Abstract
Metal speciation studies are of great importance in assessing metal bioavailability in aquatic environments. Functionalized membranes are a simple tool to perform metal chemical speciation. In this study, we have prepared and tested a polymer inclusion membrane (PIM) made of the polymer cellulose triacetate (CTA), the extractant di-(2-ethylhexyl) phosphoric acid (D2EHPA), and the plasticizer 2-nitrophenyloctyl ether (NPOE) as a sensor for Zn and Cu complexation studies. This PIM, incorporated in a device with an 0.01 M HNO3 receiving solution, is shown to effectively transport free metal ions, and it is demonstrated that the presence of ligands that form stable complexes with divalent metallic ions, such as ethylenediaminetetraacetic acid (EDTA) and humic acid (HA), greatly influences the accumulation of the metals in the receiving phase due to the increasing metal fraction complexed in the feed phase. Moreover, the effect of major ions found in natural waters has been investigated, and it is found that the presence of calcium did not decrease the accumulation of either Zn or Cu. Finally, the PIM sensor has been used successfully to evaluate metal complexation in a river water affected by Zn pollution.
Highlights
It is well known that metals in aquatic environments are found in numerous chemical or physical forms—such as free ions, inorganic and organic complexes, and colloidal forms
Even though the carrier has the central role in the transport process through the membrane, it is well known that the other components of the polymer inclusion membrane (PIM) composition are of great importance for the transport of the metals [24]
We have developed a simple sensor based on a polymer inclusion membrane consisting of 50% cellulose triacetate (CTA), 40% di-(2-ethylhexyl) phosphoric acid (D2EHPA), and 10% nitrophenyloctyl ether (NPOE) to evaluate metal complexation in natural waters
Summary
It is well known that metals in aquatic environments are found in numerous chemical or physical forms—such as free ions, inorganic and organic complexes, and colloidal forms. The dynamic process of metal partitioning depends on several chemical and physical parameters—such as the type and concentration of organic matter, ionic strength of the medium, hardness, pH, and redox conditions of the medium, among others. The combination of these abovementioned factors favors the formation of metallic species that can affect the metal bioavailability [1,2]. It is broadly accepted that the bioavailability and toxicity of metals cannot be predicted by total concentrations, but rather must be done by the concentration of various chemical species, in particular the free ions [3].
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