Preservation of water samples for arsenic(III/V) determinations: an evaluation of the literature and new analytical results |
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| Institution: | 1. US Geological Survey, 3215 Marine St., Suite E. 127, Boulder, CO 80303, USA;2. Buka Environmental, 729 Walnut St, Suite E., Boulder, CO 80302, USA;1. Department of Chemistry, Faculty of Science, Srinakharinwirot University, Sukhumvit 23, Wattana, Bangkok 10110, Thailand;2. Electrochemistry and Optical Spectroscopy Research Unit, Department of Chemistry, Faculty of Science, Chulalongkorn University, 254 Phayathai Road, Pathumwan, Bangkok 10330, Thailand;1. Centre for Geobiology, Department of Earth Science, University of Bergen, Allegaten 41, 5007 Bergen, Norway;2. Department of Earth Sciences, ETH Zurich, Clausiusstrasse 25, 8092 Zurich, Switzerland;3. School of Oceanography, University of Washington, 1503 NE Boat Street, Seattle, WA 98195, USA;1. State Key Laboratory of Heavy Oil Processing & College of Science, China University of Petroleum (East China), Qingdao 266555, China;2. The Key Laboratory of Analysis and Detection Technology for Food Safety of the MOE, College of Chemistry, Fuzhou University, Fuzhou 350002, China;3. Karlsruhe Institute of Technology (KIT), Institute for Biological Interfaces (IBG-1), Hermann-von-Helmholtz-Platz, 76344 Eggenstein-Leopoldshafen, Germany;4. Department of Chemistry and the MOE Key Laboratory of Spectrochemical Analysis & Instrumentation, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China;1. State Environmental Protection Key Laboratory of Soil Health and Green Remediation, Hubei Key Laboratory of Soil Environment and Pollution Remediation, College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, China;2. State Key Laboratory of Particle Detection and Electronics, University of Science and Technology of China, Hefei 230026, China;3. Agriculture and Environment Department, Harper Adams University, Newport, Shropshire TF10 8NB, United Kingdom;4. School of Civil Engineering, Suzhou University of Science and Technology, Suzhou 215009, China;5. Geomicrobiology, Department of Geosciences, University of Tuebingen, Tuebingen 72076, Germany |
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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, H2SO4, 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 SO4 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. |
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