Speciation of phytate ion in aqueous solution. Trimethyltin(IV) interactions in self medium.

In this paper the results of a potentiometric (ISE-[H+] glass electrode) investigation at t = 25 °C on the complexing ability of phytate towards trimethyltin(IV) (tmt) and on the acid-base properties of tmt at high metal concentration (0.050 and 0.075 mol L-1) are reported. First we determined the hydrolytic constants of tmt in aqueous solution without further addition of background salt (self medium); in these experimental conditions we verified the formation of the following hydrolytic species: tmt(OH)0, tmt(OH)2- and the binuclear species (tmt)2(OH)+. Successively, we studied the complex formation constants obtained from the interaction of phytate anion with tmt in the same experimental conditions of hydrolytic measurements; the speciation model obtained takes into account several polynuclear species (tmtH5Phy6-; tmt2H5Phy5-; tmt3H4Phy5-; tmt3H5Phy4-; tmt4H6Phy2-; tmt5HPhy6-). A comparison with literature data is reported too.