Salt effects on the protonation and on alkali and alkaline earth metal complex formation of 1,2,3-propanetricarboxylate in aqueous solution

The protonation of 1,2,3-propanetricarboxylate (tricarballylate, tca) was studied in LiCl, NaCl, KCl, MgCl(2), CaCl(2) and tetraethylammonium iodide (Et(4)NI) aqueous solutions, at 25 degrees C, in the ionic strength range 0 < I < 1M, using the pH-metric technique. The differences between protonation constants determined in Et(4)NI and those determined in the other background salts were interpreted in terms of complex formations. Least squares calculations are consistent with the formation of MLH(j) (j = 0,1.2), M(2)LH(i) (i = 0,1,2), M(2)L species, when M = Mg(2+), Ca(2+). Potentiometric measurements performed in mixed NaClKCl, NaClCaCl(2) and MgCl(2)CaCl(2) solutions showed the formation of mixed metal complexes NaKL, NaKHL, NaCaL and CaMgL. The dependence on ionic strength of protonation and complex formation constants was evaluated using a simple Debye-Hückel type equation.