This part of ISO 11905 specifies a method for the determination of nitrogen present in water, in the form of free ammonia, ammonium, nitrite, nitrate and organic nitrogen compounds capable of conversion to nitrate under the oxidative conditions described. Dissolved nitrogen gas is not determined by this method. This method is applicable to the analysis of natural fresh water, sea water, drinking water, surface water and treated sewage effluent. It is also applicable to the analysis of sewage and trade wastes in which the amount of organic matter in the test portion can be kept below 40 mg/l, expressed as carbon (C), when measured by Total Organic Carbon (TO