1.1 This standard specifies the non-dispersive infrared absorption method for the determination of total organic carbon (TOC) in surface water.
1.2 Determination range
This standard is applicable to the determination of total organic carbon in surface water. The concentration range is 0.5 to 60 mg/L and the lower detection limit is 0.5 mg/L.
1.3 Interference
When the common coexisting ions in the surface water exceed the following content (mg/L), there is interference with the determination, and appropriate pretreatment shall be performed to eliminate the interference effect on the determination: SO42- 400; Cl- 400; NO3- 100; PO43- 100; S2- 100. When the water sample contains large particle suspensions, due to the limitation of the pinhole of the water sample syringe, the determination results usually do not include all granular organic carbon.
2 Principle
2.1 Difference method for determination of total organic carbon
The sample together with the purified air (dried and removed carbon dioxide) are respectively introduced into a high temperature combustion tube (900 °C) and a low temperature reaction tube (160 °C), and the water sample of the high temperature combustion tube is subjected to high temperature catalytic oxidation to make the organic compound and inorganic carbonic acid converted into carbon dioxide; and the water sample in the low temperature reaction tube is acidified to decompose the inorganic carbonate into carbon dioxide, and the carbon dioxide formed is sequentially introduced into the non-dispersive infrared detector. Since a certain wavelength of infrared light is selectively absorbed by carbon dioxide, the infrared absorption intensity of carbon dioxide in a certain mass concentration range is proportional to its mass concentration, whereby the total carbon (TC) and inorganic carbon (IC) of the water sample may be quantitatively determined.
