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Comparison of Models for Determining Stability Constants of Metal Complexes with Humic Substances
Author(s) -
Fitch Alanah,
Stevenson F. J.
Publication year - 1984
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1984.03615995004800050019x
Subject(s) - chemistry , cooperativity , stability constants of complexes , stability (learning theory) , metal , reciprocal , plot (graphics) , constant (computer programming) , scatchard plot , yield (engineering) , thermodynamics , mathematics , binding site , physics , aqueous solution , statistics , organic chemistry , biochemistry , linguistics , philosophy , machine learning , computer science , programming language
Several recent approaches for determining apparent stability constants of metal complexes with humic and fulvic acids are shown to represent graphical modifications of the basic equation relating the formation function of binding ( v = sites bound/macromolecule concentration) to stability constants for the system v = Σ n j K j (M)/Σ[1 + K j (M)], where K j is the stability constant for binding at class j , n j is the number of binding sites of class j , and (M) is the free metal ion concentration. They include the Scatchard [ v /(M) vs. v ], reciprocal [1/ v vs. (M)], and double reciprocal [1/ v vs. 1/(M)] plots. Another approach is shown to have the same form as the Hill plot, which is based on an assumption of positive cooperativity. Comparison of the various models using a common set of experimental data revealed that approaches based on an assumption of linearity yield poor estimates for stability constants. Of the various models, the Hill plot is the least reliable.