ULF ÖRNEMARK, PHILIP D. P. TAYLOR and PAUL DE BIÈVRE
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 on87Rb from 87Sr. By using the adopted procedure, SI-traceable values with expanded uncertainties (U=2uc) 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.