Operating gases for gas chromatography
Use of zero air, nitrogen and hydrogen
Different gases are used depending on the application and detector type. Nitrogen and hydrogen are frequently used as carrier gases, as they transport the sample through the separation column, thereby enabling separation. Zero air is primarily used as an oxidation or combustion gas, for example in flame ionisation detectors, and ensures stable, interference-free measurement results.
The combination of these gases enables reliable analysis as well as high sensitivity and accuracy across a wide range of applications.
What is gas chromatography?
Gas chromatography (GC) is a widely used and highly sensitive chemical method for separating and analysing the components of a gas mixture. It is particularly suitable for volatile samples that can be easily converted into gases and remain stable when heated. Examples include residual solvent analysis, blood alcohol levels, metabolic fatty acids and the analysis of drug abuse.
How does the method work?
Gas chromatography is based on a separation principle. The sample is injected into the gas chromatograph’s injector and vaporised. A carrier gas transports the vaporised sample through a column. This is a long, hollow, coated glass tube with a narrow internal diameter. The column is coated on the inside with a substrate (the stationary phase), through which the gas (the mobile phase) containing the sample mixture is passed. As the mobile phase travels through the column, the components separate on the basis of their differing interactions with the stationary phase, which are determined by their physical and chemical properties. As a result, different compounds move through the column at different speeds, enabling the complete or partial separation of mixtures into their individual components.The separated components then leave the column and pass through a detector, which measures the quantity of each component. This is achieved using suitable detection methods such as a flame ionisation detector (FID), a thermal conductivity detector (TCD) or mass spectrometry (GC-MS).
Which gases are used in gas chromatography?
High-purity process gases and a suitable gas supply system are essential for the trouble-free and reliable operation of the gas chromatograph. A variety of gases are used for this purpose:
The use of blank air in gas chromatography
As a detector gas
The most common use of zero air in GC is to provide an oxidising gas for detection. The most common flame ionisation detectors (FID) measure the electrical conductivity of a very clean hydrogen/zero-air flame to detect the presence of hydrocarbons in the sample. As a hydrocarbon detector, good performance depends on the absence of residual hydrocarbons from sources other than the sample, such as the burner air supply. For this reason, zero air is essential for sensitive and reproducible GC-FID analysis.
The use of hydrogen in gas chromatography
As a carrier gas
Hydrogen is another commonly used carrier gas. Hydrogen offers the advantage that, due to its lower viscosity and higher diffusion coefficient compared to helium, it enables faster separations and thus shorter analysis times.
As a detector gas
Flame ionisation detectors (FID detectors) require hydrogen as the fuel gas for the flame. The sample from the GC column is passed into a hydrogen/air flame. This ionises the organic compounds in the sample. The ions generate an electric current, which is measured and converted into a signal indicating the quantity of hydrocarbon-containing substances present in the sample. Hydrogen is also used in the thermal conductivity detector (TCD) as a pure carrier gas for comparative measurements with the gas from the separation column. The TCD is used, amongst other things, to detect permanent gases and noble gases, but nitrogen, hydrogen, carbon and sulphur oxides can also be detected.
The use of nitrogen in gas chromatography
As a carrier gas
Nitrogen is frequently used as a carrier gas as it does not react with the sample components. Carrier gases transport the sample through the GC column. As helium has become significantly more expensive and harder to obtain as a carrier gas in recent years, nitrogen is gaining in importance. Nitrogen is chemically inert, readily available, cost-effective and an ideal choice for general applications in gas chromatography.
As a detector gas
In the thermal conductivity detector (TCD), nitrogen is used as a pure carrier gas for comparative measurement with the gas from the separation column. In this process, the gas to be analysed flows through one cell, whilst the other measuring cell is continuously flushed with pure gas and serves as a reference for comparison. When pure carrier gas, such as nitrogen, flows through the measuring cell, the thermal conductivities in the measuring and reference cells are the same. However, if a sample component is mixed with the carrier gas, the thermal conductivity of the gas mixture changes compared with that of the pure carrier gas in the reference cell. This change generates a signal, which is recorded.
Reliable gas supply for GC
For precise GC analyses, it is not only the choice of the right process gas that is crucial, but also a reliable, continuous and high-purity gas supply. Many laboratories face the challenge of managing rising helium costs, cylinder changes, supply bottlenecks or safety requirements. Modern gas generators offer an efficient alternative to conventional gas cylinders and provide a stable supply of zero-air, nitrogen or hydrogen directly in the laboratory.
The advantages of gas generators in analytical chemistry
GC detectors require carrier and combustion gases. These can be supplied from a cylinder or, alternatively, from a gas generator.The main advantages of gas generators over cylinders are:
1. Long-term cost reduction due to the relatively high demand for gases
2. Reduced risk associated with the delivery, handling and storage of high-pressure cylinders
3. Elimination of batch-to-batch variability between different cylinders
4. No risk of the cylinder running out during long or overnight analysis runs
5. Minimal effort required for maintenance and manual handling.
Our solutions for gas chromatography
We offer gas generators that have been specially developed to meet the requirements of gas chromatography – for FID, TCD and as a carrier gas supply. They deliver high-purity gases of consistent quality, reduce operational costs and enhance safety in the laboratory.
Our product finder
Find exactly the right compressor for your needs in just a few steps. With our product finder , you can easily filter by power, application and other criteria – and receive a bespoke recommendation for your ideal product.
Go to the product finder
Do you have any questions or need assistance?
We’re here to help.
Use our contact form and our team will get back to you shortly.
