Geochemical Mobilization of Arsenic to Ground WaterGreatest Mass Poisoning in HistoryAnalytical ProblemSpecies Separation MethodsSample Prep: Sequential ExtractionAnalytical TechniquesHydride GeneratorAtomic Absorption SpectrometerAAS Data Validated with XASX-ray Absorption Near-Edge StructureConclusionsReferencesGEOCHEMICAL MOBILIZATION OF ARSENIC TO GROUND WATERSara BaldvinsCHEM 4101December 9, 2011Greatest Mass Poisoning in HistoryNaturally occurring arsenic (As) contamination in ground water is causing widespread health problems.35 million in Bangladesh and 6 million in Bengal are at risk.As poisoning has also been reported in China, Argentina, Chile, Mexico, Thailand, and Taiwan.Analytical ProblemHypothesisThe speciation of arsenic in soils impacts how mobile the arsenic is which contributes to the high concentrations found in the ground water of some regions. Problem SummaryCertain soils easily mobilize As to the ground water.In these soils certain hydrological, geological, and chemical conditions make arsenic more mobile.Species Separation MethodsTechnique Advantages DisadvantagesSequential ExtractionLow matrix interference, high yields, can be automated, inexpensiveTime consuming, potentially large user errorCE High resolution, great separations, quick run-timesSignificant matrix interference (50% recovery), low reproducibility without considerable efforts, small sample sizeIon Chrom. Recovery better than 92% for most species, good resolution, reliableLoses resolution in presence of other anions, multiple interferences between the As compounds.Sample Prep: Sequential ExtractionOnce the soil is ground to the appropriate particle size the reagents will be applied stepwise as follows: Step Target Geologic PhaseMg Ionically bond AsPO4Strongly adsorbed AsHCl As co-precipitated w/A(V)S, oxides, and very amorphous Fe oxyhydroxidesOx As co-precipitated w/amorphous Fe oxyhydroxidesHNO3As co-precipitated w/pyrite and amorphous As2S3Hot HNO3Orpiment and remaining recalcitrant As mineralsAnalytical TechniquesTechnique Advantages DisadvantagesHG-AAS Least expensive, LODs good with HG, most commonly used for As detectionOne species at a time, slow run time, large amount of sample preparationHG-AFS Great LOD with HG, inexpensiveSome species hard to detect, large matrix interferencesICP-MS Good LOD, multiple species at one time, short running time, less sample preparation requiredRequires standards, expensive, hard to run large amount of extraction sample throughHydride GeneratorThe are large interferences when using AAS to detect As so a Hydride Generator must be used.Schematic retrieved from http://www.shsu.edu/~chm_tgc/primers/HGAAS.htmlAtomic Absorption SpectrometerFor the GBC 906AA w/HG:Precision ≤ 2% for AsLOD ≤ 0.1 ppbLOQ approx. 1 ppb99% - 107% recovery of spiked samplesAAS Data Validated with XASSamples remain in solid state which eliminates the potential error from an extraction. X-ray diffraction is used determining the arrangement of atoms in minerals and metalsPicture200 m91236401087511As XRD Map of soil sample OTT73Toner, B. M., Nicholas, S. L., Briscoe, L. J., Knaeble, A. R., Berg, J. A., and Erickson, M. L., in press. Natural sources of arsenic to Minnesota groundwater. CURA Reporter.X-ray Absorption Near-Edge StructureDetermines elements present in bulk or minute quantities.Determines the formal valence, coordination complex, and oxidation state, and spin state of the probed element.Use for quantification is not yet well defined.4.4E+11.1E+04.0E+06.0E+08.0E+01.0E+11.2E+11.4E+11.6E+11.8E+12.0E+12.2E+12.4E+12.6E+12.8E+13.0E+13.2E+13.4E+13.6E+13.8E+14.0E+14.2E+1X11882.511857.3 11860.0 11862.5 11865.0 11867.5 11870.0 11872.5 11875.0 11877.5 11880.0Ott3_73_AsQXAS_spot0_001.rOtt3_73_AsQXAS_spot0_002.rOtt3_73_AsQXAS_spot0_003.rOtt3_73_AsQXAS_spot0_004.rOtt3_73_AsQXAS_spot0_005.rOtt3_73_AsQXAS_spot0_006.rOtt3_73_AsQXAS_spot0_007.rOtt3_73_AsQXAS_spot0_008.rOtt3_73_AsQXAS_spot0_009.rOtt3_73_AsQXAS_spot0_010.rOtt3_73_AsQXAS_spot0_011.rOtt3_73_AsQXAS_spot0_012.rOtt3_73_AsQXAS_spot0_013.rOtt3_73_AsQXAS_spot0_014.rOtt3_73_AsQXAS_spot0_avg.rOtt3_73_AsXANES_spot0_forCal_000.rAs3_ cal_AsXANES_000.rSodium_ Arsenate_cal_AsXANES_001.rOtt3_73_AsXANES_spot1_avg.rOtt3_73_AsXANES_spot2_avg.dat.rXYCursor 0 11874.69041.534XY GraphAs3As5spot0spot1spot2As XANES Spectra of OTT73Toner, B. M., Nicholas, S. L., Briscoe, L. J., Knaeble, A. R., Berg, J. A., and Erickson, M. L., in press. Natural sources of arsenic to Minnesota groundwater. CURA Reporter.ConclusionsEnvironmental samples are messy. Extractions can pull off a number of species other than the analyte which makes advanced technical separations difficult.HG-AAS is cheap, effective, and a good method for bulk analysis of samples. XANES adds validity to the HG-AAS findings by providing an exact picture of the structures in the sample without the ambiguity of an extraction. GIS software can help give a holistic picture of the environmental system by compiling all geological, hydrological, and chemical conditions.References1. Anawar, Hossain M., et al. "Investigation of Sequential Chemical Extraction of Arsenic from Sediments: Variations in Sample Treatment and Extractant." Soil & Sediment Contamination 19.2 (2010): 133-41. <http://search.ebscohost.com/login.aspx?direct=true&db=aph&AN=49152119&site=ehost-live>. 2. B’Hymer, C., and J. A. Caruso. "Arsenic and its Speciation Analysis using High-Performance Liquid Chromatography and Inductively Coupled Plasma Mass Spectrometry." Journal of Chromatography A 1045.1-2 (2004): 1-13. . 3. Bernhard, Michalke. "Element Speciation Definitions, Analytical Methodology, and some Examples." Ecotoxicology and environmental safety 56.1 (2003): 122-39. . 4. Caruso, Joseph A., and Maria Montes-Bayon. "Elemental Speciation studies—new Directions for Trace Metal Analysis." Ecotoxicology and environmental safety 56.1 (2003): 148-63. . 5. Farzana Akter, Kazi, et al. "Speciation of Arsenic in Ground Water Samples: A Comparative Study of CE-UV, HG-AAS and LC-ICP-MS." Talanta 68.2 (2005): 406-15. . 6. Khalid H. Al-Assaf, Julian F. Tyson, and Peter C. Uden. "Determination of Four Arsenic Species in Soil by Sequential Extraction and High Performance Liquid Chromatography with Post-Column Hydride Generation and Inductively Coupled Plasma Optical Emission Spectrometry detectionThis Article is Part of a Themed.." JAAS (Journal of Analytical Atomic
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