Quantifying Proton-Bound Heterodimer Association Energies from Drift Time Shifts

Previously, we reported an approach to quantify the energetics of association between neutral drift gas modifiers and two common chemical warfare agent degradation species by a combination of experimental drift time shift data as well as computational modeling in collaboration with Chris Hogan at the University of Minnesota. As a continuation of this research in conjunction with Dr. Hogan, we are pleased to report the acceptance of our article for publication in The Journal of Physical Chemistry A entitled, “Deducing Proton-Bound Heterodimer Association Energies from Shifts in Ion Mobility Arrival Time Distributions.” This report describes the Gibbs free energy, enthalpy, and entropy changes as propanol is dimerized with a homologous series of alkylphosphonic acids (methyl-, ethyl-, and propylphosphonic acids) and its conformation with the Kelvin-Thomson-Raoult model.

Non-Contact, Trace Tributyl Phosphate Vapor Analysis

Following our initial experiments using ion trap mass spectrometry and atmospheric flow tube sampling (AFT-MS) for alkylphosphonic acid detection, we have applied a similar approach to the quantitation of tributyl phosphate in solution by analysis of headspace vapor. We are pleased to present this research, performed in collaboration with Robert Ewing from Pacific Northwest National Laboratory, as an accepted publication in Talanta entitled, “Ambient Vapor Sampling and Selective Cluster Formation for the Trace Detection of Tributyl Phosphate via Atmospheric Flow Tube Mass Spectrometry.” In this article, AFT-MS is shown to successfully quantitate tributyl phosphate down to tens of ppb in solution. Furthermore, analytical selectivity and quality control accuracy was enhanced by the introduction of specific dopant molecules.

Ambient Alkylphosphonic Acid Vapor Detection and Ion Traps

Atmospheric flow tube-mass spectrometry (AFT-MS) first emerged in 2012 as an ambient vapor sampling technique developed by Ewing et al. and applied to the sensing of trace quantities of RDX molecules clustered with nitrate ions. This iteration of AFT-MS used selected-ion monitoring (SIM) during analysis via a triple-quadrupole mass spectrometer and subsequently has been applied to vapor analysis of other explosives adducted with nitrate as well as positively-charged organophosphorus species clustered with amines as proton-bound dimers. Building upon these initial AFT-MS experiments, we have recently applied the atmospheric flow tube ionization method to the detection of alkylphosphonic acids from methanol solution headspace and adducted with nitrate and nitrate-nitric acid species via linear ion trap mass spectrometry. This was performed in an effort not only to demonstrate the application of ion trap MS systems with AFT-MS, but also to characterize the gas-phase ion chemistry of a homologous series of alkylphosphonic acids including methylphosphonic acid (MPA), which is an environmental pollutant and hydrolysis product of some chemical agents. Our article, “Characterization of Alkylphosphonic Acid Vapors Using Atmospheric Flow Tube-Ion Trap Mass Spectrometry,” can be found in Rapid Communications in Mass Spectrometry.

IM-MS Assessment of Cobalt-Glycan Heterodimers

Continuing along our previous work to characterize certain cationized glycans with a variety of metals and with cobalt to enhance UV photon absorption, we are pleased to show our effort to demonstrate the formation of heterodimeric cobalt-glycan adducts in published form. Now appearing as an online-first article in Journal of the American Society for Mass Spectrometry, our paper “Assessment of Dimeric Metal-Glycan Adducts via Isotopic Labeling and Ion Mobility-Mass Spectrometry” presents how important ion mobility separations are for tandem MS experiments performed on divalent metal-glycan adducts. Without the ability to use drift times to distinguish which precursor produced which fragment ions, component fragments from a heterodimeric adduct of two isomers cannot be deconvoluted. Specifically, the potential for isomers to form doubly-charged heterodimers–that are then dissociated into component fragments–will essentially create a scenario where chimeric fragmentation spectra are produced.

Recent Publication: Mobility Separation and UVPD of Co-Adducted Tetrasaccharides


Ultraviolet photodissociation (UVPD) has had its application directed primarily at biomolecule analysis, but with a common drawback of low fragment abundances. We encountered this same problem with UVPD of two sodiated isomeric glycans, but found a significantly higher fragment yield from the cobalt adducts of those same tetrasaccharides. An additional bonus was that the cobalt adduction increased the resolution of the isomers from no discernible mobility separation as sodium adducts to a resolution of 0.78. This allowed us to use UVPD for fragmenting a mobility separated mixture of the two glycans, which benefited from the higher fragment yield of the cobalt adducts.

Paper Link: http://link.springer.com/article/10.1007/s13361-017-1621-3

Recent Publication: Enhanced Mixture Separations of Metal Adducted Tetrasaccharides


Using a combination of Fourier transform ion mobility and ion trap mass spectrometry Kelsey demonstrated the degree to which different metal cations were able to enhance isomer separations across a set of tetrasaccharides.  While full resolution was not achieved for the full set of 5 isomers this work demonstrates the current state of the art for true isomeric mixture separations using IMS.  Another interesting aspect of this work was the observation of metal cation bound dimers.  Though we couldn’t tell whether they were homo or heterodimers we’ve now obtained a deuterated set of isomers which will help to answer that question.

Paper Link: http://link.springer.com/article/10.1007/s13361-016-1505-y