EDTA complexes thermodynamic data

Thermodynamic characteristics of Ca-EDTA complex formation in aqueous solution have been derived at 288, 298, and 308 K and at ionic strengths of 0.3, 0.5, and 1.0 (KNOj). Conductivity and i.r. data suggest that CaH2EDTA is an acid salt of EDTA, and that the concentration of the ionic complex (if it exists) is negligible." ... 

Under stoichiometric conditions, fluorexon and its derivatives form 1 1 complexes with Ln ions. However when the ratio Ln Fx is increased, complexes with other stoichiometries are observed, the exact nature of which has not been determined. On the other hand, luminescence data of solutions with a ratio Yb Fx < 1 clearly indicate the presence of only one luminescent species, the 1 1 complex. Monoexponential luminescence decays are observed corresponding to a lifetime of 1.9 ps, whereas multi-exponential decays are measured when the Yb Fx ratio is increased. Further proof of the existence of 1 1 complexes has been brought by mass spectrometry. Competitive titration with edta has been followed by monitoring the Yb luminescence, since the edta complex is non-luminescent, contrary to the chelate formed with Fx. After addition of 5 equivalents of edta to a solution of [Yb(fx)] in Tris-HCl buffer, the Yb luminescence intensity decreases to 12% of its initial value. The thermodynamic stability of the fluorexon chelate is, therefore, comparable to [Yb(edta)] . In addition, the luminescence decay after addition of edta aliquots is relatively slow, the estimated rate constant being 7.1 x 10" s indicating a reasonably high kinetic stability of the fluorexon chelate. 

This paper describes the approach taken to reduce the number of chemical systems to a subset, the Na-Ca-Sr-OH-COs-NOs-EDTA-HEDTA-H2O system, which incorporates all of the strongest conq>lexation/ion-inteiactions for Sr in the more complex actual Hanford tank wastes. A compilation of the previously developed thermodynamic data is presented along with previously uiqiublished experimental data for certain chemical systems used to define the key systems needing detailed research. It is hoped fliat combining all of these results into one manuscript will bodi facilitate the use of the data and provide additional essential detail on the choice of the chemical systems and the validity of the overall model to the conq>lex tank wastes. 

THERMODYNAMIC DATA FOR COMPLEX FORMATION REACTIONS WITH EDTA HOMOLOGUES AT 2CP ANOfi 0,1(KNO ). 

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