Total organic carbon (TOC) is a comprehensive indicator of the total amount of organic matter in water body expressed by the content of carbon, and the result is expressed by the concentration of C (mg / L). Because TOC is determined by combustion method, it can oxidize all organic matter. It can reflect the total amount of organic matter better than BOD5 or cod. At present, the widely used methods for the determination of TOC are combustion oxidation non dispersive infrared absorption method (gb13193-91), conductivity method, wet oxidation non dispersive infrared absorption method, etc. The combustion oxidation non dispersive infrared absorption method is widely used at home and abroad because of its simple process, good reproducibility and high sensitivity. Because some carbonaceous organic compounds are not easy to be burned and oxidized at high temperature, the measured TOC value is often lower than the theoretical value. The principle of the subtraction method is: a certain amount of water sample is injected into a quartz tube in a high-temperature furnace. At 900-950 ℃, platinum, cobalt oxide or chromium trioxide are used as catalysts to convert organic matter into carbon dioxide by combustion and pyrolysis, and then the carbon content in the water sample is determined by infrared gas analyzer. Because at high temperature, the carbonate in the water sample also decomposes to produce carbon dioxide, so the above measurement is the total carbon (TC) in the water sample. In order to obtain the organic carbon content, two methods can be used: one is to acidify the water sample in advance, aerate it with nitrogen, remove the carbon dioxide generated by the decomposition of various carbonates, and then inject it into the instrument for determination. Another method is to use the TOC measuring instrument that both high temperature furnace and low temperature furnace have. When the same amount of water sample is injected into the high temperature furnace (900 ℃) and the low temperature furnace (150 ℃), the organic carbon and inorganic carbon in the water sample are converted into CO2, while the glass wool impregnated with phosphoric acid is installed in the quartz tube of the low temperature furnace, the inorganic carbonate can be decomposed into CO2 at 150 ℃, but the organic matter can not be decomposed and oxidized. The total carbon (TC) and inorganic carbon (IC) were measured by non dispersive infrared gas analyzer, and the difference between them was total organic carbon (TOC). TOC＝TC-IC The determination process is shown in Figure 3-40. 5 mg / L.