Engineering topics

Shvartsburg, Alexandre A

Publications and source records attributed to Shvartsburg, Alexandre A.

7 records

DOE OSTI2014

Method for enhancing the resolving power of ion mobility separations over a limited mobility range

A method for raising the resolving power, specificity, and peak capacity of conventional ion mobility spectrometry is disclosed. Ions are separated in a dynamic electric field comprising an oscillatory field wave and opposing static field, or at least two counter propagating waves with different parameters (amplitude, profile, frequency, or speed). As the functional dependencies of mean drift velocity on the ion mobility in a wave and static field or in unequal waves differ, only single species is equilibrated while others drift in either direction and are mobility-separated. An ion mobility spectrum over a limited range is then acquired by measuring ion drift times through a fixed distance inside the gas-filled enclosure. The resolving power in the vicinity of equilibrium mobility substantially exceeds that for known traveling-wave or drift-tube IMS separations, with spectra over wider ranges obtainable by stitching multiple segments. The approach also enables low-cutoff, high-cutoff, and bandpass ion mobility filters.

47 OTHER INSTRUMENTATION↗

DOE OSTI2013

High-Definition Differential Ion Mobility Spectrometry with Resolving Power up to 500

As the resolution of analytical methods improve, further progress tends to be increasingly limited by instrumental parameter instabilities that could be ignored before. This is now the case with differential ion mobility spectrometry (FAIMS), where fluctuations of the voltages and gas pressure have become critical. A new high-definition generator for FAIMS compensation voltage reported here provides a stable and accurate output than can be scanned with negligible steps. This reduces the spectral drift and peak width, thus improving the resolving power (R) and resolution. The gain for multiply-charged peptides that have narrowest peaks is up to ~40%, and R ~ 400 - 500 is achievable using He/N2 or H2/N2 gas mixtures.

Environmental Molecular Sciences Laboratory↗

DOE OSTI2013

High-Resolution Differential Ion Mobility Spectrometry of a Protein

Use of elevated electric fields and helium-rich gases has recently enabled differential IMS with resolving power up to R ~ 300. Here we applied that technique to proteins (namely, mass-selected ubiquitin ions), achieving R up to ~80 and separating many previously mixed conformers. While still limited by conformational multiplicity within each observed feature, this resolution is some four times the highest previously reported using either conventional or differential IMS. The capability for fine resolution of protein conformers may open new avenues for variant separation in top-down proteomics.

Environmental Molecular Sciences Laboratory↗

DOE OSTI2012

Microchip and wedge ion funnels and planar ion beam analyzers using same

Electrodynamic ion funnels confine, guide, or focus ions in gases using the Dehmelt potential of oscillatory electric field. New funnel designs operating at or close to atmospheric gas pressure are described. Effective ion focusing at such pressures is enabled by fields of extreme amplitude and frequency, allowed in microscopic gaps that have much higher electrical breakdown thresholds in any gas than the macroscopic gaps of present funnels. The new microscopic-gap funnels are useful for interfacing atmospheric-pressure ionization sources to mass spectrometry (MS) and ion mobility separation (IMS) stages including differential IMS or FAIMS, as well as IMS and MS stages in various configurations. In particular, "wedge" funnels comprising two planar surfaces positioned at an angle and wedge funnel traps derived therefrom can compress ion beams in one dimension, producing narrow belt-shaped beams and laterally elongated cuboid packets. This beam profile reduces the ion density and thus space-charge effects, mitigating the adverse impact thereof on the resolving power, measurement accuracy, and dynamic range of MS and IMS analyzers, while a greater overlap with coplanar light or particle beams can benefit spectroscopic methods.

47 OTHER INSTRUMENTATION↗

DOE OSTI2012

Separation of Variant Methylated Histone Tails by Differential Ion Mobility

Differential ion mobility spectrometry (FAIMS) is emerging as a broadly useful tool for separation of isomeric modified peptides with post-translational modifications (PTMs) attached to alternative residues. Such separations were anticipated to become more challenging for smaller PTMs and longer peptides. Here we show that FAIMS can fully resolve localization variants involving a PTM as minuscule as methylation, even for larger peptides in the middle-down range.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2012

Ion Mobility Separation of Variant Histone Tails Extending to the “Middle-down” Range

Differential ion mobility spectrometry (FAIMS) can baseline-resolve multiple variants of post-translationally modified peptides extending to the 3 - 4 kDa range, which differ in the localization of a PTM as small as acetylation. Essentially orthogonal separations for different charge states expand the total achievable peak capacity in proportion to the number of observed states that increases for longer polypeptides. This might enable resolving localization variants for even larger peptides and intact proteins.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2011

Accelerated High-Resolution Differential Ion Mobility Separations Using Hydrogen

The resolving power of differential ion mobility spectrometry (FAIMS) was dramatically increased recently by the introduction of carrier gases comprising up to 75% He or various vapors, enabling many new applications. However, the gains were often at the expense of analysis speed, in particular making high-resolution FAIMS incompatible with online liquid-phase separations. Here, we report FAIMS employing hydrogen, specifically in mixtures with N2 containing up to 98.4% H2. Such compositions raise the mobilities of all ions and thus resolving power, while avoiding the electrical breakdown inevitable in He-rich mixtures. The increases of resolving power and ensuing peak resolution are especially significant at the greatest H2 fractions - above {approx}80 - 90%. Higher resolution can be exchanged for acceleration of the analyses by up to {approx}20 times. For more mobile species such as multiply-charged peptides, this exchange is presently forced by the constraints of existing FAIMS devices, but future designs optimized for H2 should consistently improve resolution for all analytes.

08 HYDROGEN↗