David Fetsch

The acidobasic and complexation properties of humic acids: Study of complexation of Czech humic acids with metal ions

The acid-base and complexation properties of humic acids (HAs) extracted from bohemian brown coals were studied. The acid-base behavior corresponds with the model of HA as a mixture of mono- and diprotic acids. This model was also verified on commercial HA substances (Aldrich and Fluka). HA binds strongly with heavy metal ions and the highest stability constant of HA-metal ion complexes was observed for copper(II). Stability constant values were found to decrease in the order: Cu(2+)>Ba(2+)>Pb(2+)>Cd(2+)>Ca(2+). Both acidobasic models for HA alone and those for HA-metal ion interactions were proposed and the computational methodology for polyelectrolyte equilibria studies demonstrated.

Capillary zone electrophoresis for the separation and characterization of humic acids

Abstract Capillary zone electrophoresis (CZE) was used for the separation and characterization of humic acids (HAs) of different origin. UV–Vis detection and/or fast scanning of spectra during the separation was applied for the detection. From several background electrolytes (BGEs) studied, it was found that especially those containing amino acids are the most suitable and led to the separation of HAs into several fractions. The composition and pH of buffers were optimized. Up to 30 fractions were separated using a high boric acid concentration (350 m M ) BGE. The results can be used as real “fingerprints” to characterize HAs of different origin.

Potentiometric and spectroscopic study of uranyl complexation with humic acids

By potentiometric study using a specific uranyl ion-selective electrode, the formation of 1:1 and 1:2 (metal:ligand) complexes of uranyl with various humic acids (HAs) was found. The conditional stability constants were calculated using the LETAGROP-ETITR program. Possible structures of the complexes are proposed. Stability constants were found to be rather high indicating that immobilized HA can be used, for example, to remove traces of uranyl from waste waters.

Capillary zone electrophoresis study of aggregation of humic substances

The process of humic acids (HAs) component agglomeration (oligomerization) can be followed by capillary zone electrophoresis (CZE). Oligomerization of HAs of different origin was found to be strong, it leads to kinetically robust entities which can be separated by CZE and their formation is one of the reasons for unsuccessful separation by previous authors. Another difficulty comes from the sorption of some of the HA fractions on the fused-silica capillary wall. Critical concentration for the formation of aggregates was found to be mainly around 30 mg/l. Results of CZE were confirmed by vapour pressure osmometry.

The acidobasic and complexation properties of Humic acids: III. Study of Humic acids complexation with cadmium(II) and lead(II) by pulse anodic stripping voltammetry

Complexation of Humic Acids (HA) of different origin, like Fluka, and especially those extracted from bohemian brown coal, with cadmium(II) and lead(II) was studied at pH 5.0 using differential pulse anodic stripping voltammetry. Conditions close to those present in the environment were chosen with 3‐ 10‐4 moll‐4 for HAs and 2. 10‐8‐l . 10‐5 moll‐1 for Cd(II) and Pb(II). Stability constants evaluation was done assuming the electrode process is diffusion controlled and the complexes are labile. Obtained log K values were in the range 4.49–5.25 for Cd(II) and as expected the higher log K values 6.05–6.60 were found for Pb(II). There was no significant difference between complexation properties of HA extracted from bohemian brown coal and that of Fluka. The results obtained are in good agreement with the literature and those obtained by ISE in our laboratory.