Gas Chromatography

Chromatography is a method employed to detach chemical substances and is dependent on different partitioning behaviors between a stationary phase and a flowing mobile phase for detaching elements in a mix.

The sample is moved by a stream of moving gas through a tube that holds evenly separated solid, or could be coated with a liquid film. Gas chromatography is one of the most important resources in chemistry because of its simplicity, highly effective nature, and sensitivity. It is most often employed to perform qualitative and quantitative analysis of mixtures, to purify compounds, and to decide on certain thermochemical constants.

Gas chromatography is also widely employed in the automatic monitoring of industrial processes. Take, for example, gas streams that are frequently analyzed and adjusted with manual or automatic responses to counteract undesirable differences.

There are a number of routine analyses that are conducted quickly in environmental and related fields. For instance, there are several countries with certain monitor points that exist as a way of constantly measuring emission levels of gases such as carbon monoxide, carbon dioxide, and nitrogen dioxides. Additionally, gas chromatography can be employed in analyzing pharmaceutical products.

The technique for gas chromatography launches with introducing the test mixture into a stream of inert gas, most often a gas that acts as a carrier gas such as argon or helium. Liquid samples are in the beginning vaporized before they are injected into the stream of carrier gases. Next, the gas stream moves through the packed column that contains elements of the sample moving at speeds that are based on the level of interaction between each constituent with the stationary nonvolatile phase. Those components that have a more significant interaction with the stationary phase are delayed more and thus separate from those with a lesser interaction. As these components begin to be washed out of the column with a solvent, they can be numbered by a detector and/or kept for additional analysis.

There are two prevalent types of gas chromatography: gas-solid chromatography (GSC) and gas-liquid chromatography (GLC). The first, gas-solid chromatography, is dependent on the solid stationary phase, during which retention of analytes takes place as a result of physical adsorption. Gas-liquid chromatography is often employed when dividing ions that can be dissolved in a solvent. If it crosses paths with a second solid or liquid phase, the different solutes in the sample solution will interact with the other phase to certain degrees that can change based on differences in adsorption, exchange of ions, partitioning or size. These differences give the mixture components the ability to divide from each other when they use these difference to change their moving times of the solutes through a column.

Gas Chromatography with Carrier Gases

When selecting a carrier gas, the selection depends on the nature of the detector being used and the components that are being determined. Carrier gases used in chromatographs should be highly pure and chemically inert towards the sample. To successfully get rid of water or other impurities, the carrier gas system may have a molecular sieve.

The most widely used injection systems used to introduce gas samples are the gas sampling valve and injection via syringe. Both liquid and gas samples can be injected with a syringe. When in its most simple form, the sample is initially injected into and vaporized in a heated chamber, then transferred to the column. When packed columns are employed, the first section of the column is usually used as an injection chamber and warmed to a proper temperature separately. With capillary columns a small sectionvof the vaporized sample is transferred to the column from a separate injection chamber; this is known as split-injection. This method is utilized when attempting to keep the sample volume from overloading the column.

A process called on-column injection can be utilized for capillary gas chromatography when trace components could be found in the sample. In on-column injection, the liquid sample injected with a syringe immediately into the column. After this, the solvent can evaporate and a concentration of the sample components occurs. In gas samples, the concentration is created by a technique referred to as cryo focusing. In this process, the sample components are concentrated and detached from the matrix by condensation in a cold-trap prior to the chromatography process.

To conclude, there is also a method called loop-injection, and it is often used in process control where liquid or gas samples flow constantly through the sample loop. The sample loop is filled with a syringe or an automatic pump in an off-line position. After that, the sample is moved from the loop to the column by the mobile phase, sometimes having a concentration step.

 
Whether you’re looking for specialty gases to be used in gas chromatography, or any other industry that utilizes specialty gases, PurityPlus has a wide variety of specialty gas products to meet your need. We have a large selection of specialty gases and specialty gas equipment, along with the resources and experts on hand to answer your questions and assist your needs. For more information, browse our online catalog or via email at info@westairgases.com or at 866-WESTAIR.