Shen ChangHong Terms and definitions
Chemical oxygen demand (COD)
Under certain conditions, after the potassium dichromate oxidation treatment, the mass concentration of oxygen corresponding to the dissolved substances in the water sample and the potassium dichromate consumed by the suspended substances, 1 mol of potassium dichromate (1 / 6 K2Cr2O7) is equivalent to 1 mol of oxygen (1 / 2 O).
principle
A known amount of potassium dichromate solution was added to the sample. In strong sulfuric acid medium, silver sulfate was used as catalyst, and after high temperature digestion, COD value was determined by spectrophotometry. When the COD value in the sample is 100mg / L to 2000mg / L, the absorbance of trivalent chromium (Cr3 +) produced by the reduction of potassium dichromate is measured at the wavelength of 600nm ± 20nm. The COD value in the sample is in a positive proportion to the increase of the absorbance of trivalent chromium (CR3 +), and the absorbance of trivalent chromium (Cr3 +) is converted to the COD value of the sample. When the COD value in the sample is between 15mg / L and 200mg / L, the total absorbance of Cr 6 + and Cr 3 + was measured at 440nm ± 20nm; The COD value in the sample is in positive proportion to the absorbance reduction value of Cr6 +, the absorbance increase value of Cr3 +, and the total absorbance reduction value. The total absorbance value is converted to the COD value of the sample.
The micro reflux test method of COD analyzer developed by shenchanghong company is simple, fast and economical in operation. The test results have good comparison with the traditional titration method, and can reduce the secondary pollution produced in the COD test process to the minimum. Shenchanghong company can provide a complete analysis scheme of COD micro reflux test method, and users do not need to prepare their own cod reagent. The scheme includes spectrophotometer, ds-16b / 20B / 25B / 36B digester and COD pre preparation reagent. The new cod reagent is used in combination with the digester and spectrophotometer of shenchanghong. The analytical procedure is simple and convenient, and it meets the requirements of Chinese industry standards.
Product features:
● no need to prepare cod reagent: the chemical components required for COD (chemical oxygen demand) analysis are prepared in a certain proportion
Prefabricated reagent tube can greatly save the time required for COD reagent preparation;
● time saving: the whole analysis process, including water sample digestion, colorimetric determination and other steps, takes less than 2 hours;
● compact digestion device: ds-16b / 20B / 25B / 36B, a cod digester developed by shenchanghong company, replaces the traditional cod electric furnace reflux device and can digest up to 36 water samples at the same time;
The secondary pollution to the environment is small: only a small amount of COD reagent is needed in the micro reflux method, and the carefully designed cod reagent tube can prevent the volatilization of organic matters and the escape of samples, thus ensuring the safety of the digestion process;
● simple operation and easy to learn: the operation guide with pictures and texts is convenient for mastering the analysis method of COD (chemical oxygen demand) in a short time.
Analysis steps of COD (chemical oxygen demand) micro reflux method in Changhong:
(1) Preparation of COD reagent and water sample
Each cod prefabricated reagent tube already contains the reagent components required for COD analysis. After unscrewing the cap, add 2ml water sample, and tighten the cap (when 0-20000mg / L cod prefabricated reagent tube is used, only add 0.2ml water sample).
(2) Water sample digestion
Put the pre prepared cod reagent tube that has been added into the water sample into the COD digester ds-16b / 20B / 25B / 36B, select the appropriate digestion temperature and time for thermal reflux according to the requirements of the reagent, and after the digestion process, the ds-16b digester will automatically shut down. Take out COD test tube from ds-16b / 20B / 25B / 36B digester and cool it to room temperature.
(3) Cod (chemical oxygen demand) colorimetric determination
Start the spectrophotometer (qcod-2m / qcod-3m / cn-201a / cn-201c / cn-201d / cnp-301 / cnp-301c / cnp-301d / cnpn-401 / cnpn-401 / cnpn-401 / cnpn-401d /) of Shenzhen Changhong company, select the corresponding cod (chemical oxygen demand) test program in the main menu, without establishing the standard curve, just put the COD reagent test tube into the instrument to read out the COD value expressed in concentration units, and record the experimental results.
Brief introduction of micro reflux analysis system of shenchanghong cod analyzer
The micro reflux analysis system of COD (chemical oxygen demand) provided by shenchanghong company includes spectrophotometer, digester and matched cod pre preparation reagent.
(1) According to the needs of different customers, shenchanghong company can provide various types of spectrophotometer to measure cod (chemical oxygen demand).
(2) Shenchanghong ds-16b / 20B / 25B / 36B digester is a newly developed digester of shenchanghong company. It can be used for the digestion of COD (chemical oxygen demand), total chromium, total nitrogen, total phosphorus and other water samples. The digestion time and temperature can be selected in the range of room temperature - 200 ℃ and 1 - 9999 minutes respectively.
More about cod analyzer can be checked in the COD water quality analyzer of shenchanghong.
