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 [(39)K3C2O4](+) 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](+), [(39)K3CO2](+) and [Li3CO2](+) ions also undergo a CO loss to form [M3O](+). Furthermore, product-ion spectra for [Na3C2O4](+) and [(39)K3C2O4](+) recorded at low collision energies showed an unexpected peak at m/z 63 for [Na2OH](+) and m/z 95 for [(39)K2OH](+), respectively. An additional peak observed at m/z 65 for [Na2(18)OH](+) in the spectrum recorded for [Na3C2O4](+), after the addition of some H2(18)O to the collision gas, confirmed that the [Na2OH](+) ion is formed by an ion-molecule reaction with residual water in the collision cell.