The starting material for this CRM was a composite stock of menus served in 29 households in Japan. The households were asked to duplicate all meals for 3 consecutive days in November 1997-January 1998 and for another 3 days in March-June 1998.
The meals were typical of Japanese households and consists primarily of traditional Japanese foodstuffs with some Western dishes. The meals were frozen in the households and transported to NIES in the frozen state.
The food materials were then homogenized, freeze-dried, pulverized to pass 250 μm nylon screen, blended and bottled. These procedures were compliant with ISO GUIDE 34. Then material was sterilized by 60Co irradiation (2.5 Mrad).

The homogeneity of this CRM was assessed at NIES by measuring, by inductively coupled plasma atomic emission spectrometry, the concentrations of Na, Mg, P, K, Ca, Mn, Fe and Zn in four 500 mg-subsamples from each of 6 randomly selected bottles after HNO3/HClO4/HF digestion.
No significant between-bottle variation was detected for these elements. However, a small but significant within-bottle variation was found for Fe, and which was excluded from certification. These elements were excluded from certification.

Certified Values were determined for Na, Mg, K, Ca, Mn, Cu, Zn, As, Se, Sr, Cd, Sn, Ba and U based on a collaborative analysis involving NIES, NIRS and 20 other laboratories: the resulting Certified Values are listed in Table 1. Means of the acceptable mean values from the collaborating laboratories were assigned as Certified Values (with their 95 % confidence intervals representing the uncertainty ranges) only when they were from 3 independent analytical methods based on different analytical principles, pursuant to ISO GUIDE 35.
Table 2 lists Reference Values for this CRM. Reference Values, rather than Certified Values, are reported when the collaborative analytical results were consistent among the laboratories but when within-bottle inhomogeneity was detected (Fe), when contamination during the preparation was suspected (Pb), or when the values resulted from only 2 independent analytical methods.
For the above reasons, the Reference Values may include bias. Certified and Reference Values are expressed on a dry weight basis. Analytical values should be corrected for the measured moisture content to relate to the Certified and Reference Values. See below for the drying procedure.