Abstract
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.
