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1.5: Chromatography

  • Page ID
    113852
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    Choose an appropriate definition from Column B for each phrase in Column A:

    A

    1. equilibrium concentration distribution coefficient
    2. theoretical plate
    3. height equivalent to theoretical plate
    4. retention time
    5. Rf
    6. phase

    B

    1. the length of a column in millimeters
    2. a column height related to separating ability
    3. ratio at equilibrium of the amounts of a substance dissolved in two immiscible solvents which are in contact
    4. separation of solute between two phases or immiscible solvents
    5. gas chromatography
    6. the ratio of solute mobility/solvent mobility
    7. duration of solute on a column
    8. gas, liquid, solid
    9. two solvents immiscible in each other
    1. Chromatography does not separate compounds if:
      1. they are not colored
      2. there is no chemical relationship between them
      3. the capacity factors are identical
      4. the number of theoretical plates is small
      5. the Rf value is large
    2. Gas chromatography:
      1. uses immiscible liquids
      2. has two phases
      3. uses air
      4. separates large molecules
      5. has gas-gas phase separation
    3. A substance with a greater Rf would travel a _____ distance than a substance with a lesser Rf and a method that decreases resolution will _____ the separation of the peaks:
      1. shorter/decrease
      2. shorter/increase
      3. greater/decrease
      4. greater/increase
    4. Which substances cannot be separated by GLC?:
      1. amino acids
      2. fatty acids
      3. alcohols
      4. steroids
      5. proteins
    5. If you have a GLC with a relatively polar stationary phase and are using helium as the carrier gas, you would expect n-octanol to have a shorten longer retention time than n-butanol; and, increasing the temperature of the oven would increase/decrease the retention times of both substances:
      1. shorter/increase
      2. shorter/decrease
      3. decrease/increase
      4. longer/decrease
    6. In GLC, derivitization is often done to increase/decrease the volatility and increase/decrease the stability of compounds of interest:
      1. increase/increase
      2. increase/decrease
      3. decrease/increase
      4. decrease/decrease
    7. The GLC detector which unequivocally identifies compounds of interest is:
      1. MS (mass spectrometer)
      2. TC (thermal conductivity)
      3. FID (flame ionization detector)
      4. EC (electron capture)
      5. NPD (nitrogen phosphorous detector)
    8. In an HPLC with a nonpolar stationary phase and a polar mobile phase, you would expect n-octanol/n-butanol to have the shorter retention time, and decreasing the size of the beads would increase/decrease the retention time of both substances:
      1. n-octanol/increase
      2. n-octanol /decrease
      3. n-butanol/increase
      4. n-butanol/decrease
    9. Reversed phase means a stationary phase with a mobile phase:
      1. nonpolar/nonpolar
      2. nonpolar/polar
      3. polar/polar
      4. polar/nonpolar
    10. If the peaks of your standards come out too soon on a GLC recording, this could be the result of:
      1. increased oven temperature
      2. too large a sample volume
      3. too small a sample volume
      4. increased injector temperature
      5. high detector voltage
    11. In paper chromatography, the following standards had these Rf values:
    Cystine 0.20
    Lysine 0.43
    Arginine 0.67
    Glycine 0.85

    The solvent front traveled 8 cm, and the spot representing the unknown traveled 1.6 cm. What is the identification of the unknown?

    1. cystine
    2. lysine
    3. arginine
    4. glycine
    5. none of the above

    Use the following Key to answer questions 13 through 15:

    1. 1, 2 and 3 are correct
    2. 1 and 3 are correct
    3. 2 and 4 are correct
    4. only 4 is correct
    5. all are correct
    1. Retention time in a GLC is a function of:
      1. detector temperature
      2. oven temperature
      3. solubility in the solvent
      4. length of the column
    2. Retention time is a qualitative entity obtained when utilizing HPLC and GC. For certain HPLC and GC procedures, the retention times may be unacceptably lengthy. Name the parameters which can be adjusted to decrease the retention time for HPLC
      1. mobile phase flow rate
      2. detector temperature
      3. column temperature
      4. size of sample injection
    3. Name the parameters which can be adjusted to decrease the retention time for GC:
      1. size of sample injection
      2. detector volume
      3. injector temperature
      4. column oven temperature
    Answer
    1. c (p. 110)
    2. d (p. 114)
    3. b (p. 114)
    4. g (p. 112)
    5. f (p. 116)
    6. h (p. 110)
    7. c (p. 115)
    8. b (p. 110,156)
    9. c (p. 116)
    10. e (p. 156-157, 169)
    11. b (p. 157-158, 163-164)
    12. a (p. 162)
    13. a (p. 173)
    14. c (p. 138-139)
    15. b (p. 137-138)
    16. a (p. 159-161)
    17. a (p. 116)
    18. c (p. 158-159)
    19. b (p. 132-133)
    20. d (p. 162-164)

    This page titled 1.5: Chromatography is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Lawrence Kaplan & Amadeo Pesce.

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