Analysis methods and errors for removing trace amounts of benzene, naphthalene, and tar from coke oven gas

II. Methods to Reduce Errors in Gas Chromatography Analysis Appropriate methods can be adopted to reduce errors based on their causes, and these causes can be identified by examining the analysis process; therefore, we can choose suitable measures at each stage of the operation to minimize errors. 　　1. Carrier gas The carrier gas is used in the first step of analysis, and the purity of the gas affects the sensitivity of the chromatograph; therefore, its purity is required to be over 99.999%. Impurities in the gas generate baseline noise and spurious peaks ； Particulate impurities in the gas can cause the gas path control system to fail, leading to errors in the analysis results. Therefore, in gas chromatography analysis, it is first necessary to ensure the purity of the gas, which must be strictly purified before it can be used. 　　2 Injection port The function of the injection port is to introduce the sample accurately into the chromatography system. It is necessary that no chemical changes occur to the sample during the vaporization process, so as to ensure the accuracy of the analysis results. The sample is affected by various factors during vaporization; primarily, the performance of the gaskets, seals, and lining tubes has an impact on the vaporization of the sample. 　　First, the gasket is used to prevent external gases from penetrating and contaminating the system; it effectively separates the sample flow from outside air. If the quality of the spacer is poor, ghost peaks are likely to appear, as well as issues such as sample loss and decomposition. Therefore, silicone rubber gaskets are generally chosen, as they can withstand high temperatures and have good airtightness. 　　Second, the gasket effectively connects the chromatography column to the chromatography system. The gasket must have good sealing performance, an appropriate inner diameter, and heat resistance. The gasket must be replaced every time the chromatography column is replaced or repaired ； The gasket must be kept clean and dry before use ； The gasket should be replaced promptly after 15 uses or more to maintain its performance. 　　Third, the liner is the central component of the sampling system, where the sample is converted into a gas. Therefore, when selecting a liner, the first step is to choose a liner with an appropriate volume based on the size of the sample. Secondly, if there are active groups on the inner wall of the liner, they will adsorb the components of the sample, thereby reducing the sensitivity of the chromatograph detection. Therefore, it is necessary to carry out deactivation work properly. Finally, different types of linings are selected depending on the application. An appropriate liner can ensure maximum complete evaporation of the sample, prevent uneven heat distribution, and reduce the occurrence of sample backflow. 　　3 Sampling 　Sampling must be representative so that the analysis results are also representative. Therefore, sampling is not done by using tools to collect samples directly from a single location; instead, samples from different layers and locations are combined together, while ensuring uniform mixing. 　　4. Sampling First, ensure that the sampling needle is clean; if there are impurities on the tip of the needle, these substances deposited on the walls will be transferred instantly due to vaporization at high temperatures during sampling, resulting in certain errors in the analysis results. Therefore, when injecting, first ensure that the injection needle is clean – immerse it in solvent to clean it, or clean the injection needle regularly. 　　The next factor is the amount of sample injected. When too much sample is injected, the vapor generated during vaporization can exceed the volume of the vaporization chamber; as a result, this vapor reaches the top of the chamber and condenses on the gasket. The vapor then flows back into the carrier gas stream, where it condenses on the cold surfaces, leading to loss of the sample. This results in spurious peaks in subsequent injections, thereby reducing the accuracy of the sample analysis results. Therefore, before sampling, it is necessary to select an appropriate amount of sample based on the size of the liner, as well as to choose the right vaporization temperature. 　　Finally, the injection technique. Gas chromatography analysis is a quantitative analysis method; therefore, the analysis results depend to a large extent on the reproducibility of sampling and the technical skills employed. The speed, position, and depth at which the injection needle is inserted during sampling, as well as the operator’s skill level, all affect the analysis results. Therefore, during sampling, it is necessary to select an appropriate sampling technique based on the specific characteristics of the actual sample, as well as to choose the right insertion speed, depth, and position for the sampling needle, in order to improve the accuracy of the analysis results. 　　5 Eliminate human operational errors During the operation process, operators may sometimes commit subjective or negligent errors, which can have a negative impact on the accuracy of the analysis results. The most common human errors are inaccurate readings and incorrect labeling during sampling. To improve the accuracy of the analysis results, operators must approach gas chromatography analysis with a rigorous attitude; they should check the integrity of all instruments and equipment before conducting the tests, and operate them with a high sense of responsibility throughout the process to prevent any operational errors ； When taking readings, be sure to double-check them repeatedly to ensure their accuracy; do not estimate casually. This article is excerpted from China Thesis Network; the original address is: http://www.xzbu.com/view-6210736.htm