Gas Chromatography

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Gas Chromatography
2010-10-23 16:39:50
BU Forensic Chemistry

Forensic Chemistry Lecture 5
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  1. Which type of chromatography is an analytical technique for separating compounds based primarily on their voltalities?
    gas chromatography
  2. T/F: In the sample injection process for GC, the process is reproducible, highly efficient, and provides a representative sample for chromatographic separation.
  3. What are 3 of the reasons you would derivatize your sample in GC?
    • increase volatility and polarity
    • decrease thermal stability
  4. What is the difference between split and splitless injections?
  5. T/F: As column length increases, resolution also increases.
  6. As the _____ of the mixture increases, the elution speed decreases.
  7. What are the 3 types of detectors in GC?
    • Flame Ionization Detector (FID)
    • Electron Capture Detector (ECP)
    • Flame Photometric Detector (FPD)
  8. Which detector is the most common in GC?
    flame ionization dectector
  9. Describe the FID.
    • -most common
    • -provides universal ionization by burning
    • -immediate, stable, predictable response
    • -sensitive with large dynamic range
    • -destructive analysis
    • -column effluent passes through the flame
  10. Describe the ECD.
    • Electron-Capture detector
    • -as sensitive as FIDs but with limited dynamic range
    • -uses radioactive beta-emitter to ionize carrier gas to produce current between electrodes
  11. Describe FPD.
    • Flame Photometric Detector
    • -detection of sulfur and phosphorus specifically
    • -chemiluminescent reactions occur in a hydrogen/air flame
  12. tR
    retention time
  13. tR'
    • adjusted retention time
    • tR' = tR - tM

    the time a compound spends in the stationary phase
  14. tM
    • time for unretained peak
    • -the time a compound spends in the mobile phase
  15. retention time
    the total time that a compound spends in both the mobile and the stationary phase
  16. β
    • phase ratio
  17. phase ratio
    • β= r/2df
    • relates the column diameter and film thickness of the stationary phase
  18. KD
    • distribution constant
    • = concentration of solute in stationary phase
    • concentration of solute in mobile phase
  19. T/F: A large distribution constant means there was good separation with an increase in solute retention.
  20. What are the 3 parameters affecting KD?
    • solute
    • stationary phase
    • temperature
  21. k'
    capacity factor (or partition factor)
  22. Capacity factor
    • the ration of the mass of a compound in the stationary phase relative to the mass of the compound in the mobile phase
    • - a measure of the columns retention of a compound

    • k'= (tR - tM)
    • tM