Date of Award
Doctor of Philosophy
R. S. Houk
Common polyatomic ions (NO+, H2O +, ArN+, etc.) in inductively coupled plasma - mass spectrometry (ICP-MS) are identified using high mass resolution and studied using gas kinetic temperatures (Tgas) determined from a dissociation reaction approach. Methods for making accurate mass measurements, confirming ion identifications, and correcting for mass bias are discussed. The effects of sampler and skimmer cone composition and extraction voltage on polyatomic ion formation are also explored. Neutral species densities at several locations in the extraction interface are estimated and the corresponding effects of the Tgas value are calculated. The results provide information about the origins of background ions and indicate possible locations for their formation or removal;A joint experimental and computational approach is used on N2H + and a COHx+ series. Novel calculations are performed to determine the energies and partition functions of the ions. These values are combined with experimental data to evaluate a Tgas value for the proposed reaction. The examination of N2H + and HCO+ lead to a calculated Tgas of 4550 to 4900 K. The evaluation of H2CO+ leads to a much lower Tgas (<1000 to 2000 K). Finally, the dissociation of H3CO+ generates a Tgas value between those from the other HxCO+ ions studied here. All of these calculated Tgas values correspond to formation of extra polyatomic ion in the interface or extraction region. The calculations reveal the existence of isomers such as HCO+ and COH+, and H2CO+ and HCOH+, which complicate the interpretation of results;Chromium polyatomic ions in ICP-MS are studied, including CrOH +, CrO2+, CrO2H+, CrO2H2+, CrO3+, CrO3H+, and CrO3H2 +. Accurate m/z measurements are made of these previously unidentified ions. Ion identities are confirmed using isotope ratios. The prevalence of these species is found to be independent of the oxidation state of chromium introduced into the ICP. Elements surrounding chromium on the periodic table are also studied. Results indicate that chromium is unique in its polyatomic ion formation. Finally, dissociation constants are evaluated to determine a Tgas for these chromium ions that is thought to describe the location of ion formation in the ICP-MS device.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu
Jill Wisnewski Jill Wisnewski
Ferguson, Jill Wisnewski, "High resolution studies of the origins of polyatomic ions in inductively coupled plasma-mass spectrometry " (2006). Retrospective Theses and Dissertations. 1511.