H1- Gas chromatography – Introduction
Gas chromatography (GC) is a common type of chromatography used in analytical chemistry for separating and analysing compounds that canbe vaporized without decomposition. Typical uses of GC include testing the purity of a particular substance, or separating the different components of a mixture. In preparative chromatography, GC can be used to prepare pure compounds from a mixture.
Gas chromatography is also sometimes known as vapor-phase chromatography (VPC), or gas–liquid partition chromatography (GLPC). These alternative names, as well as their respective abbreviations, are frequently used in scientific literature.
Gas chromatography ( internal linking) (https://bhawins.com/analytical-analysis-services/)is the process of separating compounds in a mixture by injecting a gaseous or liquid sample into a mobile phase, typically called the carrier gas, and passing the gas through a stationary phase. The mobile phase is usually an inert gas or an unreactive gas such as helium, argon, nitrogen or hydrogen.] The stationary phase is a microscopic layer of viscous liquid on a surface of solid particles on an inert solid support inside a piece of glass or metal tubing called a column. The surface of the solid particles may also act as the stationary phase in some columns. The glass or metal column through which the gas phase passes is located in an oven where the temperature of the gas can be controlled and the eluent coming off the column is monitored by a computerized detector.
A gas chromatograph is made of a narrow tube, known as the column, through which the vaporized sample passes, carried along by a continuous flow of inert or nonreactive gas. Components of the sample pass through the column at different rates, depending on their chemical and physical properties and the resulting interactions with the column lining or filling, called the stationary phase. The column is typically enclosed within a temperature controlled oven. As the chemicals exit the end of the column, they are detected and identified electronically.
The invention of gas chromatography(https://bhawins.com/analytical-analysis-services/) is generally attributed to Anthony T. James and Archer J.P. Martin. Their gas chromatograph used partition chromatography as the separating principle, rather than adsorption chromatography. The popularity of gas chromatography quickly rose after the development of the flame ionization detector. Martin and another one of their colleagues, Richard Synge, with whom he shared the 1952 Nobel Prize in Chemistry, had noted in an earlier paperthat chromatography might also be used to separate gases. Synge pursued other work while Martin continued his work with James.
H2- Principles of Gas Chromatography
Gas Chromatography( https://bhawins.com/analytical-analysis-services/ ) or Gas Liquid Chromatography is a technique applied for separation, identification and quantification of components of a mixture of organic compounds by selective partitioning between the stationary phase and mobile phase inside a column followed by sequential elution of separated components. The technique is suitable for separation of compounds having following characteristics :
- High volatility
- Thermal stability
- Low molecular weights
Components in the mixture are distributed between two phases, one of which is a stationary phase, and the other is a mobile phase gas, or carrier gas, that carries the mixture through the stationary phase. Compounds in the mobile phase interact with the stationary phase as they pass through. Due to the differences in properties and structures of each component, the size and affinity of each interaction with the stationary phase are different. Therefore, under the same driving force, the retention time of different components differs in the column, thus moving out of the column in different orders.
H2- Advantages of gas chromatography
1) High separation efficiency and analysis speed: for example, gasoline samples can obtain more than 200 chromatographic peaks in 2 hrs. A general sample analysis can be completed in 20 minutes.
2) Small sample consumption and high detection sensitivity: 1 ml of gas sample consumption, 0.1 µl of liquid sample consumption, a few mg of solid sample consumption. Proper detectors can detect impurities in the tens to a few parts per million.
3) Gas chromatography has good selectivity and can be used to analyze azeotropic mixtures and samples with close boiling points. For example, some isotopes, cis-trans isomers, adjacent or intertrans isomers, optical isomers, etc.
4) Wide range of applications, although mainly used to analyze gases and volatile organic substances；under certain conditions, it can also be used to analyze high boiling point substances and solid samples.
Analytical chemists have many tools at their disposal to analyze a chemical compound and one of the techniques commonly used is gas chromatography (GC). This article will discuss the advantages of this analytical technique.
Although the technique does have some limitations, there are clear advantages to using gas chromatography compared to other chromatography techniques. These include:
- H3- Improved Resolution –Closely related peaks in the data can be resolved more easily with GC techniques than with other chromatographic methods such as thin-layer chromatography (TLC.) Parameters can be adjusted in real-time, meaning appearing peaks can be resolved better. GC is suitable for incredibly complex mixtures such as smoke which are almost impossible to resolve with TLC.
- H3- Improved analysis speed– Operational parameters can be easily changed (including during the experiment) meaning that analysis of a sample can be completed in the space of a few minutes. Optimum resolution can be achieved quickly with GC.
- H3- Wider sample choice– A wider choice of volatile samples can be analyzed with GC. The ability to control the temperature of the process allows for samples with high boiling points to be analyzed.
- H3- Fully quantitative– The software used in gas chromatography provides more accurate data than other techniques, making it a fully quantitative technique. TLC, for example, requires extra equipment such as densitometers or treatment steps, increasing the cost of any experiments.
- H3- More sensitive– Specialized detectors can detect target compounds at much lower limits than other techniques, meaning that gas chromatography has a high degree of sensitivity.
- H3- Nondestructive testing capabilities– Detectors used in gas chromatographers, such as flame photometric detectors and thermal conductivity detectors, are nondestructive. This makes GC a technique suitable for nondestructive testing of samples.
- H3- Column choice– Columns available for use in a gas chromatographer have a wide range of sizes, meaning that they can be used for a wide range of applications. GC experiments can also be carried out using different stationery and liquid support phases.
- H3- Software capabilities– GC has a range of improved software capabilities. Increased normalization, peak, and baseline optimization leads to improved real-time control and results reporting. This confers a distinct advantage upon gas chromatography compared to more traditional techniques as increased data analysis capabilities lead to better and improved results.
- H3- Column reuse– The columns used in gas chromatography experiments can be reused, significantly reducing the operational costs of experiments. However, they must be stored properly as per the manufacturer’s instructions.
- H3- Storage of results and records– In TLC, the solid plates can degrade over time, meaning that there is a finite shelf-life of results unless they are digitized. Data produced by the software in GC equipment, however, can be stored indefinitely.
H2- Gas Chromatograph (GC) Analysis
Bhawin’s Scientists uses Agilent 6890N series instruments for GC Analysis. GC analysis is commonly used to separate and analyze vaporized volatile compounds. This system uses inert gas to carry the sample through a capillary column, and then detects the retention time of different compounds in the column. Bhawin’s scientists often use gas chromatography to help in the identification of an unknown compound, or mixture of compounds. Bhawin’s Gas Chromatography capabilities include auto sampling, headspace analysis, pyrolysis analysis in conjunction with flame ionization detection (FID), thermal conductivity detection (TCD), mass spectrometry (MS) and a range of polar and nonpolar columns.
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