Study on the Preparation of the Reagent Mixture used Specially for the HE 99721 COD Determinator

Composition of a reagent mixture for special use in HE 99721 COD determinator as an oxidizing and digestion reagent of the water sample was studied,and a mixed solution containing 0.75 mL of 0.05 mol·L-1 K2Cr2O7 solution,1.8 mL of Ag2SO4-H2SO4 solution (4 g of Ag2SO4 dissolved in and made up to 500 mL of conc.H2SO4) and 0.15 mL of HgSO4-H2SO4 solution (4 g of HgSO4 dissolved in 20 mL of 3 mol·L-1 H2SO4) was found suitable to be used in substitution for the imported HI 99955 reagent package.By using the self-prepared reagent mixture instead of the imported reagent package in the determination of COD in the range within 150 mg·L-1 with the determinator,no significant difference was found between the results using the 2 reagent mixture.