Analytical Sciences

Sensitive Spectrophotometric Determination of Phosphate Using Silica-Gel Collectors

Masahiro NAGAI,*  Masahito SUGIYAMA,** and Toshitaka HORI**

*Faculty of Human Environments Studies, The University of Human Environments, 6-2, Kamisanbonmatsu, Motojuku-cho, Okazaki 444-3505, Japan
**Graduate School of Human and Environmental Studies, Kyoto University, Yoshida-nihonmatsu-cho, Sakyo-ku, Kyoto 606-8501, Japan

Phosphate, 3 - 10 nmol, in 1 dm³ of natural-water samples was quantitatively collected along with 10 µmol of Fe(III) ion onto a silica-gel collector in the pH range of 5.4 - 6.2. The amount of Fe(III) ion needed was limited to such a low level that the Pyrocatechol Violet method could be applied without removing the Fe(III) ion, providing a superior determination method for phosphate. Surface-water samples of the north basin of Lake Biwa and the Tanabe Bay in the Wakayama prefecture were selected as being representative of natural water with extremely low phosphate concentrations, and were found to have phosphate concentrations of 3.68 and 4.31 nmol dm^-3, respectively.

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