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Selenium Analysis of Overburden, Coal, and Related Water Samples

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Waters 50-mL or 10-mL aliquot with same final volume, no dilution ... Digestate aliquot excited by plasma torch ... Sample aliquot digestion and GFAAS ... – PowerPoint PPT presentation

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Title: Selenium Analysis of Overburden, Coal, and Related Water Samples


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
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4
Obtaining a Representative Sample
  • Identifying geologic intervals
  • Selecting the length of core segments
  • Selecting the core section in each segment for
    analysis

5
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

6
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

7
Lower Reporting Level Objectives for Selenium
  • Overburden and Coal
  • 0.2 mg/kg
  • Water Samples
  • 0.6 µg/L

8
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

9
Instrumental Analysis Methods
  • Optical ICP ICP-OES
  • ICP-MS
  • Hydride Generation AAS
  • GFAAS

10
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11
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

12
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13
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

14
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

15
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

16
REIC Analysis Approach
  • Employ GFAAS Analysis using EPA Methods
  • Conduct all analyses under a rigorous Quality
    Assurance Program including full Quality
    Control procedures

17
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

18
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

19
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

20
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

21
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

22
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

23
Primary Contributors REIC Team
  • Tim Keeney Research Soil Scientist
  • Ivan Leef Inorganic Manager
  • Dennis Layne Metals Supervisor
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