Gas Chromatography

Chromatography refers to a method used to separate chemical substances and varies based on different partitioning actions between a stationary phase and a flowing mobile phase for separating elements in a mix.

The sample is transferred 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 significant techniques in chemistry because of its simplicity, highly effective nature, and sensitivity. It is most frequently used to conduct qualitative and quantitative analysis of mixtures, to purify compounds, and to determine certain thermochemical constants.

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

There are several routine analyses that are achieved quickly in environmental and other fields of the like. As an example, there exist many countries with certain monitor points that exist as a way of consistently assessing emission levels of gases such as carbon monoxide, carbon dioxide, and nitrogen dioxides. In addition, gas chromatography can be utilized in analyzing pharmaceutical products.

The technique for gas chromatography launches with introducing the test mixture into a stream of inert gas, usually a gas that works as a carrier gas such as argon or helium. Samples that are in the liquid state are first vaporized before being injected into the stream of carrier gases. After this, the gas stream passes 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 slowed more and thus separate from those with a lesser interaction. As these components begin to be eliminated 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 dependent on the solid stationary phase, during which retention of analytes happens as a result of physical adsorption. Gas-liquid chromatography is often used when detaching 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 are different 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 modify their transit times of the solutes through a column.

Gas Chromatography with Carrier Gases

When deciding upon a carrier gas, the selection depends on the nature of the detector being utilized and the parts that are being determined. Carrier gases used in chromatographs should be high-purity 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 are able 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 transported to the column. When packed columns are employed, the first section of the column is most often employed 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 technique is employed when trying to keep the sample volume from overloading the column.

A method called on-column injection can be utilized for capillary gas chromatography when trace measures could be found in the sample. In on-column injection, the liquid sample injected with a syringe directly into the column. After this, the solvent has the ability to evaporate and a concentration of the sample components occurs. In gas samples, the concentration is created by a process known 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.

Finally, there is also a method called loop-injection, and it is typically used in process control where liquid or gas samples flow consistently 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 transported from the loop to the column by the mobile phase, sometimes including a concentration step.

Whether you’re looking for specialty gases to be utilized 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 or at (518) 465-5229.