Analytical Sciences

Evaluation of the Calibration Method for Accurate Analysis of Dissolved Silica by Continuous Flow Analysis

Chikako CHEONG,*,** Aya SAKAGUCHI,* Keisuke SUEKI,* and Masaki OHATA**

*Graduate School of Life and Environmental Sciences, The University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8572, Japan
**National Metrology Institute of Japan (NMIJ), National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1, Umezono, Tsukuba, Ibaraki 305-8563, Japan

For accurately determining nutrients in seawater by continuous flow analysis (CFA), the characteristic of the calibration curve was examined in detail. Under absorbance below 0.8, the calibration curve and the bracketing methods showed more accurate results that the bias fell below 0.5%. The analytical results of dissolved silica in seawater from the nutrient maximum layer of the Pacific Ocean obtained by the proposed methods showed good agreement with those obtained by an ion exclusion chromatography postcolumn absorption spectrophotometry (IEC-postcolumn) and an ion exclusion chromatography isotope dilution ICP mass spectrometry (IEC-ID-ICP-MS). From the results, the analysis of nutrients in seawater could be accurately carried out by CFA with an expanded uncertainty of below 1% using both the calibration curve and the bracketing methods with an appropriate absorbance range.

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