Analytical Sciences

Isotope Dilution Analysis of Selenite and Selenate in Natural Water Using Microwave-Induced Nitrogen Plasma Mass Spectrometry

Hirotsugu MINAMI,*  Wanhong CAI,** Tatsuya KUSUMOTO,** Kaiji NISHIKAWA,** Qiangbin ZHANG,** Sadanobu INOUE,** and Ikuo ATSUYA**

*Instrumental Analysis Center, Kitami Institute of Technology, 165 Koen-cho, Kitami 090-8507, Japan
**Department of Materials Science, Kitami Institute of Technology, 165 Koen-cho, Kitami 090-8507, Japan

Isotope dilution analysis of the sub-µg l^-1 levels of selenite and selenate in natural water samples by microwave-induced nitrogen plasma mass spectrometry (MIP-MS) was performed. An appropriate amount of a spike solution containing ⁷⁸Se-selenite and ⁷⁸Se-selenate was added to the natural water sample to be analyzed. Both analytes in the water were then concentrated simultaneously by passing the sample through a column that was filled with an anionic exchange resin. After the concentration process, all of the selenite and some of the selenate on the resin were eluted by 0.03 M nitric acid. The residual selenate was eluted by 0.13 M nitric acid. The eluted sample solutions were injected into MIP-MS, and isotope dilution analyses were carried out. Selenite and selenate concentrations as low as 0.01 µg l^-1 in the natural water sample were successfully determined by the proposed method.

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