INTEGRATED
COMPRESSOR
ZA2A
Zero Air, Nitrogen and Hydrogen for Gas Chromatography
What is Gas chromatography?
Gas chromatography (GC) is a widely used and very sensitive chemical method for separating and analysing the components of a gas mixture. It is particularly suitable for volatile samples that can be easily turned into gases and are stable when heated. Examples include residual solvent analysis, blood alcohols, metabolic fatty acids and the analysis of drug abuse.
How does it work?
Gas chromatography is based on a separation principle. The sample is injected into the injector of the gas chromatograph 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 inside of the column is coated with a substrate (the stationary phase) through which the gas (the mobile phase) containing the sample mixture is passed. As the mobile phase moves through the column, the components separate due to their different interactions with the stationary phase based on physical and chemical properties. As a result, different compounds move through the column at different velocities and allow the complete or partial separation of mixtures into the individual components.
The separated components then leave the column and pass through a detector that records the quantity of each component. This is done using suitable detection methods such as Flame Ionisation Detector (FID), Thermal Conductivity Detector (TCD) or Mass Spectrometry (GC-MS).
Which gases are used in gas chromatography?
High-purity operating gases and an appropriate gas supply system are important prerequisites for the trouble-free and reliable operation of the gas chromatograph. Different gases are used for this purpose:
As detector gas
The most common use of Zero Air in GC is to provide oxidant gas for detection. The most common Flame Ionization 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 general-purpose hydrocarbon detector, good performance depends on the absence of residual hydrocarbon 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.
As carrier gas
Nitrogen is often 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 difficult to obtain as a carrier gas in recent years, nitrogen is gaining in importance. Nitrogen is chemically inert, readily available, inexpensive and an ideal choice for general applications in gas chromatography.
As 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. The gas to be analysed flows through one cell, while pure gas flows continuously through the other measuring cell and is used for comparative measurement. If 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 added to the carrier gas, the thermal conductivity of the gas mixture changes in comparison to the pure carrier gas in the reference cell. This change generates a signal that is recorded.
As carrier gas
Hydrogen is another frequently used carrier gas. Hydrogen offers the advantage that it enables faster separations and therefore shorter analysis times due to its lower viscosity and higher diffusion coefficient compared to helium.
As detector gas
Flame Ionisation Detectors (FID detectors) require hydrogen as a fuel gas for the flame. The sample from the GC column is fed 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 that indicates the amount 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 measurement with the gas from the separation column. TCD is used to detect permanent gases and noble gases, also nitrogen, hydrogen, carbon and sulphur oxides can be detected.
Installation example
SUITABLE PRODUCTS
ZERO AIR GENERATORS
NITROGEN GENERATORS - PURITY UP TO 99.9995%
HYDROGEN GENERATORS
The benefits of Gas Generators in Analytical Chemistry
GC detectors require carrier and fuel gases. These gases can be supplied by a cylinder or alternatively from a gas generator.
The main advantages of gas generators over cylinders are:
- Long-term cost reduction given the relatively high demands for gases.
- Lower risk risks due to the delivery, handling and storage of high-pressure cylinders.
- Elimination of batch-to-batch reproducibility between different cylinders.
- No risk of cylinder running out during long or overnight analytical runs.
- Low maintenance and manual handling labour requirements.