Chemical Oxygen Demand (COD)(CAL-COD) (MTI.WQMS.PRO.COD) is a test that measures the amount of oxygen required to chemically oxidize the organic material and inorganic nutrients, such as Ammonia or Nitrate, present in water. The earliest methods for quantification of COD were developed ~150 years ago and involved recording colour changes of a permanganate solution mixed when mixed with a water samples. There was, however, significant variability between samples using this compound. The use of the dichromate procedure was pioneered and perfected for wastewater in 1949. COD is measured via a laboratory assay in which a sample is incubated with a strong chemical oxidant for a specified time interval and at constant temperature (usually 2 h at 150°C). The most commonly used oxidant is potassium dichromate, which is used in combination with boiling sulphuric acid. It is important to note that the chemical oxidant is not specific to organic or inorganic compounds, hence both these sources of oxygen demand are measured in a COD assay. Furthermore, it does not measure the oxygen-consuming potential associated with certain dissolved organic compounds such as acetate. Thus, measurements are not directly comparable to Biochemical Oxygen Demand (BOD) but can be used to compliment (though is sometimes used as surrogate measure).