CERTIFICATION OF THE RUBIDIUM CONCENTRATION IN WATER MATERIALS FOR THE INTERNATIONAL MEASUREMENT EVALUATION PROGRAM (IMEP) USING ISOTOPE-DILUTION INDUCTIVELY-COUPLED PLASMA-MASS SPECTROMETRY

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