131
Appendix VIII
Derivation of the relationship between the apparent binding constant, Kapp, and the individual binding constant, K
Consider the apparent reaction (VIII.1)
Mf + Lf ⇄ MLT (VIII.1)
whose equilibrium constant is defined according to eq (VIII.2)
(VIII.2)
In the case of the Iron(III)/BHA system, it runs out that, in the range of the investigated acidity
[MLT] = [FeHL] (VIII.3)
[Lf] = [H2L] (VIII.4)
[Mf] = [FeOH]/αFeOH (VIII.5)
Introduction of eqs (VIII.3), (VIII.4) and (VIII.5) in eq (VIII.2) yields
€
K
app=
[FeHL]
[FeOH][H
2L]
α
FeOH (VIII.6)The concentration ratio in eq (VIII.6) represents KML, the stability constant of the FeHL complex formed by reaction of FeOH with H2L (reaction (12) of the text). Hence, eq
(VIII.6) converts to:
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Appendix VIII
132
The derivation of αFeOH, defined as αFeOH = [FeOH]/[Mf] requires the solution of the cubic
equation (VIII.8) to obtain [FeOH].
