Gas Chromatography

Gas Chromatography

Gas Chromatography (GC) is an analytical technique used to separate and analyse complex mixtures of substances. Here's a concise explanation of GC for secondary school students:

Components of GC:

• Mobile Phase: In GC, the mobile phase is an inert gas, such as helium.
• Stationary Phase: The stationary phase consists of a very thin layer of an inert liquid on an inert solid support, often silica beads packed into a long, thin tube.

Superior Separation:

• GC is highly effective at separating complex mixtures and is more sensitive than techniques like thin-layer or paper chromatography.
• It not only identifies the chemicals present in a mixture but also quantifies their amounts.

Working Principle:

• The mixture to be analysed is injected into a stream of carrier gas (the mobile phase) and introduced into a long, coiled column within a thermostatically controlled oven.
• As the mixture travels through the column, it separates into its individual components.

Affinity and Retention Time:

• Compounds in the mixture have varying affinities (attractions) for the mobile and stationary phases.
• Substances with a greater affinity for the mobile phase reach the detector more quickly, while those with a greater affinity for the stationary phase move more slowly.
• The time taken by a substance to pass through the column is called its retention time.

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Gas Chromatography

Affinity and Retention Time:

• GC is used in various applications, such as detecting banned substances in athletes' urine samples and identifying accelerants used in arson cases by forensic investigators.

Interpreting Results:

• Gas chromatograms provide valuable information, including:
  • The number of compounds in the mixture (represented by peaks).
  • The quantity of each compound (peak height; higher means more).
  • The retention time (position of the peak).
• Comparing the retention time of an unknown substance with reference data helps identify it.

Conclusion:

• Gas chromatography is a powerful analytical technique that separates and quantifies substances in complex mixtures. It relies on the differential affinities of compounds for the mobile and stationary phases within a coiled column. The resulting chromatogram provides crucial information about the mixture's composition.