Confirmation of40Ar+related product ions in the octopole reaction cell of an ICP-QMS/QMS with18O2enriched oxygen as the reaction cell gas

Abstract

40Ar+ related product ions in an octopole reaction cell (ORC) were observed with an inductively coupled plasma tandem quadrupole mass spectrometer (ICP-QMS/QMS). In order to simplify the ion composition of the plasma, the carrier gas was directly connected to the torch injector, i.e. without introduction of the sample solution. The m/z of the first QMS was set to 40 permitting the passage of 40Ar+. Isotope enriched oxygen gas (18O2) was used as the reaction gas in order to separate the spectra of O3+ and Ar2O2+. The intensities of the ions produced in the ORC were measured by the second QMS. As the products of the reactions among 40Ar+ ions and 18O2 molecules in the ORC, the following ions were observed: 18O+, 18O2+, 18O3+, 18O4+, 40Ar18O+, 40Ar18O2+, 40Ar218O2+, and 40Ar18O22+. At a reaction gas flow rate of 0.3 mL min−1, the ionic species with the highest signal intensity was 18O2+, followed by 40Ar+ and 18O+. The maximum signal intensities of different product ions were obtained at different flow rates of the reaction gas. A lower flow rate of the reaction gas benefited the production of 40Ar18O+ and 18O3+, while a higher flow rate of the reaction gas benefited the production of 40Ar18O2+ and 40Ar218O2+. The maximum transfer efficiency from 40Ar+ to the resulting ionic species was 91%, 2.0%, and 0.12% for 18O2+, 18O+, and 40Ar18O+, respectively. The maximum transfer efficiency to the other investigated ionic species was less than 0.023%. By using 18O2 as the reaction gas, the mechanisms of 40Ar+ resulted ionic species interfering with the measurement of 32S16O+ were confirmed. The results showed that the contributions of 16O3+ and 40Ar2O2+ were almost equivalent to each other.