Selenium Analysis

Jason Unrine Department of Plant and Soil Sciences University of Kentucky, Lexington West Virginia Mine Drainage Task Force Symposium April 1, 2009 [email protected]

•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

Overview

• Background • Techniques for total Se analysis • Techniques for Se speciation

Selenium Chemistry

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

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.

Speciation kinetically and biologically controlled

Sed water

[Se] cys proteins [Se] Met proteins [Se] cystathioinine [Se] cys Se 0 [Se] met HSeCH 3 SeH HSePO 3 (CH 3) xSe GSSeG Sec tRNA ser Selenite Ser Selenate 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.

Seleno-amino acids

Anthro pogenic & Natural Inputs

GASEOUS Se ( methylselenides) AQUEOUS Se: drainage, effluent, runoff, pore water ( selenate, selenite, organo-Se) EF bioconcentration (organo-Se, selenite, selenate, elemental Se) BAF TTF 1 trophic transfer PRIMARY CONSUMERS (invertebrates, fish) (Organo-Se) TTF 2 trophic transfer SECONDARY CONSUMERS: fish, birds, herps, mammals (Organo-Se) TTF 3 trophic transfer HIGHER-ORDER CONSUMERS: birds, herps, mammals, humans (Organo-Se)

= ADVERSE EFFECTS

Ecological

SETAC Pellston

Assessment of

Workshop, February 22-

Selenium in the

28, 2009 (Pensacola,

Aquatic

FL, USA)

Environment

•46 experts from academia, consulting, industry, government •Executive summary booklet out soon •Book to come out next year •(www.setac.org)

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.

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.

Hydride generation atomic absorption/atomic fluorescence

Multi – step derivitization proceedure Perform pre-conversion species specific spike recovery experiments.

SeMet Se(IV) Se(VI) Se Se(-II) H 2 O 2 , HNO 3 ,Heat Se(VI) HCl, Heat Se(IV) NaBH 4 SeH 2 (g)

Electrothermal (graphite furnace) AAS

• Measurement of solid samples directly.

• Measurement of water samples/digestates.

• Very susceptible to matrix interferences.

ICP-MS

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

ICP-CRC- MS

(Octopole Reaction System) Ar 2 + + H 2 + Se + Ar 2 + + H 2 + Se + Ar 2 + 2H + + Se + Charge transfer 2Ar 2 H + + Se + Proton transfer

TOTAL SE DETERMINATION RECOMMENDATIONS • •

Soil/Sed/Biota - Recommended

ICP (CRC) MS HG-AAS/AFS • •

Soil/Sed/Biota - Alternative

ICP-MS INAA

Soil/Sed/Biota – Not Recommended Water - Recommended

• • ICP (CRC) MS HG –AAS/AFS

Water - Alternative

• • • ICP-MS ETAAS INAA • ETAAS

QA/QC recommendations

HG-AAS/AFS ICP-MS

Method Blanks Method Duplicates Analytical Duplicates Inter-calibration verification Pre-digestion spikes Pre-derivitization spikes (Species specific)/method of standard additions CRMs 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

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

Sequential Hydride Generation

• Sequential hydride generation • Cannot detect unknown species • Does not work well in complex matrices TSe TSe NaBH 4 HCl, heat SeH 2 + Se (VI) + reduced Se SeH 2 + reduced Se NaBH 4 TSe S 2 O 8 -, heat Se(VI) HCl, Heat Se(IV) NaBH 4 SeH 2

AEC-CRC-ICP-MS

ICP CRC MS

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

selenomethionine

11000 O 9000 7000 5000 H O O NH 2 Se Se H 2 N O OH O O Se O -

Selenite

Se H 3 C NH 2

selenomethionine

OH O O Se O O -

selenate selenocystine

3000 1000 -1000 0 50 100 150 200 250

retention time (s)

300 350 400 450

H 3 C Se O NH 2 OH

100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% cricket feed cricket liver follicle teste

selenomethionine selenocystine Se (IV) Se (VI)

SEC

SEC-UV-ICP-CRC-MS

Fraction collector SDS PAGE, etc.

UV ICP DRC MS

12000 10000 8000 6000 4000 2000 0 8

A

10 P-1 P-2 P-3 S Se egg follicle 12 14 16 18

elution volume (mL)

<10 kD 20000 18000 16000 14000 12000 10000 8000 6000 4000 2000 0 20 22 Unrine et al 2006

Thompson and Banaszak, 2002 Generated with PDB file 1LSH

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

μSXRF analysis XANES 1.2

1 0.8

0.6

0.4

Semethionine Secystine (Se II) Selenite Se(IV) Selenate Se(VI) 0.2

0 12655 12657 12659 12661 12663 12665

energy (eV)

12667 12669 12671 12673 12675 Punshon et al. 2005

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

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.