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Effect of Humic Acid on Metal Uptake Measured by Diffusive Gradients in Thin Films Technique

B. Dočekal, V. Řezáčová-Smetková, and H. Dočekalová

Institute of Analytical Chemistry, Academy of Sciences of the Czech Republic, CZ-611 42 Brno, Czech Republic

 

E-mail: docekal@iach.cz

Received: 6 December 2004

Abstract: Impact of the presence of humic acid (HA) on the metal uptake of cadmium, copper, nickel, and lead in the diffusive gradients in thin films technique (DGT) was studied. Both the diffusive and resin gel were composed of the agarose polyacrylamide hydrogel, the resin one also with embedded Chelex-100 ion exchanger. A restrict gel, excluding high-molecular species, was used in complementary experiments. Metal concentrations of 50 μg dm−3 of Cd, Cu, Ni, and Pb, various mass concentrations of HA substance of ρ/(mg dm−3): 0, 0.3, 1, 3.1, 10, 31, 100, and 316, and concentration of 0.05 mol dm−3 sodium nitrate were adjusted in experimental solutions (pH = 6.8). The DGT probes were deployed in solutions at (26 ± 2)°C for up to 32 h. After elution, the overall DGT-accumulated masses of metals were determined by electrothermal atomic absorption spectrometry and apparent diffusion coefficients of individual metals were evaluated. The HA substance at approximately equimolar (1 mg dm−3) and higher concentrations with respect to metals ions considerably reduces the DGT-measured metals uptake. This suppression effect is more pronounced at higher concentrations of HA substance, it is element-specific and increases in the sequence Cd, Ni, Pb, Cu. HA species diffuse through the permeable gel and affect predominantly the interaction of metal ions with specific iminodiacetic groups of the resin by competitive reactions. This is documented by a very good agreement of the experimental data and the data obtained for the theoretical model of the effect of HA on the conditional equilibrium of metal-iminodiacetic group. Reduced mobility of larger molecular species of metal—humic acid complexes plays a minor role.

Full paper in Portable Document Format: 595a298.pdf

 

Chemical Papers 59 (5) 298–303 (2005)

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