EN 938:2009

SLOVENSKI STANDARD
01-maj-2009
1DGRPHãþD
SIST EN 938:2000
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 cnosommation
humaine - Chlorite de sodium
Ta slovenski standard je istoveten z: EN 938:2009
ICS:
13.060.20 Pitna voda Drinking water
71.100.80 .HPLNDOLMH]DþLãþHQMHYRGH Chemicals for purification of
water
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN 938
NORME EUROPÉENNE
EUROPÄISCHE NORM
January 2009
ICS 71.100.80 Supersedes EN 938:1999
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 European Standard was approved by CEN on 5 December 2008.
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 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 Management Centre has the same status as the
official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,
Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2009 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 938:2009: E
worldwide for CEN national Members.

Contents Page
Foreword . 3
Introduction . 4
1 Scope . 5
2 Normative references . 5
3 Description . 5
3.1 Identification . 5
3.2 Commercial form . 6
3.3 Physical properties . 6
3.4 Chemical properties . 7
4 Purity criteria . 8
4.1 General . 8
4.2 Composition of commercial product . 8
4.3 Impurities and main by-products . 8
4.4 Chemical parameters . 8
5 Test methods . 9
5.1 Sampling . 9
5.2 Analysis . 10
6 Labelling - Transportation - Storage . 20
6.1 Means of delivery . 20
6.2 Risk and safety labelling according to the EU Directives . 20
6.3 Transportation regulations and labelling . 21
6.4 Marking . 21
6.5 Storage . 21
Annex A (informative)  General information on sodium chlorite . 22
Annex B (normative) General rules relating to safety . 27
Annex C (normative) Determination of arsenic, antimony and selenium (atomic absorption
spectrometry hydride technique) . 28
Bibliography . 34

Foreword
This document (EN 938:2009) 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 July 2009, and conflicting national standards shall be withdrawn at the
latest by July 2009.
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 938:1999.
The significant technical differences between this edition and EN 938:1999 are as follows:
a) Deletion of reference to EU Directive 80/778/EEC of July 15, 1980 in order to take into account the
latest Directive in force (see [1]).
b) Replacement of ISO 5666-1 by EN 1483.
Annex A is informative.
Annexes B and C are normative.

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, Cyprus, Czech
Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,
Sweden, Switzerland and the United Kingdom.

Introduction
In respect of potential adverse effects on the quality of water intended for human consumption, caused by the
product covered by this Standard:
1) 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;
2) 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.

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 referenced documents are indispensable for the application 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.
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 3696:1987)
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 .
3.1.5 Chemical formula
NaClO .
1)
3.1.6 CAS Registry Number
7758-19-2.
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.
1)
Chemical Abstracts Service Registry Number
2)
European Inventory of Existing Commercial Chemical Substances
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.
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.

3)
100 kPa = 1 bar
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.
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
Sodium nitrate (NaNO ) max. 1
NOTE Sodium chlorate can be a by-product of the manufacturing process. Sodium nitrate is used
as a corrosion inhibitor in the sodium chlorite special grade for the textile industry.
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.
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.
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.
The concentration, c, of the sodium thiosulfate standard volumetric solution (Na S O .5H O), expressed in
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.
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, C , expressed as a percentage by mass (% of mass fraction ) is given
2 1
by the following equation; assume 90,44 g of sodium chlorite (NaClO ) is equivalent to 1 000 ml of sodium
thiosulfate c(Na S O .5H O) = 0,1 mol/l.
2 2 3 2
V × c× 2,262
C = (2)
m
where
V is the volume, in millilitres, of the sodium thiosulfate standard volumetric solution (5.2.1.3.3) used
for the titration at the end point;
c is the concentration, moles per litre, of the sodium thiosulfate standard volumetric solution
(5.2.1.3.3);
m is the mass in grams of the test portion (5.2.1.5.1).
5.2.2 Impurities
5.2.2.1 Determination of sodium chlorate content (NaClO )
5.2.2.1.1 General
This method is used to determine the chlorate content, in the range between 3,75 g/l and 15 g/l, in sodium
chlorite solutions for commercial use; it is specific for these species.
5.2.2.1.2 Principle
Direct determination of chlorate ion in a diluted solution of sodium chlorite by separation and chemical
suppressed conductimetric detection (ionic chromatography).
NOTE Calibration is linear for concentration of chlorate ion between 3,75 mg/l and 15 mg/l in the diluted solution.
5.2.2.1.3 Reagents
5.2.2.1.3.1 All reagents shall be of a recognized analytical grade and the water used shall conform to
grade 3 in accordance with EN ISO 3696.
5.2.2.1.3.2 Sodium carbonate and sodium hydrogen carbonate, eluant solution:
Mix one volume of sodium carbonate c(Na CO ) = 2 mol/l with one volume of sodium hydrogen carbonate
2 3
c(NaHCO ) = 0,75 mol/l.
5.2.2.1.3.3 Sulfuric acid solution c(H SO ) = 0,025 mol/l regenerant solution.
2 4
5.2.2.1.3.4 Helium gas, high purity, for degassing eluant and regenerant solutions.
5.2.2.1.3.5 Water, ultra pure, conductivity = 0,056 µS/cm.
5.2.2.1.3.6 Sodium chlorate stock solution at 1 g/l:
.
Weigh, to the nearest 0,000 1 g, 0,255 1 g of NaClO . Dissolve in 200 ml of the ultrapure water (5.2.2.1.3.5).
5.2.2.1.4 Apparatus
5.2.2.1.4.1 Ordinary laboratory apparatus and glassware, together with the following.
5.2.2.1.4.2 Ion chromatograph.
5.2.2.1.4.3 Chemical suppressed conductivity detector.
5.2.2.1.4.4 Anionic column and precolumn:
Resin composed of 15 µm polystyrene/divinylbenzene substrate agglomerated with anion exchange latex that
has been aminated.
5.2.2.1.4.5 Data logger/plotter able to record and display the chromatographic peak heights.
5.2.2.1.4.6 Densimeter, temperature setting 20°C.
5.2.2.1.5 Chromatographic conditions
1) Eluant flow rate: 2 ml/min;
2) regenerant flow rate: 2,5 ml/min;
3) full scale of conductivity: 30 mS;
4) residual conductivity: < 18 mS;
-
5) linearity range: ClO : 1 mg/l to 15 mg/l of injected solution.
Calibration conditions:
Four levels of calibration and a blank level. Each level is measured three times.
5.2.2.1.6 Procedure
5.2.2.1.6.1 Preparation of calibration solutions
Prepare chlorate standard solutions by diluting the sodium chlorate stock solution (5.2.2.1.3.6) with the eluant
solution (5.2.2.1.3.2), prepare calibration solutions in accordance with Table 7.
Table 7 — Calibration solution for determination of chlorate content
-
Solution
ClO in mg/l
1 3,75
2 7,5
3 11,25
4 15
5.2.2.1.6.2 Preparation of test solution
Heat the sodium chlorite laboratory sample to 20°C and check the density in grams per millilitre with a
densimeter (5.2.2.1.4.6) set for 20°C.
Prepare dilutions with the eluant solution (5.2.2.1.3.2) in order to be within the range of calibration.
5.2.2.1.6.3 Measurement of calibration and test solutions
Measure each calibration solution three times; for each solution the relative standard deviation shall be lower
than 0,5 %.
Dilute each test solution in order to obtain two levels of concentration located respectively in the lower part of
the calibration curve and in the upper part of the calibration curve. Repeat the measurements twice more in
order to keep the relative standard deviation at not more than 0,5 %.
5.2.2.1.7 Expression of results
The chlorate content, of the test solution is obtained from the regression line obtained with the five levels of
calibration results in the sodium chlorite solution.
-
The chlorate (ClO ) content of the laboratory sample, C , expressed in milligrams per litre is given by the
3 2
following general equation:
V
C = y× (3)
m
where
y is the concentration obtained from calibration curve;
V is the volume, in millilitres, of the dilution;
m is the mass, in grams, of the test solution.
The sodium chlorate (NaClO ) content, C , expressed in grams per kilogram of sodium chlorite of a mass
3 3
fraction of 100 % is given by the following equation:
C
C = C × (4)
3 2
100×ρ
where
C is the sodium chlorite content in percentage by mass (5.2.1.6);
p is the density, in grams per millilitre of the sodium chlorite solution.
5.2.2.1.8 Repeatability limit
The absolute difference between two single test results, obtained under repeatability conditions, shall not be
greater than the repeatability value, r, as calculated from the following equation:
r = 0,05 z (5)
where z is the mean of the two results, expressed in grams per kilogram.
NOTE Repeatability conditions are conditions where mutually independent test results are obtained with the same
method on identical test material in the same laboratory by the same operator using the same equipment within short
intervals of time.
-
5.2.2.2 Determination of the nitrate content (NO )
5.2.2.2.1 General
This method applies to determine the nitrate content, in the range between 0,15 g/l and 0,6 g/l, in sodium
chlorite solutions for commercial use; it is specific for these species.
5.2.2.2.2 Principle
Direct determination of nitrate ion in a diluted solution of sodium chlorite by separation and chemical
suppressed conductimetric detection (ionic chromatography).
NOTE Calibration is linear for concentration of nitrate ion, between 0,15 mg/l and 0,6 mg/l in the diluted solution.
5.2.2.2.3 Reagents
5.2.2.2.3.1 All reagents shall be of a recognized analytical grade and the water used shall conform to
grade 3 in accordance with EN ISO 3696.
5.2.2.2.3.2 Sodium carbonate and sodium hydrogen carbonate, eluant solution:
Mix one volume of sodium carbonate c(Na CO ) = 2 mol/l with one volume of sodium hydrogen carbonate
2 3
c(NaHCO ) = 0,75 mol/l.
5.2.2.2.3.3 Sulfuric acid solution c(H SO ) = 0,025 mol/l regenerant solution.
2 4
5.2.2.2.3.4 Helium gas, high purity, for degassing eluant and regenerant solutions.
5.2.2.2.3.5 Water, ultra-pure, conductivity = 0,056 µS/cm.
5.2.2.2.3.6 Sodium nitrate stock solution at 1 g/l:
Weigh, to the nearest 0,0001 g, 0,274 1 g of NaNO .
Dissolve in 200 ml of ultrapure water (5.2.2.2.3.5).
5.2.2.2.4 Apparatus
5.2.2.2.4.1 Ordinary laboratory apparatus and glassware, together with the following.
5.2.2.2.4.2 Ion chromatograph.
5.2.2.2.4.3 Chemical suppressed conductivity detector.
5.2.2.2.4.4 Anionic column and precolumn:
Resin composed of 15 µm polystyrene/divinylbenzene substrate agglomerated with anion exchange latex that
has been aminated.
5.2.2.2.4.5 Data logger/plotter able to record and display the chromatographic peak heights.
5.2.2.2.4.6 Densimeter, temperature setting 20°C.
5.2.2.2.5 Chromatographic conditions
1) Eluant flow rate: 2 ml/min;
2) regenerant flow rate: 2,5 ml/min;
3) full scale of conductivity: 30 mS;
4) residual conductivity: < 18 mS;
-
5) linearity range: NO : 0,15 mg/l to 0,6 mg/l of injected solution.
Calibration conditions:
Four levels of calibration and a blank level. Each level is measured three times.
5.2.2.2.6 Procedure
5.2.2.2.6.1 Preparation of calibration solutions
Prepare nitrate standard solutions by diluting the sodium nitrate stock solution (5.2.2.2.3.6) with the eluant
solution (5.2.2.2.3.2), prepare calibration solutions in accordance with Table 8.
Table 8 — Calibration solutions for determination of nitrate content
-
Solution
NO in mg/l
1 0,15
2 0,3
3 0,45
4 0,6
5.2.2.2.6.2 Preparation of test solution
Heat the sodium chlorite laboratory sample to 20°C and check the density in grams per millilitre with a
densimeter (5.2.2.2.4.6) set for 20°C.
Prepare dilutions with the eluant solution (5.2.2.2.3.2) in order to be within the range of calibration.
5.2.2.2.6.3 Measurement of calibration and test solutions
Measure each calibration solution three times; for each solution the relative standard deviation shall be lower
than 0,5 %.
Dilute each test solution in order to obtain two levels of concentration located respectively in the lower part of
the calibration curve and in the upper part of the calibration curve. Repeat the measurements twice more in
order to keep the relative standard deviation at not more than 0,5 %.
5.2.2.2.7 Expression of results
The nitrate content of the test solution is obtained from the regression line obtained with the five levels of
calibration results in the sodium chlorite solution.
-
The nitrate (NO ) content of the laboratory sample, C , expressed in milligrams per litre is given by the
3 4
following general equation:
V
C = y × (6)
m
where
y is the concentration obtained from calibration curve;
V is the volume, in millilitres, of the dilution;
m is the mass, in grams, of the test solution.
The sodium nitrate (NaNO ) content, C , expressed in grams per kilogram of sodium chlorite of a mass
3 5
fraction of 100 % is given by the following equation:
C
C = C × (7)
5 4
100×ρ
where
C is the sodium chlorite content in percentage by mass (5.2.1.6);
p is the density, in grams per millilitre of the sodium chlorite solution.
5.2.2.2.8 Repeatability limit
The absolute difference between two single test results, obtained under repeatability conditions, shall not be
greater than the repeatability value, r, as calculated from the following equation:
r = 0,05 z (8)
where z is the mean of the two results, expressed in grams per kilogram.
NOTE Repeatability conditions are conditions where mutually independent test results are obtained with the same
method on identical test material in the same laboratory by the same operator using the same equipment within short
intervals of time.
5.2.3 Chemical parameters
5.2.3.1 Determination of antimony (Sb), arsenic (As), cadmium (Cd), chromium (Cr), lead (Pb), nickel
(Ni) and selenium (Se)
5.2.3.1.1 Principle
The elements arsenic, antimony, cadmium, chromium, lead, nickel and selenium are determined by atomic
absorption spectrometry.
5.2.3.1.2 Reagents
5.2.3.1.2.1 All reagents shall be of a recognized analytical grade and the water used shall conform to the
appropriate grade specified in EN ISO 3696.
5.2.3.1.2.2 Nitric acid, concentrated, density ρ = 1,42 g/ml.
5.2.3.1.3 Procedure
5.2.3.1.3.1 Test portion
Weigh, to the nearest 0,001 g, 20 g (m ) from the laboratory sample into a glass beaker.
5.2.3.1.3.2 Test solution
Evaporate until a wet residue is obtained, cool, add 1 ml of nitric acid (5.2.3.1.2.2), dilute with a few millilitres
of water, transfer quantitatively to a 100 ml volumetric flask and dilute to volume with water and mix.
Carry out the evaporation carefully and not to dryness in order to avoid possible losses of arsenic and
selenium.
5.2.3.1.3.3 Determination
Determine the content of toxic substances in the test solution (5.2.3.1.3.2) in accordance with the following
methods:
 Cd, Ni and Pb : In accordance with ISO 8288:1986, Method A;
 Cr : In accordance with ISO 9174;
 As, Se and Sb : In accordance with the method given in Annex C;
These methods will give an interim result (y) expressed in milligrams per litre which needs to be corrected to
give the final concentration according to the equation in 5.2.3.1.4.
5.2.3.1.4 Expression of results
From the interim results (y) determined (see 5.2.3.1.3.3), the content, C , of each chemical parameter in the
laboratory sample, expressed in milligrams per kilogram of sodium chlorite of a mass fraction of 100 % is
calculated from the following general equation:
V 100
C = y× × (9)
m C
3 1
where
y is the interim result (5.2.3.1.3.3);
V is the volume, in millilitres, of the test solution (5.2.3.1.3.2) (= 100 ml);
m is the mass, expressed in grams, of the test portion;
C is the sodium chlorite (NaClO ) content in percentage by mass (5.2.1.6).
1 2
5.2.3.2 Determination of mercury (Hg)
5.2.3.2.1 Principle
The element mercury is determined by flameless atomic absorption spectrometry in accordance with
EN 1483.
5.2.3.2.2 Reagents
5.2.3.2.2.1 All reagents shall be of a recognized analytical grade and the water used shall conform to the
appropriate grade specified in EN ISO 3696.
5.2.3.2.2.2 Potassium permanganate solution, c(KMnO ) = 50 g/l.
5.2.3.2.2.3 Sulfuric acid, concentrated, density p = 1,84 g/ml.
5.2.3.2.2.4 Hydroxylammonium chloride, c(NH OH.HCl) = 100 g/l.
5.2.3.2.2.5 Potassium dichromate solution, c(K Cr O ) = 4 g/l in a volume fraction of 50 % of nitric acid
2 2 7
solution.
5.2.3.2.3 Procedure
5.2.3.2.3.1 Test portion
Pipette 10 g (m ) of the laboratory sample and transfer to approximately 70 ml of water taking care to avoid
sputtering.
5.2.3.2.3.2 Test solution
Quantitatively transfer the test portion to a washing flask (e.g. Durand bottle), capacity 250 ml, the gas inlet of
which is made of a porous frit. Dilute the contents of the washing flask with water to obtain a total volume of
100 ml. Transfer to a volumetric flask (solution A).
Pipette, accurately 10 ml of the solution A. Transfer to a 250 ml conical flask add 60 ml of water, 20 ml of a
potassium permanganate solution (5.2.3.2.2.2) and five 1 ml portions of sulfuric acid (5.2.3.2.2.3). Heat and
keep boiling for 10 min. Allow to cool. Just dissolve the precipitate (MnO ) with hydroxylammonium chloride
(5.2.3.2.2.4), add 5 ml of the potassium dichromate solution (5.2.3.2.2.5) and transfer to a 100 ml (V )
T
volumetric flask. Dilute to the mark with water and mix.
5.2.3.2.3.3 Determination
Proceed as described in EN 1483.
5.2.3.2.4 Expression of results
The interim result for mercury content (y) expressed in milligrams per litre is given by the following general
equation:
V
T
y=y × (10)
A
where
y is the result obtained, for the concentration of mercury in solution A, expressed in milligrams per
A
litre;
V is the volume in millilitres of the test solution.
T
The content of mercury, C , in milligrams per kilogram of sodium chlorite, mass fraction of 100 % is given by
the following equation:
10 100
C = y× × (11)
m C
where
m is the mass, expressed in grams, of the test portion;
C is the sodium chlorite content in percentage by mass (5.2.1.6).
6 Labelling - Transportation - Storage
6.1 Means of delivery
Sodium chlorite shall be delivered in polyethylene drums containers or tankers of up to 25 t capacity.
In order that the purity of the products is not affected, the means of delivery shall not have been used
previously for any different product or it shall have been specially cleaned and prepared before use.
4)
6.2 Risk and safety labelling according to the EU Directives
The following labelling requirements shall apply to sodium chlorite at the date of publication of this document.
1) Symbols and indications of danger:
Xn: Harmful;
2) nature of special risks attributed to dangerous substances:
R 22: Harmful if swallowed;
R 31: Contact with acids liberates toxic gas;
R 4 : Risk of serious damage to eyes;
3) safety advice concerning dangerous substances:
S 14: Keep away from acids;
S 17: Keep away from combustible material;
S 26: In case of contact with eyes, rinse immediately with plenty of water and seek medical advice.
NOTE Annex I of the Directive 67/548/EEC on Classification, packaging and labelling of dangerous substances and
its amendments and adaptations in the European Union contains a list of substances classified by the EU. Substances not
in this Annex I should be classified on the basis of their intrinsic properties according to the criteria in the Directive by the
person responsible for the marketing of the substance.

4)
See [2].
6.3 Transportation regulations and labelling
5)
Sodium chlorite solution is listed as UN Number 1908.
6) 7)
RID ADR : Class 8, code C9, packing group II.
8)
IMDG : Class 8, Packing group II.
9)
IATA : Class 8, Packing group II.
6.4 Marking
The marking shall include the following:
1) name "Sodium chlorite", trade name and grade;
2) net mass ;
3) name and address of supplier and/or manufacturer;
4) statement "this product conforms to EN 938, type,…".
6.5 Storage
The product shall be stored in containers used exclusively for sodium chlorite. It shall be stored away from
direct sunlight, in a cool, well-ventilated area, but at a temperature not lower than the crystallization point (see
3.3.6). Large quantities shall be stored outdoors or in a room equipped with an automatic fire-extinguishing
system. Refer to local authorities regulations.
6.5.1 Long term stability
The product is stable for at least one year.
6.5.2 Storage incompatibilities
The product shall not be allowed to come into contact with acids, acidic salts, reducing agents or organic
compounds (wood, paper, grease,…).

5)
United Nations Number
6)
Regulations concerning International carriage of Dangerous goods by rail
7)
European Agreement concerning the international carriage of Dangerous goods by Road
8)
International Maritime transport of Dangerous Goods
9)
International Air Transport Association
Annex A
(informative)
General information on sodium chlorite
A.1 Origin
A.1.1 Raw materials
Sodium chlorite is manufactured from sodium chlorate (NaClO ), sodium hydroxide (NaOH), hydrogen
peroxide (H O ), sulfuric acid (H SO ).
2 2 2 4
A.1.2 Manufacturing process
It is usually produced by reduction of sodium chlorate to chlorine dioxide and neutralization by sodium
hydroxide and hydrogen peroxide according to the following equation:
2 NaClO + 2H SO + H O -----Æ 2 ClO + 2 NaHSO + 2H O + O
3 2 4 2 2 2 4 2 2
2 ClO + 2 NaOH + H O -----Æ 2 NaClO + 2H O + O
2 2 2 2 2 2
A.2 Use
A.2.1 Function
Its function in water treatment is the generation of chlorine dioxide by reaction with chlorine or hydrochloric
acid or sodium peroxodisulfate process.
2 NaClO + Cl -----Æ2ClO + 2 NaCl
2 2 2
5 NaClO + 4HCl -----Æ 4ClO + 5 NaCl + 2 H O
2 2 2
2 NaClO + Na S O -----Æ 2 ClO + 2 Na SO
2 2 2 8 2 2 4
A.2.2 Form in which it is used
It is used as an aqueous solution.
A.2.3 Treatment dose
The treatment dose depends of the raw water composition. Care should be taken not to exceed a maximum
concentration of chlorine dioxide in the water supply, usually a few tenths of 1 mg/l and to refer to the local
regulation.
A.2.4 Means of application
It is applied by means of a chlorine dioxide generator.
A.2.5 Secondary effects
The secondary effects include the following:
1) oxidation of iron, manganese;
2) odour and colour removal;
3) oxidation of organic compounds.
A.2.6 Removal of excess product
The most practical method is the use of sodium hydrogen sulfite, sodium disulfite at pH value 5 to 6 or sodium
sulfite. Granular activated carbon can also be used, as wall as ferrous salts at neutral pH.
A.3 Routine analyses
A.3.1 Determination of sodium chlorite (NaClO )
A.3.1.1 General
This method is used to determine the content of sodium chlorite in commercial sodium chlorite solutions and it
is specific for these species.
A.3.1.2 Principle
Manual 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.
A.3.1.3 Reagents
A.3.1.3.1 All reagents should be of a recognized analytical grade and the water used should conform to
grade 3 in accordance with EN ISO 3696.
A.3.1.3.2 Potassium iodide (Kl) solution, 100 g/l.
A.3.1.3.3 Sulfuric acid solution, 50 g/l.
A.3.1.3.4 Starch solution, indicator 1 % mass fraction
Make a slurry with (1 ± 0,1) g starch and (5 ± 1) ml water. Add (90 ± 5) ml boiling water. Stir to dissolve it and
cool the solution. This solution needs refrigeration to avoid the decomposition of the starch with results in a
vague end point. Keep the solution cool and use it within one week.
NOTE Commercial indicators for iodine titration exist and can be used in place of the described starch solution
provided that their efficiency has been previously tested.
A.3.1.3.5 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 (A.3.1.3.3) and titrate to the end point, i.e. to the
disappearance of the blue-black colour. Record the volume (V) used.
The concentration,
...