Evaluation of the proficiency testing results using river water-based reference materials for heavy metal analysis

In this study, river water-based reference materials (RMs), NIER-I08RW and NIER-I09, for trace metal analysis were prepared and certified for Pb, Cd, Cr and Cu with evaluation of uncertainties. The RMs were confirmed to be homogeneous enough to be used as proficiency testing materials since within-bottle homogenieties of the RMs were lower than 0.3 times of targeted standard deviation of proficiency testing. The RMs were distributed to environmental testing laboratories for the proficiency testing and the variation of Z scores of the proficiency testing results were compared for different assigned values. The relative bias, , deviations between reference values and consensus values, were lower than 1 except for cadmium of NIERI08RW. The results showed both values were in a good agreement and only 2.9% of Z scores changed by using a different assigned values such as consensus and reference values.