Studies on fluorescein-VIII Notes on the mathematical work-up of absorbance data for systems with single and multiple dissociations, the limitations of the conventional logarithmic treatment, and the dissociation constants of fluorescein.
A mathematical study has been made of a commonly used method for obtaining dissociation constants from data for absorbace as a function of pH. Once the limiting working absorbances have been selected (usually simply the asymptotes to the curve of absorbance vs. pH), the value for the dissociation constant is fixed by the average of the values chosen and no treatment of the data, by graphical or least-squares methods, will alter the result. The mathematical reason for this is explained. An alternative procedure based on measuring the point of inflection of the curve and the slope through this point has been developed. Certain limitations of the Rosenblatt method for obtaining dissociation constants from absorbance data are also pointed out.
Diehl
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Department of Chemistry, Iowa State University, Ames, Iowa 50011 U.S.A.