Certification of the Rubidium Concentration in Water Materials for the International Measurement Evaluation Programme (IMEP) Using Isotope Dilution Inductively Coupled Plasma Mass Spectrometry

This paper describes the certification of rubidium in synthetic and natural water samples for Round 6 of the Institute for Reference Materials and Measurements International Measurement Evaluation Programme (IMEP). The analytical procedure is based on isotope dilution ICP-MS as the primary method of measurement. Ion exchange chromatography was used to eliminate the isobaric interference on 87 Rb from 87 Sr. By using the adopted procedure, SI-traceable values with expanded uncertainties ( U =2 u c ) of ≤2% were obtained for rubidium at nmol kg -1 (low µg kg -1 ) levels. Results from 42 field laboratories participating in IMEP-6 are evaluated against the certified values.