Microheterogeneity within conformational states of ubiquitin revealed by high resolution trapped ion mobility spectrometry

Danielson²,

Int. J. Ion Mobil. Spec.

et al. 2016

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Trapped ion mobility spectrometry (TIMS) is a versatile high resolution technique that provides the user with the flexibility to adjust the mobility range of interest, duty cycle (up to 100 %), and resolving power (up to~300) according to the application requirements. Furthermore, TIMS offers the flexibility of operating as either a mobility-selective or conventional ion funnel, thus permitting ion mobility separations to be turned on or off. Here, we extend the flexibility of TIMS by introducing multilinear and nonlinear scanning methods that allow enhanced resolution in user-defined mobility regions. The performance of the new method is demonstrated using a variety of nonlinear scan functions that allow the resolving power to be continuously varied across the mobility spectrum. Further, we demonstrate that mobility analysis can be targeted over disparate regions using a multilinear scan function. In this example, high resolution mobility analysis is targeted on two analytes on opposite ends of a mobility range, while other ions that fall between the regions of interest remain unanalyzed. Using this approach, the resolving power for targeted species was increased by a factor of two over the conventional linear scanning approach (R~60 versus~120) without reducing the duty cycle of the TIMS measurement. Importantly, in such an analysis, ions in the untargeted regions are not mobility analyzed, however, they are also not discarded. Rather, these ions are ejected for downstream mass analysis. In this sense, TIMS bridges the gap between dispersive and scanning mobility techniques. That is, TIMS disperses ions according to their elution voltage, however, TIMS can also perform target mobility analyses without eliminating untargeted ions.

“…Details of the instrumentation can be found in the literature [24][25][26][27][28][29][30]. Briefly, ions were produced by electrospray ionization (ESI) at atmospheric pressure.…”

Section: Methodsmentioning

confidence: 99%

Altering the mobility-time continuum: nonlinear scan functions for targeted high resolution trapped ion mobility-mass spectrometry

Danielson²,

Int. J. Ion Mobil. Spec.

et al. 2016

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“…Extrapolation of the experimental data contained in Figure 5b indicates a resolving power of 300 could be achieved for singly charged ions. Given that resolving powers betweeñ 250 and 300 have already been experimentally attained for peptide and protein ions with the existing TIMS apparatus [46,47], it seems reasonable to expect even better performance for multiply charged ions, such as those encountered in proteomics applications [49].…”

Section: Drag Forcementioning

confidence: 99%

“…Experimentally, TIMS resolving powers have exceeded 200 for singly charged ions [42,43] and approached 300 for multiply charged ions [46,47]. Previous experimental measurements have confirmed the dependence of resolving power on β and K; however, the dependence of resolving power on flow parameters has not yet been fully explored [43].…”

Section: Introductionmentioning

confidence: 99%

Fundamentals of Trapped Ion Mobility Spectrometry Part II: Fluid Dynamics

Michelmann

J. Am. Soc. Mass Spectrom.

et al. 2016

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Abstract. Trapped ion mobility spectrometry (TIMS) is a new high resolution (R up tõ 300) separation technique that utilizes an electric field to hold ions stationary against a moving gas. Recently, an analytical model for TIMS was derived and, in part, experimentally verified. A central, but not yet fully explored, component of the model involves the fluid dynamics at work. The present study characterizes the fluid dynamics in TIMS using simulations and ion mobility experiments. Results indicate that subsonic laminar flow develops in the analyzer, with pressure-dependent gas velocities between~120 and 170 m/s measured at the position of ion elution. One of the key philosophical questions addressed is: how can mobility be measured in a dynamic system wherein the gas is expanding and its velocity is changing? We noted previously that the analytically useful work is primarily done on ions as they traverse the electric field gradient plateau in the analyzer. In the present work, we show that the position-dependent change in gas velocity on the plateau is balanced by a change in pressure and temperature, ultimately resulting in near positionindependent drag force. That the drag force, and related variables, are nearly constant allows for the use of relatively simple equations to describe TIMS behavior. Nonetheless, we derive a more comprehensive model, which accounts for the spatial dependence of the flow variables. Experimental resolving power trends were found to be in close agreement with the theoretical dependence of the drag force, thus validating another principal component of TIMS theory.

“…Inverse to drift tube IMS, TIMS operates by passing gas through swarms of stationary ions that are repelled by a repulsive electric field gradient. Advantages of TIMS include: (1) high transmission efficiencies in MS and IMS-MS modes, (2) compact design allowing integration into many instrument platforms, (3) determination of reduced mobility or collisional cross section from a simple calibration [38, 39], (4) low operating potentials, (5) flexibility to alter ion mobility resolving power and duty cycle, and (6) superior mobility resolving power that can exceed 250 [37, 39, 40]. Recently, TIMS has been shown to produce mobility distributions for proteins and peptides (whose conformations are known to depend on a number of physicochemical parameters) that are virtually identical to those measured by drift tube IMS operating below the low field limit where ion temperatures are known to be near thermal [39, 40].…”

Section: Introductionmentioning

confidence: 99%

Gated trapped ion mobility spectrometry coupled to fourier transform ion cyclotron resonance mass spectrometry

Wolff

Int. J. Ion Mobil. Spec.

et al. 2016

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Analysis of molecules by ion mobility spectrometry coupled with mass spectrometry (IMS-MS) provides chemical information on the three dimensional structure and mass of the molecules. The coupling of ion mobility to trapping mass spectrometers has historically been challenging due to the large differences in analysis time between the two devices. In this paper we present a modification of the trapped ion mobility (TIMS) analysis scheme termed “Gated TIMS” that allows efficient coupling to a Fourier Transform Ion Cyclotron Resonance (FT-ICR) analyzer. Analyses of standard compounds and the influence of source conditions on the TIMS distributions produced by ion mobility spectra of labile ubiquitin protein ions are presented. Ion mobility resolving powers up to 100 are observed. Measured collisional cross sections of ubiquitin ions are in excellent qualitative and quantitative agreement to previous measurements. Gated TIMS FT-ICR produces results comparable to those acquired using TIMS/time-of-flight MS instrument platforms as well as numerous drift tube IMS-MS studies published in the literature.