This document specifies a method for the determination of total nitrogen (TNb) in water of various origins: natural water and wastewater, in a measuring range of concentration generally between 0,5 mg/l and 220 mg/l of TNb 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. Concentrations even slightly higher than the upper limit indicated in the manufacturers manual relating to the small-scale sealed tube methods used, cannot be reported as accurate results. Appropriate preliminary dilution of the sample shall be performed or a small‑scale sealed tube method with a different application measuring range shall be used. 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 maybe be applicable. Chromotropic colour reaction is applied, depending on the typical operating procedure of the small‑scale sealed tube used, see Clause 8. NOTE – The notation TNb is often reported by International Standards and represents "total bound nitrogen".