Confirmation of Ar-40(+) related product ions in the octopole reaction cell of an ICP-QMS/QMS with O-18(2) enriched oxygen as the reaction cell gas

Ar-40(+) 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 Ar-40(+). Isotope enriched oxygen gas (O-18(2)) was used as the reaction gas in order to separate the spectra of O-3(+) and Ar2O2+. The intensities of the ions produced in the ORC were measured by the second QMS. As the products of the reactions among Ar-40(+) ions and O-18(2) molecules in the ORC, the following ions were observed: O-18(+), O-18(2) +, O-18(3) +, O-18(4) +, (ArO+)-Ar-40-O-18, (ArO2+)-Ar-40-O-18, (Ar2O2+)-Ar-40-O-18, and (ArO22+)-Ar-40-O-18. At a reaction gas flow rate of 0.3 mL min (1), the ionic species with the highest signal intensity was O-18(2)+, followed by Ar-40(+) and O-18(+). 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 (ArO+)-Ar-40-O-18 and O-18(3)+, while a higher flow rate of the reaction gas benefited the production of (ArO2+)-Ar-40-O-18 and (Ar2O2+)-Ar-40-O-18. The maximum transfer efficiency from Ar-40(+) to the resulting ionic species was 91%, 2.0%, and 0.12% for O-18(2)+, O-18(+), and (ArO+)-Ar-40-O-18, respectively. The maximum transfer efficiency to the other investigated ionic species was less than 0.023%. By using O-18(2) as the reaction gas, the mechanisms of Ar-40(+) resulted ionic species interfering with the measurement of (SO+)-S-32-O-16 were confirmed. The results showed that the contributions of O-16(3)+ and (Ar2O2+)-Ar-40 were almost equivalent to each other.