In the production of industrial gases and high-purity gases, the monitoring of the oxygen content in the gas is an important issue. This is because oxygen is a chemically active substance and is the most oxidizing agent.
In some industries, when people need it as an oxidant, they hope that the higher the purity, the better. On the other hand, in other industries, the presence of oxygen in other gases is also a harmful substance. People also hope that the content of oxygen is less. The better. Therefore, the content range of oxygen in various gases is a concern.
There are many methods for detecting the oxygen content, but the methods for detecting the oxygen content according to the standards specified in the gas standard are chemical and electrochemical methods. This is because only chemical and electrochemical methods can accurately determine the oxygen content in the gas.
Some units use gas chromatograph as a detection method for a variety of gas components, and can also detect the oxygen content of various gases. However, it must be pointed out that the value of the oxygen content detected by the gas chromatograph is usually the sum of the oxygen and argon (except for the gas chromatograph where argon is the carrier gas), and it is not actually just the value of oxygen. This is because it is difficult to separate oxygen and argon under normal conditions using a gas chromatography separation method, and the resulting oxygen peak data already contains the content of argon. The complete separation of oxygen and argon is difficult in the gas chromatographic separation process, but it is not infeasible. In fact, for data accuracy and ease of operation, the gas standard specifies that the oxygen content in the gas should be measured by chemical and electrochemical methods.
When oxygen content analysis, especially trace oxygen analysis, is performed, the oxygen content in the air is as high as 21% O2. Therefore, if the improper handling, it can easily cause pollution and interference to the sample, and the analysis result data is incorrect. The main reason is the improper operation of the instrument. The following only discusses several factors that affect the determination.
1. leakage. Oxygen analyzers must be strictly leak-checked before being used for the first time. The instrument can only obtain accurate data results without rigorous leakage. Any imperfections at any connection points, solder joints, valves, etc., will cause oxygen in the air to infiltrate into the pipeline and the instrument, resulting in a high oxygen content.
2. Pollution. When reusing the instrument, it is first necessary to pay attention to whether or not air is leaked when connecting the sampling line, and it is necessary to carefully remove the leaked air and try not to pass a large amount of oxygen through the sensor to prolong the life of the sensor. In the purification process of the pipeline system, a certain method is needed to shorten the purification time. Generally, high-pressure gas discharge and small-flow blow-off are alternately used to quickly clean the pipeline.
3. The choice of pipe material. The material and surface roughness of the pipe will also affect the oxygen content of the sample gas. In general, plastic pipes, rubber pipes, etc. should not be used as connecting pipes. Copper or stainless steel tubes are usually used. For ultra-micro analysis (<0.1ppm), polished stainless steel tubes must be used.
4. Gas system simplification and cleanliness. Micro-analysis requires that the contamination of the sample gas must be effectively eliminated in the dead ends of various fittings, valves, and gauges on the gas line. Therefore, gas path systems should be simplified as much as possible, and connectors with small dead angles should be used. Also, avoid the use of water seals, oil seals, and wax seals to prevent the dissolved oxygen from escaping and causing pollution. It is even more necessary to avoid the addition of purifying equipment that can easily cause pollution when the sample gas is drawn to the instrument inlet. Only in this way can the system be clean and the data obtained be accurate.
In some industries, when people need it as an oxidant, they hope that the higher the purity, the better. On the other hand, in other industries, the presence of oxygen in other gases is also a harmful substance. People also hope that the content of oxygen is less. The better. Therefore, the content range of oxygen in various gases is a concern.
There are many methods for detecting the oxygen content, but the methods for detecting the oxygen content according to the standards specified in the gas standard are chemical and electrochemical methods. This is because only chemical and electrochemical methods can accurately determine the oxygen content in the gas.
Some units use gas chromatograph as a detection method for a variety of gas components, and can also detect the oxygen content of various gases. However, it must be pointed out that the value of the oxygen content detected by the gas chromatograph is usually the sum of the oxygen and argon (except for the gas chromatograph where argon is the carrier gas), and it is not actually just the value of oxygen. This is because it is difficult to separate oxygen and argon under normal conditions using a gas chromatography separation method, and the resulting oxygen peak data already contains the content of argon. The complete separation of oxygen and argon is difficult in the gas chromatographic separation process, but it is not infeasible. In fact, for data accuracy and ease of operation, the gas standard specifies that the oxygen content in the gas should be measured by chemical and electrochemical methods.
When oxygen content analysis, especially trace oxygen analysis, is performed, the oxygen content in the air is as high as 21% O2. Therefore, if the improper handling, it can easily cause pollution and interference to the sample, and the analysis result data is incorrect. The main reason is the improper operation of the instrument. The following only discusses several factors that affect the determination.
1. leakage. Oxygen analyzers must be strictly leak-checked before being used for the first time. The instrument can only obtain accurate data results without rigorous leakage. Any imperfections at any connection points, solder joints, valves, etc., will cause oxygen in the air to infiltrate into the pipeline and the instrument, resulting in a high oxygen content.
2. Pollution. When reusing the instrument, it is first necessary to pay attention to whether or not air is leaked when connecting the sampling line, and it is necessary to carefully remove the leaked air and try not to pass a large amount of oxygen through the sensor to prolong the life of the sensor. In the purification process of the pipeline system, a certain method is needed to shorten the purification time. Generally, high-pressure gas discharge and small-flow blow-off are alternately used to quickly clean the pipeline.
3. The choice of pipe material. The material and surface roughness of the pipe will also affect the oxygen content of the sample gas. In general, plastic pipes, rubber pipes, etc. should not be used as connecting pipes. Copper or stainless steel tubes are usually used. For ultra-micro analysis (<0.1ppm), polished stainless steel tubes must be used.
4. Gas system simplification and cleanliness. Micro-analysis requires that the contamination of the sample gas must be effectively eliminated in the dead ends of various fittings, valves, and gauges on the gas line. Therefore, gas path systems should be simplified as much as possible, and connectors with small dead angles should be used. Also, avoid the use of water seals, oil seals, and wax seals to prevent the dissolved oxygen from escaping and causing pollution. It is even more necessary to avoid the addition of purifying equipment that can easily cause pollution when the sample gas is drawn to the instrument inlet. Only in this way can the system be clean and the data obtained be accurate.
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