Determination of selenium species in the aquatic environment
Determination of selenium species in the aquatic environment
Conventional methods of analysis are unable to reliably measure the low levels of selenium species in the aquatic environment, with values typically below 50 ng 1-1. A method was developed which utilised a cryogenic trap coupled to a conventional hydride generation atomic absorption spectrophotometer (HG-AAS) which provided a reliable, accurate and precise system for the measurement of selenite concentrations with a detection limit of ca. 10 ng 1-1.
As selenite is the only detectable selenium species by HG-AAS, a reduction step, prior to analysis, was necessary in order to determine total inorganic selenium. The conflicting details reported in the literature prompted an investigation which yielded a reliable method for this reduction step. Organo-selenium compounds such as Se-Cystine and Se-Methionine require oxidation before they can be detected by HG-AAS. Therefore, a batch ultraviolet irradiation method was employed to photo-oxidise these compounds to inorganic selenium, this was then reduced to selenite and detected using the HG-AAS system. However, these procedures are time consuming and prone to losses and contamination. Therefore, a novel in-line system for the determination of selenium species was developed which utilised microwave energy for reduction of selenite and a UV source for oxidation of organic selenium species. This allowed the analysis of organic selenium species by providing a total selenium concentration and speciation information calculated by simple subtraction. Detection limits are unaffected by the in-line oxidation and reduction steps, and the method is suitable for the analysis of high salinity waters.
A number of techniques for the digestion of organic matter were investigated. Dry ashing in the presence of magnesium nitrate, magnesium oxide and nitric acid was found to give complete recovery of selenium once nitrite interferences had been overcome by the addition of sulphanilamide. The method was validated by the analysis of a standard reference material (Orchard Leaves - NBS 1571).
A preliminary investigation of the behaviour of dissolved selenium in the Tamar estuary, Devon, was conducted over the summer months July and August 1996. The distribution of dissolved selenium showed that selenium (IV) and organic selenium were present as the dominant species. Elevated selenium (IV) concentrations (ca. 50 ng 1-1) were observed in the lower reaches of the estuary. These were believed to be due to the tidally induced re-suspension of mudflat sediments.
University of Southampton
Newton, Melanie Mei-Yoong
1998
Newton, Melanie Mei-Yoong
Newton, Melanie Mei-Yoong
(1998)
Determination of selenium species in the aquatic environment.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
Conventional methods of analysis are unable to reliably measure the low levels of selenium species in the aquatic environment, with values typically below 50 ng 1-1. A method was developed which utilised a cryogenic trap coupled to a conventional hydride generation atomic absorption spectrophotometer (HG-AAS) which provided a reliable, accurate and precise system for the measurement of selenite concentrations with a detection limit of ca. 10 ng 1-1.
As selenite is the only detectable selenium species by HG-AAS, a reduction step, prior to analysis, was necessary in order to determine total inorganic selenium. The conflicting details reported in the literature prompted an investigation which yielded a reliable method for this reduction step. Organo-selenium compounds such as Se-Cystine and Se-Methionine require oxidation before they can be detected by HG-AAS. Therefore, a batch ultraviolet irradiation method was employed to photo-oxidise these compounds to inorganic selenium, this was then reduced to selenite and detected using the HG-AAS system. However, these procedures are time consuming and prone to losses and contamination. Therefore, a novel in-line system for the determination of selenium species was developed which utilised microwave energy for reduction of selenite and a UV source for oxidation of organic selenium species. This allowed the analysis of organic selenium species by providing a total selenium concentration and speciation information calculated by simple subtraction. Detection limits are unaffected by the in-line oxidation and reduction steps, and the method is suitable for the analysis of high salinity waters.
A number of techniques for the digestion of organic matter were investigated. Dry ashing in the presence of magnesium nitrate, magnesium oxide and nitric acid was found to give complete recovery of selenium once nitrite interferences had been overcome by the addition of sulphanilamide. The method was validated by the analysis of a standard reference material (Orchard Leaves - NBS 1571).
A preliminary investigation of the behaviour of dissolved selenium in the Tamar estuary, Devon, was conducted over the summer months July and August 1996. The distribution of dissolved selenium showed that selenium (IV) and organic selenium were present as the dominant species. Elevated selenium (IV) concentrations (ca. 50 ng 1-1) were observed in the lower reaches of the estuary. These were believed to be due to the tidally induced re-suspension of mudflat sediments.
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Published date: 1998
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Local EPrints ID: 463210
URI: http://eprints.soton.ac.uk/id/eprint/463210
PURE UUID: 5332df61-8a64-467b-92f6-1c42ad9123a8
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Date deposited: 04 Jul 2022 20:47
Last modified: 04 Jul 2022 20:47
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Author:
Melanie Mei-Yoong Newton
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