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    The interpretation of gas chromatograms

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    A chromatogram would feature lines instead of peaks if:
    a) the best equipment available is used
    b) the separation is done by capillary electrophoresis
    c) if the temperature nears (or is equal to) the absolute zero
    d) neither of the above cases would suffice.

    B. Most modern chromatography instruments are equipped with:
    a) digital electronic peak integrators
    b) electrode potential control devices
    c) scanning probe attachments
    d) all of the above

    C. Contaminants in gas-chromatography are revealed by:
    a) a different level of the baseline
    b) an appearance of additional peaks
    c) sharper and narrower peaks
    d) inevitable peak broadening

    D. Consider the effect of mass diffusion on band broadening in a gas chromatographic column. How does this effect depend upon the flow rate of the mobile phase?
    a. The height equivalent to a theoretical plate decreases with an increase in the flow rate of the mobile phase.
    b. The height equivalent to a theoretical plate increases with an increase in the flow rate of the mobile phase.
    c. The height equivalent to a theoretical plate is independent of the flow rate of the mobile phase.
    d. There is insufficient information to answer the question.

    © BrainMass Inc. brainmass.com December 24, 2021, 11:48 pm ad1c9bdddf
    https://brainmass.com/chemistry/chromatography/interpretation-gas-chromatograms-604844

    SOLUTION This solution is FREE courtesy of BrainMass!

    Gas chromotography works by separating a chemical into different components. The sample is vaporized and injected onto the head of a chromatographic column where each component produces a distinctive peak. The ideal chromatogram has closely spaced peaks with no overlapping peaks.

    A chromatogram would feature lines instead of peaks if:

    c) if the temperature nears (or is equal to) the absolute zero

    At absolute zero, the sample would not mobilize, so there would be no peaks.

    B. Most modern chromatography instruments are equipped with:
    a) digital electronic peak integrators

    Most modern chromatographs have digital electronic integrators that calculate accurate peak areas. A scanning probe microscope (SPM) uses an extremely sharp probe to create three-dimensional images of samples. I have never hear of an electrode potential control device.

    C. Contaminants in gas-chromatography are revealed by:
    b) an appearance of additional peaks

    As the contaminants vaporize, they produce peaks where we would not expect to see any. Slow injection or oversized samples cause band spreading and poor resolution.

    D. Consider the effect of mass diffusion on band broadening in a gas chromatographic column. How does this effect depend upon the flow rate of the mobile phase?
    a. The height equivalent to a theoretical plate decreases with an increase in the flow rate of the mobile phase.

    The plate height, H, is a function of the flow rate of the mobile phase, v, and decreases as flow rate increases past the ideal velocity. The extent of band broadening in chromatography is determined by the Van Deemter equation, which indicates opposing effects of flow rate. The three basic processes causing band broadening: eddy diffusion, diffusion in the gas phase and interphase mass transfer. The slower the velocity, the more uniformly analyze molecules may penetrate inside the particle, and the less the effect of different penetration on the efficiency. So, at low flow rates plate height decreases with increasing flow rates. On the other hand, at the faster flow rates the elation distance between molecule with different penetration depth will be high.

    This content was COPIED from BrainMass.com - View the original, and get the already-completed solution here!

    © BrainMass Inc. brainmass.com December 24, 2021, 11:48 pm ad1c9bdddf>
    https://brainmass.com/chemistry/chromatography/interpretation-gas-chromatograms-604844

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