Analytical Sciences

Current Status of Homogeneity and Stability of the Reference Materials for Nutrients in Seawater

Michio AOYAMA,*1 Hidekazu OTA,*2 Munehito KIMURA,*2 Takashi KITAO,*2 Hitoshi MITSUDA,*2 Akihiko MURATA,*3 and Kenichro SATO*4

*1 Meteorological Research Institute, 1-1 Nagamine, Tsukuba, Ibaraki 305-0052, Japan
*2 The General Environmental Technos Co., Ltd., 1-3-5 Azuchimachi, Chuo, Osaka 541-0052, Japan
*3 Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2-15 Natsushima, Yokosuka 237-0061, Japan
*4 Marine Works Japan Ltd., 2-16-32 5F Kamariyahigashi, Kanazawa, Yokohama 236-0042, Japan

The development of Reference Materials for Nutrients in Seawater (RMNS) has been in progress since 1993. When RMNS were produced for nitrate, silicate, and phosphate, their initial homogeneities were as low as 0.1 to 0.2% in samples of high-nutrient seawater, such as deep water from the Pacific Ocean. The relative standard uncertainties associated with instability during long-term (4.8 years) storage were approximately 0.2, 0.2, and 0.4% for nitrate, silicate, and phosphate, respectively. No instability was observed for 1.9 to 6.4 years based on the ISO Guide 35:2006 criteria; however, the relative standard uncertainties associated with instability during long-term storage were larger than the initial homogeneities of RMNS. RMNS produced by state-of-the-art techniques are currently available for global use to improve the comparability of nutrients data in the open ocean and, as discussed here, are reliable candidates to be used for certified reference materials.

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