1.1 Substance determined This part of ISO 7890 specifies a method for the determination of nitrate ion in water. 1.2 Type of sample The method is suitable for application to raw and potable water samples. 1.3 Range Up to a nitrate nitrogen concentration, of 0,2 mg/l using the maximum test portion volume of 25 ml. The range can be extended upwards by taking smaller test portions. 1.4 Limit of detection1) Using cells of optical path length 40 mm and a 25 ml test portion volume the limit of detection lies within the range = 0,003 to 0,013 mg/l. 1.5 Sensitivity1) A nitrate nitrogen concentration of = 0,2 mg/l gives an absorbance of about 0,68 unit, using a 25 ml test portion and cells of optical path length 40 mm. 1.6 Interferences A range of substances often encountered in water samples has been tested for possible interference with this method. Full details are given in Annex A. The main potential interferents are chloride, orthophosphate, magnesium and manganese(II), as shown in Annex A. Other tests have shown that this method will tolerate a sample colour of up to 150 mg/l Pt providing the test portion absorption correction procedure is followed. (See 6.5.)