Figure 3. GC instrumentation.
A GC system consists of several components (Figure 3). The role of each component is critical to obtain a good separation and analysis. Carrier gas is required to provide a gas flow that transports the compounds through the column and to the detector. The purity and flow of the carrier gas is crucial to achieve good separation and reproducible chromatograms; gas filters and flow regulators are used to supply high-purity and constant-flow gas to the GC. Principally, the carrier gas needs to be inert and does not interfere with the separation and detection. Helium, hydrogen and nitrogen are some of the commonly-used carrier gases. These gases have different properties and characteristics and the choice essentially depends on the sample and the type of detector and analysis. These factors, such as the required separation resolution and efficiency, cost and compatibility with the detectors, should be considered when choosing carrier gases. Table 2 provides a tabulation of the pros and cons of the most commonly-used carrier gases.
Table 2. Pros and cons of the most commonly-used carrier gases.
|• High diffusivity and linear velocities
• Gets good separation efficiencies
• Short analysis and run time (results in cheap operational cost)
• Not completely inert (e.g. reacts with some compounds at high temperature)
|• Inert (safe) and non-flammable
• Gives high resolution
|• Expensive, not easily available
|• Cheap and easily available
||• Not suited for use in temperature-programmed GC analysis
• Lower or poor separation resolution
• Long analysis and run time