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.
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.
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
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