Chemical oxygen demand (COD) is a measure of the oxygen equivalent of organic matter in the sample that is susceptible to oxidation by a strong oxidizing agent. A boiling mixture of potassium dichromate (K₂Cr₂O₇)–H₂SO₄ can oxidize most types of organic matter and it is generally used in COD determination. Other strong oxidants, such as KMnO₄–H₂SO₄, are also effective. The complete oxidation of organic compounds under such strong oxidizing conditions produces carbon dioxide and water. Colorimetric measurement of COD is faster and easier to perform than the titrimetric analysis. Hach COD vials (Hach Company, Lovedale, Co.) are commercially available for COD measurements in low, medium, and high ranges. Potassium hydrogen phthalate (KHP) is used as a reference standard for COD analysis.