CODcr

CODcr stands for chemical oxygen demand using the chromotropic acid method. It is an analytical procedure used to estimate the amount of oxidizable organic matter in water and wastewater. The test quantifies the amount of potassium dichromate that is consumed to oxidize organics under strongly acidic conditions, yielding a measure of the sample’s oxygen demand.

The procedure typically involves an acid digestion with potassium dichromate in a sealed reactor, often at elevated temperature. To mitigate interference from inorganic substances, reagents such as mercuric sulfate and silver sulfate may be added. After digestion, the remaining oxidant or the chromium species produced is determined colorimetrically using a chromotropic acid reagent, and the result is converted to an oxygen demand value, usually reported as milligrams per liter (mg/L) of COD. Some workflows use titration with ferrous ammonium sulfate instead of colorimetric detection.

CODcr is widely used in water quality assessment, wastewater treatment, and environmental monitoring to gauge organic loading, evaluate treatment efficiency, and support regulatory compliance. It provides a rapid, relatively robust alternative to standard COD methods in many laboratories and is particularly common in saline or chloride-containing samples where interference control is beneficial.

Limitations include the need for hazardous reagents and high-temperature digestion, potential interferences from certain substances, and dependence on proper calibration and quality control. The method is described in various national and international standard methods and remains a staple in routine environmental analysis.