Gas chromatography is the process whereby the various elements of a compound are separated into their distinct parts for individual analysis. It was inverted by Martin and James in 1952, and it has become one the most important and applied analytical technique in modern chemistry (reference). The GC the analytical technique that helps to separate and analyse volatile substance in the gas phase and it distribute the sample between stationary and mobile phase. The stationary phase is either a solid termed gas-solid chromatography or liquid termed gas-liquid chromatography, the mobile phase does not utilised by gas chromatography for interacting with the analyte (reference). A Gas chromatography is also another useful method which can determine the components of a given mixture using the retention times and the abundance of the samples. The retention time is the time which it takes for an element to release the solvent, and the process normally occurs when a liquid stationary element is transformed into a gaseous mobile element.
The combination of gas chromatography and mass spectrometry is an invaluable tool in the identification of molecules which known as GC-MS and is typical consist of an injection port, a column, carrier gas flow control equipment, ovens and heater for maintaining temperatures of the injection port and the column, an integrator chart recorder and a detector (reference).It is widely used for quantitative and qualitative analysis of mixtures, for the purification of Compounds, and for the determination of such thermo chemical constants as heats of solution and vaporization, vapor pressure, and activity coefficients.
In this essay the applications of gas chromatography will be explained in six industries, forensic, pharmaceutical, food, mining medical and petrochemical industry.
APPLICATION OF GAS CHROMATOGRAPHY
1. Forensic Pathology
The process has a wide variety of uses, which are discussed in more detail, but one of is most important and widely-recognised application is in the field of forensic science. The various ways in which gas chromatography is used in forensics are outlined below.
Since gas chromatography is useful in identifying the individual elements and molecules present in a compound, it has been applied in forensic pathology to determine which fluids and compounds are present inside a human body after death. This is vital in determining whether or the person was intoxicated either from alcohol or drug abuse at the time of death, or indeed whether there is any poison or other harmful substance present in their body. Of course, this is imperative knowledge to determining cause of death and possible motive and culprit in the case of foul play. For trace evidence, the ability to get the most information from the smallest sample provided, while preserving the maximum amount for tests, is critical in delivering results to solve crimes. Gas chromatography is an important technique in detection and identification of both bulk drugs and trace level drugs in biological samples.
Gas chromatography can also be used to test samples found at a crime scene, whether these be blood samples or fibre samples from clothing or other materials. This allows scientists to pinpoint exactly what happened and who was present at the scene of the crime, and it may even allow them to develop theories on where the suspect or victim had been before, depending on the variety of material found. The GC-MS is incredibly useful, since it can accurately identify substances with no error margin which in court is understandably imperative. It also used in other application such as quantification of the drug in biological samples, identification of anabolic steroids in serum, urine, sweat and hair, forensic analysis of textile dyes and determination of cocaine and metabolites in blood and also in quantification of the drug in biological samples.
The gas chromatography also is very important in arson investigation in forensic science because fires are the often started using a cocktail of hundreds of different compounds and components. In terms of strength and concentration it can be hard to determine what exactly cause the fire since many compounds are dissolved during the fire, changing the makeup of the original incendiary. With the use of gas chromatography, a selection of flammable liquids can be tested and more details and accurate results can be provided.
In the pharmaceutical industry, GC-MS is used in research and development, production and quality control. It is used in identification of impurities in active pharmaceutical ingredients.
The major success of the application of GC in pharmaceutical quantitative analysis is firstly due to the very high efficiencies of separation power, secondly to the extreme sensitivity of the detection of even very small amounts of separated species and finally to the precision and accuracy of the data from quantitative analyses of very complex mixtures. The pharmaceutical involve two steps, separation of the compound of interest and quantitation of the compounds. The GC detector have different responses to each compound. In order to determine quantitative amounts of various compounds in a separation the detector must be calibrated using standards. The detector response recorded as the standard solution of the sample injected, the comparison of the standard and sample retention time allow qualitative analysis of the sample and the comparison of the peak area of the standard with that of the sample allow quantitation of analyte.
The GC mostly used in pharmaceutical for determination of organic volatile impurities and Nicotine level during drugs formation. For an example, the organic volatile impurities are risk of quantity and stability of drug products, as well as human body. The gas chromatography used to monitor the volatile impurities using flame ionisation detector.
3. Environmental Industry
The GC-MS used to monitor environmental pollutants. It is widely used in the detection of dibenzofuras, dioxins, herbicides, sulphur, pesticides, phenols, and chlorophenols in air, soil and water.
The air samples can be analysed using GC, and most of the time , air quantity control units use GC coupled with Flame Ionisation Detector in order to determine the components of a given air samples . The FID is the most appropriate although other detectors can be useful as well, because of it sensitivity and resolution and also because it can detect very small molecules as well.
The Gas Chromatography used to monitor the environment, by helping to keep the food, air and water clean.
Also the GC used to analyse the pesticide residues, but some types including polar pesticides
4. PETROCHEMICAL INDUSTRY
The petrochemical are chemical products derived from petroleum. The gas chromatography is a core analytical technique in petrochemical sector, primary used to analyse the process stream components in fuel production but also to detect trace impurities that can impact the production process and final product.
The gas chromatography used in petrochemical industry to controlling the production of saturated hydrocarbons, olefins and light diolefins.
5. FOOD INDUSTRY
The gas chromatography is used in various application involving the qualitative and quantitative analyses of foods for several decades, in order to improve the food safety and quality. It is capable of separating and determination of trace level, thermal stable, volatile organic analytes in complex food matrices. A volatile substance is the one that passes into a gas phase, normally liquids or solids with low boiling and melting points.
The food are analysed by GC in order to determine nutritional and palatability need, check food adulteration, engineer novel food or meet process control , quality assurance, food labelling and other requirements (reference). The food constituents are primarily water, lipids, proteins, carbohydrates, vitamins and minerals, and components such as fatty acids, sterols, alcohols, aroma components.
The GC used for health checks for toxins, for example the pesticides residue in fruit and vegetables, it is used to check that the levels of pesticide are below limits and it control additives in food.
For example, determining the fatty acid content of triglycerides is an important use of GC-MS but they are not volatile enough to pass the column. The triglycerides split into fatty acids and then the fatty acid converted into methyl esters of fatty acids which are easily separated from glycerol by dissolving them in a solvent. Then it can be injected directly to the chromatography, and are easily separated and detected. The GC will determine the percentage of saturated fatty acid and trans-fatty acid in margarines, oils, spreads. It will also determines the percentage of essential fatty acids in triglycerides consumed by population and whether the average diet contains sufficient fatty acid for good health.
6. MEDICAL INDUSTRY
The GC-MS is used in screening tests for the detection of several congenital metabolic disease. It detects trace levels of compounds present in the urine of patients with genetic metabolic disorders.
Many of congenital metabolic disease called as inborn error of metabolism are now detectable in new born by screening tests using GC. The GC-MS determine the compounds in urine even in minor concentration. These compounds are normal not present but appear in individual suffering from metabolic disorders. It is effective and efficient way to diagnose the problem like in case of genetic metabolic disorders by urine test at birth. In combination with isotopic labelling of metabolite, the GC-MS is used for determining metabolic activity. Most applications are based on the use of 13C labelling and the measurement of 13C – 12C ratios with an isotope ration mass spectrometer, mass spectrometer with a detector designed to measure a few selections and return values as ratios. It is also useful to detect the presence of oils in ointments, creams, and lotions.