ISO 15661:2020

Copper and nickel sulfide ores and concentrates — Determination of total chlorine content — Alkaline fusion and potentiometric titration method

This document specifies an analytical method for the determination of total chlorine content using alkaline fusion and potentiometric titration. This method is applicable to copper and nickel sulfide ores and concentrates having chlorine content in the following ranges: a) Method 1: 80 µg/g to 4 300 µg/g b) Method 2: 70 µg/g to 4 300 µg/g

Minerais et concentrés de sulfure de cuivre et de sulfure de nickel — Détermination de la teneur totale en chlore — Méthode par fusion alcaline et par titrage potentiométrique

General Information

• Status: Published
• Publication Date: 21-Sep-2020
• ICS: 73.060.99 - Other metalliferous minerals
• Technical Committee: ISO/TC 183 - Copper, lead, zinc and nickel ores and concentrates
• Drafting Committee: ISO/TC 183 - Copper, lead, zinc and nickel ores and concentrates
• Current Stage: 6060 - International Standard published
• Start Date: 22-Sep-2020
• Due Date: 27-Sep-2020
• Completion Date: 22-Sep-2020

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 15661
First edition
2020-09
Copper and nickel sulfide ores and
concentrates — Determination of total
chlorine content — Alkaline fusion
and potentiometric titration method
Minerais et concentrés de sulfure de cuivre et de sulfure de nickel —
Détermination de la teneur totale en chlore — Méthode par fusion
alcaline et par titrage potentiométrique
Reference number
ISO 15661:2020(E)
©
ISO 2020

---------------------- Page: 1 ----------------------
ISO 15661:2020(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2020
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii © ISO 2020 – All rights reserved

---------------------- Page: 2 ----------------------
ISO 15661:2020(E)

Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Reagents . 2
6 Apparatus . 4
7 Instrument operating parameters . 4
8 Sample . 4
8.1 Laboratory sample . 4
8.2 Test sample . 5
9 Procedure. 5
9.1 Number of blank testing . 5
9.2 Number of determinations . 5
9.3 Determination . 5
9.3.1 General. 5
9.3.2 Decomposition of the test portion by fusion with a mixture of carbonate salts . 5
9.3.3 Decomposition of the test portion by fusion with a mixture of potassium salts . 6
9.3.4 Oxidation of sulfide . 7
9.3.5 Preparation of solution for titration . 7
9.3.6 Potentiometric titration . 7
10 Expression of results . 8
11 Precision and accuracy . 9
11.1 Expression of precision . 9
11.2 Method for obtaining the final result .10
11.3 Precision between laboratories .10
11.4 Check of trueness .11
12 Test report .12
Annex A (informative) Procedure for the preparation and determination of the mass of a
predried test portion .13
Annex B (normative) Flow chart of the procedure for the acceptance of analytical values for
test samples .15
© ISO 2020 – All rights reserved iii

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ISO 15661:2020(E)

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 183, Copper, lead, zinc and nickel ores and
concentrates.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
iv © ISO 2020 – All rights reserved

---------------------- Page: 4 ----------------------
INTERNATIONAL STANDARD ISO 15661:2020(E)
Copper and nickel sulfide ores and concentrates —
Determination of total chlorine content — Alkaline fusion
and potentiometric titration method
CAUTION — The use of this document can involve hazardous materials, operations and
equipment. This document does not purport to address all of the safety issues associated with
its use. It is the responsibility of the user of this document to establish appropriate safety and
health practices and determine the applicability of regulatory limitations prior to its use.
1 Scope
This document specifies an analytical method for the determination of total chlorine content using
alkaline fusion and potentiometric titration.
This method is applicable to copper and nickel sulfide ores and concentrates having chlorine content in
the following ranges:
a) Method 1: 80 µg/g to 4 300 µg/g
b) Method 2: 70 µg/g to 4 300 µg/g
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 385, Laboratory glassware — Burettes
ISO 648, Laboratory glassware — Single-volume pipettes
ISO 1042, Laboratory glassware — One-mark volumetric flasks
ISO 3696, Water for analytical laboratory use — Specification and test methods
ISO 4787, Laboratory glassware — Volumetric instruments — Methods for testing of capacity and for use
ISO 9599, Copper, lead, zinc and nickel sulfide concentrates — Determination of hygroscopic moisture
content of the analysis sample — Gravimetric method
ISO 12743, Copper, lead, zinc and nickel concentrates — Sampling procedures for determination of metal
and moisture content
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
© ISO 2020 – All rights reserved 1

---------------------- Page: 5 ----------------------
ISO 15661:2020(E)

4 Principle
The test portion is decomposed by fusion with a mixture of sodium carbonate and potassium carbonate
or with a mixture of potassium nitrate and potassium hydroxide. The fusion mixture is dissolved in
water and the sulfide contained is oxidized with hydrogen peroxide.
At the acid pH, the chloride content is determined by potentiometric titration with silver nitrate solution
after a known addition of the analyte.
5 Reagents
During the analysis, use only reagents of recognized analytical reagent grade and water that conforms
with grade 2 of ISO 3696. Particular care should be taken to ensure all reagents are high purity.
5.1 Sodium carbonate (Na CO ), high purity.
2 3
5.2 Potassium carbonate (K CO ), high purity.
2 3
5.3 Potassium nitrate (KNO ), high purity.
3
5.4 Potassium hydroxide (KOH), high purity.
5.5 Sodium chloride (NaCl), high purity.
5.6 Sodium bromide (NaBr), high purity.
5.7 Silver nitrate (AgNO ), high purity.
3
5.8 Flux mixture.
Mix one portion of anhydrous sodium carbonate (5.1) and one portion of potassium carbonate (5.2).
If the grain size of some reagent is significantly different from the other, a size reduction and
homogenization could be necessary.
Preferably use anhydrous reagent.
5.9 Methyl orange (C H N NaO ), high purity.
14 14 3 3
5.10 Nitric acid (HNO ), ρ20 = 1,4 g/ml, AR grade.
3
5.11 Hydrogen peroxide (H O ), 30 % purity.
2 2
5.12 Nitric acid solution (HNO ), volume fraction 1:1.
3
To a 1 000 ml volumetric flask add approximately 400 ml of deionized water and then 500 ml of
concentrated nitric acid (5.10). Cool to room temperature, dilute to volume and homogenize.
5.13 Sodium chloride solution (NaCl), 0,01 mol/l.
Weigh 0,584 4 g of sodium chloride (5.5), oven-dried at 105 °C for approximately 1 h, and transfer
to a 50 ml beaker. Adjust the mass before weighing according to the purity of the reagent used
(mass = 0,584 4 × 100/purity). Transfer to a glass volumetric flask of 1 000 ml using deionized water.
Dissolve, dilute to volume with deionized water and homogenize.
2 © ISO 2020 – All rights reserved

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ISO 15661:2020(E)

5.14 Sodium bromide solution (NaBr), 0,01 mol/l.
Weigh 1,028 9 g of sodium bromide (5.6), oven-dried at 105°C for approximately 1 h, and transfer to a
50 ml beaker. Adjust the mass to weigh according to the purity of the reagent used (m = 1,028 9 × 100/
purity). Transfer to a glass volumetric flask of 1 000 ml using deionized water. Dissolve and dilute to
volume with deionized water and homogenize.
5.15 Methyl orange solution, 0,1 % mass fraction.
Dissolve 0,5 g of methyl orange (5.9) into a 500 ml flask with deionized water.
5.16 Deionized water.
5.17 Silver nitrate solution (AgNO ), 0,01 mol/l.
3
Dissolve 1,698 7 g of silver nitrate (5.7) in 1 l of deionized water. Stir to dissolve and allow to cool.
Standardize this solution as specified in 5.18.
Adjust the mass to weigh according to a purity of the reagent used (m = 1,698 7 × 100/purity).
This standard solution should be prepared at the same ambient temperature as that at which the
determinations will be conducted.
5.18 Standardization — Determination of the titration factor of the silver nitrate solution
Add to three separate 250 ml beakers 2 ml of 0,01 mol/l sodium bromide solution (5.14) and 4 ml of
0,01 mol/l sodium chloride solution (5.13) and dilute to 200 ml with deionized water.
Add some drops of methyl orange solution (5.15) and adjust the pH with drops of nitric acid solution
(5.12) until the colour changes from yellow to red. Add 2 ml extra.
Insert the electrode for chloride titration (6.12) in the titration solution, stir at a constant rate and wait
about 3 min before titration.
Carry out the titration with 0,01 mol/l silver nitrate solution (5.17).
The end point (E) is detected automatically by the potentiometric sensor. The first end point represents
the consumption of silver nitrate solution (5.17) due to the bromide ion (E1) and the second due to the
chloride ion plus the bromide ion (E2). Calculate the volumes due to only the titration of chloride to
each replicate V , V and V using Formulae (1) to (3):
1 2 3
VE=−21E (1)
11 1
VE=−21E (2)
22 2
VE=−21E (3)
33 3
Calculate the standardization factors ƒ ƒ and ƒ using Formulae (4) to (6):
1, 2 3
fV= V (4)
11NaCl
fV= V (5)
22NaCl
fV= V (6)
33NaCl
where V is the volume of solution (5.13) added in ml, which in this case is equal to 4 ml.
NaCl
© ISO 2020 – All rights reserved 3

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ISO 15661:2020(E)

Calculate to four significant figures the mean standardization factor, ƒ, for the silver nitrate standard
solution, provided that the range of the values of ƒ ƒ and ƒ , does not exceed 0,02. If this range is
1, 2 3
exceeded, repeat the standardization or preparation of solutions.
It is desirable that the titration factor is in the range 0,99 to 1,01.
Use this factor at expression of results (see Clause 10) to obtain the total chlorine content of the samples.
6 Apparatus
All laboratory glassware and equipment shall be shown to be free of chlorine contamination.
Use ordinary laboratory apparatus and the following:
6.1 Volumetric glassware, of class A conforming with ISO 385, ISO 648 and ISO 1042 and used in
accordance with ISO 4787.
6.2 Glassware beakers, 250 ml and 400 ml.
6.3 Zirconium crucibles, capacity of 80 ml with caps.
6.4 Nickel crucibles, capacity of 80 ml with caps (desirable).
6.5 Weighing device, capable of weighing the test sample and test portions to an accuracy of 0,000 1 g.
6.6 Oven, capable of being maintained at 105 °C ± 5 °C.
6.7 Gas burner.
6.8 Muffle furnace, capable of being maintained at 340 °C ± 20 °C and 800 °C ± 50 °C.
6.9 Magnetic stirrer with hot plate.
6.10 Filter paper, sufficient retention capacity for filtration to clear solution.
6.11 Potentiometric titrator, commercially available.
6.12 Silver electrode for chloride titration (single-rod measuring cell).
7 Instrument operating parameters
Refer to the manufacturer’s instructions for optimizing electrode and potentiometric titrator operation.
8 Sample
8.1 Laboratory sample
The laboratory sample shall be taken and prepared in accordance with the procedures described in
ISO 12743.
4 © ISO 2020 – All rights reserved

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ISO 15661:2020(E)

8.2 Test sample
Prepare an air-equilibrated test sample in accordance with ISO 9599.
NOTE A test sample is not required if pre-dried test portions are used, see Annex A.
9 Procedure
9.1 Number of blank testing
Carry out two blank tests in parallel with the analysis using the same quantities of all reagents but
omitting the test sample as described in 9.3.
NOTE Blank tests in this method are used to subtract the known addition of bromide and chloride to the test
samples.
9.2 Number of determinations
Carry out the dete
...

FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 15661
ISO/TC 183
Copper and nickel sulfide ores and
Secretariat: SA
concentrates — Determination of total
Voting begins on:
2020­06­22 chlorine content — Alkaline fusion
and potentiometric titration method
Voting terminates on:
2020­08­17
Minerais et concentrés de cuivre et de nickel — Détermination de la
teneur en chlore - Détermination de la teneur en chlore total
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 SUPPOR TING
DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
Reference number
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
ISO/FDIS 15661:2020(E)
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN­
DARDS TO WHICH REFERENCE MAY BE MADE IN
©
NATIONAL REGULATIONS. ISO 2020

---------------------- Page: 1 ----------------------
ISO/FDIS 15661:2020(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2020
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH­1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii © ISO 2020 – All rights reserved

---------------------- Page: 2 ----------------------
ISO/FDIS 15661:2020(E)

Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Reagents . 2
6 Apparatus . 4
7 Instrument operating parameters . 4
8 Sample . 4
8.1 Laboratory sample . 4
8.2 Test sample . 5
9 Procedure. 5
9.1 Number of blank testing . 5
9.2 Number of determinations . 5
9.3 Determination . 5
9.3.1 General. 5
9.3.2 Decomposition of the test portion by fusion with a mixture of carbonate salts . 5
9.3.3 Decomposition of the test portion by fusion with a mixture of potassium salts . 6
9.3.4 Oxidation of sulfide . 7
9.3.5 Preparation of solution for titration . 7
9.3.6 Potentiometric titration . 7
10 Expression of results . 8
11 Precision and accuracy . 9
11.1 Expression of precision . 9
11.2 Method for obtaining the final result .10
11.3 Precision between laboratories .10
11.4 Check of trueness .11
12 Test report .12
Annex A (informative) Procedure for the preparation and determination of the mass of a
predried test portion .13
Annex B (normative) Flow chart of the procedure for the acceptance of analytical values for
test samples .15
© ISO 2020 – All rights reserved iii

---------------------- Page: 3 ----------------------
ISO/FDIS 15661:2020(E)

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non­governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see
www .iso .org/ iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 183, Copper, lead, zinc and nickel ores and
concentrates.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
iv © ISO 2020 – All rights reserved

---------------------- Page: 4 ----------------------
FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 15661:2020(E)
Copper and nickel sulfide ores and concentrates —
Determination of total chlorine content — Alkaline fusion
and potentiometric titration method
CAUTION — The use of this document can involve hazardous materials, operations and
equipment. This document does not purport to address all of the safety issues associated with
its use. It is the responsibility of the user of this document to establish appropriate safety and
health practices and determine the applicability of regulatory limitations prior to its use.
1 Scope
This document specifies an analytical method for the determination of total chlorine content using
alkaline fusion and potentiometric titration.
This method is applicable to copper and nickel sulfide ores and concentrates having chlorine content in
the following ranges:
a) Method 1: 80 µg/g to 4 300 µg/g
b) Method 2: 70 µg/g to 4 300 µg/g
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 385, Laboratory glassware — Burettes
ISO 648, Laboratory glassware — Single-volume pipettes
ISO 1042, Laboratory glassware — One-mark volumetric flasks
ISO 3696, Water for analytical laboratory use — Specification and test methods
ISO 4787, Laboratory glassware — Volumetric instruments — Methods for testing of capacity and for use
ISO 9599, Copper, lead, zinc and nickel sulfide concentrates — Determination of hygroscopic moisture
content of the analysis sample — Gravimetric method
ISO 12743, Copper, lead, zinc and nickel concentrates — Sampling procedures for determination of metal
and moisture content
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
© ISO 2020 – All rights reserved 1

---------------------- Page: 5 ----------------------
ISO/FDIS 15661:2020(E)

4 Principle
The test portion is decomposed by fusion with a mixture of sodium carbonate and potassium carbonate
or with a mixture of potassium nitrate and potassium hydroxide. The fusion mixture is dissolved in
water and the sulfide contained is oxidized with hydrogen peroxide.
At the acid pH, the chloride content is determined by potentiometric titration with silver nitrate solution
after a known addition of the analyte.
5 Reagents
During the analysis, use only reagents of recognized analytical reagent grade and water that conforms
with grade 2 of ISO 3696. Particular care should be taken to ensure all reagents are high purity.
5.1 Sodium carbonate (Na CO ), high purity.
2 3
5.2 Potassium carbonate (K CO ), high purity.
2 3
5.3 Potassium nitrate (KNO ), high purity.
3
5.4 Potassium hydroxide (KOH), high purity.
5.5 Sodium chloride (NaCl), high purity.
5.6 Sodium bromide (NaBr), high purity.
5.7 Silver nitrate (AgNO ), high purity.
3
5.8 Flux mixture.
Mix one portion of anhydrous sodium carbonate (5.1) and one portion of potassium carbonate (5.2).
If the grain size of some reagent is significantly different from the other, a size reduction and
homogenization could be necessary.
Preferably use anhydrous reagent.
5.9 Methyl orange (C H N NaO ), high purity.
14 14 3 3
5.10 Nitric acid (HNO ), ρ20 = 1,4 g/ml, AR grade.
3
5.11 Hydrogen peroxide (H O ), 30 % purity.
2 2
5.12 Nitric acid solution (HNO ), volume fraction 1:1.
3
To a 1 000 ml volumetric flask add approximately 400 ml of deionized water and then 500 ml of
concentrated nitric acid (5.10). Cool to room temperature, dilute to volume and homogenize.
5.13 Sodium chloride solution (NaCl), 0,01 mol/l.
Weigh 0,584 4 g of sodium chloride (5.5), oven-dried at 105 °C for approximately 1 h, and transfer
to a 50 ml beaker. Adjust the mass before weighing according to the purity of the reagent used
(mass = 0,584 4 × 100/purity). Transfer to a glass volumetric flask of 1 000 ml using deionized water.
Dissolve, dilute to volume with deionized water and homogenize.
2 © ISO 2020 – All rights reserved

---------------------- Page: 6 ----------------------
ISO/FDIS 15661:2020(E)

5.14 Sodium bromide solution (NaBr), 0,01 mol/l.
Weigh 1,028 9 g of sodium bromide (5.6), oven-dried at 105°C for approximately 1 h, and transfer to a
50 ml beaker. Adjust the mass to weigh according to the purity of the reagent used (m = 1,028 9 × 100/
purity). Transfer to a glass volumetric flask of 1 000 ml using deionized water. Dissolve and dilute to
volume with deionized water and homogenize.
5.15 Methyl orange solution, 0,1 % mass fraction.
Dissolve 0,5 g of methyl orange (5.9) into a 500 ml flask with deionized water.
5.16 Deionized water.
5.17 Silver nitrate solution (AgNO ), 0,01 mol/l.
3
Dissolve 1,698 7 g of silver nitrate (5.7) in 1 l of deionized water. Stir to dissolve and allow to cool.
Standardize this solution as specified in 5.18.
Adjust the mass to weigh according to a purity of the reagent used (m = 1,698 7 × 100/purity).
This standard solution should be prepared at the same ambient temperature as that at which the
determinations will be conducted.
5.18 Standardization — Determination of the titration factor of the silver nitrate solution
Add to three separate 250 ml beakers 2 ml of 0,01 mol/l sodium bromide solution (5.14) and 4 ml of
0,01 mol/l sodium chloride solution (5.13) and dilute to 200 ml with deionized water.
Add some drops of methyl orange solution (5.15) and adjust the pH with drops of nitric acid solution
(5.12) until the colour changes from yellow to red. Add 2 ml extra.
Insert the electrode for chloride titration (6.12) in the titration solution, stir at a constant rate and wait
about 3 min before titration.
Carry out the titration with 0,01 mol/l silver nitrate solution (5.17).
The end point (E) is detected automatically by the potentiometric sensor. The first end point represents
the consumption of silver nitrate solution (5.17) due to the bromide ion (E1) and the second due to the
chloride ion plus the bromide ion (E2). Calculate the volumes due to only the titration of chloride to
each replicate V , V and V using Formulae (1) to (3):
1 2 3
VE=−21E (1)
11 1
VE=−21E (2)
22 2
VE=−21E (3)
33 3
Calculate the standardization factors ƒ ƒ and ƒ using Formulae (4) to (6):
1, 2 3
fV= V (4)
11NaCl
fV= V (5)
22NaCl
fV= V (6)
33NaCl
where
© ISO 2020 – All rights reserved 3

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ISO/FDIS 15661:2020(E)

V is the volume of solution (5.13) added in ml, which in this case is equal to 4 ml.
NaCl
Calculate to four significant figures the mean standardization factor, ƒ, for the silver nitrate standard
solution, provided that the range of the values of ƒ ƒ and ƒ , does not exceed 0,02. If this range is
1, 2 3
exceeded, repeat the standardization or preparation of solutions.
It is desirable that the titration factor is in the range 0,99 to 1,01.
Use this factor at expression of results (see Clause 10) to obtain the total chlorine content of the samples.
6 Apparatus
All laboratory glassware and equipment shall be shown to be free of chlorine contamination.
Use ordinary laboratory apparatus and the following:
6.1 Volumetric glassware, of class A conforming with ISO 385, ISO 648 and ISO 1042 and used in
accordance with ISO 4787.
6.2 Glassware beakers, 250 ml and 400 ml.
6.3 Zirconium crucibles, capacity of 80 ml with caps.
6.4 Nickel crucibles, capacity of 80 ml with caps (desirable).
6.5 Weighing device, capable of weighing the test sample and test portions to an accuracy of 0,000 1 g.
6.6 Oven, capable of being maintained at 105 °C ± 5 °C.
6.7 Gas burner.
6.8 Muffle furnace, capable of being maintained at 340 °C ± 20 °C and 800 °C ± 50 °C.
6.9 Magnetic stirrer with hot plate.
6.10 Filter paper, sufficient retention capacity for filtration to clear solution.
6.11 Potentiometric titrator, commercially available.
6.12 Silver electrode for chloride titration (single­rod measuring cell).
7 Instrument operating parameters
Refer to the manufacturer’s instructions for optimizing electrode and potentiometric titrator operation.
8 Sample
8.1 Laboratory sample
The laboratory sample shall be taken and prepared in accordance with the procedures described in
ISO 12743.
4 © ISO 2020 – All rights reserved

---------------------- Page: 8 ----------------------
ISO/FDIS 15661:2020(E)

8.2 Test sample
Prepare an air-equilibrated test sample in accordance with ISO 9599.
NOTE A test sample is not required if pre-dried test portions are used, see Annex A.
9 Procedure
9.1 Number of blank testing
Carry out two blank tests in parallel with the
...