A COMPARATIVE-STUDY EMPLOYING 3 DIFFERENT MODELS TO INVESTIGATE THE COMPLEXATION PROPERTIES OF HUMIC-ACID AND FULVIC-ACID

The difficulties associated with quantifying trace element uptake by naturally occurring humic and fulvic acids are widely recognised. Occasionally in the past, some of the observed anomalies in the complexation behaviour of both humic and fulvic acids have been ascribed to inferred structural changes occurring during their extraction. Consequently a previous study was undertaken to compare the complexation properties of 'in-situ' and extracted humic and fulvic acids. This study being a comparative study, used a simple model based on a modified Scatchard approach, to interpret the results. Recently however, the results have been subjected to further scrutiny. The object being to determine whether the use of increasingly sophisticated models, designed to improve the representation of the humic and fulvic materials, could reveal effects not previously discernible. This study therefore describes the re-examination of the original data using: classical methods to 'improve' the complexation parameters which were derived using the simplified Scatchard approach; a continuous stability function approach (Differential Equilibrium Model); a discrete site/electrostatic approach. From the re-analysis of the data, further evidence was obtained to support the original conclusion that the extraction process had not altered the fundamental complexation properties of the HA and FA materials. The exercise also allowed the three modelling approaches to be compared in terms of their interpretive and predictive capabilities.