SIST ISO 10523:2010
Water quality - Determination of pH
Water quality - Determination of pH
ISO 10523:2008 specifies a method for determining the pH value in rain, drinking and mineral waters, bathing waters, surface and ground waters, as well as municipal and industrial waste waters, and liquid sludge, within the range pH 2 to pH 12 with an ionic strength below I = 0,3 mol/kg (conductivity at 25 °C
Qualité de l'eau - Détermination du pH
Kakovost vode - Določevanje pH
Ta mednarodni standard določa metodo določevanja pH vrednosti v deževnicah, pitnih in mineralnih vodah, kopalnih vodah, površinskih in podtalnih vodah ter tekočega mulja v razponu pH vrednosti od 2 do 12, z ionsko močjo pod I = 0.3 mol/kg (prevodnost: mS/m), solventna in pri razponu temperature od 0 do 50 °C.
General Information
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Standards Content (Sample)
SLOVENSKI STANDARD
01-september-2010
1DGRPHãþD
SIST ISO 10523:1996
.DNRYRVWYRGH'RORþHYDQMHS+
Water quality - Determination of pH
Qualité de l'eau - Détermination du pH
Ta slovenski standard je istoveten z: ISO 10523:2008
ICS:
13.060.50 3UHLVNDYDYRGHQDNHPLþQH Examination of water for
VQRYL chemical substances
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
INTERNATIONAL ISO
STANDARD 10523
Second edition
2008-12-15
Water quality — Determination of pH
Qualité de l'eau — Détermination du pH
Reference number
©
ISO 2008
PDF disclaimer
This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but
shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In
downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat
accepts no liability in this area.
Adobe is a trademark of Adobe Systems Incorporated.
Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation
parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In
the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.
© ISO 2008
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,
electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or
ISO's member body in the country of the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii © ISO 2008 – All rights reserved
Contents Page
Foreword. iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions. 1
4 Principle. 2
5 Interferences . 2
6 Reagents. 3
7 Apparatus . 3
8 Sampling. 4
9 Procedure . 5
9.1 Preparation . 5
9.2 Calibration and adjustment of the measuring equipment. 5
9.3 Measurement of the samples . 6
10 Expression of results . 6
11 Test report . 6
Annex A (informative) pH values of primary standard reference solutions. 7
Annex B (informative) Operative measurements in flow systems . 8
Annex C (informative) Field measurement (on-site measurement) . 10
Annex D (informative) Measurements of the pH value in water with low ionic strength . 11
Annex E (informative) Performance data. 12
Bibliography . 13
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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
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.
ISO 10523 was prepared by Technical Committee ISO/TC 147, Water quality, Subcommittee SC 2, Physical,
chemical and biochemical methods.
This second edition cancels and replaces the first edition (ISO 10523:1994), which has been technically
revised.
iv © ISO 2008 – All rights reserved
Introduction
The measurement of the pH value of water is of great importance for many types of sample. High and low pH
values are toxic for aquatic organisms, either directly or indirectly. The pH value is the most useful parameter
in assessing the corrosive properties of an aquatic environment. Also, it is important for the effective operation
of water treatment processes and their control (e.g. flocculation and chlorine disinfection), control of
plumbosolvency of drinking waters and biological treatment of sewage and sewage discharges.
The electrometric methods addressed in this International Standard are based on measuring the potential
difference of an electrochemical cell where one of the two half-cells is a measuring electrode and the other is
a reference electrode. The potential of the measuring electrode is a function of the hydrogen ion activity of the
measuring solution (Reference [5]).
In view of its great practical importance, universality and exactitude, only measuring using the pH glass
electrode is described in this International Standard.
In the reference electrode, electrolytes applied can be in liquid, polymer or gel form.
INTERNATIONAL STANDARD ISO 10523:2008(E)
Water quality — Determination of pH
WARNING — Persons using this International Standard should be familiar with normal laboratory
practice. This International Standard does not purport to address any safety problems associated with
its use. It is the responsibility of the user to establish appropriate safety and health practices and to
ensure compliance with any national regulatory conditions.
IMPORTANT — It is absolutely essential that tests conducted according to this International Standard
be carried out by suitably trained staff.
1 Scope
This International Standard specifies a method for determining the pH value in rain, drinking and mineral
waters, bathing waters, surface and ground waters, as well as municipal and industrial waste waters, and
liquid sludge, within the range pH 2 to pH 12 with an ionic strength below I = 0,3 mol/kg (conductivity:
γ < 2 000 mS/m) solvent and in the temperature range 0 °C to 50 °C.
25 °C
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.
ISO 3696, Water for analytical laboratory use — Specification and test methods
ISO 4796-2, Laboratory glassware — Bottles — Part 2: Conical neck bottles
ISO 5667-3, Water quality — Sampling — Part 3: Guidance on the preservation and handling of water
samples
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
pH
measure of the activity of hydrogen ions in solution
[1]
NOTE 1 Adapted from ISO 80000-9 .
NOTE 2 Whether a reaction is acid or alkaline is determined by the activity of the hydrogen ions present.
3.2
pH value
logarithm to the base 10 of the ratio of the molar hydrogen-ion activity (a ) multiplied by −1
H
pH=−lgam=−lg()γ / m° (1)
HHH
where
a is the relative (molality basis) activity of the hydrogen ions;
H
γ is the molal activity coefficient of hydrogen ions at m ;
H H
m is the molality, in moles per kilogram, of the hydrogen ions;
H
m° is the standard molality
[1]
NOTE 1 Adapted from ISO 80000-9 .
NOTE 2 pH value is an absolute measure characteristic.
NOTE 3 The pH(PS) (PS = primary standard) as a measure of single ion activity is not measurable. Therefore, the
pH(PS) of solutions of primary reference materials is established, in order to calculate it as closely as possible and enable
it to be traced back. This is achieved by using an electrochemical measuring procedure that rests upon the stringent
thermodynamic dependency of the potential of the platinum/hydrogen electrode of the activity of the hydrogen ions and
excludes diffusion current by using cells without transfer.
4 Principle
The determination of the pH value is based on measuring the potential difference of an electrochemical cell
using a suitable pH meter.
The pH of a sample also depends on the temperature because of dissociation equilibrium. Therefore, the
temperature of the sample is always stated together with the pH measurement.
5 Interferences
Deviations in the measurements are caused by additional voltages in the pH electrode, especially in the
membrane, the diaphragm, and the measuring solution, and result in incorrect measurements. These
deviations are lowest if both calibration/adjustment and measurement are carried out under similar conditions
(e.g. temperature, flow characteristics, ionic strength).
Ageing and sedimentations (coatings) on the membrane (e.g. calcium carbonate, hydroxides of metals, oil,
grease) of the measuring electrode induce an apparent decrease of the slope of the pH electrode, long
response times or the occurrence of cross-sensibilities against anions and cations.
Sedimentations (coatings) or precipitations on or in the diaphragm (e.g. silver chloride, silver sulfide and
proteins) interfere with the electrical contact to the measuring solution. Defects in the diaphragm can be
identified by measuring the dilution effect of the measuring solutions.
If reactions between the electrolyte and the measuring solution result in precipitations in the diaphragm,
establish an internal electrolyte bridge (e.g. KCl/KCl + AgCl) or an electrolyte bridge with inert electrolytes (e.g.
potassium nitrate, c(KNO ) = 0,1 mol/l) between the sample solution and the reference electrolyte.
Especially in waters with low conductivity, high diffusion voltages may occur. Stirring effects and memory
effects (back-diffusion of the measuring solution into the reference electrode) can cause deviations in the
measurements. Special pH electrodes (e.g. with a ground diaphragm or with an internal bridge with an AgCl-
free solution of reference electrolytes) shall then be used.
In waters with low buffering capacity, the pH value may change very easily (e.g. by introduction or loss of
carbon dioxide from the air or absorption of alkaline substances from glass vessels). In these cases, it is
recommended to use suitable materials and to carry out the measurements in a closed flow system.
The release of gases in the vicinity of the pH electrode can cause additional interferences and, thus, a change
of the pH value.
In suspensions, deviations in the measurements may occur. In this case, let the sample settle in a completely
filled and closed vessel and subsequently measure in the clear supernatant.
2 © ISO 2008 – All rights reserved
Deviations in the measurements may occur when measuring ground waters or mineral waters rich in carbon
dioxide. In these cases saturation with carbon dioxide under high pressure and degassing may occur during
t
...
INTERNATIONAL ISO
STANDARD 10523
Second edition
2008-12-15
Water quality — Determination of pH
Qualité de l'eau — Détermination du pH
Reference number
©
ISO 2008
PDF disclaimer
This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but
shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In
downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat
accepts no liability in this area.
Adobe is a trademark of Adobe Systems Incorporated.
Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation
parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In
the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.
© ISO 2008
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,
electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or
ISO's member body in the country of the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii © ISO 2008 – All rights reserved
Contents Page
Foreword. iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions. 1
4 Principle. 2
5 Interferences . 2
6 Reagents. 3
7 Apparatus . 3
8 Sampling. 4
9 Procedure . 5
9.1 Preparation . 5
9.2 Calibration and adjustment of the measuring equipment. 5
9.3 Measurement of the samples . 6
10 Expression of results . 6
11 Test report . 6
Annex A (informative) pH values of primary standard reference solutions. 7
Annex B (informative) Operative measurements in flow systems . 8
Annex C (informative) Field measurement (on-site measurement) . 10
Annex D (informative) Measurements of the pH value in water with low ionic strength . 11
Annex E (informative) Performance data. 12
Bibliography . 13
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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
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.
ISO 10523 was prepared by Technical Committee ISO/TC 147, Water quality, Subcommittee SC 2, Physical,
chemical and biochemical methods.
This second edition cancels and replaces the first edition (ISO 10523:1994), which has been technically
revised.
iv © ISO 2008 – All rights reserved
Introduction
The measurement of the pH value of water is of great importance for many types of sample. High and low pH
values are toxic for aquatic organisms, either directly or indirectly. The pH value is the most useful parameter
in assessing the corrosive properties of an aquatic environment. Also, it is important for the effective operation
of water treatment processes and their control (e.g. flocculation and chlorine disinfection), control of
plumbosolvency of drinking waters and biological treatment of sewage and sewage discharges.
The electrometric methods addressed in this International Standard are based on measuring the potential
difference of an electrochemical cell where one of the two half-cells is a measuring electrode and the other is
a reference electrode. The potential of the measuring electrode is a function of the hydrogen ion activity of the
measuring solution (Reference [5]).
In view of its great practical importance, universality and exactitude, only measuring using the pH glass
electrode is described in this International Standard.
In the reference electrode, electrolytes applied can be in liquid, polymer or gel form.
INTERNATIONAL STANDARD ISO 10523:2008(E)
Water quality — Determination of pH
WARNING — Persons using this International Standard should be familiar with normal laboratory
practice. This International Standard does not purport to address any safety problems associated with
its use. It is the responsibility of the user to establish appropriate safety and health practices and to
ensure compliance with any national regulatory conditions.
IMPORTANT — It is absolutely essential that tests conducted according to this International Standard
be carried out by suitably trained staff.
1 Scope
This International Standard specifies a method for determining the pH value in rain, drinking and mineral
waters, bathing waters, surface and ground waters, as well as municipal and industrial waste waters, and
liquid sludge, within the range pH 2 to pH 12 with an ionic strength below I = 0,3 mol/kg (conductivity:
γ < 2 000 mS/m) solvent and in the temperature range 0 °C to 50 °C.
25 °C
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.
ISO 3696, Water for analytical laboratory use — Specification and test methods
ISO 4796-2, Laboratory glassware — Bottles — Part 2: Conical neck bottles
ISO 5667-3, Water quality — Sampling — Part 3: Guidance on the preservation and handling of water
samples
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
pH
measure of the activity of hydrogen ions in solution
[1]
NOTE 1 Adapted from ISO 80000-9 .
NOTE 2 Whether a reaction is acid or alkaline is determined by the activity of the hydrogen ions present.
3.2
pH value
logarithm to the base 10 of the ratio of the molar hydrogen-ion activity (a ) multiplied by −1
H
pH=−lgam=−lg()γ / m° (1)
HHH
where
a is the relative (molality basis) activity of the hydrogen ions;
H
γ is the molal activity coefficient of hydrogen ions at m ;
H H
m is the molality, in moles per kilogram, of the hydrogen ions;
H
m° is the standard molality
[1]
NOTE 1 Adapted from ISO 80000-9 .
NOTE 2 pH value is an absolute measure characteristic.
NOTE 3 The pH(PS) (PS = primary standard) as a measure of single ion activity is not measurable. Therefore, the
pH(PS) of solutions of primary reference materials is established, in order to calculate it as closely as possible and enable
it to be traced back. This is achieved by using an electrochemical measuring procedure that rests upon the stringent
thermodynamic dependency of the potential of the platinum/hydrogen electrode of the activity of the hydrogen ions and
excludes diffusion current by using cells without transfer.
4 Principle
The determination of the pH value is based on measuring the potential difference of an electrochemical cell
using a suitable pH meter.
The pH of a sample also depends on the temperature because of dissociation equilibrium. Therefore, the
temperature of the sample is always stated together with the pH measurement.
5 Interferences
Deviations in the measurements are caused by additional voltages in the pH electrode, especially in the
membrane, the diaphragm, and the measuring solution, and result in incorrect measurements. These
deviations are lowest if both calibration/adjustment and measurement are carried out under similar conditions
(e.g. temperature, flow characteristics, ionic strength).
Ageing and sedimentations (coatings) on the membrane (e.g. calcium carbonate, hydroxides of metals, oil,
grease) of the measuring electrode induce an apparent decrease of the slope of the pH electrode, long
response times or the occurrence of cross-sensibilities against anions and cations.
Sedimentations (coatings) or precipitations on or in the diaphragm (e.g. silver chloride, silver sulfide and
proteins) interfere with the electrical contact to the measuring solution. Defects in the diaphragm can be
identified by measuring the dilution effect of the measuring solutions.
If reactions between the electrolyte and the measuring solution result in precipitations in the diaphragm,
establish an internal electrolyte bridge (e.g. KCl/KCl + AgCl) or an electrolyte bridge with inert electrolytes (e.g.
potassium nitrate, c(KNO ) = 0,1 mol/l) between the sample solution and the reference electrolyte.
Especially in waters with low conductivity, high diffusion voltages may occur. Stirring effects and memory
effects (back-diffusion of the measuring solution into the reference electrode) can cause deviations in the
measurements. Special pH electrodes (e.g. with a ground diaphragm or with an internal bridge with an AgCl-
free solution of reference electrolytes) shall then be used.
In waters with low buffering capacity, the pH value may change very easily (e.g. by introduction or loss of
carbon dioxide from the air or absorption of alkaline substances from glass vessels). In these cases, it is
recommended to use suitable materials and to carry out the measurements in a closed flow system.
The release of gases in the vicinity of the pH electrode can cause additional interferences and, thus, a change
of the pH value.
In suspensions, deviations in the measurements may occur. In this case, let the sample settle in a completely
filled and closed vessel and subsequently measure in the clear supernatant.
2 © ISO 2008 – All rights reserved
Deviations in the measurements may occur when measuring ground waters or mineral waters rich in carbon
dioxide. In these cases saturation with carbon dioxide under high pressure and degassing may occur during
the measurement and cause changes of the original pH value. The pH value in anaerobic water containing
Fe(II) and/or sulfide also changes in contact with air.
For the influence of temperature on the pH value of aqueous solutions, see 7.2, 7.3 and Clause 9.
6 Reagents
Use only reagents of recognized analytical grade, unless otherwise specified.
6.1 Distilled or deionized water, e.g. deionized water as specified in ISO 3696, grade 2, conductivity
< 0,1 mS/m.
6.2 Buffer solutions, preferably certified buffers with stated measurement inaccuracy for calibrating pH
meters. Follow the manufacturer's instructions regarding storage and stability.
If certified buffers are not available and it is necessary to prepare buffer solutions in-house, see Annex A. The
in-house preparation of buffer solutions should be the exception.
Atmospheric carbon dioxide influ
...
NORME ISO
INTERNATIONALE 10523
Deuxième édition
2008-12-15
Qualité de l’eau — Détermination du pH
Water quality — Determination of pH
Numéro de référence
©
ISO 2008
DOCUMENT PROTÉGÉ PAR COPYRIGHT
Droits de reproduction réservés. Sauf prescription différente, aucune partie de cette publication ne peut être reproduite ni utilisée sous
quelque forme que ce soit et par aucun procédé, électronique ou mécanique, y compris la photocopie et les microfilms, sans l’accord écrit
de l’ISO à l’adresse ci-après ou du comité membre de l’ISO dans le pays du demandeur.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
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Web www.iso.org
Version française parue en 2011
Publié en Suisse
ii © ISO 2008 – Tous droits réservés
Sommaire Page
Avant-propos .iv
Introduction .v
1 Domaine d’application . 1
2 Références normatives . 1
3 Termes et définitions . 1
4 Principe . 2
5 Interférences . 2
6 Réactifs . 3
7 Appareillage . 3
8 Échantillonnage . 4
9 Mode opératoire . 5
9.1 Préparation . 5
9.2 Étalonnage et réglage de l’équipement de mesure . 5
9.3 Mesurage des échantillons . 6
10 Expression des résultats . 6
11 Rapport d’essai . 7
Annexe A (informative) Valeurs de pH des solutions de référence (étalon primaire) . 8
Annexe B (informative) Mesurages opératoires dans des systèmes d’écoulement . 9
Annexe C (informative) Mesurage sur le terrain (mesurage sur site) . 11
Annexe D (informative) Mesurages de la valeur de pH dans l’eau à faible force ionique .12
Annexe E (informative) Données de performance .13
Bibliographie .14
Avant-propos
L’ISO (Organisation internationale de normalisation) est une fédération mondiale d’organismes nationaux de
normalisation (comités membres de l’ISO). L’élaboration des Normes internationales est en général confiée aux
comités techniques de l’ISO. Chaque comité membre intéressé par une étude a le droit de faire partie du comité
technique créé à cet effet. Les organisations internationales, gouvernementales et non gouvernementales,
en liaison avec l’ISO participent également aux travaux. L’ISO collabore étroitement avec la Commission
électrotechnique internationale (CEI) en ce qui concerne la normalisation électrotechnique.
Les Normes internationales sont rédigées conformément aux règles données dans les Directives ISO/CEI,
Partie 2.
La tâche principale des comités techniques est d’élaborer les Normes internationales. Les projets de Normes
internationales adoptés par les comités techniques sont soumis aux comités membres pour vote. Leur
publication comme Normes internationales requiert l’approbation de 75 % au moins des comités membres
votants.
L’attention est appelée sur le fait que certains des éléments du présent document peuvent faire l’objet de droits
de propriété intellectuelle ou de droits analogues. L’ISO ne saurait être tenue pour responsable de ne pas avoir
identifié de tels droits de propriété et averti de leur existence.
L’ISO 10523 a été élaborée par le comité technique ISO/TC 147, Qualité de l’eau, sous-comité SC 2, Méthodes
physiques, chimiques et biochimiques.
Cette deuxième édition annule et remplace la première édition (ISO 10523:1994), qui a fait l’objet d’une révision
technique.
iv © ISO 2008 – Tous droits réservés
Introduction
Le mesurage de la valeur du pH de l’eau revêt une importance considérable pour de nombreux types
d’échantillon. Les valeurs de pH élevées et basses sont directement ou indirectement toxiques pour les
organismes aquatiques. La valeur du pH est le paramètre le plus utile pour l’évaluation des propriétés corrosives
d’un environnement aquatique. Elle est également importante pour le bon fonctionnement des processus de
traitement de l’eau et leur contrôle (par exemple floculation et désinfection au chlore), le contrôle de la solubilité
du plomb des eaux potables et du traitement biologique des eaux usées et de leurs effluents.
Les méthodes électrométriques traitées dans la présente Norme internationale sont basées sur le mesurage
de la différence de potentiel d’une cellule électrochimique dans laquelle une des deux demi-cellules est une
électrode de mesure, tandis que l’autre est une électrode de référence. Le potentiel de l’électrode de mesure
dépend de l’activité des ions hydrogène de la solution de mesure (Référence [5]).
Compte tenu de leur importance pratique considérable, de leur universalité et de leur exactitude, seuls les
mesurages utilisant l’électrode de pH en verre sont décrits dans la présente Norme internationale.
Dans l’électrode de référence, les électrolytes appliqués peuvent se présenter sous forme de liquide, de
polymère ou de gel.
NORME INTERNATIONALE ISO 10523:2008(F)
Qualité de l’eau — Détermination du pH
AVERTISSEMENT — Il convient que l’utilisateur de la présente Norme internationale connaisse bien
les pratiques courantes de laboratoire. La présente Norme internationale n’a pas pour but de traiter
tous les problèmes de sécurité qui sont, le cas échéant, liés à son utilisation. Il incombe à l’utilisateur
d’établir des pratiques appropriées en matière d’hygiène et de sécurité, et de s’assurer de la conformité
à la réglementation nationale en vigueur.
IMPORTANT — Il est absolument essentiel que les essais réalisés conformément à la présente Norme
internationale soient exécutés par un personnel ayant reçu une formation adéquate.
1 Domaine d’application
La présente Norme internationale spécifie une méthode permettant de déterminer la valeur du pH dans les
eaux de pluie, les eaux potables et minérales, les eaux de baignade, les eaux de surface et souterraines,
ainsi que les eaux usées industrielles et urbaines, et la boue liquide, dans la plage de pH 2 à pH 12 avec une
force ionique inférieure à I = 0,3 mol/kg (conductivité: γ < 2 000 mS/m) de solvant et dans la plage de
25 °C
température de 0 °C à 50 °C.
2 Références normatives
Les documents de référence suivants sont indispensables pour l’application du présent document. Pour les
références datées, seule l’édition citée s’applique. Pour les références non datées, la dernière édition du
document de référence s’applique (y compris les éventuels amendements).
ISO 3696, Eau pour laboratoire à usage analytique — Spécification et méthodes d’essai
ISO 4796-2, Verrerie de laboratoire — Flacons — Partie 2: Flacons à col conique
ISO 5667-3, Qualité de l’eau — Échantillonnage — Partie 3: Lignes directrices pour la conservation et la
manipulation des échantillons d’eau
3 Termes et définitions
Pour les besoins du présent document, les termes et définitions suivants s’appliquent.
3.1
pH
mesurage de l’activité des ions hydrogène dans une solution
[1]
NOTE 1 Adapté de l’ISO 80000-9 .
NOTE 2 Le fait qu’une réaction soit acide ou alcaline est déterminé par l’activité des ions hydrogène présents.
3.2
valeur du pH
logarithme en base 10 du rapport de l’activité molaire des ions hydrogène (a ) multipliée par −1
H
pH = −lga = −lg m γ /m° (1)
( )
H H H
où
a est l’activité relative (molalité) des ions hydrogène;
H
γ est le facteur d’activité molal des ions hydrogène à m ;
H H
m est la molalité, en moles par kilogramme, des ions hydrogène;
H
m° est la molalité de référence
[1]
NOTE 1 Adapté de l’ISO 80000-9 .
NOTE 2 La valeur du pH est une caractéristique de mesure absolue.
NOTE 3 Le pH(PS) (PS = étalon primaire) en tant que mesure de l’activité d’un seul type d’ion n’est pas mesurable. En
conséquence, le pH(PS) des solutions de matériaux de référence primaires est établi, afin de le calculer aussi précisément
que possible et de permettre de le retracer. Pour cela, on recourt à un mode opératoire de mesurage électrochimique qui
repose sur la dépendance thermodynamique stricte du potentiel de l’électrode de platine/hydrogène de l’activité des ions
hydrogène et exclut le courant de diffusion en utilisant des cellules sans transfert.
4 Principe
La détermination de la valeur du pH est basée sur le mesurage de la différence de potentiel d’une cellule
électrochimique à l’aide d’un pH-mètre approprié.
Le pH d’un échantillon dépend également de la température en raison de l’équilibre de dissociation. C’est
pourquoi la température de l’échantillon est toujours indiquée avec la mesure du pH.
5 Interférences
Les écarts de mesurage sont liés à des tensions supplémentaires dans l’électrode de pH, en particulier dans
la membrane, le diaphragme et la solution de mesure et aboutissent à des mesurages incorrects. Les écarts
les plus faibles sont obtenus lorsque les opérations d’étalonnage/réglage et de mesurage sont réalisées dans
des conditions similaires (par exemple température, caractéristiques de flux, force ionique).
Le vieillissement et les sédimentations (dépôts) sur la membrane (par exemple carbonate de calcium,
hydroxydes de métaux, huile, graisse) de l’électrode de mesure entraînent une diminution apparente de la
pente de l’électrode de pH, des temps de réponse importants ou des sensibilisations croisées aux anions et
aux cations.
Les sédimentations (dépôts) ou précipitations sur ou dans le diaphragme (par exemple chlorure d’argent,
sulfure d’argent et protéines) interfèrent avec le contact électrique avec la solution de mesure. Il est possible
d’identifier des défauts dans le diaphragme en mesurant l’effet de dilution des solutions de mesure.
Si les réactions entre l’électrolyte et la solution de mesure entraînent des précipitations dans le diaphragme,
établir un pont électrolytique interne (par exemple KCl/KCl + AgCl) ou un pont électrolytique avec des
électrolytes inertes (par exemple nitrate de potassium, c(KNO ) = 0,1 mol/l) entre la solution d’échantillon et
l’électrolyte de référence.
Des tensions de diffusion élevées peuvent en particulier se produire dans les eaux à faible conductivité. Les
effets d’agitation et les effets de mémoire (rétrodiffusion de la solution de mesure dans l’électrode de référence)
peuvent entraîner des écarts de mesurage. Des électrodes de pH spéciales (par exemple avec un diaphragme
rodé ou avec un pont interne avec une solution d’électrolytes de référence sans AgCl) doivent alors être
utilisées.
Dans les eaux à faible pouvoir tampon, la valeur du pH peut varier très facilement (par exemple par l’introduction
ou la perte de dioxyde de carbone de l’air ou l’absorption de substances alcalines à partir de récipients en
verre). Il est alors recommandé d’utiliser des matériaux appropriés et de réaliser les mesurages dans un
dispositif en flux fermé.
2 © ISO 2008 – Tous droits réservés
La libération de gaz à proximité de l’électrode de pH peut provoquer des interférences supplémentaires, et en
conséquence, une modification de la valeur du pH.
Des écarts de mesurage peuvent se produire dans les suspensions. Dans ce cas, laisser l’échantillon se
déposer dans un récipient complètement plein et fermé, puis réaliser des mesurages dans le surnageant
limpide.
Des écarts de mesurage sont possibles lorsque les mesurages sont réalisés dans les eaux souterraines
ou des eaux minérales riches en dioxyde de carbone. Il existe alors un risque de saturation avec le dioxyde
de carbone sous haute pression et de dégazage au cours du mesurage, qui sont susceptibles de modifier
la valeur du pH d’origine. La valeur du pH dans de l’eau anaérobie contenant du Fe(II) et/ou du sulfure est
également modifiée au contact de l’air.
Pour l’influence de la température sur la valeur du pH des solutions aqueuses, voir 7.2, 7.3 et l’Article 9.
6 Réactifs
Utiliser uniquement des réactifs de qualité analytique reconnue, sauf spécification contraire.
6.1 Eau distillée ou déionisée, par
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