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Application Express | Overcoming the COD Detection Challenge in Seawater/High Chlorine Samples
Date: 2025-12-23Read: 2
The determination of chemical oxygen demand (COD) varies depending on the reducing substances in the water sample and the measurement method used.Currently, the commonly used methods are acidic potassium permanganate oxidation and potassium dichromate oxidation.
►The potassium permanganate method has a low oxidation rate, but the testing is relatively simple. It is mainly used to determine samples with relatively low organic content in water samples, such as surface water and groundwater. Permanganate index method: alkaline condition oxidation, suitable for low COD water bodies (such as seawater, circulating cooling water, etc.), but with weaker oxidation ability than potassium dichromate method.
► The potassium dichromate method has high oxidation rate and good reproducibility, and is mainly suitable for wastewater and complex industrial wastewater. Potassium dichromate method: strong acid digestion+silver salt catalysis, oxidation rate>90%, detection limit 4mg/L; Main limitations: Difficult to oxidize aromatic hydrocarbon substances (such as pyridine), high chlorine water samples require additional addition of mercuric sulfate to mask the interference of chloride ions.
At present, HJ/T 132-2003 "Determination of Chemical Oxygen Demand for High Chlorine Wastewater - Potassium Iodide Alkaline Potassium Permanganate Method" is specifically designed for high chlorine wastewater, using the potassium iodide alkaline potassium permanganate method, suitable for samples with Cl ⁻ ≤ 20000mg/L, such as high chlorine wastewater samples from oil fields/refineries.
In the COD testing process, the main interfering factor is chloride ions. If the concentration exceeds the allowable concentration, the mercury sulfate in the conventional COD testing tube is not sufficient to eliminate the interference of chloride ions. To ensure the accuracy of the measurement results, measures must be taken to solve the problem of chloride ion interference.
Chemical Oxygen Demand in Seawater/High Chlorine SamplesPre installed tube test box and related consumables, etc
Item Number |
Product description |
Packing Specification |
1.17058 |
Chemical Oxygen Demand (Seawater/High Chlorine Sample) Test Box 5.0-60.0 mg/l COD |
25 pieces/box |
1.17059 |
Chemical Oxygen Demand (Seawater/High Chlorine Sample) Test Box 50-3000 mg/l COD |
25 pieces/box |
1.06733 |
Alkali lime |
500g/bottle |
1.15333 |
LC-MS grade pure water |
1000 ml/bottle |
1.17048 |
Special sulfuric acid for COD testing |
1000 ml/bottle |
1.09136 |
2mol/l sodium hydroxide solution |
1000ml/bottle |
1.15955 |
Glass absorption tube |
Testing a sample requires the use of two samples simultaneously (blank and sample) |
/ |
300 ml conical bottle (bottle mouth specification: NS 29/32) |
Testing a sample requires the use of two samples simultaneously (blank and sample) |
/ |
NS29/32 bottle stopper |
Testing a sample requires the use of two samples simultaneously (blank and sample) |
/ |
Glass pipette or pipette gun |
5ml，20ml，25ml |
/ |
thermometer |
0-100℃ |
/ |
Adjustable speed magnetic stirrer |
1 set |
/ |
magnetic stir bar |
2 pieces of 30 * 7mm |
/ |
Ice bath device |
1 set |
1.10079 |
Chloride ion test strip 0-500-1000-1500-2000-3000 mg/l |
100 times/box, qualitative/semi quantitative |
1.09535 |
PH test strip 0-14 |
100 times/box |
laboratoryMulti parameter water quality analyzer
Item Number |
Product Name |
||
1.73028.0001 |
Prove 600 Plus Laboratory Multi Parameter Water Quality Analyzer |
||
1.73027.0001 |
Prove 300plus Expert Laboratory Multi Parameter Water Quality Analyzer |
||
1.73026.0001 |
Prove 100plus economical laboratory multi parameter water quality analyzer |
||