Instrumental Analysis: Gas Chromatography
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Questions and Answers

What is the typical flow rate of carrier gas in capillary columns?

  • 1 ml/min (correct)
  • 30-50 ml/min
  • 100-200 ml/min
  • 50-100 ml/min

    • What is the typical length range of capillary columns?

  • 2-5 meters
  • 100-200 meters
  • 5-10 meters
  • 15-100 meters (correct)

    • What is the main difference between packed and capillary columns?

  • Material used
  • Sample size (correct)
  • Inner wall coating
  • Flow rate of carrier gas

    • What is the maximum temperature for glass packed columns?

    <p>280°C</p> Signup and view all the answers

    What is the main factor affecting retention in GC?

    <p>All of the above</p> Signup and view all the answers

    What is the effect of increasing column temperature on GC resolution?

    <p>Decreases resolution</p> Signup and view all the answers

    What is the effect of increasing film thickness on GC resolution?

    <p>Increases resolution</p> Signup and view all the answers

    What is the effect of increasing internal diameter on GC resolution?

    <p>Decreases resolution</p> Signup and view all the answers

    What is the typical material used for capillary columns?

    <p>All of the above</p> Signup and view all the answers

    What is the stationary phase in capillary columns?

    <p>A liquid film coated on the inner wall</p> Signup and view all the answers

    Study Notes

    Gas Chromatography (GC) Overview

    • Sample is injected and vaporized in a chromatographic column.
    • Components are separated based on partition or adsorption between mobile (carrier gas) and stationary phases.
    • Mobile phase is inert and does not interact with the sample.

    Types of Gas Chromatography

    • Gas-Solid Chromatography (GSC): Uses a solid stationary phase; separation occurs through adsorption.
    • Gas-Liquid Chromatography (GLC): Involves a liquid stationary phase supported on solid; relies on solubility of components in the stationary phase.

    Suitable Samples for GC

    • Compounds must be volatile and thermally stable (e.g., hydrocarbons, aldehydes).
    • Non-volatile samples can be converted to volatile derivatives (e.g., fatty acids to methyl esters).
    • Suitable samples have molecular weights between 2 and 1000.

    Advantages and Limitations of GC

    • Advantages:
      • High sensitivity (detection limit: 10^-9 to 10^-12 g).
      • High accuracy and rapid analysis times.
    • Limitations:
      • Samples must be volatile and thermally stable below 400°C.
      • Dirty samples require cleanup processes.
      • Identification requires coupling with techniques like mass spectrometry.

    GC Instrumentation

    • Components include:
      • Carrier gas system (with regulator, purifier, flow meter).
      • Sample injection system.
      • GC oven for temperature control.
      • GC column for separation.
      • GC detector for analysis.
      • Data integration/computer station.

    Carrier Gas Requirements

    • Must be pure (99.999% purity) and inert, to prevent interaction with samples.
    • Common carrier gases: nitrogen, helium, hydrogen, argon.
    • Gases must be dry to avoid hydrolysis and adjusted for pressure based on viscosity and column length.

    Sample Injection System

    • Introduces sample into GC column as liquid or gas.
    • Modes include:
      • Split Injection: Diverts a portion of the sample for concentrated samples.
      • Splitless Injection: Introduces the entire sample into the column.

    GC Oven Functions

    • Houses the chromatographic column and heats samples for separation.
    • Temperature determines the degree of separation and affects sample boiling points.

    Types of GC Columns

    • Packed Columns:

      • Made of glass, metal, or Teflon; lengths of about 2 meters.
      • Filled with solid inert support coated in liquid stationary phase.
      • Carrier gas flow rate: 30-50 ml/min.

    • Capillary (Open Tubular) Columns:

      • Made from glass or fused silica; lengths between 15-100 meters.
      • Coated on the inner wall with liquid stationary phase.
      • Lower flow rates of about 1 ml/min due to minimal resistance.

    Comparison of Packed vs. Capillary Columns

    • Packed Columns: Larger diameter (2-5 mm), max temp 280°C, larger sample sizes.
    • Capillary Columns: Smaller diameter (0.2-0.5 mm), higher max temp (370°C), suitable for smaller sample sizes (100 times smaller than packed).

    Key Factors in GC Separation

    • Retention in GC influenced by:
      • Solubility in stationary phase.
      • Boiling points of compounds.
      • GC oven temperature.

    Resolution in GC

    • Influencing parameters include:
      • Column temperature.
      • Length of the column (√L).
      • Film thickness and internal diameter of the column.

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    Quiz Team

    Description

    This quiz covers the basics of gas chromatography, including sample injection, vaporization, and fractionation. Learn about the partition and adsorption processes between the mobile and stationary phases.

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