Complex samples benefit from multidimensional measurements where higher resolution enables more complete characterization of biological and environmental systems. To address this challenge, we ...developed a drift tube-based ion mobility spectrometry-Orbitrap mass spectrometer (IMS-Orbitrap MS) platform. To circumvent the time scale disparity between the fast IMS separation and the much slower Orbitrap MS acquisition, we utilized a dual gate and pseudorandom sequences to multiplex the injection of ions and allow operation in signal averaging (SA), single multiplexing (SM), and double multiplexing (DM) IMS modes to optimize the signal-to-noise ratio of the measurements. For the SM measurements, a previously developed algorithm was used to reconstruct the IMS data. A new algorithm was developed for the DM analyses involving a two-step process that first recovers the SM data and then decodes the SM data. The algorithm also performs multiple refining procedures to minimize demultiplexing artifacts. The new IMS-Orbitrap MS platform was demonstrated by the analysis of proteomic and petroleum samples, where the integration of IMS and high mass resolution proved essential for accurate assignment of molecular formulas.
We report the development and initial evaluation of a 13 m path length Structures for Lossless Manipulations (SLIM) module for achieving high resolution separations using traveling waves (TW) with ...ion mobility (IM) spectrometry. The TW SLIM module was fabricated using two mirror-image printed circuit boards with appropriately configured RF, DC, and TW electrodes and positioned with a 2.75 mm intersurface gap. Ions were effectively confined in field-generated conduits between the surfaces by RF-generated pseudopotential fields and moved losslessly through a serpentine path including 44 “U” turns using TWs. The ion mobility resolution was characterized at different pressures, gaps between the SLIM surfaces, and TW and RF parameters. After initial optimization, the SLIM IM-MS module provided about 5-fold higher resolution separations than present commercially available drift tube or traveling wave IM-MS platforms. Peak capacity and peak generation rates achieved were 246 and 370 s–1, respectively, at a TW speed of 148 m/s. The high resolution achieved in the TW SLIM IM-MS enabled, e.g., isomeric sugars (lacto-N-fucopentaose I and lacto-N-fucopentaose II) to be baseline resolved, and peptides from an albumin tryptic digest were much better resolved than with existing commercial IM-MS platforms. The present work also provides a foundation for the development of much higher resolution SLIM devices based upon both considerably longer path lengths and multipass designs.
The unanticipated discovery of recent ultra-high-resolution ion mobility spectrometry (IMS) measurements revealing that isotopomerscompounds that differ only in the isotopic substitution sitescan ...be separated has raised questions as to the physical basis for their separation. A study comparing IMS separations for two isotopomer sets in conjunction with theory and simulations accounting for ion rotational effects provides the first-ever prediction of rotation-mediated shifts. The simulations produce observable mobility shifts due to differences in gas–ion collision frequency and translational-to-rotational energy transfer. These differences can be attributed to distinct changes in the moment of inertia and center of mass between isotopomers. The simulations are in broad agreement with the observed experiments and consistent with relative mobility differences between isotopomers. These results provide a basis for refining IMS theory and a new foundation to obtain additional structural insights through IMS.
Structures for lossless ion manipulations (SLIM) provide a new paradigm for efficient, complex and extended gas phase ion manipulations. SLIM are created from electric fields generated by the ...application of DC and RF potentials to arrays of electrodes patterned on two parallel surfaces. The electric fields provide lossless ion manipulations, including effective ion transport and storage. SLIM modules have been developed using both constant and oscillatory electric fields (
e.g.
traveling waves) to affect the ion motion. Ion manipulations demonstrated to date with SLIM include: extended trapping, ion selection, ion dissociation, and ion mobility spectrometry (IMS) separations achieving unprecedented ultra high resolution. SLIM thus provide the basis for previously impractical manipulations, such as very long path length ion mobility separations where ions traverse a serpentine path multiple times, as well as new capabilities that extend the utility of these developments based on temporal and spatial compression of ion mobility separations and other ion distributions. The evolution of SLIM devices developed over the last three years is reviewed and we provide examples of various ion manipulations performed, and briefly discuss potential applications and new directions.
SLIM utilize manipulations in ion conduits created from electric fields generated by applying potentials to arrays of electrodes patterned on two planar surfaces.
Understanding the biological roles and mechanisms of lipids and glycolipids is challenging due to the vast number of possible isomers that may exist. Mass spectrometry (MS) measurements are currently ...the dominant approach for studying and providing detailed information on lipid and glycolipid presence and changes. However, difficulties in distinguishing the many structural isomers, due to the distinct lipid acyl chain positions, double bond locations or specific glycan types, inhibit the delineation and assignment of their biological roles. Here we utilized ultra-high resolution ion mobility spectrometry (IMS) separations by applying traveling waves in a serpentine multi-pass Structures for Lossless Ion Manipulations (SLIM) platform to enhance the separation of selected lipid and glycolipid isomers. The multi-pass arrangement allowed the investigation of paths ranging from ~16 m (one pass) to ~60 m (four passes) for the distinction of lipids and glycolipids with extremely small structural differences. These ultra-high resolution SLIM IMS-MS analyses provide a foundation for exploring and better understanding isomer-specific biological activities and disease processes.
Ion mobility (IM) separations have a broad range of analytical applications, but insufficient resolution often limits their utility. Here, we report on ion mobility separations in a structures for ...lossless ion manipulations (SLIM) serpentine ultralong path with extended routing (SUPER) traveling wave (TW) ion mobility (IM) module in conjunction with mass spectrometry (MS). Ions were confined in the SLIM by rf fields in conjunction with a DC guard bias, enabling essentially lossless TW transmission over greatly extended paths. The extended routing utilized multiple passes (e.g., ∼1094 m over 81 passes through the 13.5 m serpentine path) and was facilitated by the introduction of a lossless ion switch that allowed ions to be directed to either the MS detector or for another pass through the serpentine separation region, allowing theoretically unlimited IM path lengths. The multipass SUPER IM-MS provided resolution approximately proportional to the square root of the number of passes (or total path length). More than 30-fold higher IM resolution (∼340 vs ∼10) for Agilent tuning mix m/z 622 and 922 ions was achieved for 40 passes compared to commercially available drift tube IM and other TWIM-based platforms. An initial evaluation of the isomeric sugars lacto-N-hexaose and lacto-N-neohexaose showed the isomeric structures to be baseline resolved, and a new conformational feature for lacto-N-neohexaose was revealed after 9 passes. The new SLIM SUPER high resolution TWIM platform has broad utility in conjunction with MS and is expected to enable a broad range of previously challenging or intractable separations.
We report on separations of ion isotopologues and isotopomers using ultrahigh-resolution traveling wave-based Structures for Lossless Ion Manipulations with serpentine ultralong path and extended ...routing ion mobility spectrometry coupled to mass spectrometry (SLIM SUPER IMS-MS). Mobility separations of ions from the naturally occurring ion isotopic envelopes (e.g., M, M+1, M+2, ... ions) showed the first and second isotopic peaks (i.e., M+1 and M+2) for various tetraalkylammonium ions could be resolved from their respective monoisotopic ion peak (M) after SLIM SUPER IMS with resolving powers of ∼400–600. Similar separations were obtained for other compounds (e.g., tetrapeptide ions). Greater separation was obtained using argon versus helium drift gas, as expected from the greater reduced mass contribution to ion mobility described by the Mason–Schamp relationship. To more directly explore the role of isotopic substitutions, we studied a mixture of specific isotopically substituted (15N, 13C, and 2H) protonated arginine isotopologues. While the separations in nitrogen were primarily due to their reduced mass differences, similar to the naturally occurring isotopologues, their separations in helium, where higher resolving powers could also be achieved, revealed distinct additional relative mobility shifts. These shifts appeared correlated, after correction for the reduced mass contribution, with changes in the ion center of mass due to the different locations of heavy atom substitutions. The origin of these apparent mass distribution-induced mobility shifts was then further explored using a mixture of Iodoacetyl Tandem Mass Tag (iodoTMT) isotopomers (i.e., each having the same exact mass, but with different isotopic substitution sites). Again, the observed mobility shifts appeared correlated with changes in the ion center of mass leading to multiple monoisotopic mobilities being observed for some isotopomers (up to a ∼0.04% difference in mobility). These mobility shifts thus appear to reflect details of the ion structure, derived from the changes due to ion rotation impacting collision frequency or momentum transfer, and highlight the potential for new approaches for ion structural characterization.
The collision cross section (CCS) is an important property that aids in the structural characterization of molecules. Here, we investigated the CCS calibration accuracy with traveling wave ion ...mobility spectrometry (TWIMS) separations in structures for lossless ion manipulations (SLIM) using three sets of calibrants. A series of singly negatively charged phospholipids and bile acids were calibrated in nitrogen buffer gas using two different TW waveform profiles (square and sine) and amplitudes (20, 25, and 30 V0‑p). The calibration errors for the three calibrant sets (Agilent tuning mixture, polyalanine, and one assembled in-house) showed negligible differences using a sine-shaped TW waveform. Calibration errors were all within 1–2% of the drift tube ion mobility spectrometry (DTIMS) measurements, with lower errors for sine waveforms, presumably due to the lower average and maximum fields experienced by ions. Finally, ultrahigh-resolution multipass (long path length) SLIM TWIMS separations demonstrated improved CCS calibration for phospholipid and bile acid isomers.
We report on the development and characterization of a traveling wave (TW)-based Structures for Lossless Ion Manipulations (TW-SLIM) module for ion mobility separations (IMS). The TW-SLIM module uses ...parallel arrays of rf electrodes on two closely spaced surfaces for ion confinement, where the rf electrodes are separated by arrays of short electrodes, and using these TWs can be created to drive ion motion. In this initial work, TWs are created by the dynamic application of dc potentials. The capabilities of the TW-SLIM module for efficient ion confinement, lossless ion transport, and ion mobility separations at different rf and TW parameters are reported. The TW-SLIM module is shown to transmit a wide mass range of ions (m/z 200–2500) utilizing a confining rf waveform (∼1 MHz and ∼300 Vp‑p) and low TW amplitudes (<20 V). Additionally, the short TW-SLIM module achieved resolutions comparable to existing commercially available low pressure IMS platforms and an ion mobility peak capacity of ∼32 for TW speeds of <210 m/s. TW-SLIM performance was characterized over a wide range of rf and TW parameters and demonstrated robust performance. The combined attributes of the flexible design and low voltage requirements for the TW-SLIM module provide a basis for devices capable of much higher resolution and more complex ion manipulations.
Probing molecular properties in the gas phase requires the integration of complementary ion manipulation approaches such as ion mobility spectrometry. Structures for lossless ion manipulations (SLIM) ...have recently been developed to perform ultra-high resolution ion mobility separations using traveling waves as well as providing other advanced capabilities. Despite its success, the design aspects of SLIM have not been fully explored and remained largely unchanged. Here, we report on a computational study using SIMION simulations of a number of traveling wave (TW) patterns that can be used in SLIM. The TW pattern used in the current SLIM device is a set of 8 electrodes where, at any time, 4 electrodes are held at high voltage (
i.e.
, 1111), while the other 4 electrodes are held at low voltage (
i.e.
, 0000), forming one micro-trapping region of 11110000 pattern. Ion trajectory simulations demonstrated the feasibility to simplify the 8-electrode set to a shorter pattern (
e.g.
, 6-electrode or 4-electrode set) while maintaining or improving the performance. The RF and TW amplitudes, guard voltage, and TW speed were optimized subsequently on the symmetric patterns of the 4-, 6-, and 8-electrode sets to further improve the performance. The resolution, peak broadening, peak capacity, and peak generation rate of each pattern were evaluated, showing that the 111000 pattern of the 6-electrode set has comparable performance to the current 11110000 pattern and is always better than the 1100 pattern. This work provides insight into the feasibility for simplification and modification of the TW configuration in SLIM and other traveling wave devices.
Probing molecular properties in the gas phase requires the integration of complementary ion manipulation approaches such as ion mobility spectrometry.
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