INTERPRETATION OF COMPETITIVE ADSORPTION-ISOTHERMS IN TERMS OF AFFINITY DISTRIBUTIONS

In the present study we evaluate affinity distributions for competitiv e adsorption isotherms which involve several components. In such a mul ticomponent situation, the affinity distribution becomes a function of several affinity constants, and already in the case of two components , little is known about their features. In the two-component situation , we have calculated the affinity distributions from the adsorption is otherms with a numerical inversion technique. This technique is based on a constrained least-squares algorithm and uses a regularization fun ction which biases the resulting affinity distribution toward a smooth function. The applicability of the procedure was tested with a newly derived isotherm, which is based on a fully uncorrelated affinity dist ribution, and with the generalized Langmuir-Freundlich (LF) isotherm, which is known to have a perfectly correlated distribution. The presen t study demonstrates that the extended Henderson-Hasselbalch (HH) isot herm has an underlying affinity distribution, which displays a partial correlation, while the non-ideal competitive adsorption (NICA) isothe rm has an affinity distribution with a varying degree of correlation. In the competitive situation, the affinity distribution thus provides an interesting means to characterize the corresponding isotherms. As a n illustration of the present techniques, experimental data of metal i on binding for a humic acid are analyzed in the same context. (C) 1997 Academic Press.