Title: Selenium Analysis of Overburden, Coal, and Related Water Samples
1Selenium Analysis of Overburden, Coal, and
Related Water Samples
- Clarence L. Haile, Ph.D.
- General Manager,
- REI Consultants, Inc.
-
2Analysis Process Components
- Obtaining a representative sample
- Sample preparation
- Sample digestion
- Instrumental analysis
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4Obtaining a Representative Sample
- Identifying geologic intervals
- Selecting the length of core segments
- Selecting the core section in each segment for
analysis
5REIC 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
6Sample 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
7Lower Reporting Level Objectives for Selenium
- Overburden and Coal
- 0.2 mg/kg
- Water Samples
- 0.6 µg/L
8Sample 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
9Instrumental Analysis Methods
- Optical ICP ICP-OES
- ICP-MS
- Hydride Generation AAS
- GFAAS
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11Optical 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
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13ICP-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
14Hydride 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
15Graphite 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
16REIC Analysis Approach
- Employ GFAAS Analysis using EPA Methods
- Conduct all analyses under a rigorous Quality
Assurance Program including full Quality
Control procedures
17Analytical 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
18Quality 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
19Quality 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
20Quality 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
21Additional 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
22REIC 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
23Primary Contributors REIC Team
- Tim Keeney Research Soil Scientist
- Ivan Leef Inorganic Manager
- Dennis Layne Metals Supervisor