SIST EN ISO 7393-2:2018

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
• Public Enquiry End Date: 09-May-2017
• Publication Date: 06-May-2018
• ICS: 13.060.50 - Examination of water for chemical substances
• Technical Committee: KAV - Water quality
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 02-Mar-2018
• Due Date: 07-May-2018
• Completion Date: 07-May-2018
• Directive: 2002-01-3394 - Pravilnik o imisijskem monitoringu kakovosti površinske vode za življenje sladkovodnih vrst rib
• Directive: 2014-01-3849 - Pravilnik o prvih meritvah in obratovalnem monitoringu odpadnih voda
• Directive: 98/83/EC - Quality of water intended for human consumption
• Directive: TRRTP064 - Rules on initial measurements and operational monitoring of wastewater
• Ref Project: EN ISO 7393-2:2018 - 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)

Relations

• Replaces: SIST EN ISO 7393-2:2000 - Water quality - Determination of free chlorine and total chlorine - Part 2: Colorimetric method using N, N-diethyl-1, 4-phenylenediamine, for routine control purposes (ISO 7393-2:1985)
• Effective Date: 01-Jun-2018

Standards Content (Sample)

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

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.

Contents Page
European foreword . 3

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.
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
ISO 7393-2:2017(E)
© 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. [phone]
Fax [phone]
[e-mail]
www.iso.org
ii © ISO 2017 – All rights reserved

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 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

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 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

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 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

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 laboratory.
Mix 250
...