This environmental certified reference material (CRM) was developed and certified by the National Institute for Environmental Studies (NIES) for the determination of multi-elements in tea leaves and materials of similar matrix. The property values of the material were statistically determined based on chemical analyses by 12 organizations (including 16 laboratories) using a wide range of methods. A property value satisfying the following conditions was accepted as a certified value (Table 1): 1) the relative standard deviation associated with the mean of the laboratory means was 5% or less; 2) the number of laboratories contributing to the mean of the laboratory means was at least eight; 3) the number of methods contributing to the mean of the laboratory means was at least two. The uncertainty attached to the certified values is the expanded uncertainty using a coverage factor k = 2, corresponding to a confidence interval of approximately 95%. A property value failing to satisfy the NIES criteria for certification but supplying valuable additional information about the material is given as a reference value (Table 2). All certified and reference values were determined based on dry mass. Keywords: Biological material, Plant material, Agricultural food products, Foodstuff, trace elements , heavy metals |
