SIST EN 938:2016

SLOVENSKI STANDARD
oSIST prEN 938:2014
01-september-2014
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: prEN 938
ICS:
13.060.20 Pitna voda Drinking water
71.100.80 .HPLNDOLMH]DþLãþHQMHYRGH Chemicals for purification of
water
oSIST prEN 938:2014 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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oSIST prEN 938:2014

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oSIST prEN 938:2014

EUROPEAN STANDARD
DRAFT
prEN 938
NORME EUROPÉENNE

EUROPÄISCHE NORM

June 2014
ICS 71.100.80 Will supersede 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 sodium menschlichen Gebrauch - Natriumchlorit
This draft European Standard is submitted to CEN members for enquiry. It has been drawn up by the Technical Committee CEN/TC 164.

If this draft becomes a European Standard, 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.

This draft European Standard was established by CEN 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.

Recipients of this draft are invited to submit, with their comments, notification of any relevant patent rights of which they are aware and to
provide supporting documentation.

Warning : This document is not a European Standard. It is distributed for review and comments. It is subject to change without notice and
shall not be referred to as a European Standard.


EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2014 CEN All rights of exploitation in any form and by any means reserved Ref. No. prEN 938:2014 E
worldwide for CEN national Members.

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Contents Page
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
6.3 Transportation regulations and labelling . 18
6.4 Marking . 18
6.5 Storage . 18
6.5.1 Long term stability . 18
6.5.2 Storage incompatibilities . 18
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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.3.2 Determination of chlorate ion (ClO ) . 22
3
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 General principle . 25
C.2 Interferences . 25
C.3 Reagents. 25
C.4 Apparatus . 27
C.5 Procedure . 28
C.5.1 Preparation of the apparatus . 28
C.5.2 Preparation of calibration solutions . 29
C.5.3 Preparation of test solutions and standard solutions . 29
C.5.4 Determination of arsenic with sodium borohydride . 29
C.5.5 Determination of selenium with sodium borohydride . 30
C.5.6 Determination of antimony with sodium borohydride . 30
C.6 Calculation . 30
Bibliography . 31

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Foreword
This document (prEN 938:2014) has been prepared by Technical Committee CEN/TC 164 “Water supply”, the
secretariat of which is held by AFNOR.
This document is currently submitted to the CEN Enquiry.
This document will supersede EN 938:2009.
The 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]).
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Introduction
In respect of potential adverse effects on the quality of water intended for human consumption, caused by the
product covered by this Standard:
a) this 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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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 1483, Water quality — Determination of mercury — Method using atomic absorption spectrometry
EN ISO 3696, Water for analytical laboratory use — Specification and test methods (ISO 3696)
ISO 3165, Sampling of chemical products for industrial use — Safety in sampling
ISO 6206, Chemical products for industrial use — Sampling — Vocabulary
ISO 8288:1986, Water quality — Determination of cobalt, nickel, copper, zinc, cadmium and lead — Flame
atomic absorption spectrometric methods
ISO 9174, Water quality — Determination of total 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 .
2
3.1.5 Chemical formula
NaClO .
2
1)
3.1.6 CAS Registry Number )
7758-19-2.

1) Chemical Abstracts Service Registry Number.
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2)
3.1.7 EINECS reference
231-836-6.
3.2 Commercial form
The product is supplied as an aqueous solution of sodium chlorite.
3.3 Physical properties
3.3.1 Appearance
The products are greenish-yellow aqueous solution.
3.3.2 Density
The density of sodium chlorite is given in Table 1.
Table 1 — Density of sodium chlorite
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)
3.3.5 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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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.
NOTE 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.
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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 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 an aqueous solution with sodium chlorite content of 24,5 percent by mass
fraction to 35 percent by mass fraction.
Solutions of 25 percent by mass fraction and 31 percent by mass fraction of sodium chlorite are the most
commonly used.
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
3

NOTE Sodium chlorate can be a by-product of the manufacturing process.
4.4 Chemical parameters
NOTE For the purpose 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 in mg/kg
of sodium chlorite 100 % of 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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5 Test methods
5.1 Sampling
5.1.1 General
Observe the general recommendations of ISO 3165 and take account of ISO 6206.
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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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
5.2.1.3.1 All reagents shall be of a recognized analytical grade and the water used shall conform to grade 3
in accordance with EN ISO 3696.
5.2.1.3.2 Sulfuric acid solution, c(H SO ) = 0,5 mol/l.
2 4
5.2.1.3.3 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 with
2 2 3 2
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. Titrate with the sodium thiosulfate solution until
the solution is pale yellow. Add (5 ± 1) ml of starch solution 1 % (mass fraction) and titrate to the end point, i.e.
to the disappearance of the blue-black colour. Record the volume (V) used.
S O .5H O), expressed in
The concentration, c, of the sodium thiosulfate standard volumetric solution (Na
2 2 3 2
moles per litre is given by the following equation:
m
c= (1)
V× 49,0317
where
m is the mass, in milligrams, of potassium dichromate (K Cr O ) weighed;
2 2 7
V is the volume, in millilitres, of the sodium thiosulfate standard volumetric solution used.

5.2.1.3.4 Potassium iodid
5.2.1.4 Apparatus
5.2.1.4.1 Ordinary laboratory apparatus and glassware with together the following:
5.2.1.4.2 Automatic potentiometric titrimeter.
5.2.1.4.3 Automatic burette, 10 ml, equipped with an injection tip.
5.2.1.4.4 Electromechanical stirrer.
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5.2.1.4.5 Glass titration beaker, 400 ml.
5.2.1.4.6 Platinum – Silver/Silver-chloride combination electrode with a porous plug electrolytic junction.
5.2.1.5 Procedure
5.2.1.5.1 Test solution
Weigh, to the nearest 0,1 mg, a test portion (m) between 0,11 g and 0,15 g the laboratory sample.
5.2.1.5.2 Determination
Transfer the test solution (5.2.1.5.1) to a 400 ml titration beaker with 300 ml of water and 4 g of potassium
iodide (5.2.1.3.4) and add, with stirring, 20 ml of H SO (5.2.1.3.2).
2 4
Input the calculation data in the titration microprocessor in accordance with the instruction manual.
Introduce the electrode into the titration beaker and titrate with the sodium thiosulfate standard volumetric
solution (5.2.1.3.3).
5.2.1.6 Expression of results
The sodium chlorite (NaClO ) content
...