The COD (CHEMICAL OXYGEN DEMAND) test measures the quantity of oxidizable substances (organic and reducing substances) present in the water. Though there is a relation between COD and BOD (BIOLOGICAL OXYGEN DEMAND) it generally is not possible to derive the BOD from the COD. Only for similar waters it is possible to find an empirical approximate proportionality between these two values. Therefore the simpler, quicker and easier COD test can be used also to estimate the course of the BOD, for example in water treatment plants, where the knowledge of this course is very important for the control of the process. For this reason the COD test is very popular.


To carry out the COD test one must have :

– the reagent kit (HYDROCHECK MONOTEST COD of the needed concentration)

precision pipette  to measure an exact quantity of sample (if not available, the HYDROCHECK TITRATOR can be used)

– heating block to heat the sample in the test tube which already contains the   needed quantity of reagents (if not available we can supply the Velp reactor)

– rack for cooling the hot test tubes

– photometer (SPECTRONIC GENESYS or other available spectrophotometer)


Each MONOTEST COD HYDROCHECK kit contains 21 test tubes closed by a cap. 20 are prefilled with the reagents needed for the test, based on potassium dichromate, the twentyfirst being the blank needed to zero the photometer


The spectrophotometric method is accepted as a standard method in USA and in Europe (ISO 15705). Compared with the old standard method (titration of a much bigger sample after heating in a flask with reflux  condenser) the photometric method uses only a minimum amount of reagents. In the meantime it is much simpler and highly reproducible. It is enough to put a precise amount of sample in a test tube already containing the reagents. After heating in a heat reactor, the absorbance of the sample is measured at room temperature in a spectrophotometer.


Whatever method is used, it is necessary that the sample is perfectly homogeneous.