INVESTIGATION OF THE EFFECT OF E AND F PARAMETERS ON THE MINIMIZED ERROR FUNCTION IN THE CALCULATION OF STABILITY CONSTANTS FOR TUNGSTEN (VI) AND MOLYBDENUM (VI) COMPLEXES WITH NITRILOTRIACETIC ACID AND GLUTAMIC ACID AT DIFFERENT IONIC STRENGTHS

The formation constants of species formed in the systems H⁺+W (VI) + nitrilotriacetic acid and H⁺+ nitrilotriacetic acid have been determined in aqueous solution for pH=4-9 at 25^oC and different ionic strengths ranging from (0.1 to 1.0) mol dm^-3 (NaClO₄), using potentiometric and spectrophotometric techniques. It was shown that tungsten (VI) forms a mononuclear 1:1 complex with NTA of the type (WO₃L^3-) at pH=7.5. The composition of the complex was determined by the continuous variations method.
The complexation of molybdenum (VI) with glutamic acid was investigated in aqueous solution ranging in pH from 4 to 9, using polarimetric, potentiometric and spectrophotometric techniques. The composition of the complex was determined by the continuous variations method. It was shown that molybdenum (VI) forms a mononuclear 1:1 complex with glutamic acid of the type (MoO₃L^2-) at pH=6.0. The dissociation constants of glutamic acid and the stability constants of the complex were determined at 25^oC and at ionic strengths ranging from (0.1 to 1.0) mol dm^3- sodium perchlorate.
In both complex formation reactions by introducing two new parameters, E and F, the dependence of the dissociation and stability constants on ionic strength is described by a Debye-Huckel type equation and the effect of the aforementioned parameters on the minimized error function is discussed. Finally, a comparison has been made between the patterns of ionic strength dependence for the two complexes and the results have been compared with data previously reported.