5813 International Standard (ISO INTE RNATIONAL ORGANIZATION FOR STANDARDIZATION+MEXYHAPOAHAR OPrAHW3AUMA IO CTAHAAPTW3ALMM+ORGANISATION INTERNATIONALE DE NORMALISATION Water quality -- Determination of dissolved oxygen - lodometric method Qualite de I'eau -- Dosage de I'oxygene dissous -- Methode iodometrique First edition -- 1983-09-15 UDC 543.37 : 543.242.3 : 546.21 Ref. No. ISO 5813-1983 (E) Descriptors : water, quality, water treatment, iodometric analysis, determination, oxygen, soluble matter. Price based on 5 pages Copyright International Organization for Standardization Not for Resale Foreword Iso (the fnternational 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 5813 was developed by Technical Committee ISo/TC 147, Water quality, and was circulated to the member bodies in July 1982. It has been approved by the member bodies of the following countries : Poland Australia Germany, F.R. Austria Hungary Romania india Belgium South Africa, Rep. of Iran Canada Spain Chile Irag Sweden China Italy Switzerland Czechoslovakia Japan Thailand Denmark Korea, Rep. of United Kingdom Egypt, Arab Rep. of Mexico USA USSR Finland Netherlands France Norway No member body expressed disapproval of the document. International Organization for Standardization, 1983 Printed in Switzerland nited without license from IHs Not for Resale ISO 5813-1983 (E) INTERNATIONAL STANDARD Water quality --- Determination of dissolved oxygen lodometric method Scope and field of application quantity of iodine. Determination of the quantity of iodine 1 liberated by titration with sodium thiosulphate. This International Standard specifies an iodometric method for the determination of dissolved oxygen in water by the so-called "Winkler procedure" modified in order to make allowance for Reagents 4 certain interferences. During the analysis, use only reagents of recognized analytical The iodometric method is the reference method for the deter. grade and oniy distilled water or water of equivalent purity. mination of dissolved oxygen in water. It is applicable to all types of water having dissolved oxygen concentrations greater Sulphuric acid, solution.2) than 0,2 mg/l, up to double saturation of oxygen (approxi- 4.1 mately 20 mg/l), which are free from interfering substances. Cautiously add 500 ml of concentrated sulphuric acid Readily oxidizable organic substances such as tannins, humic acid and lignins, interfere. Oxidizable sulphur compounds such (o = 1,84 g/ml) to 500 ml water, stirring continuously. as sulphides and thiourea also interfere, as do actively respiring systems which readily consume oxygen. In the presence of 4.2 Sulphuric acid, solution, c(1/2 H2SO4) = 2 mol/l. such substances, it is preferable to use the electrochemical probe method specified in Iso 5814. 4.3 Alkaline iodide-azide reagent. Nitrites up to a concentration of 15 mg/l do not interfere with Sodium azide is an extremely strong WARNING the determination because they are destroyed by the addition poison. If nitrites are known to be absent, this reagent of sodium azide. may be omitted. If oxidizing or reducing substances are present, it is necessary Dissofve 35 g of sodium hydroxide (NaOH) [or 50 g of to make modifications to the method; these are described in potassium hydroxide (KOH)) and 30 g of potassium iodide (KI) clause 9. [or 27 g of sodium iodide (Nal)] in approximately 50 ml of water. if suspended matter, capable of fixing or consuming iodine, i