Special thread on experience sharing in gas chromatography

Daily maintenance of gas chromatography I. Ensuring the airtightness of the vaporization chamber gasket 1. The lifespan of the silicone rubber gasket at the sample injection port is related to the temperature of the vaporization chamber; it can generally be used for dozens of times. When the silicone rubber gasket leaks, it causes fluctuations in the baseline, reducing the reproducibility of the analysis and leading to inaccurate results. 2. Excessive punctures by the sampler cause silicon rubber debris to enter the vaporization chamber; if there is too much of this debris, it can affect the stability of the baseline at high temperatures or result in spurious peaks. Therefore, to ensure the proper progress of the analysis, please replace the gaskets frequently and check the airtightness of the vaporization chamber regularly. II. Regularly clean the vaporization chamber or liner tubes. 1. Due to long-term use, a large amount of high-boiling-point substances often accumulate inside the vaporization chamber and liner tubes; when analyzing such substances, excess peaks are generated, which affects the analysis results. Therefore, it is necessary to clean the vaporization chamber and liner tubes regularly using organic solvents. 2. Cleaning of the vaporization chamber: Remove the chromatography column, and under conditions of heating and ventilation, inject anhydrous ethanol or propane from the sample inlet several times; finally, dry it by heating and ventilation. III. Regular leak detection of the gas circuit 1. Under normal circumstances, leak detection is carried out when a new instrument is purchased. However, if issues such as reduced sensitivity, prolonged retention times, or a wavy baseline occur during use, leak detection should be performed again. This is especially true for hydrogen gas circuits, where regular leak detection is necessary to avoid potential dangers. 2. Some control valves use O-rings; due to long-term wear, they may leak air ； Failing to replace the silicone gasket at the injection port regularly, or not connecting the chromatography column properly... can all cause air leakage. Therefore, leak checks must be done regularly! IV. Cleaning of the Thermal Conductivity Detector (TCD) 1. Remove the chromatography column and replace it with an empty, short chromatography column. Introduce carrier gas, and raise the temperatures of the column oven and the detection chamber to 200–250 degrees. Inject 2 ml of organic solvent at the injection port, repeating this several times until the area is dried out by the gas flow. 2. The bridge current must not be applied during cleaning. Otherwise, it will damage the detector! ! ! ! V. Cleaning of the Electron Capture Detector (ECD) 1. The cleaning method is the same as that for the thermal conductivity detector. 2. For cleaning organic solvents, electronegative organic solvents such as trichloromethane and carbon tetrachloride should not be used; benzene, n-hexane, etc. can be employed instead. At 250 degrees. 3. For Ni63 radiation sources, the detector temperature should be between 250 and 300 degrees, while the temperature for tritium-scandium sources should not be too high. 4. When cleaning the ECD, take proper personal protective measures if necessary! ! VI. Cleaning of the Hydrogen Flame Detector (FID) 1. The purpose of cleaning is to improve the insulation level of the detector. 2. When pollution is severe, the collector, polarizing electrode, and nozzle can be removed. The collector and polarizing electrode can be soaked and scrubbed with anhydrous ethanol; the base and nozzle should be rinsed repeatedly with organic solvents. The air passage system also needs to be thoroughly cleaned. The nozzle opening must be smooth and even – if there are burrs, they can be polished smooth using an oil stone, a variety of files, or sandpaper. After that, it should be rinsed repeatedly with ethanol, and then dried by alternating hot and cold air. 3. The insulators that hold these electrodes in place can be soaked in anhydrous ethanol for 10–15 minutes, and then wiped clean with silk or gauze. Dry and ready for installation. 4. During assembly, it should be restored to its original state, ensuring that the nozzle, the polarization pole, and the collector are concentric when viewed from above, and that the polarization pole and the nozzle opening are at the same level when viewed from the side. 5. Note: After cleaning, all components must not be touched with bare hands; clean gloves should be worn during installation, and all tools must be cleaned and dried before use. VII. Cleaning of the Nitrogen Phosphorus Detector (NPD) and Flame Photometric Detector (FPD): Since the structure of these two detectors is basically similar to that of the FID, the cleaning methods are based on those for the FID. NPD pays close attention to thorough cleaning ； FPD, on the other hand, should focus on cleaning the light window, being careful not to expose the phototube to strong light.

Problems encountered: 1. It is difficult to perform quantitative determination using a gas chromatograph due to low moisture content. It often fails to reach a peak. 2. The chromatography column is prone to corrosion by impurity gases, especially when analyzing process control gases. 3. Trace gases do not show a peak. 4. Sometimes, for the same sample gas, the analysis results vary significantly. Since I’m not very good at analysis, I hope everyone can discuss this topic more.

Cleaning of the Thermal Conductivity Detector (TCD): 1. Remove the chromatography column and replace it with an empty, shorter one. Introduce carrier gas, and raise the temperatures of the column oven and the detection chamber to 200–250 degrees. Inject 2 ml of organic solvent at the injection port, repeating this several times until the area is dried out. 2. The bridge current must not be applied during cleaning. Otherwise, it will damage the detector! ! ! !