regions are populated by positive polarities). In separation mode, where the traveling wave speed is greater than the ion velocity, the two polarities can interact during rollovers over the traveling wave. Strategies to minimize overlap of the two ion populations to prevent reactive losses during separations are presented. A theoretical treatment of the time scales over which two populations (injected into a dc field-free region of the dual polarity SLIM device) interact is considered, and SLIM designs for allowing ion/ion interactions and other manipulations with dual polarities at 4 torr are presented.

Ion packets introduced from gates, ion funnel traps, and other conventional ion injection mechanisms produce ion pulse widths typically around a few microseconds or less for ion mobility spectrometry (IMS)-based separations on the order of 100 milliseconds. When such ion injection techniques are coupled with ultralong path length traveling wave (TW)-based IMS separations (i.e., on the order of seconds) using structures for lossless ion manipulations (SLIMs), typically very low ion utilization efficiency is achieved for continuous ion sources [e.g., electrospray ionization (ESI)]. Even with the ability to trap and accumulate much larger populations of ions than being conventionally feasible over longer time periods in SLIM devices, the subsequent long separations lead to overall low ion utilization. Here, we report the use of a highly flexible SLIM arrangement, enabling concurrent ion accumulation and separation and achieving near-complete ion utilization with ESI. We characterize the ion accumulation process in SLIM, demonstrate >98% ion utilization, and show both increased signal intensities and measurement throughput. This approach is envisioned to have broad utility to applications, for example, involving the fast detection of trace chemical species.

Enhancing the sensitivity of low-abundance ions in a complex mixture without sacrificing measurement throughput is highly desirable. This work demonstrates a way to greatly improve the sensitivity of ion mobility (IM)-selected ions by accumulating them in an array of high-capacity ion traps located inside a novel structures for lossless ion manipulations ion mobility spectrometer (SLIM-IMS) module. The array of ion traps used in this work consisted of seven independently controllable traps. Each trap was 386 mm long and possessed a charge capacity of ∼4.5 × 10 8 charges, with a linear range extending to ∼2.5 × 10 8 charges. Each ion trap could be used to extract a peak (or ions over a mobility range) from an ion mobility separation based on arrival time. Ions could be stored without losses for long times (>100 s) and then released all at once or one trap at a time. It was possible to accumulate large ion populations by extracting and storing ions over repeated IM separations. Enrichment of up to seven individual ion distributions could be performed using the seven independently controllable ion traps. Additionally, the ion trapping process effectively compressed ion populations into narrow peaks, which provides a greatly improved basis for subsequent ion manipulations. The array of high charge capacity ion traps provides a flexible addition to SLIM and a powerful tool for IMS-MS applications requiring high sensitivity.

Ion mobility (IM) is rapidly gaining attention for the separation and analysis of biomolecules due to the ability to distinguish the shapes of ions. However, conventional constant electric field drift tube IM separations have limited resolving power, constrained by practical limitations on the path length and maximum applied voltage. The implementation of traveling waves (TW) in IM removes the latter limitation, allowing higher resolution to be achieved using extended path lengths. Both of these can be readily obtained in structures for lossless ion manipulations (SLIM), which are fabricated from arrays of electrodes patterned on two parallel surfaces where potentials are applied to generate appropriate electric fields between the surfaces. Here we have investigated the relationship between the primary SLIM variables, such as electrode dimensions, inter-surface gap, and the applied TW voltages, that directly impact the fields experienced by ions. Ion trajectory simulations and theoretical calculations have been utilized to understand the dependence of SLIM geometry and effective electric fields on IM resolution. The variables explored impact both ion confinement and the observed IM resolution using SLIM modules.