The certified values and uncertainties are expressed as mass fraction.

All certified values were determined based on dry mass. 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 %.
AAS, atomic absorption spectroscopy; ICP-OES, inductively coupled plasma optical emission spectrometry; ICP-MS, inductively coupled plasma mass spectrometry; ID-ICP-MS, isotope dilution-ICP-MS

The referece values are expressed as mass fraction.

All reference values were determined based on dry mass. 
AAS, atomic absorption spectroscopy; ICP-OES, inductively coupled plasma optical emission spectrometry; ICP-MS, inductively coupled plasma mass spectrometry

The property values of the material were statistically determined based on chemical analyses by 8 organizations (including 14 laboratories) using a wide range of methods. A property value satisfying the following conditions was accepted as a certified value: 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 analytical 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 one or two of the NIES criteria for certification but supplying valuable additional information about the material is given as a reference value. All certified and reference values were determined based on dry mass.

The CRM is supplied as fine powder in an amber glass bottle. It is off-white in color.

This CRM was produced from rice that had been hydroponically cultivated under strictly controlled conditions within the Ecosystem Research Field of NIES. The raw material for the CRM was unpolished rice (about 10 kg)　that had been harvested by hand. It was dried at 70 ºC for 24 h, crushed in a rotor mill with a 200 µm-sieving ring and homogenized with a V-blender. The powdered unpolished rice was placed in amber glass bottles (15 g in each bottle, 609 bottles), and sterilized by 60Co irradiation (20 kGy) . All procedures complied with ISO GUIDE 34.

Mass fractions of multi-elements, including those for which certified values are given, were determined by ICP-OES and ICP-MS in material taken from 10 bottles selected from the total 609 bottles by stratified random sampling. The between-bottle variation evaluated by a one-way analysis of variance (ANOVA) showed the homogeneity standard deviations between bottles for the analytes to be less than 1 %. The material, therefore, is sufficiently homogeneous for its intended use as a reference material.

Stability tests demonstrated that long-term (6 months) and short-term (2 weeks at -20 ºC or 50 ºC) variations in the concentrations of all measured elements in the material were insignificant.