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

摘要

Upon collisional activation, gaseous metal adducts of lithium, sodium and potassium oxalate salts undergo an expulsion of CO_2, 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 CO_2 requires less energy than an expulsion of a Na~+ and that the [Na_3CO_2]~+ product ion formed in this way bears a planar geometry. Furthermore, spectra of [Na_3C_2O_4]~+ and [~(39_K_3C_2O_4]~+ recorded at higher collision energies showed additional peaks at m/z 90 and m/z 122 for the radical cations [Na_2CO_2]~(+?) and [K_2CO_2]~(+?), respectively, which represented a loss of an M~? from the precursor ions. Moreover, [Na_3CO_2]~+, [~(39)K_3CO_2]~+ and [Li_3CO_2]~+ ions also undergo a CO loss to form [M_3O]~+. Furthermore, product-ion spectra for [Na_3C_2O_4]~+ and [~(39)K_3C_2O_4]~+ recorded at low collision energies showed an unexpected peak at m/z 63 for [Na_2OH]~+ and m/z 95 for [~(39)K_2OH]~+, respectively. An additional peak observed at m/z 65 for [Na_2~(18)OH] ~+ in the spectrum recorded for [Na_3C_2O_4]~+, after the addition of some H_2~(18)O to the collision gas, confirmed that the [Na_2OH] ~+ ion is formedby an ion-molecule reaction with residual water in the collision cell.