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Selenium Analysis of Overburden, Coal, and Related Water Samples

Selenium Analysis of Overburden, Coal, and Related Water Samples. Clarence L. Haile, Ph.D. General Manager, REI Consultants, Inc. Analysis Process Components. Obtaining a representative sample Sample preparation Sample digestion Instrumental analysis. Obtaining a Representative Sample.

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Selenium Analysis of Overburden, Coal, and Related Water Samples

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  1. Selenium Analysis of Overburden, Coal, and Related Water Samples Clarence L. Haile, Ph.D. General Manager, REI Consultants, Inc.

  2. Analysis Process Components • Obtaining a representative sample • Sample preparation • Sample digestion • Instrumental analysis

  3. Obtaining a Representative Sample • Identifying geologic intervals • Selecting the length of core segments • Selecting the core section in each segment for analysis

  4. REIC Approach and Experience • All cores are reviewed and sections selected by an Experienced Soil Scientist or Geologist • Selenium levels are frequently higher in silt, clay, or carbonaceous zones near and within the coal strata

  5. Sample Preparation • Grinding and homogenizing the core sections • Sub sampling for analysis • REIC Approach – Utilize EPA-600/2-78-054, Field and Laboratory Methods Applicable to Overburden and Minesoils

  6. Lower Reporting Level Objectives for Selenium • Overburden and Coal • 0.2 mg/kg • Water Samples • 0.6 μg/L

  7. Sample Digestion • Digest by heating with strong acids to dissolve Se • Sample concentration • Solids – 1 g, concentrate to 50-mL final volume • Waters – 50-mL or 10-mL aliquot with same final volume, no dilution

  8. Instrumental Analysis Methods • Optical ICP – ICP-OES • ICP-MS • Hydride Generation AAS • GFAAS

  9. Optical ICP • Emission Spectroscopy • Multi-element capability • Digestate aliquot excited by plasma torch • Measures emission of characteristic wavelengths • Good precision • Robust for high dissolved solids digestates • Typically cannot achieve required reporting levels

  10. ICP-MS • Mass Spectrometry • Multi-element capability • Digestate aliquot excited by plasma torch • Measures individual elements with a mass selective detector • Very low detection level capability • Typically cannot tolerate high dissolved solids

  11. Hydride Generation Atomic Absorption Spectroscopy • Absorption Spectroscopy • Digestate aliquot reduced with a hydride reagent to form gaseous selenium hydride • Selenium measured in gaseous hydride by absorption of light from Se lamp • Good sensitivity • Results from manual reaction systems can be variable

  12. Graphite Furnace Atomic Absorption Spectroscopy • Absorption Spectroscopy • Digestate aliquot heated in graphite tube – dry, combust, and volatize metals • Selenium measured in vaporized aliquot by absorption of light from Se lamp • Good sensitivity • Generally tolerant to high dissolved solids • Acceptable compromise between variability and sensitivity

  13. REIC Analysis Approach • Employ GFAAS Analysis using EPA Methods • Conduct all analyses under a rigorous Quality Assurance Program – including full Quality Control procedures

  14. Analytical Methods • Solid Samples – Overburden and Coal • Digestion using SW-846-3050 • Analysis by GFAAS using SW-846-7740 • Water Samples • Digestion using EPA Method 200.2 • Analysis using GFAAS using EPA Method 200.9 or 270.2

  15. Quality Control Procedures -- Digestion • Maximum of 20 samples per batch • Method Blank – background check • Laboratory Control Sample – accuracy check • Matrix Spike – accuracy check • Duplicate Sample – precision check

  16. Quality Control Procedures – GFAAS Analysis • Calibration -- Min of 3 standard levels, plus blank • Initial Calibration Checks – verify instrument response and standards • Continuing Calibration Checks -- verify continuing calibration

  17. Quality Control Procedures • Method Lower Reporting Levels -- evaluation and verification of MDLs and PQLs • Post-Digestion Spikes – check for matrix interferences • Sample Dilution – check for matrix interferences

  18. Additional Practices for Low Level Se Measurements • Zeeman background correction – reduce matrix interferences and false positives • Tailored GFAAS temperature program • Matrix modifiers • Continuously monitor analysis to ensure consistent sample introduction • Maintain low signal baseline

  19. REIC Approach Summary • Cores reviewed and samples selected by experienced soil scientist • Sample preparation by EPA methods • Sample aliquot digestion and GFAAS analysis by EPA methods • All analysis conducted under strong QA program using appropriate QC procedures

  20. Primary Contributors – REIC Team • Tim Keeney – Research Soil Scientist • Ivan Leef – Inorganic Manager • Dennis Layne – Metals Supervisor

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