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Chromatography Principles Quiz
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Chromatography Principles Quiz

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Questions and Answers

What happens to the separation quality when k' is less than 1.0?

  • Separation is poor. (correct)
  • Separation is excellent.
  • Separation is very fast.
  • Separation is optimal.

    • What k' range indicates optimum separation?

  • k' = 20-30
  • k' = 1-5 (correct)
  • k' < 1.0
  • k' > 30

    • What effect does increasing the partition factor (K) have on the solute's retention (k')?

  • Retention increases. (correct)
  • Retention becomes unpredictable.
  • Retention decreases.
  • Retention remains constant.

    • Which type of stationary phase is used in gas-solid chromatography?

    <p>Solid, underivatized support</p> Signup and view all the answers

    What role does the selectivity factor (α) play in separations?

    <p>It indicates the strength of partitioning between two solutes.</p> Signup and view all the answers

    Which chromatography method employs a stationary phase containing fixed charges?

    <p>Ion-exchange chromatography</p> Signup and view all the answers

    What is the Rf value in chromatography used to represent?

    <p>The ratio of component distance to solvent front distance</p> Signup and view all the answers

    Which k' range indicates slow separation?

    <p>k' = 20-30</p> Signup and view all the answers

    For effective separation between two solutes, what is required regarding their partition factors (K)?

    <p>They must have a significant difference.</p> Signup and view all the answers

    What type of stationary phase is used in liquid-bonded-phase chromatography?

    <p>Chemically-derivatized support</p> Signup and view all the answers

    What type of chromatography utilizes porous support as its stationary phase?

    <p>Size exclusion chromatography</p> Signup and view all the answers

    What is the main consequence of poor separation in chromatography?

    <p>Increased overlap between peaks.</p> Signup and view all the answers

    When the partition factor (distribution constant) of a solute increases, what generally happens to its interaction with the stationary phase?

    <p>It becomes more favorable.</p> Signup and view all the answers

    Which chromatography technique involves applying a solution of a mixture at the bottom of a plate?

    <p>Thin Layer Chromatography</p> Signup and view all the answers

    Which type of chromatography is categorized as open tubular (capillary) chromatography?

    <p>Gas-liquid chromatography</p> Signup and view all the answers

    What type of support is used in affinity chromatography?

    <p>Support with immobilized ligand</p> Signup and view all the answers

    What does the term ‘theoretical plates’ refer to in the context of chromatography?

    <p>Conceptual stages in the separation process</p> Signup and view all the answers

    How does the number of theoretical plates (N) relate to column efficiency?

    <p>Higher number of plates indicates better separation</p> Signup and view all the answers

    What is the formula used to relate standard deviation (σ), height (H), and length (L) in the context of theoretical plates?

    <p>$H = \frac{σ}{L}$</p> Signup and view all the answers

    Rate Theory of Chromatography quantitatively describes which aspect of elution bands?

    <p>The shape and breadth of elution bands</p> Signup and view all the answers

    What mechanism does the Rate Theory of Chromatography use to describe the migration of analytes?

    <p>Random-walk mechanism</p> Signup and view all the answers

    In chromatography, what would be the effect of an insufficient number of theoretical plates?

    <p>Reduced efficiency in separating solutes</p> Signup and view all the answers

    In the context of column chromatography, what does H primarily represent?

    <p>The height equivalent of a theoretical plate</p> Signup and view all the answers

    What main factor does the efficiency of a chromatographic column rely on?

    <p>The nature of the stationary phase</p> Signup and view all the answers

    What primarily causes band broadening due to longitudinal diffusion?

    <p>Diffusion of the solute away from the concentrated center</p> Signup and view all the answers

    How does flow rate affect band broadening due to longitudinal diffusion?

    <p>Is inversely proportional to band broadening</p> Signup and view all the answers

    What factor is NOT associated with band broadening due to mobile phase mass transfer?

    <p>Temperature of the stationary phase</p> Signup and view all the answers

    Why does a solute in the center of a channel move more quickly than one at the edges?

    <p>It experiences less resistance compared to the edges</p> Signup and view all the answers

    Which band broadening effect is related to the interaction of solute with the stationary phase?

    <p>Stationary phase mass transfer</p> Signup and view all the answers

    How can peak broadening due to longitudinal diffusion be minimized?

    <p>By increasing the flow rate</p> Signup and view all the answers

    What does the term 'band broadening' refer to in chromatography?

    <p>An increase in the width of a peak on a chromatogram</p> Signup and view all the answers

    Which of the following is a consequence of the flow rate when considering band broadening?

    <p>Higher flow rates typically increase the separation efficiency</p> Signup and view all the answers

    What effect does increasing the column length have on resolution in chromatography?

    <p>Resolution is increased by a factor of approximately 1.41.</p> Signup and view all the answers

    What is the role of the retention factor (k') in determining column resolution?

    <p>It reflects the performance of the slower-moving species.</p> Signup and view all the answers

    Which factor does NOT directly affect column resolution?

    <p>Temperature of the mobile phase</p> Signup and view all the answers

    Which method can be used to increase column resolution?

    <p>Increase the capacity factor</p> Signup and view all the answers

    What is the primary consequence of a complete separation with Rs = 1.5 in chromatography?

    <p>The solutes are well-resolved and distinct.</p> Signup and view all the answers

    The selectivity factor (a) in chromatography is primarily influenced by what?

    <p>The composition of the stationary and mobile phases.</p> Signup and view all the answers

    Which statement accurately describes a system with Rs of 0.75?

    <p>The solutes are indistinguishable from one another.</p> Signup and view all the answers

    What is the effect of increasing the fraction of time a solute spends in the stationary phase?

    <p>It enhances resolution.</p> Signup and view all the answers

    Study Notes

    Partition Factor (K)

    • The ratio of concentrations of solute in the stationary and mobile phase
    • As K increases, the interaction of the solute with the stationary phase becomes more favorable, and the solute's retention (k') increases.

    Selectivity Factor (α)

    • Provides a measure of how well the column will separate two solutes.
    • The selectivity factor, α, is the ratio of the retention factors for two solutes, where B has stronger partitioning than A.

    Column Efficiency - Theoretical Plates (N)

    • The efficiency of a separation can be thought of as a series of extractions.
    • The number of theoretical plates (N) allows us to compare the efficiencies of a system for solutes that have different retention times.
    • The efficiency of a column increases with the number of plates (N).

    Rate Theory of Chromatography

    • The rate theory describes the breadth of elution bands quantitatively based on the migration of analytes through a column via a random-walk mechanism.

    Types of Chromatography Based on Stationary Phase

    • Gas Chromatography (GC)
      • Gas-solid chromatography: uses a solid, underivatized support
      • Gas-liquid chromatography: uses a liquid-coated support
      • Bonded-phase gas chromatography: uses chemically derivatized support
    • Liquid Chromatography (LC)
      • Adsorption chromatography: uses a solid, underivatized support
      • Partition chromatography: uses a liquid-coated or derivatized support
      • Ion-exchange chromatography: uses a support containing fixed charges
      • Size-exclusion chromatography: uses a porous support
      • Affinity chromatography: uses a support with an immobilized ligand

    Types of Chromatography Based on Support Material

    • Packed bed chromatography: uses a column packed with stationary phase
    • Open tubular (capillary) chromatography: uses a column with a thin layer of stationary phase
    • Open bed (planar) chromatography: uses a flat surface coated with stationary phase

    Thin Layer Chromatography (TLC) & Paper Chromatography

    • A solution of a mixture is applied as a spot or band at the bottom of the plate and allowed to travel with the solvent up the plate.
    • The ratio of the distance traveled by the component (from origin) compared with the distance traveled by the solvent front (from origin) is called the Rf value.

    Band Broadening

    • Longitudinal Diffusion (B/U)
      • Diffusion of the solute away from the concentrated center of a band.
      • The degree of band broadening due to longitudinal diffusion depends on the diffusion of the solute and the flow rate of the solute through the column.
      • To minimize broadening, use a faster flow rate.
    • Mobile phase mass transfer (CMu)
      • Peak broadening caused by different flow profiles within channels or between particles of the support in the column.
      • The degree of band broadening due to mobile phase mass transfer depends on the size of the packing material and the diffusion rate of the solute.
    • Stationary phase mass transfer (Csu)
      • Band broadening due to the movement of solute between the liquid phase and the stationary phase.

    Column Resolution (Rs)

    • Rs is the ratio of the distance between the peaks to the average peak width.
    • Rs = 1.5 indicates a complete separation, while Rs = 0.75 indicates incomplete separation.
    • To improve resolution, we need to increase the number of theoretical plates (N), the retention factor (k'), and the selectivity factor (α).

    Factors Affecting Resolution

    • The number of theoretical plates (N), the partition coefficient (K), the capacity factor (k'), and the column length all affect resolution.
    • Methods to increase resolution:
      • Increase column length (increase N)
      • Change phase interaction (increase α)
      • Increase capacity factor (increase k')

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    Description

    Test your knowledge on the key concepts of chromatography, including partition factor, selectivity factor, column efficiency, and rate theory. This quiz will help you understand how these principles affect the separation of solutes in a chromatographic process.

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