Abstract
A supported liquid membrane-hollow fiber system (HFSLM) has been developed to determine zinc speciation in aquatic environments. The liquid membrane consisted of an organic solution of bis-(2-ethylhexyl)phosphoric acid (D2EHPA) impregnated in the microporous of a polypropylene hollow fiber. The membrane contacted both the donor solution, that contained the metal and the stripping solution, placed in the lumen of the hollow fiber, where the metal was preconcentrated. Different parameters affecting the Zn2+ transport efficiency have been evaluated such as the composition of both the donor and stripping solutions as well as the membrane phase. Extraction and transport efficiencies of free Zn(II) higher than 90% were obtained with a liquid membrane consisting of a 0.1 M D2EHPA solution in dodecane and a 0.1 M HNO3 solution as the stripping phase. The developed HFSLM was used to study the effect of different ligands (EDTA and citric acid) in the donor phase of Zn(II) transport and to investigate the selectivity of the membrane towards Zn when other metals were also present. Finally, the HFSLM system was successfully applied to estimate the free Zn(II) concentrations in three water samples from a mining area. Moreover, the HFSLM system facilitates the analytical determination of trace Zn(II) levels allowing the achievement of enrichment factors of around 700 in the stripping phase.
Highlights
The total concentration of metals present in the aquatic environment does not provide information regarding their distribution, mobility, biological availability and toxicity
Mean enrichment factors of 730 ± 50 for Zn(II) were obtained under the optimal conditions, which consisted of a 0.1 M D2EHPA solution in dodecane as the liquid membrane phase, 600 μL of 0.1 M
Which consisted of a 0.1 M D2EHPA solution in dodecane as the liquid membrane phase, 600 μ L of
Summary
The total concentration of metals present in the aquatic environment does not provide information regarding their distribution, mobility, biological availability and toxicity. The different species in which metal ions may be present in the aquatic environment lead to different types of interactions with biological membranes depending on their bioavailability [1]. The metal bioavailability depends on their chemical speciation and, in general, it is considered that the most bioavailable metallic species are dissolved and that the amount of metal that can be bio-assimilated by a living organism is proportional to the fraction of free metal or labile metal species present in the media [2]. Among the different metal species that are present at trace concentration levels in natural waters, some of them are considered toxic (e.g., Cd, Hg and Pb species) while others are nutrients for plants and animals (e.g., Cu, Fe, Mn, Zn species) they can be toxic at elevated concentrations. An excess of Zn can produce oxidative stress in plants and toxic effects in microalgae and other aquatic organisms [6]
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