Water quality - Determination of free chlorine and total chlorine - Part 2: Colorimetric method using N,N-dialkyl-1,4-phenylenediamine, for routine control purposes (ISO 7393-2:2017)

ISO 7393-2:2017 specifies a method for the determination of free chlorine and total chlorine in water, readily applicable to lab- and field-testing. It is based on measurement of the absorption, the red DPD colour complex in a photometer or the colour intensity by visual comparison of the colour with a scale of standards that is regularly calibrated.
This method is appropriate for drinking water and other waters, where additional halogens like bromine, iodine and other oxidizing agents are present in almost negligible amounts. Seawater and waters containing bromides and iodides comprise a group for which special procedures are to be carried out.
This method is in practice applicable to concentrations, in terms of chlorine (Cl2), from, for example, 0,000 4 mmol/l to 0,07 mmol/l (e.g. 0,03 mg/l to 5 mg/l) total chlorine. For higher concentrations, the test portion is diluted.
Commonly, the method is applied as a field method with mobile photometers and commercially available ready-for-use reagents (liquid reagents, powders and tablets). It is essential that those reagents comply with minimum requirements and contain the essential reagents and a buffer system suitable to adjust the measurement solution to a pH range of typically 6,2 to 6,5. If there is doubt that water samples have uncommon pH values and/or buffer capacities, the user has to check and, if necessary, to adjust the sample pH to the required range. The pH of the sample is within the range of pH 4 and 8. Adjust, if necessary, with sodium hydroxide solution or sulfuric acid before the test.
A procedure for the differentiation of combined chlorine of the monochloramine type, combined chlorine of the dichloramine type and combined chlorine in the form of nitrogen trichloride is presented in Annex A. In Annex C, a procedure is presented for the determination of free and total chlorine in drinking and other low polluted waters, for disposable planar reagent-filled cuvettes using a mesofluidic channel pump/colorimeter.

Wasserbeschaffenheit - Bestimmung von freiem Chlor und Gesamtchlor - Teil 2: Kolorimetrisches Verfahren mit N,N-Diethyl-1,4-Phenylendiamin für Routinekontrollen (ISO 7393-2:2017)

Qualité de l'eau - Dosage du chlore libre et du chlore total - Partie 2: Méthode colorimétrique à la N,N-diéthylphénylène-1,4 diamine destinée aux contrôles de routine (ISO 7393-2:2017)

ISO 7393-2:2017 spécifie une méthode de dosage du chlore libre et du chlore total dans l'eau, aisément applicable dans le cadre d'essais en laboratoire et sur le terrain. Elle est basée sur le mesurage de l'absorption du composé DPD rouge dans un photomètre ou sur le mesurage de l'intensité de la couleur par comparaison visuelle de la couleur avec une échelle d'étalons régulièrement calibrée.
Cette méthode convient pour l'eau potable et d'autres eaux, où des halogènes supplémentaires comme le brome et l'iode, et d'autres agents oxydants sont présents dans des quantités presque négligeables. L'eau de mer et les eaux contenant des bromures et des iodures constituent un groupe nécessitant la mise en ?uvre de procédés particuliers.
Cette méthode est applicable dans la pratique à des concentrations, en termes de chlore (Cl2), comprises par exemple entre 0,000 4 mmol/l et 0,07 mmol/l (c'est-à-dire entre 0,03 mg/l et 5 mg/l) pour le chlore total. À plus forte concentration, la prise d'essai est diluée.
En général, la méthode est appliquée en tant que méthode de terrain avec des photomètres mobiles et des réactifs prêts à l'emploi disponibles dans le commerce (réactifs liquides, poudres et tablettes). Il est essentiel que ces réactifs satisfassent aux exigences minimales, et qu'ils comportent les réactifs essentiels et un système tampon permettant d'ajuster le pH de la solution de mesure sur une gamme généralement comprise entre 6,2 et 6,5. En cas de doute concernant les valeurs de pH et/ou les pouvoirs tampon inhabituels que pourraient présenter les échantillons d'eau, l'utilisateur doit contrôler et, si nécessaire, ajuster le pH de l'échantillon à la gamme requise. Le pH de l'échantillon doit être compris entre 4 et 8. Procéder, si nécessaire, à un ajustement au moyen d'acide sulfurique ou d'une solution d'hydroxyde de sodium avant l'essai.
Une méthode permettant la différenciation du chlore combiné de type monochloramine, du chlore combiné de type dichloramine et du chlore combiné sous forme de trichlorure d'azote est présentée à l'Annexe A. L'Annexe C présente quant à elle un mode opératoire pour le dosage du chlore libre et du chlore total dans les eaux de boisson et les autres types d'eau faiblement polluée, avec des cuves planes à usage unique remplies de réactif, utilisées avec une pompe ou un colorimètre à canal mésofluidique.

Kakovost vode - Določevanje prostega in celotnega klora - 2. del: Kolorimetrijska metoda z N,N-dialkil-1,4-fenilendiaminom za redno kontrolo (ISO 7393-2:2017)

Ta dokument določa metodo za določevanje prostega in celotnega klora v vodi, ki je zlahka uporabna pri laboratorijskem preskušanju in preskušanju na terenu. Temelji na meritvi absorpcije, rdečem barvnem kompleksu DPD
v fotometru ali barvni intenziteti prek vizualnega primerjanja barve z lestvico
standardov, ki se redno umerja.
Ta metoda je primerna za pitno in drugo vodo, kjer so dodatni halogeni, kot so brom, jod in drugi oksidanti, prisotni v skoraj zanemarljivih količinah. Morska voda in voda, ki vsebuje bromide in jodide, sestavljata skupino, za katero se morajo izvesti posebni postopki.
Ta metoda se v praksi uporablja za koncentracije klora (Cl2) od na primer 0,0004 mmol/l do 0,07 mmol/l (npr. 0,03 mg/l do 5 mg/l) celotnega klora. Pri višjih koncentracijah se preskusna količina razredči.
Metoda se običajno uporablja na terenu z mobilnimi fotometri in komercialno razpoložljivimi reagenti, pripravljenimi za uporabo (tekoči reagenti, praški in tablete). Ključnega pomena je, da so ti reagenti skladni z minimalnimi zahtevami in da vsebujejo bistvene reagente ter blažilni sistem, primeren za prilagajanje merilne raztopine na razpon pH, ki je običajno med 6,2 in 6,5. Če obstajajo dvomi o tem, ali vzorci vode vključujejo neobičajne vrednosti pH in/ali zmogljivosti blažilnika, mora uporabnik preveriti in po potrebi prilagoditi vzorčni pH na ustrezen razpon. Vrednost pH vzorca je v razponu med pH 4 in 8. Po potrebi pred preskusom prilagodite z raztopino natrijevega hidroksida ali žveplove kisline.
Postopek za diferenciacijo sestavljenega klora monokloraminskega tipa, sestavljenega klora dikloraminskega tipa in sestavljenega klora v obliki dušikovega triklorida je opisan v dodatku A. V dodatku C je opisan postopek za določevanje prostega in celotnega klora v pitni in drugi vodi z nizko stopnjo onesnaženja, za ravne kivete za enkratno uporabo, napolnjene z reagentom z uporabo
črpalke/kolorimetra mezofluidnega kanala.

General Information

Status
Published
Publication Date
30-Jan-2018
Current Stage
6060 - Definitive text made available (DAV) - Publishing
Due Date
31-Jan-2018
Completion Date
31-Jan-2018

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SLOVENSKI STANDARD
SIST EN ISO 7393-2:2018
01-junij-2018
1DGRPHãþD
SIST EN ISO 7393-2:2000

.DNRYRVWYRGH'RORþHYDQMHSURVWHJDLQFHORWQHJDNORUDGHO.RORULPHWULMVND

PHWRGD]11GLDONLOIHQLOHQGLDPLQRP]DUHGQRNRQWUROR ,62

Water quality - Determination of free chlorine and total chlorine - Part 2: Colorimetric

method using N,N-dialkyl-1,4-phenylenediamine, for routine control purposes (ISO 7393-

2:2017)
Wasserbeschaffenheit - Bestimmung von freiem Chlor und Gesamtchlor - Teil 2:

Kolorimetrisches Verfahren mit N,N-Diethyl-1,4-Phenylendiamin für Routinekontrollen

(ISO 7393-2:2017)
Qualité de l'eau - Dosage du chlore libre et du chlore total - Partie 2: Méthode

colorimétrique à la N,N-diéthylphénylène-1,4 diamine destinée aux contrôles de routine

(ISO 7393-2:2017)
Ta slovenski standard je istoveten z: EN ISO 7393-2:2018
ICS:
13.060.50 3UHLVNDYDYRGHQDNHPLþQH Examination of water for
VQRYL chemical substances
SIST EN ISO 7393-2:2018 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
SIST EN ISO 7393-2:2018
---------------------- Page: 2 ----------------------
SIST EN ISO 7393-2:2018
EN ISO 7393-2
EUROPEAN STANDARD
NORME EUROPÉENNE
January 2018
EUROPÄISCHE NORM
ICS 13.060.50 Supersedes EN ISO 7393-2:2000
English Version
Water quality - Determination of free chlorine and total
chlorine - Part 2: Colorimetric method using N,N-dialkyl-
1,4-phenylenediamine, for routine control purposes (ISO
7393-2:2017)

Qualité de l'eau - Dosage du chlore libre et du chlore Wasserbeschaffenheit - Bestimmung von freiem Chlor

total - Partie 2: Méthode colorimétrique à la N,N- und Gesamtchlor - Teil 2: Kolorimetrisches Verfahren

diéthylphénylène-1,4 diamine destinée aux contrôles mit N,N-Diethyl-1,4-Phenylendiamin für

de routine (ISO 7393-2:2017) Routinekontrollen (ISO 7393-2:2017)
This European Standard was approved by CEN on 9 December 2017.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this

European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references

concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN

member.

This European Standard exists in three official versions (English, French, German). A version in any other language made by

translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management

Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,

Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,

Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,

Turkey and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels

© 2018 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 7393-2:2018 E

worldwide for CEN national Members.
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SIST EN ISO 7393-2:2018
EN ISO 7393-2:2018 (E)
Contents Page

European foreword ....................................................................................................................................................... 3

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SIST EN ISO 7393-2:2018
EN ISO 7393-2:2018 (E)
European foreword

This document (EN ISO 7393-2:2018) has been prepared by Technical Committee ISO/TC 147 " Water

quality" in collaboration with Technical Committee CEN/TC 230 “Water analysis”, the secretariat of

which is held by DIN.

This European Standard shall be given the status of a national standard, either by publication of an

identical text or by endorsement, at the latest by July 2018, and conflicting national standards shall be

withdrawn at the latest by July 2018.

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. CEN shall not be held responsible for identifying any or all such patent rights.

This document supersedes EN ISO 7393-2:2000.

According to the CEN-CENELEC Internal Regulations, the national standards organizations of the

following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,

Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia,

France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,

Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,

Turkey and the United Kingdom.
Endorsement notice

The text of ISO 7393-2:2017 has been approved by CEN as EN ISO 7393-2:2018 without any

modification.
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SIST EN ISO 7393-2:2018
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SIST EN ISO 7393-2:2018
INTERNATIONAL ISO
STANDARD 7393-2
Second edition
2017-12
Water quality — Determination of free
chlorine and total chlorine —
Part 2:
Colorimetric method using N,N-
dialkyl-1,4-phenylenediamine, for
routine control purposes
Qualité de l'eau — Dosage du chlore libre et du chlore total —
Partie 2: Méthode colorimétrique à la N,N-dialkylphénylène-1,4
diamine destinée aux contrôles de routine
Reference number
ISO 7393-2:2017(E)
ISO 2017
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SIST EN ISO 7393-2:2018
ISO 7393-2:2017(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2017, Published in Switzerland

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form

or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior

written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of

the requester.
ISO copyright office
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
ii © ISO 2017 – All rights reserved
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SIST EN ISO 7393-2:2018
ISO 7393-2:2017(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 2

4 Principle ........................................................................................................................................................................................................................ 2

4.1 Determination of free chlorine.................................................................................................................................................. 2

4.2 Determination of total chlorine ................................................................................................................................................ 3

5 Interferences ............................................................................................................................................................................................................ 3

5.1 General ........................................................................................................................................................................................................... 3

5.2 lnterference by other chlorine compounds .................................................................................................................... 3

5.3 lnterference by compounds other than chlorine compounds ........................................................................ 3

5.4 Interference due to the presence of oxidized manganese ................................................................................. 3

5.5 Interference due to turbid and coloured samples .................................................................................................... 4

6 Reagents ........................................................................................................................................................................................................................ 4

7 Apparatus ..................................................................................................................................................................................................................... 6

8 Sampling ........................................................................................................................................................................................................................ 7

9 Procedure..................................................................................................................................................................................................................... 7

9.1 Test sample ................................................................................................................................................................................................. 7

9.2 Test portions ............................................................................................................................................................................................. 7

9.3 Calibration .................................................................................................................................................................................................. 7

9.4 Determination of free chlorine.................................................................................................................................................. 7

9.5 Determination of total chlorine ................................................................................................................................................ 8

10 Calculation .................................................................................................................................................................................................................. 9

10.1 Calculation of the free chlorine concentration ............................................................................................................ 9

10.2 Calculation of the total chlorine concentration .......................................................................................................... 9

10.3 Conversion of amount of substance concentration to mass concentration ....................................... 9

11 Expression of results ........................................................................................................................................................................................ 9

12 Test report ................................................................................................................................................................................................................... 9

Annex A (informative) Separate determinations of combined chlorine of the
monochloramine type, combined chlorine of the dichloramine type and of

combined chlorine in the form of nitrogen trichloride ............................................................................................11

Annex B (informative) Performance data ....................................................................................................................................................14

Annex C (informative) Disposable planar reagent-filled cuvettes using a mesofluidic

channel pump/colorimeter ....................................................................................................................................................................17

Bibliography .............................................................................................................................................................................................................................19

© ISO 2017 – All rights reserved iii
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SIST EN ISO 7393-2:2018
ISO 7393-2:2017(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, governmental 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.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www.iso.org/patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to the

World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following

URL: www.iso.org/iso/foreword.html.

This document was prepared by Technical Committee ISO/TC 147, Water quality, Subcommittee SC 2,

Physical, chemical and biochemical methods.

This second edition cancels and replaces the first edition (ISO 7393-2:1985), which has been technically

revised.
The main changes compared to the previous edition are as follows:

— a new Annex C has been included with the title: Disposable planar reagent-filled cuvettes using a

mesofluidic channel pump/colorimeter.
A list of all parts in the ISO 7393 series can be found on the ISO website.
iv © ISO 2017 – All rights reserved
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SIST EN ISO 7393-2:2018
INTERNATIONAL STANDARD ISO 7393-2:2017(E)
Water quality — Determination of free chlorine and total
chlorine —
Part 2:
Colorimetric method using N,N-dialkyl-1,4-
phenylenediamine, for routine control purposes

WARNING — Persons using this document should be familiar with normal laboratory practice.

This document does not purport to address all of the safety problems, if any, associated with its

use. It is the responsibility of the user to establish appropriate safety and health practices.

IMPORTANT — It is essential that tests conducted in accordance with this document be carried

out by suitably qualified staff.
1 Scope

This document specifies a method for the determination of free chlorine and total chlorine in water,

readily applicable to lab- and field-testing. It is based on measurement of the absorption, the red DPD

colour complex in a photometer or the colour intensity by visual comparison of the colour with a scale

of standards that is regularly calibrated.

This method is appropriate for drinking water and other waters, where additional halogens like

bromine, iodine and other oxidizing agents are present in almost negligible amounts. Seawater and

waters containing bromides and iodides comprise a group for which special procedures are to be

carried out.

This method is in practice applicable to concentrations, in terms of chlorine (Cl ), from, for example,

0,000 4 mmol/l to 0,07 mmol/l (e.g. 0,03 mg/l to 5 mg/l) total chlorine. For higher concentrations, the

test portion is diluted.

Commonly, the method is applied as a field method with mobile photometers and commercially available

ready-for-use reagents (liquid reagents, powders and tablets). It is essential that those reagents comply

with minimum requirements and contain the essential reagents and a buffer system suitable to adjust

the measurement solution to a pH range of typically 6,2 to 6,5. If there is doubt that water samples

have uncommon pH values and/or buffer capacities, the user has to check and, if necessary, to adjust

the sample pH to the required range. The pH of the sample is within the range of pH 4 and 8. Adjust, if

necessary, with sodium hydroxide solution or sulfuric acid before the test.

A procedure for the differentiation of combined chlorine of the monochloramine type, combined

chlorine of the dichloramine type and combined chlorine in the form of nitrogen trichloride is

presented in Annex A. In Annex C, a procedure is presented for the determination of free and total

chlorine in drinking and other low polluted waters, for disposable planar reagent-filled cuvettes using a

mesofluidic channel pump/colorimeter.
2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any amendments) applies.

ISO 3696, Water for analytical laboratory use — Specification and test methods

ISO 5667-3, Water quality — Sampling — Part 3: Preservation and handling of water samples

© ISO 2017 – All rights reserved 1
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SIST EN ISO 7393-2:2018
ISO 7393-2:2017(E)

ISO 8466-1, Water quality — Calibration and evaluation of analytical methods and estimation of

performance characteristics — Part 1: Statistical evaluation of the linear calibration function

3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— IEC Electropedia: available at http://www.electropedia.org/
— ISO Online browsing platform: available at https://www.iso.org/obp
3.1
free chlorine

chlorine present in the form of hypochlorous acid, hypochlorite ion or dissolved elemental chlorine

Note 1 to entry: See Table 1.
3.2
combined chlorine
bound chlorine

fraction of total chlorine (3.3) present in the form of chloramines (3.4) and organic chloramines

Note 1 to entry: See Table 1.
3.3
total chlorine
chlorine present in the form of free chlorine (3.1) and combined chlorine (3.2)
Note 1 to entry: See Table 1.
3.4
chloramines

derivatives of ammonia by substitution of one, two or three hydrogen atoms with chlorine atoms

Note 1 to entry: Derivatives are monochloramine NH Cl, dichloramine NHCl , nitrogen trichloride NCl and all

2 2 3

chlorinated derivatives of organic nitrogen compounds as determined by the method specified in this document.

Table 1 — Terms and synonyms in relation to actual compounds in the solution
Term Synonym Compounds
Active free chlorine Elemental chlorine, hypochlorous acid
Free chlorine Free chlorine
Potential free chlorine Hypochlorite
Elemental chlorine, hypochlorous acid, hy-
Total chlorine Total residual chlorine
pochlorite, and chloramines
Bound chlorine Combined chlorine Difference of total and free chlorine
4 Principle
4.1 Determination of free chlorine

Free chlorine is determined by a direct reaction with N,N-dialkyl-1,4-phenylenediamine (DPD) in a pH

range of 6,2 to 6,5. This leads to the formation of a red colour complex. Measure the colour intensity

by photometry, or alternatively, by visual comparison of the colour with a scale of permanent glass,

plastics standards or colour card comparators.
2 © ISO 2017 – All rights reserved
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SIST EN ISO 7393-2:2018
ISO 7393-2:2017(E)

If ready-to-use test kits are used, deviant pH ranges (buffer systems) may be provided. The user of

these test kits has to validate the suitability of the provided buffer systems for the range of sample

matrices of interest.
4.2 Determination of total chlorine

The reaction is carried out with DPD in the presence of an excess of potassium iodide. The measurement

is then carried out as described in 4.1.
5 Interferences
5.1 General
Manufacturers’ instructions on additional interferences shall be considered.
5.2 lnterference by other chlorine compounds

Chlorine dioxide that might be present in the sample in addition to chlorine is measured as total

chlorine. This interference may be corrected by specific determination of chlorine dioxide in the water

(see References [3], [5] and [6]).

If chlorine dioxide is present in the sample as the only disinfectant, it may be measured with the DPD

method described in Clause 9 with the appropriate conversion factor. Other chlorine compounds do not

specifically cause oxidation of DPD.
5.3 lnterference by compounds other than chlorine compounds

Depending on the concentration and the chemical oxidation potential, other oxidizing agents affect the

reaction, for example, bromine, iodine, bromamines, iodoamines, ozone, hydrogen peroxide, chromate,

oxidized manganese, nitrite, iron(III) ions, peracetic acid and copper ions. The interference from Cu(II)

(<8 mg/l) and iron (<20 mg/l) is suppressed by the disodium EDTA in reagents 6.2 and 6.3.

NOTE Bromine and monobromamine contribute to the disinfection effect and regularly occur in chlorine-

based disinfection products.

lnterference by chromate may be eliminated by addition of excess barium chloride.

The user has to validate how to cope with these interferences. In particular, for waste waters or cooling

waters, it has to be considered that high amounts of interfering compounds may be present.

5.4 Interference due to the presence of oxidized manganese

Determine the effect of oxidized manganese by carrying out a supplementary determination on a

further test portion (see 9.2) previously treated with the arsenite or thioacetamide solution (6.10) in

order to neutralize all oxidizing compounds other than oxidized manganese.

Place this test portion in a 250 ml conical flask, add 1 ml of sodium arsenite solution (6.10) or

thioacetamide solution (6.10) and mix. Again add 5,0 ml of buffer solution (6.2) and 5,0 ml of DPD

reagent (6.3) and mix. This procedure to quantify the oxidized manganese interference is given as

example. For ready-to-use reagents, other quantities may be required.

Fill the measuring cell with this treated solution and immediately measure the colour under the same

conditions as adopted for the calibration. Record c , the concentration reading from the comparator

scale or calibration graph, corresponding to the oxidized manganese present.

In using comparators with permanent glass colour standards or plastics standards or colour card

comparators, the arsenite or thioacetamide treated sample may be used as a blank to compensate for

any interference colour so long as the time of addition of reagents is the same for both blank and sample.

© ISO 2017 – All rights reserved 3
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SIST EN ISO 7393-2:2018
ISO 7393-2:2017(E)
5.5 Interference due to turbid and coloured samples

If the blank value matching is not possible, then, in case of turbid samples or in the case precipitation

occurs due to the addition of the buffer solution, the samples have to be filtered. The filtration equipment

and the filter material shall be chlorine demand free. This shall be checked accordingly. See 7.3 for a

procedure to prepare the glassware.

Filtration of samples may lead to losses in free chlorine. This can happen although the filters are chlorine

demand free. Therefore, the user has to demonstrate that this step does not lead to false results if it

cannot be avoided.
6 Reagents

During the analysis, use only reagents of recognized analytical grade, and only water as specified in 6.1.

6.1 Water as specified in ISO 3696, grade 2, free from oxidizing and reducing substances. Demineralized

or distilled water of which the quality is checked as follows.
In two 250 ml chlorine-demand-free conical flasks (7.3) place, in order,

a) in the first: 100 ml of the water to be checked and about 1 g of potassium iodide (6.4); mix and after

1 min, add 5 ml of buffer solution (6.2) and 5,0 ml of DPD reagent (6.3), and

b) in the second: 100 ml of the water to be checked and two drops of sodium hypochlorite solution

(6.7); then, after 2 min, 5,0 ml of buffer solution (6.2) and 5 ml of DPD reagent (6.3).

No colouration should appear in the first flask whereas it is essential that a light pink colouration

appears in the second flask.

If the demineralized or distilled water does not have the desired quality, it shall be chlorinated according

to the following procedure.

— First, chlorinate the demineralized or distilled water to a level of about 0,14 mmol/l (10 mg/l) and

store it in a well-stoppered carboy for at least 16 h.

— Then decholorinate the water by exposure to UV irradiation, sunlight for several hours or by contact

with active carbon.

— Finally, check the quality using the procedures as given in Clause 9. The user has to make sure that

the glassware is also chlorine demand free. The procedure is described in 7.3.
— Recheck the quality after a period of contact followed by dechlorination.

The volumes given to qualify the water are given as example, since for ready-to-use reagents, other

quantities of reagents could be used.
6.2 Buffer solution, pH 6,5.

Dissolve in water (6.1) in this order: 24 g of anhydrous disodium hydrogen phosphate (Na HPO ) or

2 4

60,5 g of the dodecahydrate form (Na HPO ·12H O) and 46 g of potassium dihydrogen phosphate

2 4 2

(KH PO ). Add 100 ml of 8 g/l disodium dihydrogenethylenedinitrilotetraacetate dihydrate (disodium

2 4
EDTA dihydrate, C H N O Na ·2H O) solution (or 0,8 g of the solid form).
10 14 2 8 2 2

If necessary, add 0,020 g of mercury(II) chloride (HgCl ), to prevent mould growth and interference in

the free chlorine test caused by any trace amounts of iodide in the reagents.

Dilute to 1 000 ml and mix. The buffer solution is stable for up to 3 months if stored in a tightly sealed

container in the dark. In reference to guaranteed stability of ready-to-use buffer solutions, see the

recommendations of the manufacturer.
4 © ISO 2017 – All rights reserved
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SIST EN ISO 7393-2:2018
ISO 7393-2:2017(E)

The buffer solution is an essential part for a proper reaction of DPD with chlorine. Therefore, this buffer

system also applies to the various reagents provided in ready-to-use test kits. Such ready-to-use test

kits are commonly intended for a certain range of buffer capacities in the samples. Therefore, the buffer

capacity of the test kit may be too low. Therefore, the user should make sure that the pH of the final

reagent sample mix lies between 6,2 and 6,5. If test kits use modified buffer systems with a deviant

pH range, it is up to the user to validate the suitability of this system for the matrices and samples of

interest.

To prevent contamination of the sample, pH checks may be carried out using a pH-meter or non-bleeding

pH-test strips. If necessary, samples should be adjusted to the correct pH range using hydrochloric acid

or sodium hydroxide solution. If there is no information on the buffer used or the buffer capacity of the

test kit, the manufacturer of the test kit shall not refer to this document.
Solutions containing mercury shall be disposed of safely.
6.3 N,N-dialkyl-1,4-phenylenediamine sulfate (DPD), solution, 1,1 g/l.

The DPD reagent is commercially available. It is available from numerous sources and the usage is handy

especially when tests are carried out with test kits on site. It is essential that commercially available

DPD reagents contain suitable amounts of acid and EDTA as well as a suitable DPD concentration. If

ready-to-use DPD regents are used, evidence has to be given that the composition is as suitable as the

formulation given below. If there is no such information, the manufacturer of the ready-to-use test kit

shall not refer to this document.
Alternatively, the DPD reagent can be prepared in the laborato
...

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