Polyatomic ions in inductively coupled plasma–mass spectrometry: Part II: Origins of N2H+ and HxCO+ ions using experimental measurements combined with calculated energies and structures

Several polyatomic ions in inductively coupled plasma–mass spectrometry are studied experimentally and by computational methods. Novel calculations based on spin-restricted open shell second order perturbation theory (ZAPT2) and coupled cluster (CCSD(T)) theory are performed to determine the energies, structures and partition functions of the ions. These values are combined with experimental data to evaluate a dissociation constant and gas kinetic temperature (Tgas) value. In our opinion, the resulting Tgas value can sometimes be interpreted to deduce the location where the polyatomic ion of interest is generated. The dissociation of N2H+ to N2+ leads to a calculated Tgas of 4550 to 4900 K, depending on the computational data used. The COH+ to CO+ system yields a similar temperature, which is not surprising considering the similar energies and structures of COH+ and N2H+. The dissociation of H2CO+ to HCO+ leads to a much lower Tgas (< 1000 to 2000 K). Finally, the dissociation of H2COH+ to HCOH+ generates a Tgas value between those from the other HxCO+ ions studied here. All of these measured Tgas values correspond to formation of extra polyatomic ion in the interface or extraction region. The computations reveal the existence of isomers such as HCO+ and COH+, and H2CO+ and HCOH+, which have virtually the same m/z values and need to be considered in the interpretation of results.