A Potentiometric investigation on the behaviour of taurine as a ligand

The ligand capability of taurine was studied at 25 degrees C towards cadmium(II), cobalt(Il) and nickel(II) in 1.00 mol/L NaCl as constant ionic medium and towards cobalt(II), nickel(II), calcium(II) and magnesium(II) in 1.00 mol/L NaClO4 as constant ionic medium. In the former ionic medium, potentiometric measurements were carried out by means of galvanic cells with a glass electrode and, for cadmium(ll), with an amalgam electrode, as well. In the latter ionic medium, free hydrogen ion concentration and free taurine concentration were obtained from electromotive force measurements of cells containing a glass and a silver electrode, respectively. The experimental data were explained by assuming the formation of complexes of the type ML and ML2, where M is the cation and L the taurine in basic form. The inspection of the values obtained for the stability constants seems to exclude the formation of chelates. A comparison among the values of the constants shows differences between the two ionic media and can be deduced a stability order.