SIST EN 17215:2019
(Main)Chemicals used for treatment of water intended for human consumption - Iron-based coagulants - Analytical methods
Chemicals used for treatment of water intended for human consumption - Iron-based coagulants - Analytical methods
This document is applicable to iron-based coagulants used for treatment of water intended for human consumption. It specifies analytical methods to be used for products described in EN 888, EN 889, EN 890, EN 891 and EN 14664.
Produkte zur Aufbereitung von Wasser für den menschlichen Gebrauch - Flockungsmittel auf Eisenbasis - Analysenverfahren
Dieses Dokument gilt für Flockungsmittel auf Eisenbasis zur Aufbereitung von Wasser für den menschlichen Gebrauch. Es legt die anzuwendenden Analysenverfahren für Produkte fest, die in EN 888, EN 889, EN 890, EN 891 und EN 14664 beschrieben sind.
Produits chimiques utilisés pour le traitement de l'eau destinée à la consommation humaine - Coagulants à base de fer - Méthodes d'analyse
La présente Norme européenne est applicable aux coagulants à base de fer utilisés pour le traitement de l’eau destinée à la consommation humaine. Elle spécifie les méthodes d’analyse à utiliser pour les produits décrits dans l’EN 888, l’EN 889, l’EN 890, l’EN 891 et l’EN 14664.
Kemikalije, ki se uporabljajo za pripravo pitne vode - Sredstvo za strjevanje na osnovi železa - Analitske metode
Ta dokument se uporablja za sredstva za strjevanje na osnovi železa, ki se uporabljajo za pripravo pitne vode. Določa analitične metode, ki se uporabljajo za izdelke, opisane v standardih EN 888, EN 889, EN 890, EN 891 in EN 14664.
General Information
Standards Content (Sample)
SLOVENSKI STANDARD
SIST EN 17215:2019
01-maj-2019
Kemikalije, ki se uporabljajo za pripravo pitne vode - Sredstvo za strjevanje na
osnovi železa - Analitske metode
Chemicals used for treatment of water intended for human consumption - Iron-based
coagulants - Analytical methods
Produkte zur Aufbereitung von Wasser für den menschlichen Gebrauch -
Flockungsmittel auf Eisenbasis - Analysenverfahren
Produits chimiques utilisés pour le traitement de l'eau destinée à la consommation
humaine - Coagulants à base de fer - Méthodes d'analyse
Ta slovenski standard je istoveten z: EN 17215:2019
ICS:
13.060.20 Pitna voda Drinking water
71.100.80 .HPLNDOLMH]DþLãþHQMHYRGH Chemicals for purification of
water
SIST EN 17215:2019 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST EN 17215:2019
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SIST EN 17215:2019
EN 17215
EUROPEAN STANDARD
NORME EUROPÉENNE
March 2019
EUROPÄISCHE NORM
ICS 71.100.80
English Version
Chemicals used for treatment of water intended for human
consumption - Iron-based coagulants - Analytical methods
Produits chimiques utilisés pour le traitement de l'eau Produkte zur Aufbereitung von Wasser für den
destinée à la consommation humaine - Coagulants à menschlichen Gebrauch - Flockungsmittel auf
base de fer - Méthodes d'analyse Eisenbasis - Analysenverfahren
This European Standard was approved by CEN on 10 December 2018.
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
© 2019 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 17215:2019 E
worldwide for CEN national Members.
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SIST EN 17215:2019
EN 17215:2019 (E)
Contents Page
European foreword . 4
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Methods of analysis . 6
5 Sampling . 8
5.1 General. 8
5.2 Solids . 8
5.3 Solutions . 8
5.3.1 Sampling from drums and bottles . 8
5.3.2 Sampling from tanks and tankers . 8
6 Expression of results . 9
6.1 Iron content . 9
6.2 Free acid . 9
6.3 Insoluble matters . 9
6.4 Impurities . 9
6.5 Repeatability . 9
Annex A (normative) Analysis of the iron content . 10
A.1 Determination of iron (II) concentration by titration against cerium (IV) sulfate . 10
A.2 Determination of total iron . 11
A.3 Determination of iron (III) . 12
Annex B (informative) Alternative analysis of the iron content . 13
B.1 Determination of iron (II) concentration by titration against potassium
dichromate . 13
B.2 Determination of iron (III) concentration by iodometric titration . 14
Annex C (normative) Analysis of the chemical parameters and impurities . 16
C.1 Determination of free acid . 16
C.2 Determination of insoluble matters . 18
C.3 Determination of manganese by Flame Atomic Absorption Spectroscopy (FAAS) . 20
C.4 Determination of arsenic, antimony and selenium by hydride generation atomic
absorption spectrometry (HGAAS) . 22
C.5 Determination of mercury by cold vapour atomic absorption spectrometry
(CVAAS) . 26
C.6 Determination of cadmium, chromium, nickel and lead by graphite furnace atomic
absorption spectrometry (GFAAS) . 29
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Annex D (informative) Determination of arsenic, antimony, cadmium, chromium,
manganese, nickel and lead and selenium (inductively coupled plasma optical
emission spectrometry (ICP-OES)) . 34
D.1 General . 34
D.2 Principle . 34
D.3 Reagents . 34
D.4 Apparatus . 35
D.5 Sample solution . 36
D.6 Procedure . 36
D.7 Calculation and expression of results . 37
Annex E (informative) Determination of arsenic, antimony, cadmium, lead and selenium
(inductively coupled plasma mass spectrometry (ICP-MS)) . 38
E.1 General . 38
E.2 Principle . 38
E.3 Reagents . 38
E.4 Apparatus . 39
E.5 Sample solution . 39
E.6 Procedure . 39
E.7 Calculation and expression of results . 40
Bibliography . 41
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EN 17215:2019 (E)
European foreword
This document (EN 17215:2019) 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 September 2019, and conflicting national standards shall
be withdrawn at the latest by September 2019.
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.
According to the CEN-CENELEC Internal Regulations, the national standards organisations 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.
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EN 17215:2019 (E)
1 Scope
This document is applicable to iron-based coagulants used for treatment of water intended for human
consumption. It specifies analytical methods to be used for products described in EN 888 (Iron (III)
chloride), EN 889 (Iron (II) sulfate), EN 890 (Iron (II) sulfate, solution), EN 891 (Iron (III) chloride
sulfate) and EN 14664 (Iron (III) sulfate, solid).
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.
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 8213, Chemical products for industrial use — Sampling techniques — Solid chemical products in the
form of particles varying from powders to coarse lumps
ISO 5790:1979, Inorganic chemical products for industrial use – General method for determination of
chloride content – Mercurimetric method
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 http://www.iso.org/obp
3.1
laboratory sample
sample as prepared for sending to the laboratory and intended for inspection or testing
Note 1 to entry: in accordance with ISO 8213.
3.2
test sample
sample prepared from the laboratory sample and from which test portions will be taken
Note 1 to entry: in accordance with ISO 6206:1979.
3.3
test portion
quantity of material drawn from the test sample (or from the laboratory sample if both are the same) and
on which the test or observation is actually carried out
Note 1 to entry: in accordance with ISO 6206:1979.
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4 Methods of analysis
The methods to analyse the main product of standards EN 888, EN 889, EN 890, EN 891 and EN 14664
are listed in Table 1.
The methods to be used for analysis of iron-based coagulants and the principles of each method are listed
in Table 1 and described in full in Annex A (normative methods) and in Annex B (informative methods)
for analysis of iron content. The methods to be used for other parameters are listed in Table 2 and
described in Annexes C, D and E.
Table 1 — Determination of the iron content (normative and informative method)
Standard Main Test method annex and principle
number product
EN 888 Iron (III) A.3 Iron (III) chloride is determined as iron (III) content in the test
chloride sample. Iron (III) content is determined as the difference
B.2
between total iron content and iron (II) content.
EN 889 Iron (II) A.1 Iron (II) sulfate is determined as iron (II) content in the test
sulfate sample by titrimetry with cerium sulfate solution.
B.1
EN 890 Iron (III) A.3 Iron (III) sulfate is determined as iron (III) content in the test
sulfate, sample. Iron (III) content is determined as the difference
B.2
solution between total iron content and iron (II) content.
EN 891 Iron (III) A.3 Iron (III) chloride sulfate is determined as iron (III) content in
chloride the test sample. Iron (III) content is determined as the difference
B.2
sulfate between total iron content and iron (II) content.
EN 14664 Iron (III) A.3 Iron (III) sulfate is determined as iron (III) content in the test
sulfate, solid sample. Iron (III) content is determined as the difference
B.2
between total iron content and iron (II) content.
NOTE 1 An alternative method for determination of iron (II) and iron (III) content is described in Annex B.
Table 2 — Determination of parameters (normative and informative methods)
Parameter EN 888 EN 889 EN 890 EN 891 EN 14664 Method Principle
Insoluble X X X X X C.2 Weighted mass of the filtered
matters sample
Iron (II) X X X X A.1 Determination of iron (II) by
titration against cerium sulfate
B.1
Determination of iron (II) by
titration against potassium
dichromate
Free acid X X X X C.1 Titration with sodium hydroxide
Antimony X X X X X C.4 hydride generation atomic
absorption spectrometry
D
ICP/OES
E
ICP/MS
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EN 17215:2019 (E)
Parameter EN 888 EN 889 EN 890 EN 891 EN 14664 Method Principle
Arsenic X X X X X C.4 hydride generation atomic
absorption spectrometry
D
ICP/OES
E
ICP/MS
Cadmium X X X X X C.6 graphite furnace atomic
absorption spectrometry
D
ICP/OES
E
ICP/MS
Chromium X X X X X C.6 graphite furnace atomic
absorption spectrometry
D
ICP/OES
Manganese X X X X X C.3 flame atomic absorption
spectrometry (FAAS)
D
ICP-OES
E
ICP-MS
Mercury X X X X X C.5 cold vapour atomic absorption
spectrometry
Lead X X X X X C.6 graphite furnace atomic
absorption spectrometry
D
ICP/OES
E
ICP/MS
Nickel X X X X X C.6 graphite furnace atomic
absorption spectrometry
D
ICP/OES
Selenium X X X X X C.4 hydride generation atomic
absorption spectrometry
D
ICP/OES
E
ICP/MS
NOTE 2 An alternative method for determination of arsenic, antimony, cadmium, lead and selenium with the ICP
mass spectrometry is described in Annex E. An alternative method for analysis on arsenic, antimony, cadmium,
chromium, manganese, nickel, lead and selenium with the ICP/OES is described in Annex D.
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EN 17215:2019 (E)
5 Sampling
5.1 General
Observe the general recommendations in ISO 3165 and take into account ISO 6206.
5.2 Solids
Prepare the laboratory sample required by the relevant procedure described in ISO 8213.
5.3 Solutions
5.3.1 Sampling from drums and bottles
5.3.1.1 General
Mix the contents of each 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.
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 5.3.1.3.
Examine the surface of the liquid. If there are signs of surface contamination, take samples from the
surface as described in 5.3.1.2. Otherwise, take samples as described in 5.3.1.3.
5.3.1.2 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.
5.3.1.3 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 at 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.
5.3.2 Sampling from tanks and tankers
A representative sample should be taken as appropriate:
a) from the surface of the liquid, using a ladle as described in 5.3.1.2;
b) from the bottom of the tank or tanker, using a sampling tube as described in 5.3.1.3 or using 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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6 Expression of results
6.1 Iron content
The iron content shall be expressed as iron (II) or iron (III) mass fraction in %.
6.2 Free acid
Free acid shall be expressed as mass fraction in %.
6.3 Insoluble matters
Insoluble matters shall be expressed as mass fraction in %.
6.4 Impurities
Impurities shall be expressed as mg/kg.
6.5 Repeatability
Each laboratory shall calculate the repeatability of the method under their laboratory conditions
according to the procedure.
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Annex A
(normative)
Analysis of the iron content
NOTE The strengths of iron salt solutions are measured on the basis of the iron (II) and iron (III) concentration
alone.
A.1 Determination of iron (II) concentration by titration against cerium (IV)
sulfate
A.1.1 General
This method applies to products with iron contents greater than a mass fraction of 0,2 %.
A.1.2 Principle
Iron (II) is directly titrated with cerium (IV) sulfate solution, which oxidises it to iron (III).
A.1.3 Reagents
All reagents shall be of a recognized analytical grade and the water used shall conform to the grade 3 in
accordance with EN ISO 3696.
A.1.3.1 Hydrochloric acid solution (HCl) 5,0 mol/l
A.1.3.2 1,10-Phenanthroline ferrous complex solution (ferroin, ferrous indicator) ([Fe(o-
phen) ]SO ) 0,025 mol/l
3 4
A.1.3.3 Cerium (IV) sulfate solution, in 10 % w/v sulfuric acid, (Ce(SO ) ) 0,1 mol/l
4 2
A.1.4 Apparatus
Ordinary laboratory apparatus and glassware.
A.1.5 Procedure
A.1.5.1 Test solution
Weigh to the nearest 0,01 g, between 5 g and 10 g (m) of the laboratory sample and transfer to a conical
flask. Dilute with 50 ml ± 5 ml of water.
A.1.5.2 Determination
With mixing, add 0,5 ml of hydrochloric acid (A.1.3.1) to the conical flask. A clear deep yellow solution is
formed.
Add 2 to 4 drops (only) of the ferrous indicator (A.1.3.2). The solution will turn red.
Titrate the solution with cerium (IV) sulfate solution (A.1.3.3) from a volumetric burette. The end point
is achieved when a colour change from red to blue-green occurs and is sharp. Record the volume (V) of
cerium (IV) sulfate required for the titration.
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A.1.6 Calculation and expression of results
The iron (II) content, C , expressed as mass fraction in %, is given by the following formula:
(II)
V× 0,5585
C = (A.1)
(II)
m
where
V is the volume, in millilitres, of cerium (IV) sulfate required for the titration;
m is the mass, in grams, of the sample used for the test solution.
A.2 Determination of total iron
A.2.1 General
This method applies to the products at the supply concentration.
A.2.2 Principle
Iron is reduced by tin (II) chloride and is subsequently titrated with cerium (IV) sulfate.
A.2.3 Reagents
All reagents shall be of a recognized analytical grade and the water used shall conform to the grade 3 in
accordance with EN ISO 3696.
A.2.3.1 Hydrochloric acid, HCl concentrated 1,19 g/ml
A.2.3.2 Tin (II) chloride solution (SnCl · 2H O) 0,5 mol/l
2 2
Dissolve 22,6 g of SnCl · 2H O with 20 ml of hydrochloric acid (A.2.3.1) and dilute with water to 200 ml.
2 2
Keep this solution in the dark.
A.2.3.3 Mercury (II) chloride, saturated solution (HgCl ) 0,27 mol/l
2
A.2.3.4 1,10-Phenanthroline ferrous complex solution (ferroin, ferrous indicator) ([Fe(o-
phen) ]SO ) 0,025 mol/l
3 4
A.2.3.5 Cerium (IV) sulfate (Ce(SO ) ) 0,1 mol/l
4 2
A.2.4 Apparatus
Ordinary laboratory apparatus and glassware.
A.2.5 Procedure
A.2.5.1 Test solution
Weigh to the nearest 0,01 g, between 5 g and 10 g of the laboratory sample (m) and transfer to a 200 ml
volumetric flask, dilute to the mark with water. Pipette 10 ml ± 0,2 ml of this solution into a 500 ml
conical flask.
A.2.5.2 Determination
Add 3 to 4 drops of hydrochloric acid (A.2.3.1) and heat until boiling while stirring.
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Add drop by drop tin (II) chloride solution (A.2.3.2) until discoloration. (Reduction shall be achieved with
great care. Two drops of tin (II) chloride (A.2.3.2) are necessary, more shall be avoided.)
Cool the solution rapidly in cool water. Add 10 ml ± 0,2 ml of mercury (II) chloride (A.2.3.3). Dilute to
200 ml ± 5 ml with water and wait 3 min. A slight white cloud will appear regarding to mercury (II)
chloride addition. If a precipitate appears, stop the titration and reduce another aliquot of the laboratory
sample. Add 2 ml ± 0,2 ml of concentrated hydrochloric acid (A.2.3.1) and 4 to 6 drops of ferroin indicator
solution (A.2.3.4).
NOTE An alternative reduction method is given in Annex B.
Titrate the solution with cerium (IV) sulfate (A.2.3.5) from a volumetric burette. The end point is achieved
when a colour change from red to blue/green occurs. Record the volume (V) of cerium (IV) sulfate
required for the titration.
SAFETY PRECAUTIONS — Collect the residual solutions obtained from titrations and treat them in
accordance with Annex B of ISO 5790:1979, in order to prevent pollution of waste water.
A.2.6 Calculation and expression of results
The total iron content, C , expressed as mass fraction in %, is given by the following formula:
tot
V × 11,17
(A.2)
C =
tot
m
where
V is the volume, in millilitres, of cerium (IV) sulfate required for the titration;
m is the mass, in grams, of the sample used for the test solution.
A.3 Determination of iron (III)
The iron (III) content, C , expressed as mass fraction in %, is given by the following formula:
(III)
C C−C (A.3)
tot
III II
( ) ( )
where
C is the total iron content (A.2), expressed as mass fraction in %;
tot
C is the iron (II) content (A.1), expressed as mass fraction in %.
(II)
12
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Annex B
(informative)
Alternative analysis of the iron content
B.1 Determination of iron (II) concentration by titration against potassium
dichromate
B.1.1 General
This method applies to product with iron contents greater than a mass fraction of 0,2 %.
B.1.2 Principle
Iron is directly titrated with potassium dichromate solution.
B.1.3 Reagents
All reagents shall be of a recognized analytical grade and the water used shall conform to the grade 3 in
accordance with EN ISO 3696.
B.1.3.1 Sulfuric acid, H SO concentrated 1,84 g/ml
2 4
B.1.3.2 Phosphoric acid, H PO concentrated 1,71 g/ml
3 4
B.1.3.3 Barium diphenylamine sulfonate solution (Ba(C H -NH-C H SO ) ) 8 mmol/l
6 5 6 4 3 2
B.1.3.4 Potassium dichromate solution (K Cr O ) 0,0166 mol/l
2 2 7
B.1.4 Apparatus
Ordinary laboratory apparatus and glassware.
B.1.5 Procedure
B.1.5.1 Test solution
Into a 500 ml conical flask, pour 200 ml ± 10 ml of water, 10 ml ± 1 ml of sulfuric acid (B.1.3.1) and
10 ml ± 1 ml of phosphoric acid (B.1.3.2). Cool with water. Weigh to the nearest 0,1 mg, between 3 g and
10 g of the laboratory sample and transfer to the conical flask containing the acid solution.
B.1.5.2 Determination
Titrate the test solution with potassium dichromate solution (B.1.3.4) with a volumetric burette and add
five drops of barium diphenylamine sulfonate (B.1.3.3) near the end-point.
End-point is achieved when a persistent purple colour appears, record the volume (V) of potassium
dichromate solution required for the complete titration.
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B.1.6 Calculation and expression of results
The iron (II) content, C , expressed as mass fraction in %, is given by the following formula:
(II)
V× 0,5585
C = (B.1)
(II)
m
where
V is the volume, in millilitres, of potassium dichromate required for the titration;
m is the mass, in grams, of the sample used for the test solution.
B.2 Determination of iron (III) concentration by iodometric titration
B.2.1 General
This method applies to products with iron contents greater than a mass fraction of 0,2 %.
B.2.2 Principle
Iron (III) oxidises iodide ions to iodine, which is titrated with sodium thiosulfate solution.
3+ - 2+
2Fe + 2I → 2Fe + I
2
2- - 2-
I + 2S O → 2I + S O .
2 2 3 4 6
B.2.3 Reagents
All reagents shall be of a recognized analytical grade and the water used shall conform to the grade 3 in
accordance with EN ISO 3696.
B.2.3.1 Sodium thiosulfate solution (Na S O ) 0,1 mol/l
2 2 3
B.2.3.2 Potassium iodide, solid
B.2.3.3 Iodine indicator (starch), solid
B.2.3.4 Hydrochloric acid solution (HCl) 5,0 mol/l
B.2.4 Apparatus
Ordinary laboratory apparatus and glassware.
B.2.5 Procedure
B.2.5.1 Test solution
Weigh to the nearest 0,01 g, between 10 g and 20 g of sample (m) into a 250 ml volumetric flask, and
dilute to the mark with water. Transfer 20 ml ± 0,2 ml of the diluted solution to a 500 ml conical flask.
Add approximately 200 ml of water.
B.2.5.2 Determination
Add 20 ml ± 2 ml of hydrochloric acid (B.2.3.4).
Add 5 g ± 0,5 g of potassium iodide (B.2.3.2).
Mix the solution and allow the solution to stand in darkness for 5 min.
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