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Selenium Analysis

This article discusses selenium chemistry and toxicosis, as well as analytical techniques and recommendations for total selenium determination in soil, water, and biota. It addresses the ecological impact and detection challenges associated with selenium contamination.

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Selenium Analysis

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  1. Selenium Analysis Jason Unrine Department of Plant and Soil Sciences University of Kentucky, Lexington West Virginia Mine Drainage Task Force Symposium April 1, 2009 Jason.unrine@uky.edu

  2. Jason Unrine, University of Kentucky, Lexington • Dirk Wallschlager, Trent University, Peterborough, ON • Nicholas Ralston, University of North Dakota, Grand Forks Available for download on conference website or at www.namc.org

  3. Overview • Background • Techniques for total Se analysis • Techniques for Se speciation

  4. SeleniumChemistry • Member of the chalcogens or oxygen family • Borderline non-metal/metalloid • Chemically analogous to sulfur

  5. Selenium Toxicosis • Critical effects: teratogenesis and reproductive impairment • Efficient trophic and maternal transfer • Precise mode of action: poorly understood Photos from: Lemly A.D. 1998. Pathology of Se poisoning in fish. In: Frankenburger, W.T., Engberg, R.A. (eds). Environmental Chemistry of Selenium. Marcel Dekker, NY.

  6. Speciation kinetically and biologically controlled Sed water

  7. [Se] cysproteins [Se] cys [Se] cystathioinine Se0 [Se] Met proteins [Se] met Selenite Selenate SeH - GSSeG HSeCH3 HSePO3- Ser Sec tRNA ser (CH3)xSe Sec tRNA sec Urine, breath Sec proteins Adapted from: Sunde, R.A. 1997. Selenium. In: Handbook of Nutritionally Essential Mineral Elements (O'Dell, B.L. and R.A. Sunde, Eds.), Marcel Dekker, New York, NY, p. 493.

  8. Seleno-amino acids

  9. TTF1 trophic transfer TTF3 TTF2 trophic transfer trophic transfer = ADVERSE EFFECTS Anthro- pogenic & Natural Inputs SOLID Se: rock, ore, waste, soil, sediment, dust (elemental Se, selenite, selenate) GASEOUS Se (methylselenides) AQUEOUS Se: drainage, effluent, runoff, pore water (selenate, selenite, organo-Se) EF PARTICULATE-Se: biofilm, phytoplankton, plants, detritus, sediment (organo-Se, selenite, selenate, elemental Se) BAF bioconcentration PRIMARY CONSUMERS (invertebrates, fish) PRIMARY CONSUMERS: invertebrates, fish, other vertebrates (Organo-Se) SECONDARY CONSUMERS: fish, birds, herps, mammals(Organo-Se) HIGHER-ORDER CONSUMERS: birds, herps, mammals, humans (Organo-Se)

  10. Ecological Assessment of Selenium in the Aquatic Environment SETAC Pellston Workshop, February 22-28, 2009 (Pensacola, FL, USA) • 46 experts from academia, consulting, • industry, government • Executive summary booklet out soon • Book to come out next year • (www.setac.org)

  11. Analytical Problems • Detection at environmentally significant levels requires high sensitivity, esp. in the aqueous phase. • Many techniques suffer from matrix and spectral interferences. • Some species are volatile.

  12. Hydride generation atomic absorption/atomic fluorescence • Simple, sensitive, inexpensive, widely available. • Potential for interferences (Fe, Mn, Cu, Zn, etc) with HG step in certain samples, response is strongly species dependent. • All Se must be converted to Se (IV) prior to hydride generation.

  13. Hydride generation atomic absorption/atomic fluorescence Multi – step derivitizationproceedure Perform pre-conversion species specific spike recovery experiments. SeMet Se(IV) Se(VI) Se Se(-II) Se(VI) Se(IV) SeH2(g) HCl, Heat H2O2, HNO3,Heat NaBH4

  14. Electrothermal (graphite furnace) AAS • Measurement of solid samples directly. • Measurement of water samples/digestates. • Very susceptible to matrix interferences.

  15. ICP-MS Fast, sensitive, mutli-element technique. Minimal sample prep, no derivitization proceedure Potential for matrix and spectral interferences

  16. ICP-CRC-MS (Octopole Reaction System) Ar2+ + H2 + Se+ Ar2 + 2H+ + Se+ Charge transfer Ar2+ + H2 + Se+ 2Ar2H+ + Se+ Proton transfer

  17. TOTAL SE DETERMINATION RECOMMENDATIONS Soil/Sed/Biota - Recommended Water - Recommended ICP (CRC) MS HG –AAS/AFS • ICP (CRC) MS • HG-AAS/AFS Soil/Sed/Biota - Alternative Water - Alternative • ICP-MS • INAA • ETAAS • ICP-MS • ETAAS • INAA Soil/Sed/Biota – Not Recommended

  18. QA/QC recommendations HG-AAS/AFS ICP-MS Method Blanks Method Duplicates Analytical Duplicates Inter-calibration verification Pre-digestion spikes Agreement of 2 isotopes within 10% Method of standard additions, standard addition calibration or Te internal standard CRMs Method Blanks Method Duplicates Analytical Duplicates Inter-calibration verification Pre-digestion spikes Pre-derivitization spikes (Species specific)/method of standard additions CRMs

  19. Certified Reference Materials • Available for purchase for a variety of biota, soil and water (NRCC, NIST, BCR). • Should be sent by client to analytical lab along with other samples to be analyzed blindly and methodically processed along with other samples. • SRM 1643e –Trace elements in water • SRM 2711 – Montana Soil • SRM 2780 – Hard rock mine waste • SRM 1947 – Michigan fish tissue • SRM 2704 –Buffalo river sediment

  20. Sequential Hydride Generation • Sequential hydride generation • Cannot detect unknown species • Does not work well in complex matrices TSe SeH2 + Se (VI) + reduced Se NaBH4 TSe SeH2 + reduced Se HCl, heat NaBH4 TSe Se(VI) Se(IV) SeH2 HCl, Heat S2O8-, heat NaBH4

  21. AEC-CRC-ICP-MS CRC MS ICP

  22. Stationary phase: Hamilton PRP-X100, Mobile phase, pH 5.0, 10 mM citrate

  23. 100% 90% selenomethionine 80% selenocystine 70% Se (IV) 60% Se (VI) % of Total Se 50% 40% 30% 20% 10% 0% cricket cricket liver follicle teste feed

  24. SEC-UV-ICP-CRC-MS SDS-PAGE, etc. Fraction collector SEC DRC MS ICP UV

  25. Unrine et al 2006

  26. Thompson and Banaszak, 2002 Generated with PDB file 1LSH

  27. Solid phase Se speciation- x-ray absorption spectroscopy. • x-ray absorption near edge spectroscopy (XANES) • Extended x-ray absorption fine structure (EXAFS) • Requires access to synchrotron light source

  28. μSXRF analysis XANES Punshon et al. 2005

  29. Take home messages • Analysis of Se requires special care; technicians need to be educated on the analytical issues associated with Se. • Use of approved regulatory methods by state-certified labs does not guarantee accurate results. • Stake-holders should insist on a QA plan that will leave them convinced of data quality (i.e. test the hypothesis that the results are accurate). • Speciation of Se can help clarify issues associated with environmental mobility, bioavailability and toxicity

  30. Acknowledgements North American Metals Council (www.namc.org) North American Industry Selenium Working Group U.S. Department of Energy SETAC Dirk Wallschlager Nick Ralston Brian Jackson Tracey Punshon Bill Hopkins Chris Romanek Brandon Staub Jennifer Baianno Paul Bertsch Portions of this work were performed at Beamline X26A, National Synchrotron Light Source (NSLS), Brookhaven National Laboratory. X26A is supported by the Department of Energy (DOE) - Geosciences (DE-FG02-92ER14244 to The University of Chicago - CARS) and DOE - Office of Biological and Environmental Research, Environmental Remediation Sciences Div. (DE-FC09-96-SR18546 to the University of Kentucky). Use of the NSLS was supported by DOE under Contract No. DE-AC02-98CH10886. Office of Biological and Environmental Research, U.S. Department of Energy Financial Assistance Award No. DE-FC09-96-SR18546 to the University of Georgia Research Foundation.

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