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Analytical chemistry has long been a mainstay in qualitative chemistry circles where the use of separation science is widely applied. This segment of qualitative chemistry and analytical chemistry gas chromatography (GC) has long been used whenever there is need to separate and purify certain substances that do not decompose whenever vaporization is used as a means of separation. The technique is efficient in analysis of compounds through determining purity of substances and classifying components in a mixture into its separate entities. It can also be used in making an analysis in environmental pollutants (Blumberg 2010, p.122). This ensures that whatever a particular mixture is comprised of can be analysed to the extent of identifying the pure compound from a cluster of environmentally harmful substances. This is done through a complex set up that consists of a moving and stationary phase which makes up the gas chromatograph.
In the moving phase, an inert gas is used to act as a carrier and most suitably a less reactive gas can be used. On the other hand, the stationary phase comprises of a liquid that is placed in glass which provides inert conditions and forms tubing that can now act as a fractionating column to bring about gas separation (Larsen 1996, p.47). Upon placing gaseous compounds into the gas chromatograph, the stationary phases act as holding points for the various segments of the compound that need to be separated. Thus, it stipulates the significance of gas chromatography which uses different stationary phases to create different retention durations for those components that need to be separated. In the long run this can be used in the environment to rid it of trace compounds that act as pollutants. The most significant technique used is GC-mass spectroscopy which can perform analysis and still give a quantitative report of the substances especially if the analysis is done on to detect trace organic compounds.
Gas chromatography can be used in various points within the industrial setting especially when the industrial waste is toxic to the environment. Thus, as a starting point we look at a few ways in which the environment can be exposed to pollution and still use certain Gas Chromatography techniques to rid it of these toxins. Therefore, we are going to look at the two examples that can bring about environmental pollution and the gas chromatography technique that is employed (Kolb 2006, p. 20). For instance, in the pulp paper mills a system for purification and separation of toxic substances has to be done to bring about the environmental balance that is required. This means that the effluent that emanates from the mill has to undergo purification stages that employ the gas chromatography technique through the PCP-degrading bacterial strains. In such cases there is reduction of colour, BOD, PCP, lignin, phenol and COD through a well modulated mixed culture treatment hence bringing about the overall reduction in the toxicity of the effluent.
Again, organic trace compound that requires the GC technique to bring about reduction in environmental pollution is the analysis in toxaphene in the great lakes fish. This requires the use of GC-EI/MS/MS (gas Chromatography electron ionization tandem mass spectrometry) and GC-ECNI-MS (gas chromatography electron capture negative ionization Mass spectrometry) as comparison techniques that bring out the platform for toxaphene quantification. Toxaphene is a stubborn pollutant in its nature as being an organochlorin and it is evidenced as bioaccumulation in aquatic environments. The use of toxaphene as a pesticide has not been well received but has been consistently used for quite a while. Its use of chlorinated bornanes and bornenes makes it quite volatile hence capable of being transported to areas far away from the point of application (Holsen 2009, p.461). This increases chances of having pollution all over including in fish, air, water and sediment in great lakes regions where it is used. Its elimination from the environment should be prompt as its continual presence can be carcinogen. Thus, the two techniques mentioned above in GC have been efficiently used to detect the presence and quantity of toxaphene in the environment to bring about sobriety in its usage as a pesticide.
3.2 Headspace-Gas Chromatography (HS-GC) and the Programmed Temperature Vaporizer
This technique is used in an analysis of chlorophenols in water whereby the temperature vaporizer is used to bring about sensitivity of the technique. This is used in tandem with an in situ derivatization reaction to bring about seamless use of the headspace sampler results. This application can be quite efficient in the detection of sparingly volatile substances in order to make the result accurate (Pavon et al 2009, p.1195). Moreover, Headspace sampling can be quite helpful in the minimization of sample treatment hence reducing any analytical problems. In order to make detection more sufficient it is necessary to use other techniques in the pre-concentration stage before the chromatographic system receives the sample. The stipulated techniques are solid-phase microextraction and headspace single-drop microextration which allow transfer of the extraction medium from the vial to the injector. The derivatization reaction in this technique is important because it increases the viability of the HS sampling technique owing to the fact that compounds that could otherwise be less volatile might not be efficiently analysed.
Through the use of experimental samples and standard solutions such as 2-chlorophenol, 2, 4-dichlophenol, 4-chloro-3-methylphenol and 2, 4, 6-trichlorophenol put in water from various places, the technique was demonstrated to show its large application viability. For the derivatization reaction process NaCl was systematically added into the HS sampler vial with other reagents of 0.4 potassium hydrogen carbonate, 50 ÂµL of methanol containing the sample analytes culminating in the use of 100 ÂµL acetic anhydride. This preparation was done in order to show a typical analysis process that is required when using a headspace sampler. The configuration in the instruments requires on-line measurement of the analyte with no other steps such as in the SPME and SBSE modes. However as a result of the degradation of derivatized chlorophenols, it is important that a suitable liner be used. When all these conditions have been fulfilled to the letter the technique is known to work satisfactorily.
Chromatography requires that there exist an extra pre-concentration phase so that there is ease when introducing an individual sample. The temperatures in the gas columns should also be stabilized in order to preserve the separation. The use of a programmed temperature vaporizer is important as it increases the sensitivity in analysing the chlorophenols in water sample. In addition, there is an introduction of rapid temperatures in the water that will allow the sediments to be added faster into the GC column. Through this it is possible to eliminate the volatile substances that produce saturation and consequently overload the GC column. Such overloading reduces the chances of the inlet in the GC column from admitting any additional analytes thus slowing down the entire process. The addition of an instrumental configuration like the temperature vaporizer allows the degradation of the derivatized chronophenols so that they are able to float on the surface of the adsorbent. This kind of high sensitivity can only be realized if there is an accurate and pre-determined method as mentioned above.
3.3 Enantioselective Chromatography GC of Chiral Environmental Pollutants
The use of enantioselective chromatographic techniques follows the possibility of having organic pollutants in the environment to form various conformations. Therefore the use of chromatograms follows the principle of chirality through various methods such as HPLC, multidimensional GC, high-resolutions GC and CE. This makes separation of biotic and abiotic substances quite easy and can be significant in transformation processes that help in elimination of pollutants from the sea and air (Shah 2009, p.493). The stationary phases are made to be achiral when the capillary gas chromatography technique is used. This ensures that the chiral environment that is present in the active sites selects matching chirality in the racemic mixture leading to diastereomeric complexes formation inactive sites of the enzymes, their chiral xenobiotics and their metabolites. There are important considerations that should be done as pertains to the enantioselective separations. These considerations are in a manner in which the separation can be done through diastereomeric derivatives and the use of chiral stationary phases.
The use of diastereomeric derivatives are first formed through chiral compounds reacting with chiral reagents. The separation procedure is done on a stationary phase that is not required to be set as chiral. This procedure brings in the advantage that the separation exercise can be done by using any chromatographic system but still provide the selectivity that is required. This means that at least providing a functional group will give the reaction the direction from which to pick the process of separation. Though a proven method in separation, reduction and identifying environmental pollutants, it can be prone to systematic errors or even diastereomeric errors that arise as a result of derivation of differences in the energy of the transition states. On the other hand, using the chiral stationary phases which incorporates direct enantiomer separation can reduce energy differentiation. Thus, enantioselective chromatography as a GC technique can be quite helpful in making substantial separation of pollutants that are organic in nature.
3.4 GC-MS Method using Isotope-Labelled Standards for testing environmental pollutants in aqueous environment
For the environmental organic trace detection, the gas chromatography- mass spectroscopy method has a significant role to play in separation science but not without problems. For instance, in the use of MS-detector isotope labelled standards, it becomes quite uncertain in obtaining accurate results. This could be as a result of calibration problems in the GS-MS system, the amount of internal standard and the addition technique used. Therefore determination of PAHs in sediments is done by obtaining the relevant ratios of individual compounds and analysing how they differ internally. This is then compared to the internal standard which is obtained by adding either of the samples to 0.1ml to 1m of the organic solvent. The range of using the organic solvent is determined by how complex the sample is especially when dealing with environmental analyses where there exist many compounds in a specific sample (Renes et al 2019, p.193). The method is very vital in circumstances where there is need to evaluate and analyse polycyclic aromatic hydrocarbons. In order to be successful, the analytes must be i a position to dissolve in the aqueous phase but still have some suspended particles. Again, there should be a number of organs and tissues from living organisms in those sediments.
In the calibration of GC-MS system, the compounds compounds must be analysed individually then compared to the deuterated internal standard. This means that the internal solution will; be injected several times into the individual sediment samples to ease comparison with the standard sample. If the analysis was successful, then the concentration levels of the deuterated samples in the environmental extract should be almost the same as those in the pre-determined PAHs. In this method the technique of adding the internal standard solution is not very influential to the eventual result but the amount added is very vital. Moreover, the best results while using this method of gas chromatography is to ensure that for every 100ng of the analyte or sediment 1ml of acetone is used to wet it. Thus, the method is very effective in the samples that exist in aqueous environment but sometimes when analysing the environmental pollutants problems may still be in existence. The mass spectrometer has a lower response coefficient for the deuterated PAHs than in non-deuterated ones. This brings a problem in the creation of differences in the ionization potential of the samples hence false determination results. Again, there are complications as pertains to the technique of internal addition of the standard solution in that it needs to be very accurate. If the solution is added in wrong measurements to the analyte, the final result may not be as accurate as intended. Despite the flaws mentioned, the method is very important in analysing environmental pollutants in water. The key points to establishing brilliant results lie in the fact that there should be proper internal solution addition, acetone solvent and continuous stirring to create identical binding between the solution added and the matter obtained from the analyte.
3.5 Screening of persistent organohalogenated pollutants in environmental samples
This is done by the use of a comprehensive two-dimensional gas chromatograph that has two GC columns and a modulator. The modulator is used to transfer all the effluents in the initial column to the second one without any lag. There should be hot and cold temperatures set in the right proximities in the columns to avoid mix up of the sediments after separation. The method is very effective in testing for environmental pollutants that may exist in food flavours, fragrances and oils (Ramos 2010, p.193). This is because it has a high peak capacity and superior separation capability that reduces the sediments into various components that can be duly analysed. It can also be used to test for the effects of biogenic substances that exist in any kind of food substances. However, for best results it is important to allow the analytes to be pre-treated in order to ensure that there is faster exhaustive extraction. When testing for such organohalogenated pollutants it is important to be keen in the GC stationary phases as they promote faster degradation of the compounds more than the glycol-type phases.
3.6 Reducing pollutants in pulp and paper mills through gas chromatography
Pulp and paper mills use large amounts of lignocellulosic components during manufacturing that pollute the environment. The pulp effluents are comprised of complex mixtures that have multiple compounds (Chandra 2009, p.9). There are also bacterial strains that exist and can be used to treat the pulp and paper to reduce the pollutants. Gas chromatography helps in the identification ad evaluation of metabolic products that are derived after the bacteria have been degraded. These products help in decolorizing the pulp within the permissible limit thus reduce the contamination through bio-treatment.
The future of gas chromatography lies in a manner in which the process of detection and separation can be done with much ease assuming a reduction in intermediary processes. This means that ensuring the process can be carried out by anyone without posing any much problems or errors in the result. The process of simplifying the collection of data has really made tremendous improvement with the shift of the systems from analogue to digital allowing even non-specialists to use them in routine work. For instance, it is clear that in the use of Headspace-Gas Chromatography (HS-GC) in separation, a lot of steps and reagents are required to bring about the end result which a regular person cannot be able operate. If this is done away with as stipulated by scientists in the separation science field, then it will reduce the cost that sometimes is insurmountable and improve efficiency whilst reducing errors in gas chromatography techniques (Mills 2002, p.20).
The future will thus incorporate an independent channel in each step of analysis that is digitised to collect data instantaneously. This means that everything from the injector temperature, volume of the sample, column temperature and detector sensitivity need not require a trained technician as the entire system balances itself to achieve the result. The future of GC separation should therefore look into maximizing the outcome at every stage such as column selectivity and efficiency, sample introduction as pure or impure and the required volumes, detector volume and overall functioning of the column. Finally, efficiency should be increased as pertains to how it does its selection.