Gas chromatography

What is GC analysis used for?

Gas chromatography is an effective method for separating and calculating the yields of components in a volatile mixture. As GC is a highly reliable physical technique for quality control, it is commonly used in the pharmaceutical and petroleum industries. One example of the latter is using gas chromatography in CHN(O)S analysis of fuels.

Gas chromatography can be used to analyze fatty acids and essential oils, which are important in many industries. It is also an excellent technique for air quality analysis and for detecting environmental pollution, as GC analysis can easily identify the contents of an air sample. Other gas analyses (e.g. on fuel and process gases) can also be performed.

GC is also prevalent in its use in gas chromatography-mass spectrometry (GC-MS). This combined technique operates by passing a sample through the gas chromatograph before the separated components are ionized and analyzed by a mass spectrometer. GC-MS provides more information on the molecular weights of the constituents in the sample and can therefore add an extra dimension to the identification of unknown compounds.

How does gas chromatography work?

Gas chromatography is performed within a column that contains two distinct phases: one stationary, and one mobile. The stationary phase is usually comprised of a material like silica and lines the inside of the column tubing. The mobile phase is an inert, unreactive gas, which carries the sample through the column without reacting with it.

In GC analysis, the sample is initially injected into the column, where it is vaporized by heat. Then, the inert mobile phase will carry the vaporized sample through the length of the column. Different chemical components have different affinities for the stationary phase. Depending on this, they will either get swept through the column quickly by the carrier gas or slowly as they interact with the stationary phase. Components with a high affinity for the stationary phase will have a long retention time, whereas more volatile components will be carried through at a greater rate.

This effect causes different components in the sample to become distanced from each other, effectively separating them. As the individual components reach the end of the column, they are detected, and the data is recorded. Thus, gas chromatography provides insight into the presence and relative abundances of each component in a mixture.

GC vs HPLC - which method to choose?

High-performance liquid chromatography (HPLC) is an alternative technique to GC, based on similar, albeit slightly different, principles. Where GC uses an inert gas as a mobile phase, HPLC instead uses a variety of solvents. This means that the mixture to be separated will have more interaction with the mobile phase, making it more important for the separation process.

GC analysis is best suited for the separation of volatile compounds, which are either gaseous at room temperature or can be readily vaporized. This makes GC-based methods ideal for air quality analysis and VOC testing of construction materials, pharmaceuticals, consumer products, and environmental samples.

HPLC is instead used for the separation of components based on their polarity, meaning that it is more appropriate for inorganic ions and larger molecules, such as polymers and proteins, which are difficult to vaporize.

Sample requirements and preparation

Gas chromatography is suitable for samples that can be vaporized at a reasonable temperature. This means that the ideal sample is a mixture of volatile organic components that can be easily vaporized during the analysis. For involatile compounds, preparation can be performed using techniques such as pyrolysis (read more on our py-GC-MS analysis page).

Need a gas chromatography analysis?

Measurlabs offers high-quality gas chromatography testing services with fast results and affordable prices for large sample batches. If you have any questions about your sample or its suitability for the method, our experts are also always happy to help. You can contact us through the form below to request a quote, and we'll get back to you in one business day.