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

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Abstract
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.