The water hyacinth for this CRM was control-cultivated in a managed water pool in the NIES Aquatron. The raw material (about 300 kg) was washed with distilled water, dried, crushed in a rotor mill, sieved (106μm sieve), and homogenized with a V-blender. All procedures complied with ISO GUIDE 34. The powdered water hyacinth (about 9 kg) was placed in amber glass bottles (5 g in each bottle), and stabilized by 60Co irradiation (2.5 Mrad) .

Mass fractions of multi-elements, including those for which certified values are given, were determined by ICP-AES and ICP-MS in material taken from 10 bottles selected from the total 1054 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.

The property values of the material were statistically determined based on chemical analyses by 13 organizations (including 20 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 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; HR ICP-MS, high resolution inductively coupled plasma - mass spectrometry; IC, ion chromatography; ICP-AES, inductively coupled plasma - atomic emission spectrometry; ICP-MS, inductively coupled plasma - mass spectrometry; ID-ICP-MS, isotope dilution ICP-MS; INAA, instrumental neutron activation analysis; XRF/WDX, wavelength dispersive X-ray fluorescence spectroscopy

The referece values are expressed as mass fraction.

All reference values were determined based on dry mass. AAS, atomic absorption spectroscopy; EA, elemental analysis; HR-ICP-MS, high resolution inductively coupled plasma - mass spectrometry; ICP-AES, inductively coupled plasma - atomic emission spectrometry; ICP-MS, inductively coupled plasma - mass spectrometry; INAA, instrumental neutron activation analysis; XRF/WDX, wavelength dispersive X-ray fluorescence spectroscopy

1. Care should be taken to avoid contamination when opening the bottles. It is desirable to use up the contents as quickly as possible after opening.
2. This CRM should be kept tightly closed in its original bottle and stored in a desiccator at room temperature ( ≤30 ℃).
3. Prior to weighing aliquots for analysis, the contents of the bottle should be shaken gently.
4. It is recommended that a sample intake of 0.1 g is the minimum for convenient handling.
5. Precautions should be taken to avoid inhalation of the material.
6. This CRM should not be used for purposes other than research. When disposing of the material, local laws concerning processing and disposal of waste materials should be strictly adhered to.
7. The mass fractions of elements in this CRM are reported on a dry mass basis. This CRM, as received, contains 2-4 % water measured in NIES by drying a separate sub-sample for 4 h at 85 ℃ Correction to dry mass should be determined by drying a separate sub-sample at the time of use.

The expiration date for the certified values of this CRM is September 2021 assuming that the recommended storage conditions are adhered to. NIES will notify via its website if any changes in the contents are recognized within the term of validity.