Gas-phase fragmentation of metal adducts of alkali-metal oxalate salts.

Upon collisional activation, gaseous metal adducts of lithium, sodium and potassium oxalate salts undergo an expulsion of CO2, followed by an ejection of CO to generate a product ion that retains all three metals atoms of the precursor. Spectra recorded even at very low collision energies (2 eV) showed peaks for a 44-Da neutral fragment loss. Density functional theory calculations predicted that the ejection of CO2 requires less energy than an expulsion of a Na+ and that the [Na3CO2]+ product ion formed in this way bears a planar geometry. Furthermore, spectra of [Na3C2O4]+ and [39K3C2O4]+ recorded at higher collision energies showed additional peaks at m/z 90 and m/z 122 for the radical cations [Na2CO2]+• and [K2CO2]+•, respectively, which represented a loss of an M• from the precursor ions. Moreover, [Na3CO2]+, [39K3CO2]+ and [Li3CO2]+ ions also undergo a CO loss to form [M3O]+. Furthermore, product-ion spectra for [Na3C2O4]+ and [39K3C2O4]+ recorded at low collision energies showed an unexpected peak at m/z 63 for [Na2OH]+ and m/z 95 for [39K2OH]+, respectively. An additional peak observed at m/z 65 for [Na218OH] + in the spectrum recorded for [Na3C2O4]+, after the addition of some H218O to the collision gas, confirmed that the [Na2OH] + ion is formed by an ion–molecule reaction with residual water in the collision cell. Copyright © 2014 John Wiley & Sons, Ltd.