The University of Southampton
University of Southampton Institutional Repository

Determination of selenium species in the aquatic environment

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
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.

This record has no associated files available for download.

More information

Published date: 1998

Identifiers

Local EPrints ID: 463210
URI: http://eprints.soton.ac.uk/id/eprint/463210
PURE UUID: 5332df61-8a64-467b-92f6-1c42ad9123a8

Catalogue record

Date deposited: 04 Jul 2022 20:47
Last modified: 04 Jul 2022 20:47

Export record

Contributors

Author: Melanie Mei-Yoong Newton

Download statistics

Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.

View more statistics

Atom RSS 1.0 RSS 2.0

Contact ePrints Soton: eprints@soton.ac.uk

ePrints Soton supports OAI 2.0 with a base URL of http://eprints.soton.ac.uk/cgi/oai2

This repository has been built using EPrints software, developed at the University of Southampton, but available to everyone to use.

We use cookies to ensure that we give you the best experience on our website. If you continue without changing your settings, we will assume that you are happy to receive cookies on the University of Southampton website.

×