Gas Chromatography

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

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

Likewise, gas chromatography is 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 cancel out undesirable differences.

There are a number of routine analyses that are achieved quickly in environmental and similar fields. As an example, there are several countries with certain monitor points that are used as a means of continuously measuring emission levels of gases such as carbon monoxide, carbon dioxide, and nitrogen dioxides. In addition, gas chromatography can be employed in analyzing pharmaceutical products.

The technique for gas chromatography begins with introducing the test mixture into a stream of inert gas, typically a gas that serves as a carrier gas such as argon or helium. Samples in liquid form are first vaporized prior to being 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 pieces that have a more significant interaction with the stationary phase are restricted more and thus separate from those with a lesser interaction. As these components begin to be wiped out of the column with a solvent, they can be numbered by a detector and/or collected for further analysis.

There are two prominent types of gas chromatography: gas-solid chromatography (GSC) and gas-liquid chromatography (GLC). The first, gas-solid chromatography, is centered around the solid stationary phase, during which retention of analytes occurs as a result of physical adsorption. Gas-liquid chromatography is often employed when detaching ions that can be dissolved in a solvent. If it comes into 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 differences 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 employed and the elements that are being determined. Carrier gases used in chromatographs should be of the highest purity and chemically inert towards the sample. In order to eliminate 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 first injected into and vaporized in a heated chamber, then transported 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 portionvof the vaporized sample is transported to the column from a separate injection chamber; this is known as split-injection. This method is used when hoping to keep the sample volume from overloading the column.

A method called on-column injection can be employed for capillary gas chromatography when trace measures 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 made by a process known as cryo focusing. In this process, the sample components are concentrated and separated 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 continuously 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 moved from the loop to the column by the mobile phase, sometimes containing a concentration step.

 
Whether you’re looking for specialty gases to be used in gas chromatography, or any other industry that uses 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 answer your questions and assist your needs. For more information, browse our online catalog or via email at starrant@weldstar.com or at 855-998-4875.