Gas chromatography is a technique suitable for the separation of volatile, thermally stable molecules. In GC, the injected sample is vaporized at the start of the column. Separation of the analytes takes place because of the differences in the partition coefficient of each analyte between a stationary liquid phase and an inert gaseous mobile phase.
GC systems have the following major components (Figure 1):
Column. This is housed in an oven that can be temperature programmed. There are two types of GC columns: packed capillary and open tubular
Sample injection port. Samples are usually injected directly into the mobile phase gas flow using a syringe.
Carrier gas supply. Typical carrier gases used in GC are helium, argon, and nitrogen.
Detector. There are several detectors available, with flame ionization detector (FID) as the most popular. FID uses hydrogen/air flame to decompose the analyte molecules into ions by burning them and then measuring the change in current. A mass spectrometric detector can also be coupled to a GC to provide better sensitivity and selectivity. Other detectors include: nitrogen phosphorus (NPD), electron capture (ECD), photoionization (PID), flame photometric (FPD), and thermal conductivity detector (TCD).
Figure 1. Schematic of a gas chromatograph
GC-MS is the preferred method for the analysis of volatile organics (VOCs) in water. VOCs are ground water contaminants of concern because they are released to the environment in large quantities, their human toxicity, and a tendency for some of these compounds to persist and migrate to drinking water supply wells.
For more detailed information about VOCs, click here.
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