Forensic Chem

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Author:
Anonymous
ID:
43617
Filename:
Forensic Chem
Updated:
2010-10-20 00:05:13
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forensic chemistry
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Quiz 2 material
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  1. Mobile phase/ medium
    gas or liquid that carries the components
  2. Stationary medium/ phase
    the part of the apparatus that does not move with the sample
  3. What are the 4 uses for chromatography?
    analyze, identify, purify, quantify
  4. How does affinity affect the distance traveled by a sample in TLC?
    The greater the affinity for the stationary phase, the shorter the distance the sample will travel. The greater the affinity for the mobile phase, the greater the distance the sample will have traveled.
  5. T/F: In TLC, substances that are very soluble in the liquid used will have an Rf value closer to zero.
    False! Substances that are very soluble in the liquid will have an Rf value closer to one. Substances that are more insoluble in the liquid will have an Rf value closer to zero.
  6. What are some of the limitations and disadvantages to SPME?
    • 1. Compounds should be volatile. Less volatile compounds need more heating and longer desorption times.
    • 2. The coating on the fiber is very thin and can be easily overloaded with analyte.
  7. Manipulation of what factor will maximize separation efficiency with LLE and SPE's?
    pH
  8. Specific to LLE, what 4 R groups are ionizable?
    • 1. Carboxylic Acids
    • 2. Amines
    • 3. Hydroxyls
    • 4. Phenolic Protons
  9. T/F: In GC, as the polarity of the compound increases, the speed of elution also increases.
    False! As polarity increases, the speed of elution decreases due to the affinity for the stationary phase.
  10. How are column efficiency and HETP related?
    As efficiency increases, the HETP decreases. Also, efficiency increases as the # of theoretical plates increases.
  11. What is Plate Theory?
    It explains the Gaussian shape of chromatographic peaks and their rate of movement down a column.
  12. What is rate theory?
    It accounts for the finite time necessary for a species to equilibrate between both phases in the column.
  13. In normal phase LC, the ______ polar compounds elute first.
    least
  14. In reverse phase LC, the ______ polar compounds elute first.
    most
  15. Resolution
    degree of peak separation
  16. Efficiency
    sharp chromatographic peaks
  17. HPLC is a better choice than GC under these circumstances:
    • 1. the samples lack thermal stability in GC
    • 2. low volatility samples that do not vaporize in GC
    • 3. Ionic materials that cannot be separated in GC
  18. What three things make HPLC a better choice?
    • 1. more separation variables exist
    • 2. higher capacity for volume of samples
    • 3. increased quantitation

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