Chemical Oxygen Demand (COD) Reagent, TNTplus, UHR. Hach. determination of Chemical Oxygen Demand (COD) by the Reactor Digestion Method, using TNTplus™ vials. Hach Method 10212. Range: 250-15,000 mg/L COD. Reduce Errors with Bar-coded Vials and RFID No Reagent Blank Necessary Innovative Vial and Reagent Delivery Helpful package.