Analytical Sciences

Kinetic Spectrophotometric Determination of Trace Cadmium in Environmental Fresh Water with 5,10,15,20-Tetraphenyl-21H,23H-porphinetetrasulfonic Acid

Yuya SASAKI,*,** Natsuki YAMAMOTO,* Yasutada SUZUKI,* Ikuo UETA,* and Susumu KAWAKUBO*

*Graduate School, Department of Interdisciplinary Research, University of Yamanashi, Takeda, Kofu 400-8511, Japan
**Yamanashi Institute for Public Health and Environment, 1-7-31 Fujimi, Kofu, Yamanashi 400-0027, Japan

Cadmium-catalyzed complexation of zinc with 5,10,15,20-tetraphenyl-21H,23H-porphinetetrasulfonic acid (TPPS) was monitored spectrophotometrically. A kinetic parameter for the determination was obtained under kinetic consideration. Absorbance of zinc-TPPS at a fixed reaction time was proportional to the concentration of cadmium at pH 8 and 25°C. Tolerable concentration of interfering ions were 200, 200, 2000, 50, 500 and 1 μg L⁻¹ for Mg(II), Al(III), Ca(II), Fe(III), Zn(II) and Hg(II), respectively, in the determination of 20 μg L⁻¹ of cadmium, indicating Ca(II) and Mg(II) interferes with the analysis of natural fresh water. Such interference became tolerable at 5 mg L⁻¹ by the addition of an excess Ca(II) (50 mg L⁻¹) in the reacting solution of sample and cadmium standards. A calibration curve of Cd(II) was linear up to 100 μg L⁻¹ with a detection limit of 2 μg L⁻¹. The reliability of the proposed method was confirmed by the recovery test of cadmium spiked into tap, river and reservoir water samples.

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