Determination of Rubidium by ID-ICP-QMS/QMS with Fluoromethane as the Reaction Cell Gas to Separate Spectral Interference from Strontium.

A determination of rubidium (Rb) was carried out by isotope dilution (ID) using an inductively coupled plasma tandem quadrupole mass spectrometer (ICP-QMS/QMS) with an octupole reaction-cell (ORC). Spectral interference of 87 Sr with the measurement of 87 Rb was effectively removed by using fluoromethane (CH3 F) as the reaction cell gas at the optimum flow rate. In comparison to the measurement obtained with a mathematical correction, good precision for the analysis of the Rb isotope could be obtained independent of the concentration of Sr without any chemical separation in advance. The usefulness of the present approach was confirmed by an analysis of Rb in multiple certified reference materials (CRMs) for food and environmental analysis, for which the results agreed with their certified values in the range of expanded uncertainty.