gas chromatograph

The gas chromatograph is composed of different elements: the injection chamber, a chromatographic column and a detector. The compounds are driven through these three elements with a stream of gas, called the carrier gas, which may hydrogen, nitrogen or a rare gas such as helium or argon.

In the injection chamber, located at the entrance of the chromatographic column, a known volume of sample is injected through a device that can be manual, via a syringe, or automatic via a multi port injection valve.

The chromatographic column, capillary or filled, is made from one phase to defined physicochemical properties, called the stationary phase, which aims to separate chemical compounds. The different interactions of chemical compounds with the stationary phase allows the compounds in the mixture to be separated. The compounds exit the column at different times (called the retention time). Besides the interaction between compounds and the stationary phase, other parameters that influence the retention times are the temperature of the column, the flow rate of the carrier gas and the molecular weight of the compounds.

Finally, the detector transforms the separated compound into a signal. This signal forms a chromatographic peak the surface of which is related to the concentration of the compound. Various detectors can be used depending on the application required: such as a flame ionization detector (FID), a photo ionization detector (PID) or a thermal conductivity detector (TCD). Specific detectors such as a flame photometric detector (FPD) or an electrochemical detector for measuring sulfur compounds can also be used.

The company CHROMATOTEC provides gas chromatograph analyzers for analysis of BTEX (Benzene, Toluene, Ethylbenzene and Xylenes) with its airmoBTX (FID) and airTOXIC (PID) range, other VOCs (Volatile Organic Compounds) with its range airmoVOC (FID) and airTOXICVOC (PID) and sulfur compounds in natural gas or ambient air (hydrogen sulfide H2S, DMS dimethyl sulfide, methyl mercaptan MeSH EtSH ethyl mercaptan, disulfide dimethyl DMDS) with its MEDOR range.