EN 938:2016

Chemicals used for treatment of water intended for human consumption - Sodium chlorite

This European Standard is applicable to sodium chlorite used for treatment of water intended for human consumption. It describes the characteristics of sodium chlorite and specifies the requirements and the corresponding test methods for sodium chlorite. It gives information on its use in water treatment.

Produkte zur Aufbereitung von Wasser für den menschlichen Gebrauch - Natriumchlorit

Diese Europäische Norm gilt für Natriumchlorit zur Aufbereitung von Wasser für den menschlichen Gebrauch. Sie beschreibt die Eigenschaften von Natriumchlorit und legt die Anforderungen sowie die entsprechenden Prüfverfahren für Natriumchlorit fest. Sie enthält Angaben zu dessen Anwendung in der Wasseraufbereitung.

Produits chimiques utilisés pour le traitement de l'eau destinée à la consommation humaine - Chlorite de sodium

La présente Norme européenne s’applique au chlorite de sodium utilisé pour le traitement de l’eau destinée à la consommation humaine. Elle décrit les caractéristiques du chlorite de sodium et spécifie les exigences et les méthodes d’essai correspondantes. Elle donne des informations sur son emploi pour le traitement de l’eau.

Kemikalije, ki se uporabljajo za pripravo pitne vode - Natrijev klorit

Ta evropski standard se uporablja za natrijev klorit, ki se uporablja za pripravo pitne vode. Opisuje lastnosti natrijevega klorita ter določa zahteve in ustrezne preskusne metode zanj. Podaja informacije za njegovo uporabo pri pripravi vode.

General Information

• Status: Published
• Publication Date: 30-Aug-2016
• Withdrawal Date: 29-Nov-2016
• ICS: 71.100.80 - Chemicals for purification of water
• Technical Committee: CEN/TC 164 - Water supply
• Drafting Committee: CEN/TC 164/WG 9 - Drinking water treatment
• Current Stage: 6060 - Definitive text made available (DAV) - Publishing
• Start Date: 25-May-2016
• Due Date: 29-Jun-2016
• Completion Date: 25-May-2016
• Ref Project: SIST EN 938:2016 - Chemicals used for treatment of water intended for human consumption - Sodium chlorite

Relations

• Replaces: EN 938:2009 - Chemicals used for treatment of water intended for human consumption - Sodium chlorite
• Effective Date: 10-Jul-2013
• Amended By: EN 938:2016/prA1 - Chemicals used for treatment of water intended for human consumption - Sodium chlorite
• Effective Date: 20-Feb-2019

Standards Content (Sample)

SLOVENSKI STANDARD
SIST EN 938:2016
01-julij-2016
1DGRPHãþD
SIST EN 938:2009
Kemikalije, ki se uporabljajo za pripravo pitne vode - Natrijev klorit
Chemicals used for treatment of water intended for human consumption - Sodium
chlorite

Produkte zur Aufbereitung von Wasser für den menschlichen Gebrauch - Natriumchlorit

Produits chimiques utilisés pour le traitement de l'eau destinée à la consommation

humaine - Chlorite de sodium
Ta slovenski standard je istoveten z: EN 938:2016
ICS:
13.060.20 Pitna voda Drinking water
71.100.80 .HPLNDOLMH]DþLãþHQMHYRGH Chemicals for purification of
water
SIST EN 938:2016 en,fr,de

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

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SIST EN 938:2016
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SIST EN 938:2016
EN 938
EUROPEAN STANDARD
NORME EUROPÉENNE
May 2016
EUROPÄISCHE NORM
ICS 71.100.80 Supersedes EN 938:2009
English Version
Chemicals used for treatment of water intended for human
consumption - Sodium chlorite

Produits chimiques utilisés pour le traitement de l'eau Produkte zur Aufbereitung von Wasser für den

destinée à la consommation humaine - Chlorite de menschlichen Gebrauch - Natriumchlorit

sodium
This European Standard was approved by CEN on 18 March 2016.

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, 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: Avenue Marnix 17, B-1000 Brussels

© 2016 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 938:2016 E

worldwide for CEN national Members.
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SIST EN 938:2016
EN 938:2016 (E)
Contents Page

European foreword ....................................................................................................................................................... 4

Introduction .................................................................................................................................................................... 5

1 Scope .................................................................................................................................................................... 6

2 Normative references .................................................................................................................................... 6

3 Description ........................................................................................................................................................ 6

3.1 Identification .................................................................................................................................................... 6

3.1.1 Chemical name ................................................................................................................................................. 6

3.1.2 Synonym or common name ......................................................................................................................... 6

3.1.3 Relative molecular mass ............................................................................................................................... 6

3.1.4 Empirical formula ........................................................................................................................................... 6

3.1.5 Chemical formula ............................................................................................................................................ 6

3.1.6 CAS Registry Number .................................................................................................................................... 6

3.1.7 EINECS reference ............................................................................................................................................ 7

3.2 Commercial form ............................................................................................................................................. 7

3.3 Physical properties ......................................................................................................................................... 7

3.3.1 Appearance ........................................................................................................................................................ 7

3.3.2 Density ................................................................................................................................................................ 7

3.3.3 Solubility in water ........................................................................................................................................... 7

3.3.4 Vapour pressure .............................................................................................................................................. 7

3.3.5 Boiling point at 100 kPa ............................................................................................................................... 7

3.3.6 Crystallization point ....................................................................................................................................... 7

3.3.7 Specific heat ...................................................................................................................................................... 8

3.3.8 Viscosity (dynamic) ........................................................................................................................................ 8

3.3.9 Critical temperature ...................................................................................................................................... 8

3.3.10 Critical pressure .............................................................................................................................................. 8

3.3.11 Physical hardness ........................................................................................................................................... 8

3.4 Chemical properties ....................................................................................................................................... 8

4 Purity criteria ................................................................................................................................................... 8

4.1 General ................................................................................................................................................................ 8

4.2 Composition of commercial product ........................................................................................................ 9

4.3 Impurities and main by-products ............................................................................................................. 9

4.4 Chemical parameters ..................................................................................................................................... 9

5 Test methods ................................................................................................................................................. 10

5.1 Sampling .......................................................................................................................................................... 10

5.1.1 General ............................................................................................................................................................. 10

5.1.2 Sampling from drums and bottles .......................................................................................................... 10

5.1.3 Sampling from tanks and tankers .......................................................................................................... 10

5.2 Analysis ............................................................................................................................................................ 11

5.2.1 Determination of sodium chlorite (main product) .......................................................................... 11

5.2.2 Impurities ....................................................................................................................................................... 12

5.2.3 Chemical parameters .................................................................................................................................. 15

6 Labelling - Transportation - Storage ..................................................................................................... 17

6.1 Means of delivery ......................................................................................................................................... 17

6.2 Labelling according to the EU Legislation .......................................................................................... 17

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6.3 Transportation regulations and labelling ........................................................................................... 17

6.4 Marking ............................................................................................................................................................ 18

6.5 Storage .............................................................................................................................................................. 18

6.5.1 General ............................................................................................................................................................. 18

6.5.2 Long term stability ....................................................................................................................................... 18

6.5.3 Storage incompatibilities ........................................................................................................................... 18

Annex A (informative) General information on sodium chlorite ............................................................... 19

A.1 Origin ................................................................................................................................................................ 19

A.1.1 Raw materials ................................................................................................................................................ 19

A.1.2 Manufacturing process ............................................................................................................................... 19

A.2 Use ...................................................................................................................................................................... 19

A.2.1 Function ........................................................................................................................................................... 19

A.2.2 Form in which it is used.............................................................................................................................. 19

A.2.3 Treatment dose ............................................................................................................................................. 19

A.2.4 Means of application .................................................................................................................................... 19

A.2.5 Secondary effects .......................................................................................................................................... 19

A.2.6 Removal of excess product ........................................................................................................................ 20

A.3 Routine analyses ........................................................................................................................................... 20

A.3.1 Determination of sodium chlorite (NaClO2) ....................................................................................... 20

A.3.2 Determination of chlorate ion (ClO ).................................................................................................... 22

A.3.3 Determination of chemical parameters ............................................................................................... 23

Annex B (normative) General rules relating to safety ................................................................................... 24

B.1 Rules for safe handling and use ............................................................................................................... 24

B.2 Emergency procedures ............................................................................................................................... 24

B.2.1 First aid ............................................................................................................................................................ 24

B.2.2 Spillage ............................................................................................................................................................. 24

B.2.3 Fire ..................................................................................................................................................................... 24

Annex C (normative) Determination of arsenic, antimony and selenium (atomic absorption

spectrometry hydride technique) .......................................................................................................... 25

C.1 Safety precautions ........................................................................................................................................ 25

C.2 General principle .......................................................................................................................................... 25

C.3 Interferences .................................................................................................................................................. 25

C.4 Reagents ........................................................................................................................................................... 25

C.5 Apparatus ........................................................................................................................................................ 27

C.6 Procedure ........................................................................................................................................................ 29

C.6.1 Preparation of the apparatus ................................................................................................................... 29

C.6.2 Preparation of calibration solutions ..................................................................................................... 30

C.6.3 Preparation of test solutions and standard solutions ..................................................................... 30

C.6.4 Determination of arsenic with sodium borohydride ....................................................................... 30

C.6.5 Determination of selenium with sodium borohydride ................................................................... 30

C.6.6 Determination of antimony with sodium borohydride .................................................................. 31

C.7 Calculation....................................................................................................................................................... 31

Bibliography ................................................................................................................................................................. 32

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SIST EN 938:2016
EN 938:2016 (E)
European foreword

This document (EN 938:2016) has been prepared by Technical Committee CEN/TC 164 “Water supply”,

the secretariat of which is held by AFNOR.

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 November 2016, and conflicting national standards

shall be withdrawn at the latest by November 2016.

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

patent rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent

rights.
This document supersedes EN 938:2009.

Significant technical differences between this edition and EN 938:2009 are as follows:

a) deletion of reference to EU Directive 67/548/EEC of June 27, 1967 in order to take into account the

latest Regulation in force (see [2]);
b) use of the changed classification and labelling (see [2]).

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, Slovakia, Slovenia, Spain, Sweden, Switzerland,

Turkey and the United Kingdom.
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SIST EN 938:2016
EN 938:2016 (E)
Introduction

In respect of potential adverse effects on the quality of water intended for human consumption, caused

by the product covered by this European Standard:

a) this European Standard provides no information as to whether the product may be used without

restriction in any of the Member States of the EU or EFTA;

b) it should be noted that, while awaiting the adoption of verifiable European criteria, existing

national regulations concerning the use and/or the characteristics of this product remain in force.

NOTE Conformity with the standard does not confer or imply acceptance or approval of the product in any of

the Member States of the EU or EFTA. The use of the product covered by this European Standard is subject to

regulation or control by National Authorities.
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SIST EN 938:2016
EN 938:2016 (E)
1 Scope

This European Standard is applicable to sodium chlorite used for treatment of water intended for

human consumption. It describes the characteristics of sodium chlorite and specifies the requirements

and the corresponding test methods for sodium chlorite. It gives information on its use in water

treatment.
2 Normative references

The following documents, in whole or in part, are normatively referenced in this document and are

indispensable for its application. For dated references, only the edition cited applies. For undated

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

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

EN ISO 12846, Water quality — Determination of mercury — Method using atomic absorption

spectrometry (AAS) with and without enrichment (ISO 12846)
ISO 3165, Sampling of chemical products for industrial use — Safety in sampling
ISO 6206, Chemical products for industrial use — Sampling — Vocabulary

ISO 8288, Water quality — Determination of cobalt, nickel, copper, zinc, cadmium and lead — Flame

atomic absorption spectrometric methods

ISO 9174, Water quality — Determination of chromium — Atomic absorption spectrometric methods

3 Description
3.1 Identification
3.1.1 Chemical name
Sodium chlorite.
3.1.2 Synonym or common name
None.
3.1.3 Relative molecular mass
90,44.
3.1.4 Empirical formula
NaClO .
3.1.5 Chemical formula
Na-O-Cl = O.
3.1.6 CAS Registry Number
7758-19-2.
1) Chemical Abstracts Service Registry Number.
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EN 938:2016 (E)
3.1.7 EINECS reference
231-836-6.
3.2 Commercial form

The product is supplied as a powder or as an aqueous solution of sodium chlorite.

3.3 Physical properties
3.3.1 Appearance
The products are either a white powder or a greenish-yellow aqueous solution.
3.3.2 Density
The density of sodium chlorite solutions is given in Table 1.
Table 1 — Density of sodium chlorite solutions
Aqueous solution concentration Density
% (mass fraction) g/ml at 20 °C
25 1,210
31 1,270
3.3.3 Solubility in water
The solubility of sodium chlorite depending on temperature is given in Table 2.
Table 2 — Solubility of sodium chlorite
Temperature Solubility
°C g/l
5 340
17 390
30 460
45 530
60 550
3.3.4 Vapour pressure
Not applicable.
3.3.5 Boiling point at 100 kPa
Not applicable.
3.3.6 Crystallization point

The crystallization point of sodium chlorite depending on concentration is given in Table 3.

2) European Inventory of Existing Commercial Chemical Substances.
3) 100 kPa = 1 bar.
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EN 938:2016 (E)
Table 3 — Crystallization point of sodium chlorite
Aqueous solution concentration Crystallization point
% (mass fraction) °C
25 − 14,5
31 3
3.3.7 Specific heat
Not known.
3.3.8 Viscosity (dynamic)
The viscosity of sodium chlorite depending on concentration is given in Table 4.
Table 4 — Viscosity of sodium chlorite
Aqueous solution concentration Viscosity
% (mass fraction) mPa.s at 20 °C
25 2,33
31 3,26
3.3.9 Critical temperature
Not applicable.
3.3.10 Critical pressure
Not applicable.
3.3.11 Physical hardness
Not applicable.
3.4 Chemical properties

Sodium chlorite is a strong oxidizing agent. It generates chlorine dioxide with acidic solutions or

chlorine and reacts with organic compounds.
4 Purity criteria
4.1 General

This European Standard specifies the minimum purity requirements for sodium chlorite used for the

treatment of water intended for human consumption. Limits are given for impurities commonly present

in the product. Depending on the raw material and the manufacturing process other impurities may be

present and, if so, this shall be notified to the user and when necessary to the relevant authorities.

Users of this product should check the national regulations in order to clarify whether it is of

appropriate purity for treatment of water intended for human consumption, taking into account raw

water quality, required dosage, contents of other impurities and additives used in the product not

stated in the product standard.

Limits have been given for impurities and chemicals parameters where these are likely to be present in

significant quantities from the current production process and raw materials. If the production process

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EN 938:2016 (E)

or raw materials leads to significant quantities of impurities, by-products or additives being present,

this shall be notified to the user.
4.2 Composition of commercial product

The sodium chlorite is available as a powder or as an aqueous solution with sodium chlorite content

of 7,5 percent by mass fraction to 35 percent by mass fraction.

The content of sodium chlorite shall be equal to or greater than the manufacturer’s declared value.

4.3 Impurities and main by-products
The product shall conform to the requirements specified in Table 5.
Table 5 — Impurities
Impurity Limit
g/kg sodium chlorite
100 % mass fraction
Sodium chlorate (NaClO ) max. 40
Sodium nitrate (NaNO ) max. 1
NOTE Sodium chlorate can be a by-product of the manufacturing process.
4.4 Chemical parameters

NOTE For the purposes of this standard, “chemical parameters” are those defined in the

EU Directive 98/83/EC of November 13, 1998 (see [1]).

The content of chemical parameters shall conform to the requirements specified in Table 6.

Table 6 — Chemical parameters
Parameter Limit
mg/kg sodium chlorite
100 % mass fraction
Type 1 Type 2
Arsenic (As) max. 1,1 7,5
Cadmium (Cd) max. 1,5 7,5
Chromium (Cr) max. 1,1 7,5
Mercury (Hg) max. 1,1 3,7
Nickel (Ni) max. 1,1 7,5
Lead (Pb) max. 1,1 7,5
Antimony (Sb) max. 1,1 7,5
Selenium (Se) max. 1,1 7,5
NOTE Cyanide which does not exist in a strong oxidizing medium such as
sodium chlorite is not a relevant chemical parameter. Pesticides and polycyclic
aromatic hydrocarbons are not by-products of the manufacturing process.
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EN 938:2016 (E)
5 Test methods
5.1 Sampling
5.1.1 General
Observe the general recommendations of ISO 3165 and take ISO 6206 into account.
5.1.2 Sampling from drums and bottles
5.1.2.1 General

5.1.2.1.1 Mix the contents of the container to be sampled by shaking the container, by rolling it or by

rocking it from side to side, taking care not to damage the container or spill any of the liquid.

5.1.2.1.2 If the design of the container is such (for example, a narrow-necked bottle) that it is

impracticable to use a sampling implement, take a sample by pouring after the contents have been

thoroughly mixed. Otherwise, proceed as described in 5.1.2.3.

5.1.2.1.3 Examine the surface of the liquid. If there are signs of surface contamination, take samples

from the surface as described in 5.1.2.2; otherwise, take samples as described in 5.1.2.3.

5.1.2.2 Surface sampling

Take a sample using a suitable ladle. Lower the ladle into the liquid until the rim is just below the

surface, so that the surface layer runs into it. Withdraw the ladle just before it fills completely and allow

any liquid adhering to the ladle to drain off. If necessary, repeat this operation so that, when the other

selected containers have been sampled in a similar manner, the total volume of sample required for

subsequent analysis is obtained.
5.1.2.3 Bottom sampling

Take a sample using an open sampling tube, or a bottom-valve sampling tube, suited to the size of

container and the viscosity of the liquid.

When using an open sampling tube, close it at the top and then lower the bottom end to the bottom of

the container. Open the tube and move it rapidly so that the bottom of the tube traverses the bottom of

the container before the tube is filled. Close the tube, withdraw it from the container and allow any

liquid adhering to the outside of the tube to drain off.

When using a bottom-valve sampling tube, close the valve before lowering the tube into the container

and then proceed in a similar manner to that when using an open sampling tube.
5.1.3 Sampling from tanks and tankers
From each access point, take samples as follows:
a) from the surface of the liquid, using a ladle as described in 5.1.2.2;

b) from the bottom of the tank or tanker, using a sampling tube as described in 5.1.2.3 or using a

specially designed bottom-sampling apparatus;

c) from one or more positions, depending on the overall depth, between the bottom and the surface

using a weighted sampling can.
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EN 938:2016 (E)
5.2 Analysis
5.2.1 Determination of sodium chlorite (main product)
5.2.1.1 General

This method applies to the measurements of sodium chlorite content in commercial sodium chlorite

solutions and is specific for these species.
5.2.1.2 Principle

Automated iodometric titration with an excess of sulfuric acid. This method is based on the reducing

action of the iodide ion on the chlorite species and on the subsequent determination of iodine formed,

by redox titration against sodium thiosulfate; the potential step is located around 230 mV.

5.2.1.3 Reagents

All reagents shall be of a recognized analytical grade and the water used shall conform to grade 3 in

accordance with EN ISO 3696.
5.2.1.3.1 Sulfuric acid solution, c(H SO ) = 0,5 mol/l.
2 4

5.2.1.3.2 Sodium thiosulfate standard volumetric solution, c(Na S O .5H O) = 0,1 mol/l.

2 2 3 2

Dissolve 24,8 g of Na S O .5H O in water. Add 0,5 ml of chloroform as preservative, dilute to volume

2 2 3 2
with water in a 1 000 ml one-mark volumetric flask and mix thoroughly.

To standardize: Weigh, to the nearest 0,1 mg, (160 ± 10) mg (m) of primary standard potassium

dichromate into a tared glass beaker. Place the contents of the beaker in a 500 ml stoppered conical

flask, add 100 ml of water and (2 ± 0,5) g of potassium iodide and stir to dissolve. Add (15 ± 1) ml of

hydrochloric acid solution (diluted 1 + 1 by volume), swirl, and allow to stand for 5 min.

...