title: Voltammetric determination of arsenic in high iron and manganese groundwaters.
abstract: Determination of the speciation of arsenic in groundwaters, using cathodic stripping voltammetry (CSV), is severely hampered by high levels of iron and manganese. Experiments showed that the interference is eliminated by addition of EDTA, making it possible to determine the arsenic speciation on-site by CSV. This work presents the CSV method to determine As(III) in high-iron or -manganese groundwaters in the field with only minor sample treatment. The method was field-tested in West-Bengal (India) on a series of groundwater samples. Total arsenic was subsequently determined after acidification to pH 1 by anodic stripping voltammetry (ASV). Comparative measurements by ICP-MS as reference method for total As, and by HPLC for its speciation, were used to corroborate the field data in stored samples. Most of the arsenic (78±0.02%) was found to occur as inorganic As(III) in the freshly collected waters, in accordance with previous studies. The data shows that the modified on-site CSV method for As(III) is a good measure of water contamination with As. The EDTA was also found to be effective in stabilising the arsenic speciation for longterm sample storage at room temperature. Without sample preservation, in water exposed to air and sunlight, the As(III) was found to become oxidised to As(V), and Fe(II) oxidised to Fe(III), removing the As(V) by adsorption on precipitating Fe(III)-hydroxides within a few hours.
authors.affiliation: School of Environmental Sciences, University of Liverpool, Liverpool, UK.
authors.forename: Kristoff
authors.initials: K
authors.lastname: Gibbon-Walsh
authors.forename: Pascal
authors.initials: P
authors.lastname: Salaün
authors.forename: M Kalle
authors.initials: MK
authors.lastname: Uroic
authors.forename: Joerg
authors.initials: J
authors.lastname: Feldmann
authors.forename: John M
authors.initials: JM
authors.lastname: McArthur
authors.forename: Constant M G
authors.initials: CM
authors.lastname: van den Berg
mesh_terms: D001151:Arsenic / Q000032:analysis* / Q000737:chemistry; D002851:Chromatography, High Pressure Liquid; D004492:Edetic Acid / Q000494:pharmacology; D055664:Electrochemical Techniques / Q000379:methods*; D004784:Environmental Monitoring / Q000379:methods; D007194:India; D007501:Iron / Q000032:analysis* / Q000737:chemistry; D008345:Manganese / Q000032:analysis* / Q000737:chemistry; D013058:Mass Spectrometry / Q000379:methods; D010084:Oxidation-Reduction / Q000187:drug effects; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D014874:Water Pollutants, Chemical; D008345:Manganese; D004492:Edetic Acid; D007501:Iron; D001151:Arsenic