Gas chromatography

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Instrumental Analysis
Gas chromatography
Jack Lee E.P. Department
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Introduction

• GC Gas Chromatography
• GC was invented by A. J. P. Martin.
• The first gas chromatographic separation was a
  series of fatty acids.
• A more sophisticated GC was constructed by James
  and Martin in 1955.

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The Modern GC

• The modern gas chromatograph is a really complex
  instrument mostly computer controlled.
• The samples are mechanically or manually
  injected.
• The analytical results are automatically
  calculated and printed out.

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Block diagram of GC structure
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The first unit

• It provides all the necessary gas supplies.
• A minimum of three different gases would be
  required. (FID)
• Three flow controllers, three flow monitors would
  be required.
• A microprocessor is employed to monitor flow
  rates, adjust individual gas flow rates.
• Use gas generators instead of gas tanks.

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The second unit

• It contains a manual (1. 2. 3)or an automatic
  injector.
• It is situated inside a thermostatically
  controlled enclosure.
• We use a syringe to inject sample onto the
  column.
• Automatic injector(carousel) can carry out a
  series of sample preparation procedures before
  injecting the sample onto the column.

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The third unit

• It contains the column and an oven.
• The column is the essential device to achieve the
  necessary separation.
• The oven is used to control the column
  temperature.
• The column has two kinds
• Packed column Capillary column

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The fourth unit

• It contains the detector which is situated in its
  own oven.
• There is a wide range of detectors available each
  having unique operating parameters and its own
  performing characteristics.
• The output of detector is electronically modified.

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The detectors

• Types of the detectors
• TCD Thermal Conductivity Detector
• FID Flame Ionization Detector
• ECD Electron Capture Detector
• FPD Flame Photometric GC Detector
• NPD Nitrogen Phosphorus Detector
• Principles of the detectors

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TCD Thermal Conductivity Detector
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The bridge circuit for TCD detector
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FID Flame Ionization Detector
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ECD Electron Capture Detector
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FPD Flame Photometric GC Detector
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NPD Nitrogen Phosphorus Detector