First, a tiny sample of the mixture of substances being studied is placed in a syringe and injected into the machine. The components of the mixture are heated and instantly vaporize. Next, we add a carrier (the eluant), which is simply a neutral gas such as hydrogen or helium, designed to help the gases in our sample move through the column. In this case, the column is a thin glass or metal tube usually filled with a liquid that has a high boiling point (or sometimes a gel or an adsorbent solid). As the mixture travels through the column, it's adsorbed and separates out into its components. Each component emerges in turn from the end of the column and moves past an electronic detector (sometimes a mass spectrometer), which identifies it and prints a peak on a chart. The final chart has a series of peaks that correspond to all the substances in the mixture. Gas chromatography is sometimes called vapor-phase chromatography (VPC) or gas-liquid partition chromatography (GLPC).
Here's a very simplified overview of what happens in the gas chromatography process:
1.The eluant (carrier gas) is introduced from a gas cylinder outside the machine. It's called the carrier because that's exactly what it does—carry the sample we're studying through the machine. In gas chromatography, the carrier gas is the mobile phase.
2.The rate of flow of the carrier is carefully controlled to give the clearest separation of the components in the sample.
3.The carrier enters the machine through an inlet port/splitter.
4.The sample being measured is injected into the carrier gas using a syringe and instantly vaporizes (turns into gas form).
5.The gases that make up the sample separate out as they move along the column (orange), which is the stationary phase. The column is a very thin (capillary) tube, sometimes as much as 30–60m (100-200ft) long, coiled and entirely contained inside an oven (blue) that keeps it at a high enough temperature to ensure that the sample remains in gas form. The temperature of the oven can be carefully controlled.
6.As the sample separates out and its constituent gases travel along the column at different speeds, a detector senses and records them. Various different detectors can be used, including flame ionization detectors, thermal conductivity detectors, and mass spectrometers (usually separate machines).
7.The data analyzer/recorder attached to the machine draws a chromatogram (chart) with peaks corresponding to the relative amounts of the different chemicals in the sample.
Gas Chromatograph Manufacturer and Supplier from China: YK Scientific Instrument
Email: sales@yk-instrument.com
