SOLUBILITY OF BARIUM(II) TAURODEOXYCHOLATE

The solubility of barium(II) taurodeoxycholate was studied as a function of taurodeoxycholate ion concentration at 25-degrees-C and in 0.100, 0.200, 0.300, 0.400, 0.500, 0.600 and 0.750 mol l-1 N(CH3)4Cl as a constant ionic medium. For this purpose the total concentration of barium(II) was determined by means of atomic absorption spectrometric and polarographic measurements in solutions equilibrated with solid barium(II) taurodeoxycholate and at known hydrogen ion concentration. An attempt was also made to determine the free concentration of barium(II) ions by measuring the electromotive force (e.m.f.) of galvanic cells involving a barium(II) membrane electrode. The free concentration of hydrogen ion was measured by use of a glass electrode. The results of solubility and e.m.f. measurements could be explained by assuming the presence of associated species between barium(II) and taurodeoxycholate with different ratios depending on the concentration of the ionic medium. The solubility product and the association constants were determined for all the ionic medium concentrations. On the basis of the results, a relationship between solubility and free concentration of taurodeoxycholate ions can be deduced.