Ringbom coefficient

It is also important to state the conditions at which the pFe is determined, as the value will change with the conditions (54). Fig. 4 shows an example of how the pFe value can vary over a range of pH values. This variation is due to the inclusion of a value known as the Ringbom coefficient in the determination of pFe values. The Ringbom coefficient, a, is determined from the mass balance equation as shown below for the ligand Ringbom coefficient. 

Note that Eq. (33) is simplified, as the equilibria observed in solution must take into account the pH at which the experiment is performed. Corrections must be made using the Ringbom coefficients for the ligand systems. 

Silver was critical of the lack of use by plutonium chemists of a-coefficients. Assuming that Silver was referring to a-coeffi-cients defined as the fraction of the total concentration of a substance that exists as a particular species, he was wrong to say that plutonium chemists have not used them. Phil Horwitz at ANL has used them. Publications from ORNL have reported them to easily show relative concentrations of plutonium species, and L. M. Toth used such a-coefficients as percent of Pu(IV) polymer in his symposium talk Tuesday. Alpha coefficients are a commonly used, simple concept - certainly since Ringbom s article in the Journal of Chemical Education in 1958."... 

The side reactions can considerably change the concentration of the free metal ion and the free organic ligand. To account for their effect on the main equilibrium, the side-reaction coefficients qcm, Kl and Mml as defined by Ringbom et al. need to be introduced into the stability constant (106). The side reaction coefficients are, of course, functions of the equilibrium constants of the side reactions if [M ] is the conditional concentration of M (all the forms of M not complexed with L), [L ] is the conditional concentration of L (all the forms of L not coordinated by M) and [ML ] is the conditional concentration of ML (the metal complex present in all the forms, even as mixed complexes, then the mathematical relationships to describe m, ocl and aML are ... 

FIGURE 8.1 The relationship between the activity coefficient (-log y ) and the ionic strength for aqueous solutions of mono-, di-, and trivalent ions. (From Ringbom, A., Complexation in Analytical Chemistry, Wiley Interscience, New York, 1963, 24. With permission.)... 

The concept of side reaction coefficients, introduced by A. Ringbom, is useful in describing the effect of pH on various equilibria. These coefficients combine the total (analytical) concentration, [X ], of the species of interest, with the concentration of its form [X], which luidergoes reaction. For example, for eth-ylenediaminetetraacetic acid (EDTA) the reacted form is the EDTA" anion, but the total concentration also includes all protonated forms. Thus, the side reaction coefficient, o edta(H) > is given by... 

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