Gas chromatography (GC or GLC) is an analytical technique commonly used in many industrial and research laboratories for quality control as well as identification and quantification of compounds in a mixture. GC is also a frequently used technique in many environmental and forensic laboratories because it allows the detection of very small quantities. A wide variety of samples can be analyzed as long as the compounds are sufficiently thermally stable and reasonably volatile. Say no to plagiarism. Get a tailor-made essay on "Why Violent Video Games Shouldn't Be Banned"? Get an Original Assay Gas-liquid chromatography requires a sample to be vaporized and then injected through a layer into a chromatography column. The vaporized sample is moved along the column by a mobile phase. The mobile phase used in gas-liquid chromatography is an inert gas. Instead, the column contains a liquid stationary phase that has been adsorbed onto an inert solid surface. The mobile phase must be chemically inert so that it does not react with the vaporized sample or other chemicals present. In capillary gas chromatography the capillary columns have a very small internal diameter. It is mainly a few tenths of a millimetre. Two types of capillary columns can be used. An open tubular capillary column coated with wall or an open tubular capillary column coated with support. Wall-coated columns are coated with the liquid stationary phase while in the support-coated column the inner wall is coated with a thin layer of material that absorbs the liquid stationary phase. Both columns are more efficient than packed columns, however support-lined columns are less efficient than wall-lined columns. The steps of gas chromatography would be to inject the sample through a rubber septum and into a vaporization chamber where a carrier gas inlet will flood the vaporization chamber with carrier gas. The chamber is surrounded by a heated metal block with two glass liners that direct the gas mixture towards the opening of the capillary column. The inert gas transports the vaporized sample through a capillary column whose internal wall is covered by the liquid stationary phase. In the column the temperature is managed within tenths of a degree. The optimum temperature for the column should be midway between the upper limit and lower limit values ​​for the boiling point of the sample. If the boiling point of the sample varies too much for you to manually manage the column temperature, a computer program can be used to automatically make the necessary temperature changes. At this point the sample will have reached a detector. Initially it is possible to calculate the retention time, i.e. the time taken for a sample to reach the detector from the injection point to the arrival point. It is also possible to connect multiple detectors to the retention time detector, however there are many types of detectors specialized for different purposes. There are two categorizations for all detectors in gas chromatography. These are: Mass flow dependent detector which will destroy the sample but determines the rate at which solute molecules enter the detector. The others would be concentration-dependent detectors. Concentration-dependent detectors do not destroy the solute. HPLCHigh performance liquid chromatography is an improved version of column chromatography that revolves around forcing the solvent through very high pressures of up to 400 atmospheres through the column, making it much faster. Not only that, butallows the column to have smaller particle size packing material to provide greater surface area for greater interactions between the stationary phase and molecules moving beyond. There are several types of high-performance liquid chromatography that can be used, depending on the polarity of the solvent and the stationary phase. These are normal-phase high-performance liquid chromatography and reverse-phase high-performance liquid chromatography. Normal phase HPLC is the standard textbook HPLC used, which is just a modified variant of column chromatography. While reversed phase HPLC has the silica coating modified to be non-polar. This is done by attaching long chains of hydrocarbons to the surface. A polar solvent is then used. This means that fewer molecules will be attracted to the coating, resulting in more molecules progressing through the column faster. On the other hand, due to Van Der Waal dispersion forces, the non-polar compounds in the mixture will form attractions towards the hydrocarbon coating on the silica layer. Because of this attraction the non-polar compounds spend more time being attracted to the hydrocarbons and less time progressing through the column. Due to the 400 atmospheres of pressure, the sample will be automatically injected from a solvent tank. There are several factors that influence the retention time of a compound. These are the pressures used that determine the solvent flow rate, the material and particle size of the stationary phase coating within the column, and the column temperature. The usable detectors remain the same as for gas chromatography. However it is possible to use a combination, for example, from a UV detector to a mass spectrometer. Once the UV detector has recognized the missing wavelengths of UV radiation that has been absorbed by the solvent passing through the column, a peak is generated on the graph that depends on the absorbed wavelength. Once a peak is recorded, a portion of the sample is automatically siphoned and funneled into a mass spectrometer where it will produce a fragmentation pattern and destroy the small sample that was siphoned. A qualitative analysis involves the identification of a component using the peak data on the chromatogram. The retention of a component is the result of a specific interaction of that component with the stationary phase and the mobile phase. Since retention time is a specific property of a component, it can be used as a means of identifying the component. The retention time of the unknown component is compared with the retention time of a so-called standard. It is a compound whose identity is known and which probably has the same identity as the unknown component. When the retention times of both compounds are similar, the unknown is considered identified. If the analyte itself is not available as a pure substance, identification based on chromatographic results alone is not possible. The analyst must always keep in mind that the retention time depends not only on the component but also on the system (column, stationary phase, conditions and settings and instrumental performance). This means that a correct comparison is only possible when two chromatographic analyzes are performed under identical conditions on the same GC system. Only under these circumstances can differences in retention times due to stationary phase, mobile phase, flow, column length, column temperature etc. be ignored. System validation can demonstrate the performance and stability of the instrument,.