Analytical Sciences

Determination of Trace Levels of Iron in a Seawater Sample Using Isotope Dilution/Inductively Coupled Plasma Mass Spectrometry

Yuichi TAKAKU,* Takuma HAYASHI,** Ikuko OTA,** Hidenao HASEGAWA,* and Shinji UEDA*

*Institute for Environmental Sciences, Department of Radioecology, 1-7 Ienomae, Obuchi, Rokkasho-mura, Kamikita-gun, Aomori 039-3212, Japan
**Tohoku Nuclear LTD. Advanced Technology of Science, 2-41-14 Higashi Okamisawa Misawa, Aomori 033-0024, Japan

An analytical method for trace levels of iron in a seawater sample using isotope dilution ICP-MS was developed. Preconcentration of iron and the removal of major elements in seawater such as alkali and alkaline-earth elements can be carried out quickly using a chelating resin disk by adjusting the sample pH to 3. The collision cell option of the ICP-MS instrument method was used to improve the performance of the instrument for iron measurements since ArO and ArN interferences could be reduced using this analytical method. About 4 ml min^-1 helium, as the collision gas, were introduced into the cell. ⁴⁰Ar¹⁴N and ⁴⁰Ar¹⁶O which interfere with ⁵⁴Fe and ⁵⁶Fe in water had their amounts decreased by 5 orders of magnitude. Then, the isotope dilution method was used for iron determination below ng g^-1 level of trace iron in four environmental reference materials (river water standard sample JAC-0031 (Japan Soc. for Analytical Chemistry), estuarine standard sample SLEW-2 (NRC Canada) and seawater standard samples CASS-3 and NASS-5 (NRC Canada)) were measured. Good agreement between analytical results and certified values of reference materials was obtained, which confirmed the effectiveness of this method.

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