Analytical Sciences

Development of a Certified Reference Material (NMIJ CRM 7512-a) for the Determination of Trace Elements in Milk Powder

Yanbei ZHU, Tomohiro NARUKAWA, Shin-ichi MIYASHITA, Takayoshi KUROIWA, Kazumi INAGAKI, Koichi CHIBA, and Akiharu HIOKI

National Metrology Institute of Japan (NMIJ), National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki 305-8563, Japan

A certified reference material (CRM), NMIJ CRM 7512-a, was developed for the determination of trace elements in milk powder. At least three independent analytical methods were applied to characterize the certified value of each element; all of these analytical methods were based on microwave acid digestions and carried out using different analytical instruments. The certified value was given on a dry-mass basis, where the dry-mass correction factor was obtained by drying the sample at 65°C for 15 to 25 h. The certified values in the units of mass fractions for 13 elements were as follows: Ca, 8.65 (0.38) g kg⁻¹; Fe, 0.104 (0.007) g kg⁻¹; K, 8.41 (0.33) g kg⁻¹; Mg, 0.819 (0.024) g kg⁻¹; Na, 1.87 (0.09) g kg⁻¹; P, 5.62 (0.23) g kg⁻¹; Ba, 0.449 (0.013) mg kg⁻¹; Cu, 4.66 (0.23) mg kg⁻¹; Mn, 0.931 (0.032) mg kg⁻¹; Mo, 0.223 (0.012) mg kg⁻¹; Rb, 8.93 (0.31) mg kg⁻¹; Sr, 5.88 (0.20) mg kg⁻¹; and Zn, 41.3 (1.4) mg kg⁻¹, where the numbers in the parentheses are the expanded uncertainties with a coverage factor of 2. The expanded uncertainties were estimated considering the contribution of the analytical methods, the method-to-method variance, the sample homogeneity, the dry-mass correction factor, and the concentrations of the standard solutions for calibration. The concentrations of As (2.1 μg kg⁻¹), Cd (0.2 μg kg⁻¹), Cr (1.3 μg kg⁻¹), Pb (0.3 μg kg⁻¹), and Y (64 μg kg⁻¹) were given as information values for the present CRM.

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