6778 (ISO International Standard INTERNATIONAL ORGANIZATION FOR STANDARDIZATION MEKAYHAPOAHAH OPTAHM3ALIWA HO CTAHAAPTW3ALWM+ORGANISATION INTERNATIONALE DE NORMALISATION Water quality - Determination of ammonium Potentiometric method QualitédeI'eau-DosagedeI'ammonium--Methodepotentiometrique First edition - 1984-06-01 UDC 543.342 : 543.257.1 Ref. No. 1SO 6778-1984 (E) 0 6778-1984 Descriptors : water, quality, chemical analysis, determination of content, ammoniacal nitrogen, ammonium ion, potentiometric methods. Copyright International Organization for Standardization Price based on 5 pages d without license from IHS Not for Resale Foreword IsO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of developing International Standards is carried out through ISO technical committees. Every member body interested in a subject for which a technical committee has been authorized has the and non-governmental, in liaison with iso, also take part in the work. 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. International Standard ISO 6778 was developed by Technical Committee ISO/TC 147, Water quality, and was circulated to the member bodies in December 1982. It has been approved by the member bodies of the following countries: Austria Iran Romania Belgium Irag South Africa, Rep. of Brazil Italy Spain Canada Japan Sweden China Korea, Dem. P. Rep. of Switzerland Czechoslovakia Mexico Thailand Egypt, Arab Rep. of Netherlands United Kingdom Germany, F.R. New Zealand USSR Hungary Norway India Poland The member bodies of the following countries expressed disapproval of the document on technical grounds: Australia France International Organization for Standardization, 1984 Printed in Switzerland mited without license from IHS Not for Resale INTERNATIONAL STANDARD ISO 6778-1984 (E) Water quality - Determination of ammonium Potentiometric method Scope species in solution, in moles per litre) greater than 0,1 mol/! 1 should be diluted before measurement, provided that this dilu This International Standard specifies a potentiometric method, tion does not reduce the ammonium concentration to less than using an ammonia-sensing membrane probe, for the deter- O,2 mg of nitrogen per fitre. mination of ammonium in raw and waste water and sewage. Amines may give positive interferences; the interferences listed in table 1 have been reported. 2 Field of application Table 1 2.1 Range Apparent The method is applicable, without dilution of the test portion, increase in Concentration of to the determination of an ammonium nitrogen concentration, Interferent an ammonium interferent concentration of ON, of up to 50 mg/1. Qn = 1 mg/l mg/l mg/l 2.2 Limit of detection 0,06 Hydrazine 4 The limit of detection is defined as the limit of Nernstian 1 Cyclohexylamine 0,03 response (see clause 3) under the conditions specified, and has Morpholine 10 0,03 a value corresponding to approximately on =- o,2 mg/l. Octadecylamine 0,4 0,14 3,4 0,15* Methanolamine 2.3 Sensitivity 11 Urea 0,01 The potential of the probe changes by approximately 60 mV per Apparent increase,in an ammonium concentration of decadic change in ammonium concentration, in accordance Qn = 0,5 mg/l. with the Nernst equation. Surface-active agents and some organic solvents reduce the 2.4 Interferences life of the membrane of the probe, and hence increase the fre quency with which the probe requires servicing. This effect The ammonia-sensing membrane probe does not respond may be severe, leading to rapid probe faifure, in samples con- satisfactorily if it is continually used for determinations on taining high concentrations of these interferents. waters having ammonium concentrations exceeding On = 50 mg/l; for such waters, it is recommended that the test portions be diluted to bring the