This document specifies a method for the determination of nitrate as NO3-N in water of various origin such as natural water (including groundwater, surface water and bathing water), drinking water and wastewater, in a measuring range of concentration between 0,10 mg/l and 225 mg/l of N03-N using the small-scale sealed tube method. Different measuring ranges of small-scale sealed tube methods can be required. The measuring ranges can vary depending on the type of the small-scale sealed tube method of different manufacturers. It is up to the user to choose the small-scale sealed tube test with the appropriate application range or to adapt samples with concentrations exceeding the measuring range of a test by preliminary dilution. NOTE 1 The results of a sealed-tube test are most precise in the middle of the application range of the test. Manufacturers' small-scale sealed tube methods are based on dimethylphenol colour reaction depending on the typical operating procedure of the small-scale sealed tube used, see Clause 9. NOTE 2 Laws, regulations or standards can require that the data is expressed as NO3- after conversion with the stoichiometric conversion factor 4,426 81 in Clause 11. NOTE 3 In the habitual language, use of sewage treatment and on the displays of automated sealed-tube test devices, NO3 without indication of the negative charge has become the common notation for the parameter nitrate and especially for the parameter nitrate-N. This notation is adopted in this document even though not being quite correct chemical nomenclature.