The Japan Society for Analytical Chemistry has developed new certified reference materials (CRMs) (JSAC 0301-1, JSAC 0301-2, JSAC 0302) for the analysis of 18 elements in river water. A study team has been organized to prepare two kinds of water for reference materials: one is natural river water, and the other is water spiked with small amounts of some elements to the river water. Interlaboratory testing, in which 30 laboratories participated, was carried out. In a statistical analysis of all data, z scores in a robust method were applied to reject outliers, followed by the usual statistical procedure.
