Speciation of selenium and mercury

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Abstract

Mercury is one of the most toxic elements that may be found in natural water bodies and can negatively affect living organisms, human health as well as drinking water quality. In addition, water is the main transportation and transformation pathway of mercury into the environment and living organisms. Therefore, specific strategies have been developed to reduce mercury releases and to remediate mercury contaminated areas. Mercury analysis in water is of great importance, in order to monitor water quality and associated environmental stresses, thus a considerable number of new publications appear every year. Many of these publications deal with the determination of mercury’s chemical form; others with the development of new analytical techniques, while there are also studies that focus on areas of particular environmental interest. Classic analytical chemistry methods for mercury analysis and speciation in water, namely CVAAS and ICP-MS, have achieved sub-ppt detection limits; while even though, atomic and nuclear analytical methods are promising, especially XRF which has achieved sub-ppb detection limits, they are scarcely used. Other promising analytical methods include CVAFS, FIA-AFS, CVAES, Raman probe, Raman scattering and anodic stripping voltammetry. This paper is a review of the state of the art of mercury analysis and speciation in water (including seawater) with emphasis given on the last 5 years. It highlights the novelties of the referenced papers; the applied analytical techniques, mercury speciation, preconcentration procedures, selectivity, achieved detection limits, the type of the analyzed waters; systems for on-site analysis and mercury analysis in real water samples.

A non-chromatographic separation and preconcentration method for Se species determination based on the use of an on-line ionic liquid (IL) dispersive microextraction system coupled to electrothermal atomic absorption spectrometry (ETAAS) is proposed. Retention and separation of the IL phase was achieved with a Florisil®-packed microcolumn after dispersive liquid–liquid microextraction (DLLME) with tetradecyl(trihexyl)phosphonium chloride IL (CYPHOS® IL 101). Selenite [Se(IV)] species was selectively separated by forming Se–ammonium pyrrolidine dithiocarbamate (Se–APDC) complex followed by extraction with CYPHOS® IL 101. The methodology was highly selective towards Se(IV), while selenate [Se(VI)] was reduced and then indirectly determined. Several factors influencing the efficiency of the preconcentration technique, such as APDC concentration, sample volume, extractant phase volume, type of eluent, elution flow rate, etc., have been investigated in detail. The limit of detection (LOD) was 15 ng L−1 and the relative standard deviation (RSD) for 10 replicates at 0.5 μg L−1 Se concentration was 5.1%, calculated with peak heights. The calibration graph was linear and a correlation coefficient of 0.9993 was achieved. The method was successfully employed for Se speciation studies in garlic extracts and water samples.

The essential micronutrient selenium (Se) is retained better in animal and human tissues in its organic forms while nonprotein selenoamino acids, such as selenomethylselenocysteine (SeMetSeCys), are considered as functional organic Se species. We studied the ability of oilseed rape Brassica napus to metabolize inorganic selenate/selenite (SeVI/SeIV) into various organic Se species, including SeMetSeCys. At 14 d after the inorganic Se application, 33% of the Se had accumulated as selenomethionine (SeMet) and 60% as SeVI, whereas no SeMetSeCys was detected. SeMet was the main organic Se species (53−94%) in seeds. Brassica napus selenocysteine methyltransferase (SMT) protein sequence revealed a substitution typical of nonaccumulators explaining the low SeMetSeCys accumulation. Brassica napus absorbs rapidly inorganic Se and converts it into organic Se forms, mainly SeMet, that are suitable for augmenting animal feed and thereby supplementing the human food chain in Se-deficient countries. In contrast, Se biofortification did not result in accumulation of the more valuable SeMetSeCys.

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A non-chromatographic separation and preconcentration method for Se species determination based on the use of an on-line ionic liquid (IL) dispersive microextraction system coupled to electrothermal atomic absorption spectrometry (ETAAS) is proposed. Retention and separation of the IL phase was achieved with a Florisil ® -packed microcolumn after dispersive liquid-liquid microextraction (DLLME) with tetradecyl(trihexyl)phosphonium chloride IL (CYPHOS ® IL 101). Selenite [Se(IV)] species was selectively separated by forming Se-ammonium pyrrolidine dithiocarbamate (Se-APDC) complex followed by extraction with CYPHOS ® IL 101. The methodology was highly selective towards Se(IV), while selenate [Se(VI)] was reduced and then indirectly determined. Several factors influencing the efficiency of the preconcentration technique, such as APDC concentration, sample volume, extractant phase volume, type of eluent, elution flow rate, etc., have been investigated in detail. The limit of detection (LOD) was 15 ng L −1 and the relative standard deviation (RSD) for 10 replicates at 0.5 g L −1 Se concentration was 5.1%, calculated with peak heights. The calibration graph was linear and a correlation coefficient of 0.9993 was achieved. The method was successfully employed for Se speciation studies in garlic extracts and water samples.

A non-chromatographic separation and preconcentration method for Se species determination based on the use of an on-line ionic liquid (IL) dispersive microextraction system coupled to electrothermal atomic absorption spectrometry (ETAAS) is proposed. Retention and separation of the IL phase was achieved with a Florisil ® -packed microcolumn after dispersive liquid-liquid microextraction (DLLME) with tetradecyl(trihexyl)phosphonium chloride IL (CYPHOS ® IL 101). Selenite [Se(IV)] species was selectively separated by forming Se-ammonium pyrrolidine dithiocarbamate (Se-APDC) complex followed by extraction with CYPHOS ® IL 101. The methodology was highly selective towards Se(IV), while selenate [Se(VI)] was reduced and then indirectly determined. Several factors influencing the efficiency of the preconcentration technique, such as APDC concentration, sample volume, extractant phase volume, type of eluent, elution flow rate, etc., have been investigated in detail. The limit of detection (LOD) was 15 ng L −1 and the relative standard deviation (RSD) for 10 replicates at 0.5 g L −1 Se concentration was 5.1%, calculated with peak heights. The calibration graph was linear and a correlation coefficient of 0.9993 was achieved. The method was successfully employed for Se speciation studies in garlic extracts and water samples.