Gas chromatography (GC or GLC) is an analytical technique commonly used in many research and industrial laboratories for quality control as well as for 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 provided the compounds are sufficiently thermally stable and reasonably volatile. Say no to plagiarism. Get a tailor-made essay on "Why violent video games should not be banned"?Get the original essayGas-liquid chromatography requires a sample to be vaporized and then injected through a layer into a chromatographic column. The vaporized sample is returned to the column by a mobile phase. The mobile phase used in gas-liquid chromatography is an inert gas. While the column contains a stationary liquid phase which has been adsorbed on an inert solid surface. The mobile phase must be chemically inert so as not to react with the vaporized sample or other chemicals present. In capillary gas chromatography, capillary columns have a very small internal diameter. It is mainly a few tenths of a millimeter. Two types of capillary columns can be used. A wall-lined open tubular capillary column or a backing-lined open tubular capillary column. Coated wall columns are coated with the liquid stationary phase while in the carrier coated column the inner wall is covered with a thin layer of material which absorbs the liquid stationary phase. Both columns are more efficient than packed columns, but support-lined columns are less efficient than wall-lined columns. The steps in gas chromatography would be injection of the sample through a rubber septum and into a vaporization chamber where an inlet of carrier gas will flood the vaporization. chamber with the carrier gas. The chamber is surrounded by a heated metal block with two glass liners that direct the gas mixture toward the opening of the capillary column. The inert gas transports the vaporized sample through a capillary column whose inner wall is covered with stationary liquid phase. In the column, the temperature is managed to the nearest tenth of a degree. The optimum temperature for the column should be halfway between its upper and lower limit values ​​for the boiling point of the sample. If the boiling point of the sample varies too much for the column temperature to be managed manually, a computer program can be used to automatically make the necessary temperature changes. At this point the sample will have reached a detector. Initially, the retention time can be calculated, i.e. the time required for a sample to reach the detector from the injection point to the arrival point. Additionally, more detectors can be attached to the retention time detector, but there are many types of specialized detectors for different purposes. There are two categorizations for all detectors in gas chromatography. This is a mass flow dependent detector that will destroy the sample, but it determines the rate at which solute molecules enter the detector. The other would be concentration dependent detectors. Concentration-dependent detectors do not destroy the solute. HPLCHigh performance liquid chromatography is an improved version ofColumn chromatography which involves forcing the solvent via very high pressures up to 400 atmospheres through the column, making it much faster. Not only that, but it allows the column to have smaller particle size packing material to provide greater surface area for more interactions between the stationary phase and the molecules passing it. There are different 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 reversed phase high performance liquid chromatography.Normal phase HPLC is the standard HPLC used which is just a modified variant of column chromatography . Whereas 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 molecules moving through the column more quickly. On the other hand, due to Van Der Waal dispersion forces, nonpolar compounds present in the mixture will form attractions toward the hydrocarbon coating on the silica layer. Because of this attraction, nonpolar 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 injected automatically from a solvent tank. Several factors affect the retention time of a compound. It is the pressures used that determine the flow rate of the solvent, the material and particle size of the stationary phase coating within the column as well as the column temperature. The detectors that can be used remain the same as in gas chromatography. However, a combination can be used, for example a UV detector with a mass spectrometer. Once the UV detector recognizes the missing wavelengths of UV radiation absorbed by the solvent passing through the column, a peak is generated on the graph that depends on the absorbed wavelength. Once a peak has been recorded, a portion of the sample is automatically siphoned off and fed to a mass spectrometer where it will produce a fragmentation pattern and destroy the small sample that was siphoned off. Qualitative analysis involves identifying a component using 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 to the retention time of a so-called standard. It is a compound whose identity is known and which is likely to have the same identity as the unknown component. When the retention times of the two compounds are similar, the unknown is considered identified. If the analyte itself is not available as a pure substance, identification based solely on chromatographic results is not possible. The analyst must always be aware that the retention time depends not only on the component but also on the system (column, stationary phase, conditions and instrumental settings and performance). This means that a correct comparison is only possible when two chromatographic analyzes are performed under identical conditions on the same GC system. It is only in these circumstances that the differences in residence time due to the phase.