Taurine as a ligand. An investigation of Ag(I)- and Cd(II)-taurine complex equilibria by direct and competitive techniques, and use of the Ag(I)-taurine complex electrode to assess taurine in solution

The behaviour of taurine as a ligand (L) towards silver(I) and cadmium(II) was studied at 25 degrees C and in 1 mol dm(-3) NaClO4, as a constant ionic medium. Experimental data, obtained for both cations from electromotive force measurements performed by using silver and cadmium amalgam and glass electrodes, were explained by assuming the formation of the AgL, AgL2, CdL, and CdL2 complexes. The taurine protonation constant and stability constants of the above complexes were determined. The cadmium(II)-taurine system was investigated by determining the free concentration of taurine from the Ag electrode potential and the knowledge of equilibria existing between silver(I) and taurine. Experimental data obtained from this approach were explained by assuming the presence of the above species with very close stability constant values. The success of this method supports the possibility of using the Ag/Ag-taurine, taurine electrode to measure the free concentration of taurine in its solutions. (C) 1998 Elsevier Science B.V. All rights reserved.