This document specifies a method for the determination of total bound nitrogen？(ST-TN_b) in water of various origins: groundwater, surface water and wastewater, in a measuring range of concentration generally between 0,5？mg/l and 150？mg/l of ST-TN_b 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 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？The results of a small-scale sealed tube test are most precise in the middle of the application range of the test.

All small-scale sealed tube methods are based on a heated alkaline potassium persulfate oxidation in a heating block at 100？°C and different digestion times are applicable. Chromotropic colour reaction is applied, depending on the typical operating procedure of the small-scale sealed tube used, see Clause？9.