Chromatography: Theoretical Plates Calculation
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Questions and Answers

What is the primary division of chromatographic techniques based on?

  • Type of stationary phase
  • Type of analyte
  • Type of supporting medium
  • Type of mobile phase (correct)

    • What is the definition of a chromatogram?

  • Retention time versus elution time
  • Concentration versus retention time
  • Concentration versus elution time (correct)
  • Elution time versus concentration

    • What is the relationship between k’ and the interaction between a solute and the phases?

  • k’ is partly related to the strength of interaction
  • k’ is not related to the strength of interaction
  • k’ is inversely related to the strength of interaction
  • k’ is directly related to the strength of interaction (correct)

    • What is the definition of the stationary phase in chromatography?

    <p>A layer or coating on the supporting medium that interacts with the analytes</p> Signup and view all the answers

    What does k’ represent in chromatography?

    <p>The ratio of moles of solute in the stationary phase to the mobile phase</p> Signup and view all the answers

    What are the two phases involved in chromatography?

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

    What is the formula for calculating k’?

    <p>k’ = Moles Astationary phase / Moles Amobile phase</p> Signup and view all the answers

    What is the purpose of chromatography?

    <p>To separate compounds based on their interactions with two phases</p> Signup and view all the answers

    What is the result of a chromatographic separation?

    <p>A chromatogram</p> Signup and view all the answers

    What is the secondary division of chromatographic techniques based on?

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

    Study Notes

    Theoretical Plates and Resolution

    • Number of theoretical plates (N) is calculated by: N = (tr2 – tr1) (Wb2 + Wb1)/2
    • N is a measure of the column's efficiency
    • Resolution (Rs) is a measure of how well two peaks are separated, and is preferred over N since it considers both retention time and column efficiency
    • Rs ≥ 1.5 represents baseline resolution, or complete separation of two neighboring solutes
    • Rs ≥ 1.0 is considered adequate for most separations

    Plate Height and Van Deemter Equation

    • Plate height or height equivalent of a theoretical plate (H or HETP) is a measure of the column's efficiency
    • H = L/N, where L is the column length and N is the number of theoretical plates
    • The Van Deemter equation relates flow rate to H: H = A + B/m + Cm
    • H is used to relate kinetic processes to band broadening

    Sources of Band Broadening

    • Eddy diffusion is a source of band broadening
    • Mobile phase mass transfer is a source of band broadening
    • Stagnant mobile phase mass transfer is a source of band broadening due to differences in diffusion rates between the mobile phase outside and inside the pores of the support
    • Stationary phase mass transfer is a source of band broadening
    • Longitudinal diffusion is a source of band broadening

    Chromatography Introduction

    • Chromatography is a separation technique based on the interactions of compounds with two phases, a mobile phase and a stationary phase
    • A chromatogram is a graph of concentration versus elution time
    • Types of chromatography include gas chromatography (GC) and liquid chromatography (LC)
    • The capacity factor (k') is a useful parameter in understanding retention mechanisms, defined as: k' = Moles Astationary phase / Moles Amobile phase

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    Description

    Calculate the number of theoretical plates (N) in a chromatography column using the given formula and understand the significance of each variable.

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