How to Preserve Water Samples for COD Preformed Reagent Testing

Proper preservation of water samples before testing with COD preformed reagents is critical to ensure that final results are accurate, repeatable, and consistent with actual water quality conditions. Improper storage can easily lead to organic matter degradation, microbial activity interference, and data deviation, which will undermine the performance of these pre-calibrated, time-saving reagent products.

The most widely used preservation method for COD test water samples is acidification. After sampling, add concentrated sulfuric acid to the water sample immediately to adjust its pH value to below 2, which can effectively inhibit most microbial activities that consume organic pollutants. Under normal room temperature conditions, acidified COD water samples can be stably stored for up to 7 days, which fully covers the conventional time window from on-site sampling to laboratory testing.

For water samples that cannot be tested in a short period or contain easily degradable organic components, low-temperature refrigeration serves as an effective supplementary or independent preservation measure. Place the well-sealed sampling container in a constant temperature refrigerator at 2-4℃, which can further slow down the rate of organic matter decomposition. Even without acidification, properly refrigerated COD water samples can maintain stable measured values for 3 to 6 days.

No matter which preservation method is adopted, it is strongly recommended to complete the COD test as soon as possible. Before formal detection, fully shake the preserved water sample to mix any settled suspended solids evenly, and then take it directly for reaction with the COD preformed reagent, to avoid unnecessary errors caused by long-term storage and incomplete sample mixing.