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Preservation of water samples for arsenic(III/V) determinations: An evaluation of the literature and new analytical results

Applied Geochemistry

By:
, , and
https://doi.org/10.1016/j.apgeochem.2004.01.003

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Abstract

Published literature on preservation procedures for stabilizing aqueous inorganic As(III/V) redox species contains discrepancies. This study critically evaluates published reports on As redox preservation and explains discrepancies in the literature. Synthetic laboratory preservation experiments and time stability experiments were conducted for natural water samples from several field sites. Any field collection procedure that filters out microorganisms, adds a reagent that prevents dissolved Fe and Mn oxidation and precipitation, and isolates the sample from solar radiation will preserve the As(III/V) ratio. Reagents that prevent Fe and Mn oxidation and precipitation include HCl, H 2SO4, and EDTA, although extremely high concentrations of EDTA are necessary for some water samples high in Fe. Photo-catalyzed Fe(III) reduction causes As(III) oxidation; however, storing the sample in the dark prevents photochemical reactions. Furthermore, the presence of Fe(II) or SO 4 inhibits the oxidation of As(III) by Fe(III) because of complexation reactions and competing reactions with free radicals. Consequently, fast abiotic As(III) oxidation reactions observed in the laboratory are not observed in natural water samples for one or more of the following reasons: (1) the As redox species have already stabilized, (2) most natural waters contain very low dissolved Fe(III) concentrations, (3) the As(III) oxidation caused by Fe(III) photoreduction is inhibited by Fe(II) or SO4.

Additional publication details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Preservation of water samples for arsenic(III/V) determinations: An evaluation of the literature and new analytical results
Series title:
Applied Geochemistry
DOI:
10.1016/j.apgeochem.2004.01.003
Volume:
19
Issue:
7
Year Published:
2004
Language:
English
Publisher:
Elseiver
Contributing office(s):
Toxic Substances Hydrology Program
Description:
15 p.
First page:
995
Last page:
1009