GC031 Instrument Overview

 The main components of the chromatographic system are (1) carrier gas, (2) flow control, (3) sample inlet and sampling devices, (4) columns, (5) controlled temperature zones (ovens), (6) detectors, and (7) data systems.

A gas chromatograph functions essentially as follows:

An inert gas flows continuously from a gas cylinder through the inlet, the column and the detector. The flow rate of the carrier gas is controlled to ensure reproducible retention times and minimize detector drift and noise. The sample is injected into the inlet, where it is vaporized and carried into the column by the carrier gas. The capillary column has a typical length of 15-30 m and is coated inside with the stationary phase; a thin layer (0.2-1 µm) of a high boiling liquid. The sample interacts with the stationary phase, and partitions between the mobile and stationary phases. The sample is separated into individual components due to their differences in solubilities in the liquid and their vapor pressures.

Once it exits the column, the carrier gas with the separated compounds, pass through the detector, which detect the quantity of the sample and generates an electrical response in return. The signal goes to a data system that generates the graphic record of the analysis; the chromatogram. These data systems usually generate a complete report with retention times, calculations and peak areas.

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