For non-high purity nitrogen, nitrogen is regarded as the binary mixture of oxygen and nitrogen. Analysis of nitrogen purity often adopts the method of analyzing the oxygen content, and the rest is nitrogen purity.
According to the national standard of the gas state for industrial use, when the oxygen content in nitrogen is less than 0.5%, use the copper ammonia solution colorometry to measure; when the oxygen content in nitrogen is more than 0.5%, use the scorched gallic acid alkaline solution absorption method to measure. The specific method of absorption method is as follows: take 100 ml sample nitrogen from the air tube, and then send the sample into the absorber filled with scorched gallic acid alkaline solution, and let it absorb the oxygen in it for several times repeatedly. After the absorption is complete, measure the absorbed oxygen by using the air tube, then the purity of nitrogen can be read directly from the air tube.
The analyser adopts the orbitt gas analyser. Put sodium chloride saturated solution into the measuring tube and level bottle, and add 5% sulfuric acid and 0.1% methyl orange solution 3 ~ 5 drops of dyeing. Load the absorbent into the absorber. The absorption liquid is prepared by the following methods: weigh 20g of scorched gallic acid (analytically pure), dissolve it in 100 ml distilled water; weigh 60g of potassium hydroxide (analytically pure), dissolve it in 40 ml distilled water, and cool it to room temperature; mix the two solutions above evenly.
Since the volume of the gas left after absorption accounts for a large proportion, in order to ensure the accuracy of the test, in addition to ensuring the air tightness, the air in the measuring pipe and connecting pipe should be replaced clean. To operate repeatedly until the reading is constant, you should also pay attention to the following points:
1) add a water jacket outside the measuring tube, and fill it with water at room temperature, resulting in the condition of constant temperature. Prevent the heat released in the reaction from rising the temperature and the volume of nitrogen from expanding, which can not be measured accurately. Before and After analysis, the gas should stay in the measuring tube for 1 ~ 2 min, and read after balancing with the water temperature.
2) add liquid paraffin on the liquid level exposed to the air to make it isolated from the air and avoid absorbing the oxygen in the air so as to shorten the service life of the absorbed liquid.
3) use two absorbers each time. First use the first absorption, then use the second absorption. When the oxygen absorbed by the absorbed liquid in the first absorber is less than 50% of the oxygen content, it should be replaced immediately.
