ISO INTERNATIONAL STANDARD 7890-3 First edition 1988-12-01 INTERNATIONALORGANIZATIONFOR STANDARDIZATION ORGANISATION INTERNATIONALE DENORMALISATION Water quality - Determination of nitrate Part 3 : Spectrometric method using sulfosalicylic acid Qualite de I'eau -- Dosage des nitrates - Partie 3 : Methode spectrometrique avec I'acide sulfosalicylique Referencenumbe ISO 7890-3 : 1988 (E) ISO7890-3:1988(E) Foreword ISo (the International Organization for Standardization) is a worldwide federation of national standards bodies (Iso member bodies). The work of preparing International Standards is normally carried out through ISo technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, govern- mental and non-governmental, in liaison with Iso, also take part in the work. Iso collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. Draft International Standards adopted by the technical committees are circulated to the member bodies for approval before their acceptance as International Standards by the ISo Council. They are approved in accordance with ISo procedures requiring at least 75% approval by the member bodies voting. International Standard ISO 7890-3 was prepared by Technical Committee ISO/TC 147, Waterquality. Iso 7890 consists of the following parts, under the general title Water quality -- Deter- mination of nitrate : Part 1 : 2,6-Dimethylphenol spectrometric method Part 2 : 4-Fluorophenol spectrometric method after distillation Part 3 : Spectrometric method using sulfosalicylic acid Annex A forms an integral part of this International Standard. @ International Organization for Standardization, 1988 Printed in Switzerland ISO 7890-3 : 1988 (E) INTERNATIONAL STANDARD Water quality Determination of nitrate Part 3 : Spectrometric method using sulfosalicylic acid Scope sample of sodium salicylate and sulfuric acid)withnitrate and subsequent treatment with alkali. 1.1 Substance determined Disodium dihydrogen ethylenedinitrilotetraacetate (EDTANa2) This part of ISo 7890 specifies a method for the determination isaddedwiththealkali topreventprecipitationofcalciumand of nitrate ion in water. magnesium salts. Sodium azide is added to overcome in- terference from nitrite. 1.2 Type of sample The method is suitable for application to raw and potable water Reagents samples. During the analysis, use only reagents of recognized analytical 1.3Range grade, and only distilled water or water of equivalent purity. Up to a nitrate nitrogen concentration, On of 0,2 mg/I using the 3.1 Sulfuric acid, c(H2S04) = 18 mol/l, Q = 1,84 g/ml. maximum test portion volume of 25 ml. The range can be ex- tended upwards by taking smaller test portions. WARNING - When using this reagent, eye protection and protective clothing are essential. 1.4 Limit of detection1) 3.2 Glacial acetic acid, c(CH3COOH) ~ 17 mol/l, Using cells of optical path length 40 mm and a 25 ml test por- tion volume the limit of detection lies within the range 9 = 1,05g/ml. n = 0,003 to 0,013 mg/l. WARNING - When using this reagent, eye protection 1.5 Sensitivity1) and protective clothing are essential. A nitrate nitrogen concentration of gn = 0,2 mg/l gives an ab- 3.3 Alkali solution, QNaoH = 200 g/l, sorbance of about 0,68 unit, using a 25 ml test portion and cells of optical path length 40 mm. Cautiously dissolve 200 g ± 2 g of sodium hydroxide pellets in 1.6 Interferences about 800 ml of water. Add 50 g ± 0,5 g of disodium dihydrogen ethylenedinitrilotetraacetate dihydrate (EDTANa2) A range of substances often encountered in water samples has [CH2-N(CH2COOH)CH2-COONal2-2H2O) and dissolve. Cool been tested for possible interference with this method. Full to room temperature and make up to 1 litre with water in a measuringcylinder.Storeinapolyethylenebottle.Thisreagent chloride,