SIST EN ISO 10523:2012

SLOVENSKI STANDARD
SIST EN ISO 10523:2012
01-junij-2012
.DNRYRVWYRGH'RORþHYDQMHS+,62
Water quality - Determination of pH (ISO 10523:2008)
Wasserbeschaffenheit - Bestimmung des pH-Wertes (ISO 10523:2008)
Qualité de l'eau - Détermination du pH (ISO 10523:2008)
Ta slovenski standard je istoveten z: EN ISO 10523:2012
ICS:
13.060.50 3UHLVNDYDYRGHQDNHPLþQH Examination of water for
VQRYL chemical substances
SIST EN ISO 10523:2012 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 10523:2012

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SIST EN ISO 10523:2012


EUROPEAN STANDARD
EN ISO 10523

NORME EUROPÉENNE

EUROPÄISCHE NORM
February 2012
ICS 13.060.50
English Version
Water quality - Determination of pH (ISO 10523:2008)
Qualité de l'eau - Détermination du pH (ISO 10523:2008) Wasserbeschaffenheit - Bestimmung des pH-Wertes (ISO
10523:2008)
This European Standard was approved by CEN on 15 January 2012.

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, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland,
Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and United Kingdom.





EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2012 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 10523:2012: E
worldwide for CEN national Members.

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SIST EN ISO 10523:2012
EN ISO 10523:2012 (E)
Contents Page
Foreword .3
2

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SIST EN ISO 10523:2012
EN ISO 10523:2012 (E)
Foreword
The text of ISO 10523:2008 has been prepared by Technical Committee ISO/TC 147 “Water quality” of the
International Organization for Standardization (ISO) and has been taken over as EN ISO 10523:2012 by
Technical Committee CEN/TC 230 “Water analysis” the secretariat of which is held by DIN.
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 August 2012, and conflicting national standards shall be withdrawn at
the latest by August 2012.
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.
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, Croatia, 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, Turkey and the United Kingdom.
Endorsement notice
The text of ISO 10523:2008 has been approved by CEN as a EN ISO 10523:2012 without any modification.

3

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SIST EN ISO 10523:2012

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SIST EN ISO 10523:2012

INTERNATIONAL ISO
STANDARD 10523
Second edition
2008-12-15

Water quality — Determination of pH
Qualité de l'eau — Détermination du pH




Reference number
ISO 10523:2008(E)
©
ISO 2008

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SIST EN ISO 10523:2012
ISO 10523:2008(E)
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ii © ISO 2008 – All rights reserved

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SIST EN ISO 10523:2012
ISO 10523:2008(E)
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

© ISO 2008 – All rights reserved iii

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SIST EN ISO 10523:2012
ISO 10523:2008(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.
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

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SIST EN ISO 10523:2012
ISO 10523:2008(E)
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.

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SIST EN ISO 10523:2012

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SIST EN ISO 10523:2012
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
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SIST EN ISO 10523:2012
ISO 10523:2008(E)
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.
3
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.
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SIST EN ISO 10523:2012
ISO 10523:2008(E)
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 influences buffer solutions, especially those of alkaline pH. Purging the gas in the
headspace with protective gas improves stability. For all buffer solutions, avoid frequent opening and closing
of the vessels and removal of small amounts. Mark the time of the first opening on the reagent bottle.
6.3 Electrolytes for liquid-filled reference electrodes. Use the electrolyte solutions recommended by the
manufacturer.
6.4 Potassium chloride solution, c(KCl) = 3 mol/l. To prepare the KCl solution as electrolyte for reference
electrodes, use a suitable amount of solid potassium chloride and dissolve it in water (6.1).
7 Apparatus
7.1 Sampling bottle, sealable, flat-bottomed, made of polyethylene or glass, e.g. laboratory bottle as
specified in ISO 4796-2, designation 100 WS. The type of stopper used shall allow the exclusion of all air from
the sample bottle.
7.2 Temperature measurement device, capable of measurement with a total uncertainty not greater than
0,5 °C. The temperature sensor (7.2.2) is preferred.
7.2.1 Thermometer with a 0,5 °C scale.
7.2.2 Temperature sensor, separate or integrated into the pH electrode, e.g. Pt 100, Pt 1 000 or negative
temperature coefficient.
Temperature measurement deviations due to the device shall be corrected against a calibrated thermometer.
7.3 pH meter, providing the following means for adjustment:
a) zero point of the pH electrode (or offset voltage);
b) slope of the pH electrode;
c) temperature of the pH electrode;
12
d) input resistance > 10 Ω.
Moreover, it shall be possible to change the display of the pH meter to give readings of either the pH value or
the voltage.
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SIST EN ISO 10523:2012
ISO 10523:2008(E)
The resolution of the pH value reading on the pH meter shall be 0,01 or better.
Whether the pH meter is provided with a manual or an automatic routine calibration is not a limiting
characteristic within the scope of this International Standard.
NOTE The temperature compensation carried out by commercially available pH meters is based on the Nernst
equation; i.e. it is dependent on temperature, and the corresponding t
...