2019/4/30 · High Range Plus COD is designed to eliminate the dilution step normally required for COD samples which have concentrations from 1500 mg/L up to 15,000 mg/L. When the High Range Plus vial is manufactured, dilution water is added directly to the High Range COD Reagent to accomplish a 1 to 10 dilution when 0.20 mL of sample is added to the reagent vial.