Features high chlorine determination of chemical oxygen demand in wastewater chlorine commonly used correction method, this method eliminates the chloride ions on the CODcr. Determination of impact, but in practice the results on the determination that this method can produce a positive error, if we adopt chlorinated correction method blank test, the results show that the relative error between 0.1% and 1.1%, and the recovery was 102% and 105%, can improve the accuracy of the method. 
 The instrument uses computer technology to control the heating furnace can be tapered back on five digestion heating device at the same time. Save energy, reduce load and improve efficiency. 
 Instruments used instead of spherical glass burr return pipe return pipe, and air-cooled technology to replace the water cooling method, either to make water-saving equipment and standardization, but also improve the safety of the instrument used. Another plus is equipped with pneumatic equipment like devices, automatic zero burette, simplifying the operation of the late titration procedures, improve the method reliability. 
 In water samples by adding known amount of potassium dichromate solution and mercury sulfate solution and sulfuric acid in acid medium under the silver as a catalyst, after boiling reflux by 2h to 1, 10 - phenanthroline as the indicator, with ammonium ferrous sulfate in water samples by titration of potassium dichromate is not restored by the consumption amount of ferrous ammonium sulfate converted into mass concentration of oxygen consumed, is the apparent COD. Complex water samples will not be part of the oxidation of chloride ions to form chlorine gas export, and then absorbed by sodium hydroxide solution, adding potassium iodide, pH adjusted with sulfuric acid is about 3 to 2, 
 Starch as indicator, titrated with sodium thiosulfate standard solution titration, the amount of sodium thiosulfate consumed converted into mass concentration of oxygen consumed, is the correction of chloride ion. COD and chloride ions apparent difference between the correction value, that is, the real water samples measured by COD. 
 Application of this method is suitable for chloride ion content of less than 20000mg / L of chlorine in waste water of high chemical oxygen demand (COD) determination. The detection limit is 30mg / L. For oil, coastal refineries, oil depots, chlor-alkali plants, waste water discharge and other deep-sea determination of COD in wastewater.