gas chromatography

• Separation by relative solubility:

  • Components dissolve in the liquid stationary phase
  • The greater the solubility in the stationary phase, the more the component molecules are slowed down
• GC stands for gas chromatography
• Gas chromatography is useful for separating and identifying volatile organic compounds present in a mixture
• GC: The stationary phase is a high boiling liquid adsorbed onto an inert solid support.
• GC: The mobile phase is an inert carrier gas such as helium or neon.
• Gas Chromatography

  1. A small amount of the volatile mixture is injected into the apparatus, called a gas chromatograph
  2. The mobile carrier gas carries the components in the sample through the capillary column which contains the liquid stationary phase absorbed onto the solid support
  3. The components slow down as they interact with the liquid stationary phase inside the column
  4. The more soluble the component is in the liquid stationary phase, the slower it moves through the capillary column
  5. The components of the mixture are separated depending on their solubility in the liquid stationary phase
• GC: The compound retained in the column for the shortest time has the lowest retention time and is detected first
• GC: The retention time is the time taken for each component to travel through the column
• Interpretation of a gas chromatogram

  Two pieces of information can be obtained from a gas chromatogram

  • Retention times
  • Peak integrations
• Each component is detected as a peak on the gas chromatogram.
• One piece of information obtained from a GC is retention times which can be used to identify the components present in the sample by comparing these to retention times for known components
• Another piece of information obtained from a GC is peak integrations (the areas under each peak) which can be used to determine the concentrations of components in the sample
• The concentration of a component in a sample is determined by comparing its peak integration (peak area with values obtained from standard solutions of the component
• GC - concentration of components

  • External calibration is when you plot a calibration curve of peak area against concentration
  • It offers a method for converting a peak area into a concentration
• Finding the concentration of components from a GC is just a matter of running the sample through the gas chromatograph and comparing the compounds peak area with the calibration curve.