Gas-Liquid Chromatography? Easy Way To Learn Chromatography

Principle Of Gas-Liquid Chromatography

Gas-liquid chromatography is based upon the distribution of compounds between a liquid and gaseous phase. This is used for qualitative and quantitative analysis of various compounds. This technique is highly sensitive and speed resolution is also quite high. The stationary phase is liquid material such as silicone grease supported on granular insert material. This material is packed into a narrow coiled glass or steel column. The column length is between 1 to 3 meters and the diameter is 2-4 mm. through this tube an inert carrier gas (which is a mobile phase) is passed. Examples – Nitrogen, Helium, or Argon.

What Is Chromatography?

Chromatography is a technique by which a mixture of organic compounds carried in the mobile phase (liquid or gas) is separated into its constituents on the stationary phase.

What Is Gas-Liquid Chromatography

The column is maintained in an over at high temp, which volatilizes the compounds to be separated. The basis for separation is the difference in the partition coefficient of the volatilized compound between the liquid and gaseous phases. These compounds are carried out by the carrier gas.

After leaving the column the compounds pass through a detector which is linked via an amplifier to a chart recorder. This chart recorder the peaks as the compounds pass through the detector.

Gas-Liquid Chromatography Plate

The efficiency of the gas-liquid chromatography column depends upon the no of theoretical plates. As the no of theoretical plates increases the efficiency of the column increase. For achieving maximum column efficiency. The flow of the carrier gas is kept on optimum value so that the distribution can take place between the stationary liquid phase and the mobile gaseous phase. The decrease in the column diameter should give a proportional increase in the number of plates per unit length.

Solid Support Of Gas-Liquid Chromatography

A solid support is required on which a thin film of the stationary liquid phase is coated so the solid support should be inserted into the sample. The most commonly used support is elite but this contains OH (hydroxyl) group which can interact with the sample. So these groups should be modified. This modification is done by treating the support with hexamethyl disilazane.

Stationary Phase Of Gas-Liquid Chromatography

The stationary phase should be involatile and thermally stable at temperature, Which is used in gas-liquid chromatography. The phases are of two types.

  1. Selective Gas-Liquid Chromatography
  2. Non-Selective Gas-Liquid Chromatography

1. Selective Gas-Liquid Chromatography – In these kinds of stationary phases the characterization of different components is based on the chemical characteristics.

2. Non-selective Gas-Liquid Chromatography In these kinds of phases the separation is achieved on the basis of difference boiling. Physical characteristics of the components commonly used stationary phases include polyethylene glycol, methyl phenyl and, methyl vinyl siliongums, apizone, esters of adipic succinic and phthalic acids.

Mobile Phases Of Gas-Liquid Chromatography

One sample is Chromatography is dissolved in a suitable solvent such as either, heptanes or methanol chlorinated organic solvents are generally avoided since they can contaminate the detector. The sample is injected onto the column using a microsyringe through the septum which is present in the injection part. Normally 0.1-10 mm3 of the solution is injected the injection region of the column is maintained at a slightly higher temp than the column because this helps incomplete visualization of the sample in the latest design instruments the sample injection is automated. Nitrogen, helium, and argon are the three most commonly used carrier gases.

Detection System In Gas-Liquid Chromatography?

The most commonly used detector is the flame ionization detector (FID). It can detect as low as 1 nanogram (ng) of the substance. A mixture of Hydrogen and air is introduced into the detector to produce a flame the other detector system used are:

  1. Nitrogen-phosphorus detector(NPD)
  2. Electron-capture detector(ECD)
  3. Infra-red spectro-photometer
  4. Nuclear magnetic resonance(NMR) spectrometer 

Application Of Gas-Liquid Chromatography

Gas-liquid chromatography has been commonly used for the detection of volatile, nonpolar compounds. This can be used for example to identify unknown fatty acid ester in the fat hydrolysate. A more important method of quantitative analysis is one use of internal standards. Here the sample and STD are spiked with an equal amount of a solute whose retention time is near to that of the analyst. The ratio of the area of the std analysis to that of the internal std used to prepare the calibration curve and determine the unknown concentration.
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