CCQM-K124 Trace elements and ehromium speciation in drinking water : Part A: Trace elements in drinking water Part B: chromium speciation in drinking water. Final report

CCQM-K124 was an activity of the Inorganic Analysis Working Group (IAWG) and was jointly coordinated by the National Metrology Institute of Japan (NMIJ) and the Government Laboratory, Hong Kong SAR (GLHK). The Part A of CCQM-K124 was organized by NMIJ and trace elements in drinking water were the measurands. The Part A of the key comparison was undertaken for NMIs and DIs to demonstrate their capabilities in measuring part-per-billion level (in μg/kg) or part-per-million level (in mg/kg) of trace elements in drinking water. It should also facilitate the acquisition of claims in Calibration and Measurement Capabilities (CMCs) as listed in Appendix C of Key Comparison Database (KCDB) under the Mutual Recognition Arrangement of the International Committee of Weights and Measures (CIPM MRA). Results were submitted by 14 NMIs and nine DIs. The participants used different measurement methods, though most of them used direct measurement using inductively coupled plasma-optical emission spectrometry (ICP-OES), inductively coupled plasma-mass spectrometry (ICP-MS) and high resolution ICP-MS and isotope dilution technique with ICP-MS. Other methods were graphite furnace atomic absorption spectrophotometry (GFAAS) and flame atomic absorption spectrophotometry (FAAS). The results of B, Ca, Cr, As and Cd show good agreement except some outliers. Concerning Hg, instability was observed when the sample was stored in the light. And some participants observed instability of Mo. Therefore, it was agreed to abandon the Hg and Mo analysis as this sample was not satisfactory for KC. Accounting for relative expanded uncertainty, comparability of measurement results for each of B, Ca, Cr, As and Cd was successfully demonstrated by the participating NMIs or DIs. Furthermore, the results of this key comparison can be utilized along with the IAWG core capability approach. It is expected that arsenic, boron, cadmium, calcium and chromium at mass fractions greater than approximately 0.1 µg/kg, 1 µg/kg, 0.01 µg/kg, 1 mg/kg and 0.1 µg/kg respectively in drinking water and similar matrices (groundwater and river water etc.) can be determined by each participant using the same technique(s) employed for this key comparison to achieve similar uncertainties mentioned in the present report