Gas Chromatography

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

The sample is transported by a stream of moving gas through a tube that contains 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 easiness, 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.

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 undo undesirable differences.

There are several routine analyses that are achieved quickly in environmental and other fields of the like. For example, there are several countries with certain monitor points that are used as a means of consistently measuring emission levels of gases such as carbon monoxide, carbon dioxide, and nitrogen dioxides. Additionally, 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, typically a gas that acts as a carrier gas such as argon or helium. Liquid samples are first vaporized before they are injected into the stream of carrier gases. Next, the gas stream transfers through the packed column that contains elements of the sample moving at speeds that are decided by the level of interaction between each constituent with the stationary nonvolatile phase. Those parts that have a bigger interaction with the stationary phase are delayed more and thus detach from those with a less prominent interaction. As these components begin to be wiped out of the column with a solvent, they can be numbered by a detector and/or kept for more analysis.

There are two main 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 takes place 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 vary 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 modify their transport 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 used and the parts that are being determined. Carrier gases used in chromatographs should be of the highest purity 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 prominent 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 utilized, 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 moved to the column from a separate injection chamber; this is called split-injection. This method 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 amounts could be found in the sample. In on-column injection, the liquid sample injected with a syringe straight 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 process called 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 technique known as loop-injection, and it is commonly 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. After that, the sample is transported 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 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 provide assistance in any areas you may need. For additional information, browse our online catalog or via email at info@cal-tool.com or at (951) 686-7822.