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The certified values and uncertainties are expressed as mass fraction.

The property value of the material was statistically determined based on chemical analyses by 9 organizations using a wide range of methods. The 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 under 10 %; 2) the number of laboratories contributing to the mean of the laboratory means was at least 8; 3) the number of analytical methods contributing to the mean of the laboratory means was at least two. The uncertainty attached to the certified value is the expanded uncertainty using a coverage factor k=2, corresponding to the half-width of a confidence interval of approximately 95 %. The certified value was determined based on dry mass.

The CRM is supplied as fine powder in a glass bottle. The CRM is ocher in color.

Bluegills used for the preparation of this CRM were caught in Biwa Lake in Shiga Prefecture, Japan, from November 2011 to February 2012. A total of 200 kg of fish yielded 46 kg of fillets, which were minced, freeze-dried, pulverized, sieved (106 μm), and homogenized. The final material (3.8 kg) was placed in glass bottles (5 g in each bottle, 597 bottles), and sterilized by 60Co irradiation (20 kGy). All procedures complied with ISO GUIDE 34 with particular care to avoid contamination by PFOS.

The homogeneity of the CRM was determined by analysing 10 bottles selected from the total 597 bottles by stratified random sampling. PFOS was determined by the LC-MS/MS method. The between-bottle variation evaluated by a one-way analysis of variance (ANOVA) showed the relative 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 referece values are expressed as mass fraction.

AAS, atomic absorption spectroscopy 
CVAAS, cold vapor atomic absorption spectrometry 
ICP-MS, inductively coupled plasma mass spectrometry 
ICP-OES, inductively coupled plasma optical emission spectrometry
Molybdenum blue-FIA, molybdenum blue flow injection analysis

Of the measured values reported by 7 organizations, those with z-scores of 2 or more, obtained by use of robust statistics, were rejected. Reference values are means of reported values after those rejected were removed. These values were determined based on dry mass.

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 freezer at under -20 oC.
3. Prior to weighing portions for analysis, the bottle should be allowed to come to room temperature and the contents of the bottle should be shaken gently.
4. It is recommended that a sample intake of 0.2 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 certified and reference values in this CRM are reported on a dry mass basis. This CRM has 4 % water as measured (n=20) in NIES by drying for 4 h at 85 oC. Correction to dry mass should be determined by drying a separate sub-sample.

The expiry date for the certified values of this CRM is March 2026 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.

The certified and reference values for this CRM were based on analytical values from the following 11 participating organizations: 
National Institute for Environmental Studies; Environmental Control Center Co., Ltd.; Hyogo Prefectural Institute of Environmental Sciences; IDEA Consultants, Inc.; Kaneka Techno Research Corporation; Japan Food Research Laboratories; Murata Keisokuki Service Co., Ltd.; Nippon Steel & Sumikin Technology Co., Ltd.; Seikan Kensa Center Inc. ; Shimadzu Techno-Research Inc.; The University of Tokyo

Shiga Prefecture Federation of Fishermen’s Co-operative Association; Kasumigaura Fishermen’s Co-operative Association

Appendix Table 1
Information values of Mass fractions of Perfluoro compounds (PFCs) in NIES CRM No.32