Gas Chromatography

Chromatography refers to a method used to detach chemical substances that depends on different partitioning actions between a stationary phase and a flowing mobile phase for detaching elements in a mix.

The sample is transported 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 critical techniques in chemistry because of its simplicity, highly effective nature, and sensitivity. It is most frequently used to perform qualitative and quantitative analysis of mixtures, to purify compounds, and to decide on certain thermochemical constants.

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

There are many routine analyses that are performed quickly in environmental and similar fields. For instance, there are several countries with certain monitor points that serve the purpose of consistently assessing 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 first vaporized prior to being injected into the stream of carrier gases. After this, the gas stream transfers through the packed column that contains elements of the sample moving at speeds that are determined by the level of interaction between each constituent with the stationary nonvolatile phase. Those pieces that have a more prominent interaction with the stationary phase are delayed more and thus divide from those with a less prominent interaction. As these components begin to be wiped out of the column with a solvent, they can be measeured by a detector and/or collected 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 relevant to the solid stationary phase, during which retention of analytes happens as a result of physical adsorption. Gas-liquid chromatography is often used when dividing ions that can be dissolved in a solvent. If it makes contact 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 changes give the mixture components the ability to separate from each other when they use these difference to alter their moving times of the solutes through a column.

Gas Chromatography with Carrier Gases

When choosing a carrier gas, the selection depends on the type of 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 ensure that there is no additional water or other impurities, the carrier gas system may have a molecular sieve.

The most prevalent injection systems used to introduce gas samples are the gas sampling valve and injection via syringe. Both liquid and gas samples have the ability to be injected with a syringe. When in its most simple form, the sample is at the start injected into and vaporized in a heated chamber, then transferred to the column. When packed columns are utilized, the first section of the column is typically utilized as an injection chamber and warmed to a proper temperature separately. With capillary columns a small componentvof the vaporized sample is transported to the column from a separate injection chamber; this is known as split-injection. This technique is employed when trying to keep the sample volume from overloading the column.

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

Finally, there is also a technique referred to as loop-injection, and it is commonly 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. Next, the sample is transferred from the loop to the column by the mobile phase, sometimes containing a concentration step.

 
Whether you’re looking for specialty gases to be employed in gas chromatography, or any other industry that utilizes specialty gases, PurityPlus has a plethora 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 assist you with any questions or needs. For further information, browse our online catalog or via email at jcmazoch@coastalws.com or at 800-852-4177.