Water quality - Characterization of analytical methods - Guidelines for the selection of a representative matrix

This document specifies representative materials suitable for the determination of the performance
characteristics, including uncertainty, during the initial assessment of a quantitative method, used in a
laboratory, for physico-chemical water analysis.
This document focuses on five main types of water:
— waters intended for consumption (5.2);
— natural waters (5.3);
— waste waters (5.4);
— marine waters (5.5);
— recreational waters (5.6).
NOTE Other more specific or less common types of water can be incorporated in any of the above types
provided appropriate justifications. The characteristics of the standard matrix are compatible with the
characteristics of the samples handled.

Qualité de l'eau - Caractérisation des méthodes d'analyses - Lignes directrices pour la sélection d'une matrice représentative

Kakovost vode - Karakterizacija analiznih metod - Smernice za izbiro reprezentativnega matriksa

Ta dokument določa reprezentativne materiale, primerne za določanje značilnosti zmogljivosti, vključno z negotovostjo, med začetno oceno kvantitativne metode, uporabljene v
laboratoriju, za fizikalno-kemijsko analizo vode.
Ta dokument se osredotoča na pet glavnih vrst vod:
– vodo, ki je namenjena za pitje (5.2);
– naravno vodo (5.3);
– odpadno vodo (5.4);
– morsko vodo (5.5);
– rekreacijsko vodo (5.6).
OPOMBA: Druge bolj specifične ali manj pogoste vrste vod je mogoče vključiti v katero koli od naštetih vrst z ustrezno utemeljitvijo. Značilnosti standardne matrike so združljive z značilnostmi obravnavanih vzorcev.

General Information

Status
Published
Public Enquiry End Date
04-Jun-2019
Publication Date
03-Sep-2019
Technical Committee
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
09-Aug-2019
Due Date
14-Oct-2019
Completion Date
04-Sep-2019

Buy Standard

Technical specification
ISO/TS 21231:2019 - Water quality -- Characterization of analytical methods -- Guidelines for the selection of a representative matrix
English language
34 pages
sale 15% off
Preview
sale 15% off
Preview
Technical specification
SIST-TS ISO/TS 21231:2019
English language
39 pages
sale 10% off
Preview
sale 10% off
Preview

e-Library read for
1 day
Technical specification
oSIST-TS ISO/TS 21231:2019
English language
39 pages
sale 10% off
Preview
sale 10% off
Preview

e-Library read for
1 day

Standards Content (sample)

TECHNICAL ISO/TS
SPECIFICATION 21231
First edition
2019-02
Water quality — Characterization of
analytical methods — Guidelines for
the selection of a representative matrix
Reference number
ISO/TS 21231:2019(E)
ISO 2019
---------------------- Page: 1 ----------------------
ISO/TS 21231:2019(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2019

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: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2019 – All rights reserved
---------------------- Page: 2 ----------------------
ISO/TS 21231:2019(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Principle ........................................................................................................................................................................................................................ 4

5 Influence parameters ...................................................................................................................................................................................... 5

5.1 Common parameters for all matrices .................................................................................................................................. 5

5.2 Water intended for consumption ............................................................................................................................................ 6

5.3 Natural waters ......................................................................................................................................................................................... 6

5.4 Waste waters ............................................................................................................................................................................................ 6

5.5 Marine waters .......................................................................................................................................................................................... 6

5.6 Recreational waters ............................................................................................................................................................................ 7

6 Selection of characteristic parameters of a matrix .......................................................................................................... 7

6.1 General ........................................................................................................................................................................................................... 7

6.2 All waters ..................................................................................................................................................................................................... 7

6.3 Waters intended for consumption ......................................................................................................................................... 7

6.4 Natural waters ......................................................................................................................................................................................... 7

6.5 Waste waters ............................................................................................................................................................................................ 7

6.6 Marine waters .......................................................................................................................................................................................... 8

6.7 Recreational waters ............................................................................................................................................................................ 8

7 Available materials ............................................................................................................................................................................................ 8

7.1 General ........................................................................................................................................................................................................... 8

7.2 Material obtained by reasonable dilution of a real matrix ................................................................................ 8

7.3 Artificial material .................................................................................................................................................................................. 9

7.4 Analyte-specific blank values in matrices........................................................................................................................ 9

8 Report .............................................................................................................................................................................................................................. 9

Annex A (informative) Characterization of waters intended for human consumption and

mineral waters .....................................................................................................................................................................................................10

Annex B (informative) Examples of preparation of artificial matrices and representative

characteristics ......................................................................................................................................................................................................11

Annex C (informative) Occurrence of chemical substances in waste water, by industrial

activity sector ........................................................................................................................................................................................................23

Annex D (informative) Leachate .............................................................................................................................................................................32

Bibliography .............................................................................................................................................................................................................................33

© ISO 2019 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO/TS 21231:2019(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 147, Water quality, Subcommittee SC 2,

Physical, chemical and biochemical methods.

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 2019 – All rights reserved
---------------------- Page: 4 ----------------------
ISO/TS 21231:2019(E)
Introduction

This document has been prepared for the validation of analytical methods applied to the water quality

field. It enables a laboratory to determine the characteristics of a material suitable for determination of

the performances of an analytical method itself.

It is not intended to provide an exhaustive inventory of all published recipes, but to propose a selection

of recipes supporting the characterization of the performances of analytical methods used by a

laboratory. For this reason, a restricted number of recipes are proposed. References giving access to

other recipes are available in the Bibliography.

This document includes four recipes for preparing marine waters and five recipes for waste waters

with controlled characteristics.
© ISO 2019 – All rights reserved v
---------------------- Page: 5 ----------------------
TECHNICAL SPECIFICATION ISO/TS 21231:2019(E)
Water quality — Characterization of analytical methods —
Guidelines for the selection of a representative matrix
1 Scope

This document specifies representative materials suitable for the determination of the performance

characteristics, including uncertainty, during the initial assessment of a quantitative method, used in a

laboratory, for physico-chemical water analysis.
This document focuses on five main types of water:
— waters intended for consumption (5.2);
— natural waters (5.3);
— waste waters (5.4);
— marine waters (5.5);
— recreational waters (5.6).

NOTE Other more specific or less common types of water can be incorporated in any of the above types

provided appropriate justifications. The characteristics of the standard matrix are compatible with the

characteristics of the samples handled.
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 5667-3, Water quality — Sampling — Part 3: Preservation and handling of water samples

ISO 6107 (all parts), Water quality — Vocabulary
3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 6107 (all parts) and the

following apply.

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/
3.1 General vocabulary
3.1.1
matrix
set of constituents of the test sample, except the analyte (3.2.1)

Note 1 to entry: By extension, a matrix defines a group of waters characterized by similar analytical behaviour in

relation to the analytical method used.
© ISO 2019 – All rights reserved 1
---------------------- Page: 6 ----------------------
ISO/TS 21231:2019(E)
3.1.2
accepted reference value

value that serves as an agreed-upon reference for comparison, and which is derived as:

a) a theoretical or established value, based on scientific principles;

b) an assigned or certified value, based on experimental work of some national or international

organization;

c) a consensus or certified value, based on collaborative experimental work under the auspices of a

scientific or engineering group;

d) when a), b) and c) are not available, the expectation of the (measurable) quantity, i.e. the mean of a

specified population of measurements

Note 1 to entry: In the specific context of this document, the accepted reference value (or conventionally true

value) of the sample is provided according to possibilities by:
— the value from a certified reference material certificate,
— the consensus value obtained from an inter-laboratory comparison,

— the arithmetic mean of the repeated measurement values according to the reference method,

— the target value by adding analyte to a representative matrix of the scope in question.

[SOURCE: ISO 5725-1:1994, 3.5]
3.1.3
reference material

material, sufficiently homogeneous and stable with respect to one or more specified properties, which

has been established to be fit for its intended use in a measurement process
[SOURCE: ISO Guide 35:2017, 3.1]
3.1.4
certified reference material

reference material (3.1.3), accompanied by a certificate, one or more of whose property values are

certified by a procedure which establishes traceability to an accurate realization of the unit in which

the property values are expressed, and for which each certified value is accompanied by an uncertainty

at a stated level of confidence
[SOURCE: ISO/TS 13530:2009, 3.2.7]
3.1.5
assessment procedure

procedure related to the establishment of the specifications for the performance of a new method and/

or experimental verification that a method meets theoretically derived quality criteria

3.2 Terms related to analytical methods
3.2.1
analyte
subject of the analytical method
3.2.2
analytical method

unambiguously written procedure describing all details required to carry out the analysis of the analyte

(3.2.1), namely: scope and field of application, principle and/or reactions, definitions, reagents, apparatus,

analytical procedures, calculations and presentation of results, performance data and test report

[SOURCE: ISO/TS 16489:2006, 3.3]
2 © ISO 2019 – All rights reserved
---------------------- Page: 7 ----------------------
ISO/TS 21231:2019(E)
3.2.3
quantitative analytical method

analytical method for measuring the quantity of analyte (3.2.1)contained in the test sample

Note 1 to entry: The result can consist of a quantity in a given quantity of test sample.

3.2.4
limit of detection

output signal or value above which it can be affirmed, with a stated level of confidence, for example

95 %, that a sample is different from a blank sample containing no determinand of interest, and which

could be estimated by different means and shall be verified in the intended matrix

[SOURCE: ISO 6107-2:2006, 60, modified — “and which could be estimated by different means and shall

be verified in the intended matrix” has been added.]
3.2.5
limit of quantification
LOQ

lowest value of a determinand that can be determined with an acceptable level of accuracy, which could

be estimated by different means and shall be verified in the intended matrix

Note 1 to entry: For each matrix, this limit is related to the pair [analyte (3.2.1), method].

3.2.6
reasonable dilution

dilution conditions for reducing the concentration of a substance in a matrix without substantially

modifying the intrinsic characteristics of the matrix
3.2.7
matrix blank values

values of a given parameter obtained using a test conducted on a matrix giving rise to a result below the

limit of detection (3.2.4) for the analyte (3.2.1) in question
3.2.8
scope of the analytical method

combination of the various types of matrix and the analyte (3.2.1) concentration range covered, to

which the analytical method applies

Note 1 to entry: In addition to an indication of all the satisfactory performance conditions for each factor, the

scope of the analytical method may also include warnings in respect of known interferences from other analytes,

or inapplicability to some matrices or conditions.
3.3 Terms related to matrix
3.3.1
influence parameter

intrinsic characteristic of the matrix, independent of the analyte (3.2.1) concentration, a variation of

which is liable to modify the analytical result
3.3.2
representative matrix

sample for which all the intrinsic characteristics are characteristic of a type of water or the source of a

group of samples
3.3.3
salinity

mass in grams of solid substances contained in one kilogram of sea water, when the bromide and iodide

ions are replaced by their chloride equivalent, carbonates converted into oxides and all the organic

matter oxidized
© ISO 2019 – All rights reserved 3
---------------------- Page: 8 ----------------------
ISO/TS 21231:2019(E)
3.3.4
leachate

water which has percolated through tipped refuse or other specified permeable material

Note 1 to entry: See Annex D.
[SOURCE: ISO 6107-7:2006, 23]
4 Principle

The purpose of this document is to specify the concept of a representative matrix and its characteristics

with a view to studying the performance of an analytical method.

For each analyte under test, the scope of an analytical method includes all the matrices under test,

their descriptive parameters, and the concentration ranges of the influence parameters for which the

method is applicable. The laboratory should define its requirements beforehand in respect of the scope

of the analytical method, selecting the materials most in line with requirements.

WARNING — The definition of the scope is entirely dependent on the analyst (the validation or

characterization study manager) and their knowledge acquired while developing the method.

It is sometimes preferable to segment a scope rather than seek to validate an overly general

method. In this case, a validation file should be compiled for each scope.
See Figure 1.
4 © ISO 2019 – All rights reserved
---------------------- Page: 9 ----------------------
ISO/TS 21231:2019(E)
Figure 1 — Summary flow chart
5 Influence parameters
5.1 Common parameters for all matrices

The following influence parameters are liable to have an impact on analysis procedures. They shall help

classify the types of water on which the laboratory has validated its method or determined performance

characteristics.
— pH;
— ion composition and/or conductivity;
© ISO 2019 – All rights reserved 5
---------------------- Page: 10 ----------------------
ISO/TS 21231:2019(E)
— salinity;
— dissolved organic carbon (DOC) and/or total organic carbon (TOC);
— colour or turbidity;
— suspended particular matter (SPM) content.
During the validation or characterization study, it is up to the laboratory to:

— define, for its practice, the characteristic ranges associated with each of the above parameters;

— justify, if applicable, the lack of influence thereof on the characterized method;

— complement this list with other characteristic parameters based on the methods and the source of

the samples analysed, using for example Annex A or Annex C.
5.2 Water intended for consumption

Water intended for human and livestock consumption is water considered to be fit for drinking.

Drinking water belongs to this category. It includes groundwater that has been chlorinated in the

resource.
The minimum additional characteristics to be included for this category are:

— disinfectant presence and content (distributed waters or groundwater chlorinated in the resource);

— CO content (natural mineral water), if relevant to subsequent specified analysis requirements.

5.3 Natural waters

Natural waters are waters taken from the natural environment not undergoing to any treatment other

than the addition of reagents for analyte preservation.

Surface waters and groundwater belong to this category. Brackish waters with salinity lower than

30 g/l are incorporated in this category.

Rainwater, which is generally not intended for consumption, are incorporated in this category.

5.4 Waste waters

Waste waters can originate from any combination of household, industrial or commercial activities.

They include collected run-offs and those from any spillage or infiltration from the waste water

collection system, including the contents of storm water tanks or ponds, discharged into collection

systems or into the environment.
NOTE 1 Waste waters can be collected in common systems or in separate systems.

NOTE 2 For the purposes of this document, the definition of waste water also includes untreated sanitary

waters.

NOTE 3 National or local regulations can include lists of substances of concern in relation to sewer discharges.

Annex C gives a list of examples of additional characteristics associated with some sectors of activity.

Some waste waters may have a high salinity.
5.5 Marine waters

Sea water consists of a large number of compounds distributed over the following categories: gases,

particulate matter, colloids, and dissolved elements (see Reference [7]).
6 © ISO 2019 – All rights reserved
---------------------- Page: 11 ----------------------
ISO/TS 21231:2019(E)

The dissolved elements consist of 92 natural chemical elements, approximately two-thirds of which

are present in ultra-trace amounts and are difficult to detect. Sea water is characterized in that the

[8]

relative proportions of its 11 main constituents are substantially constant (Dittmar's law ) within

1 %. Dittmar's law can thus be used to determine the salinity of sea water by measuring only one of its

components.

The average salinity of sea water is 35 g/kg. It is generally between 30 g/kg (North Atlantic) and 40 g/

kg (Red Sea) but exhibits extreme values in closed or semi-closed seas (6 g/kg in the Baltic Sea, 330 g/

kg in the Dead Sea). The pH of sea water is approximately 8,2.
5.6 Recreational waters

Recreational waters are bathing, swimming pool, thermal bath and spa waters. They may be sourced

from natural waters or waters intended for human consumption and are characterized, in addition to

the influence parameters defined in 5.2, by the potential presence of specific disinfection products and

by-products, and the potential presence of sulfur compounds.
6 Selection of characteristic parameters of a matrix
6.1 General

For the purposes of characterization of the applicability and the performances of an analytical method

to a matrix, the laboratory shall describe the limits of the ranges associated with the characteristic

parameters discussed in this clause.
6.2 All waters
The parameters are those defined in 5.1.
6.3 Waters intended for consumption

In addition to the characteristics listed in 5.1, waters intended for consumption are characterized by:

— their free and total chlorine content;
— the nature and content of disinfection reagents and by-products;
— their CO content, if relevant.

Refer to Annex A for more detailed characterization of waters intended for human consumption.

6.4 Natural waters

In addition to the characteristics listed in 5.1, natural waters are characterized by:

— the sampling location, including the sampling depth;
— the identified surrounding anthropic pressures.

In the case of groundwater used as drinking water resources, which are treated in situ, free and total

chlorine content should be verified.
6.5 Waste waters

In addition to the characteristics listed in 5.1, waste waters are characterized by:

— the original activity sector (see Annex C);
© ISO 2019 – All rights reserved 7
---------------------- Page: 12 ----------------------
ISO/TS 21231:2019(E)

— the connected activity sectors in the case of municipal waste water treatment plants (MWWTP)

discharges.
6.6 Marine waters

In addition to the characteristics listed in 5.1, marine waters are characterized by:

— the sampling location, including sampling depth;
— their salinity.
6.7 Recreational waters

In addition to the characteristics listed in 5.1, recreational waters are characterized by:

— the sampling location;
— the nature and content of disinfection reagents and by products.
7 Available materials
7.1 General

The laboratory shall select study matrices for one or more of the above water types from, in order of

preference:
— reference materials if the matrix is sufficiently characterized;

— supernumerary material from interlaboratory tests if stable and sufficiently characterized;

— material obtained by spiking with the real matrix free from the analytes of interest;

— material obtained by spiking a reasonable dilution of a real matrix, after adjusting the characteristics

modified by the dilution;

— material obtained by spiking of an artificial matrix based on a recipe (see Annex B).

At least three different representative samples of each water type should be studied to provide a

realistic evaluation of performance of the method on the selected water type. Wherever possible, the

method performances shall be characterized on a non-artificial sample.
7.2 Material obtained by reasonable dilution of a real matrix

When the laboratory cannot select a real matrix free from analyte(s) of interest, but it is possible to

select a real matrix containing the analyte(s) of interest at a concentration lower than 10× the limit

of quantification (LOQ) defined for the method under examination, a representative matrix can be

prepared by diluting the low-concentration real matrix, so as to lower the concentration of analyte(s) of

interest to less than the LOQ defined for the method.

The dilution factor, f, shall be lower than 10. For this dilution, a water free from analyte(s) of interest

having a similar composition to the chosen matrix (major elements and influence factors) shall be used.

Before dilution, the selected matrix shall be characterized on the basis of the influence parameters

chosen for the study. After dilution, these parameters shall be readjusted if required using solid state

reagents or stock solutions of solid state reagents so that the value of each influence parameter remains

within the scope defined by the laboratory.
8 © ISO 2019 – All rights reserved
---------------------- Page: 13 ----------------------
ISO/TS 21231:2019(E)
7.3 Artificial material

Artificial materials can be prepared according to Annex B, after adjusting the influence parameters

selected based on a bibliographic study, and/or on Annex C, within the concentration range defining the

scope of the method.
7.4 Analyte-specific blank values in matrices

For some analytes, such as heavy metals, no analyte-free natural or artificial matrix can be obtained.

After proper justification, the laboratory should study LOQ as follows.
— Determine LOQ on ultrapure water.

— Calculate LOQ by correcting LOQ using the recovery of the analyte in the intended matric,

water i MQ
i.e. water by using Formula (1):
LOQ
LOQ = (1)
water i
water i
where
LOQ is the LOQ of the method for the analyte in water type i;
water i
LOQ is the LOQ of the method for the analyte in ultra pure water;
is the mean recovery of the method for the analyte in water type i.
water i
8 Report

The quantitative analytical method assessment report, for a given matrix, shall include, in addition to

the information requested by the assessment procedure:
a) the name of the tested matrix according to the typology defined in Clause 5;

b) the characteristic parameters of the matrix according to Clause 6 and the associated representative

ranges (scope);

c) the influence parameters tested, the justification for their selection and the representative

contents;
d) the source of the matrix and, if applicable, its preparation method.
© ISO 2019 – All rights reserved 9
---------------------- Page: 14 ----------------------
ISO/TS 21231:2019(E)
Annex A
(informative)
Characterization of waters intended for human consumption and
mineral waters
Water intended for human consumption produced, is generally characterized by:
— the absence of suspended solids;
— a relatively low organic content (TOC < 4 mg/ l);
— a conductivity at 25 °C between 50 µS/cm and 1 100 µS/cm and
— a pH between 6 and 9.

Waters sampled during the production cycle, or at distribution point, often show traces of oxidants

used to disinfect resource water, usually chlorine, chlorine dioxide or ozone at levels between 0,2 mg/l

and 2 mg/l. Depending on the parameters to
...

SLOVENSKI STANDARD
SIST-TS ISO/TS 21231:2019
01-oktober-2019
Kakovost vode - Karakterizacija analiznih metod - Smernice za izbiro
reprezentativnega matriksa

Water quality - Characterization of analytical methods - Guidelines for the selection of a

representative matrix

Qualité de l'eau - Caractérisation des méthodes d'analyses - Lignes directrices pour la

sélection d'une matrice représentative
Ta slovenski standard je istoveten z: ISO/TS 21231:2019
ICS:
13.060.50 Preiskava vode na kemične Examination of water for
snovi chemical substances
SIST-TS ISO/TS 21231:2019 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
SIST-TS ISO/TS 21231:2019
---------------------- Page: 2 ----------------------
SIST-TS ISO/TS 21231:2019
TECHNICAL ISO/TS
SPECIFICATION 21231
First edition
2019-02
Water quality — Characterization of
analytical methods — Guidelines for
the selection of a representative matrix
Reference number
ISO/TS 21231:2019(E)
ISO 2019
---------------------- Page: 3 ----------------------
SIST-TS ISO/TS 21231:2019
ISO/TS 21231:2019(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2019

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: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2019 – All rights reserved
---------------------- Page: 4 ----------------------
SIST-TS ISO/TS 21231:2019
ISO/TS 21231:2019(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Principle ........................................................................................................................................................................................................................ 4

5 Influence parameters ...................................................................................................................................................................................... 5

5.1 Common parameters for all matrices .................................................................................................................................. 5

5.2 Water intended for consumption ............................................................................................................................................ 6

5.3 Natural waters ......................................................................................................................................................................................... 6

5.4 Waste waters ............................................................................................................................................................................................ 6

5.5 Marine waters .......................................................................................................................................................................................... 6

5.6 Recreational waters ............................................................................................................................................................................ 7

6 Selection of characteristic parameters of a matrix .......................................................................................................... 7

6.1 General ........................................................................................................................................................................................................... 7

6.2 All waters ..................................................................................................................................................................................................... 7

6.3 Waters intended for consumption ......................................................................................................................................... 7

6.4 Natural waters ......................................................................................................................................................................................... 7

6.5 Waste waters ............................................................................................................................................................................................ 7

6.6 Marine waters .......................................................................................................................................................................................... 8

6.7 Recreational waters ............................................................................................................................................................................ 8

7 Available materials ............................................................................................................................................................................................ 8

7.1 General ........................................................................................................................................................................................................... 8

7.2 Material obtained by reasonable dilution of a real matrix ................................................................................ 8

7.3 Artificial material .................................................................................................................................................................................. 9

7.4 Analyte-specific blank values in matrices........................................................................................................................ 9

8 Report .............................................................................................................................................................................................................................. 9

Annex A (informative) Characterization of waters intended for human consumption and

mineral waters .....................................................................................................................................................................................................10

Annex B (informative) Examples of preparation of artificial matrices and representative

characteristics ......................................................................................................................................................................................................11

Annex C (informative) Occurrence of chemical substances in waste water, by industrial

activity sector ........................................................................................................................................................................................................23

Annex D (informative) Leachate .............................................................................................................................................................................32

Bibliography .............................................................................................................................................................................................................................33

© ISO 2019 – All rights reserved iii
---------------------- Page: 5 ----------------------
SIST-TS ISO/TS 21231:2019
ISO/TS 21231:2019(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 147, Water quality, Subcommittee SC 2,

Physical, chemical and biochemical methods.

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 2019 – All rights reserved
---------------------- Page: 6 ----------------------
SIST-TS ISO/TS 21231:2019
ISO/TS 21231:2019(E)
Introduction

This document has been prepared for the validation of analytical methods applied to the water quality

field. It enables a laboratory to determine the characteristics of a material suitable for determination of

the performances of an analytical method itself.

It is not intended to provide an exhaustive inventory of all published recipes, but to propose a selection

of recipes supporting the characterization of the performances of analytical methods used by a

laboratory. For this reason, a restricted number of recipes are proposed. References giving access to

other recipes are available in the Bibliography.

This document includes four recipes for preparing marine waters and five recipes for waste waters

with controlled characteristics.
© ISO 2019 – All rights reserved v
---------------------- Page: 7 ----------------------
SIST-TS ISO/TS 21231:2019
---------------------- Page: 8 ----------------------
SIST-TS ISO/TS 21231:2019
TECHNICAL SPECIFICATION ISO/TS 21231:2019(E)
Water quality — Characterization of analytical methods —
Guidelines for the selection of a representative matrix
1 Scope

This document specifies representative materials suitable for the determination of the performance

characteristics, including uncertainty, during the initial assessment of a quantitative method, used in a

laboratory, for physico-chemical water analysis.
This document focuses on five main types of water:
— waters intended for consumption (5.2);
— natural waters (5.3);
— waste waters (5.4);
— marine waters (5.5);
— recreational waters (5.6).

NOTE Other more specific or less common types of water can be incorporated in any of the above types

provided appropriate justifications. The characteristics of the standard matrix are compatible with the

characteristics of the samples handled.
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 5667-3, Water quality — Sampling — Part 3: Preservation and handling of water samples

ISO 6107 (all parts), Water quality — Vocabulary
3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 6107 (all parts) and the

following apply.

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/
3.1 General vocabulary
3.1.1
matrix
set of constituents of the test sample, except the analyte (3.2.1)

Note 1 to entry: By extension, a matrix defines a group of waters characterized by similar analytical behaviour in

relation to the analytical method used.
© ISO 2019 – All rights reserved 1
---------------------- Page: 9 ----------------------
SIST-TS ISO/TS 21231:2019
ISO/TS 21231:2019(E)
3.1.2
accepted reference value

value that serves as an agreed-upon reference for comparison, and which is derived as:

a) a theoretical or established value, based on scientific principles;

b) an assigned or certified value, based on experimental work of some national or international

organization;

c) a consensus or certified value, based on collaborative experimental work under the auspices of a

scientific or engineering group;

d) when a), b) and c) are not available, the expectation of the (measurable) quantity, i.e. the mean of a

specified population of measurements

Note 1 to entry: In the specific context of this document, the accepted reference value (or conventionally true

value) of the sample is provided according to possibilities by:
— the value from a certified reference material certificate,
— the consensus value obtained from an inter-laboratory comparison,

— the arithmetic mean of the repeated measurement values according to the reference method,

— the target value by adding analyte to a representative matrix of the scope in question.

[SOURCE: ISO 5725-1:1994, 3.5]
3.1.3
reference material

material, sufficiently homogeneous and stable with respect to one or more specified properties, which

has been established to be fit for its intended use in a measurement process
[SOURCE: ISO Guide 35:2017, 3.1]
3.1.4
certified reference material

reference material (3.1.3), accompanied by a certificate, one or more of whose property values are

certified by a procedure which establishes traceability to an accurate realization of the unit in which

the property values are expressed, and for which each certified value is accompanied by an uncertainty

at a stated level of confidence
[SOURCE: ISO/TS 13530:2009, 3.2.7]
3.1.5
assessment procedure

procedure related to the establishment of the specifications for the performance of a new method and/

or experimental verification that a method meets theoretically derived quality criteria

3.2 Terms related to analytical methods
3.2.1
analyte
subject of the analytical method
3.2.2
analytical method

unambiguously written procedure describing all details required to carry out the analysis of the analyte

(3.2.1), namely: scope and field of application, principle and/or reactions, definitions, reagents, apparatus,

analytical procedures, calculations and presentation of results, performance data and test report

[SOURCE: ISO/TS 16489:2006, 3.3]
2 © ISO 2019 – All rights reserved
---------------------- Page: 10 ----------------------
SIST-TS ISO/TS 21231:2019
ISO/TS 21231:2019(E)
3.2.3
quantitative analytical method

analytical method for measuring the quantity of analyte (3.2.1)contained in the test sample

Note 1 to entry: The result can consist of a quantity in a given quantity of test sample.

3.2.4
limit of detection

output signal or value above which it can be affirmed, with a stated level of confidence, for example

95 %, that a sample is different from a blank sample containing no determinand of interest, and which

could be estimated by different means and shall be verified in the intended matrix

[SOURCE: ISO 6107-2:2006, 60, modified — “and which could be estimated by different means and shall

be verified in the intended matrix” has been added.]
3.2.5
limit of quantification
LOQ

lowest value of a determinand that can be determined with an acceptable level of accuracy, which could

be estimated by different means and shall be verified in the intended matrix

Note 1 to entry: For each matrix, this limit is related to the pair [analyte (3.2.1), method].

3.2.6
reasonable dilution

dilution conditions for reducing the concentration of a substance in a matrix without substantially

modifying the intrinsic characteristics of the matrix
3.2.7
matrix blank values

values of a given parameter obtained using a test conducted on a matrix giving rise to a result below the

limit of detection (3.2.4) for the analyte (3.2.1) in question
3.2.8
scope of the analytical method

combination of the various types of matrix and the analyte (3.2.1) concentration range covered, to

which the analytical method applies

Note 1 to entry: In addition to an indication of all the satisfactory performance conditions for each factor, the

scope of the analytical method may also include warnings in respect of known interferences from other analytes,

or inapplicability to some matrices or conditions.
3.3 Terms related to matrix
3.3.1
influence parameter

intrinsic characteristic of the matrix, independent of the analyte (3.2.1) concentration, a variation of

which is liable to modify the analytical result
3.3.2
representative matrix

sample for which all the intrinsic characteristics are characteristic of a type of water or the source of a

group of samples
3.3.3
salinity

mass in grams of solid substances contained in one kilogram of sea water, when the bromide and iodide

ions are replaced by their chloride equivalent, carbonates converted into oxides and all the organic

matter oxidized
© ISO 2019 – All rights reserved 3
---------------------- Page: 11 ----------------------
SIST-TS ISO/TS 21231:2019
ISO/TS 21231:2019(E)
3.3.4
leachate

water which has percolated through tipped refuse or other specified permeable material

Note 1 to entry: See Annex D.
[SOURCE: ISO 6107-7:2006, 23]
4 Principle

The purpose of this document is to specify the concept of a representative matrix and its characteristics

with a view to studying the performance of an analytical method.

For each analyte under test, the scope of an analytical method includes all the matrices under test,

their descriptive parameters, and the concentration ranges of the influence parameters for which the

method is applicable. The laboratory should define its requirements beforehand in respect of the scope

of the analytical method, selecting the materials most in line with requirements.

WARNING — The definition of the scope is entirely dependent on the analyst (the validation or

characterization study manager) and their knowledge acquired while developing the method.

It is sometimes preferable to segment a scope rather than seek to validate an overly general

method. In this case, a validation file should be compiled for each scope.
See Figure 1.
4 © ISO 2019 – All rights reserved
---------------------- Page: 12 ----------------------
SIST-TS ISO/TS 21231:2019
ISO/TS 21231:2019(E)
Figure 1 — Summary flow chart
5 Influence parameters
5.1 Common parameters for all matrices

The following influence parameters are liable to have an impact on analysis procedures. They shall help

classify the types of water on which the laboratory has validated its method or determined performance

characteristics.
— pH;
— ion composition and/or conductivity;
© ISO 2019 – All rights reserved 5
---------------------- Page: 13 ----------------------
SIST-TS ISO/TS 21231:2019
ISO/TS 21231:2019(E)
— salinity;
— dissolved organic carbon (DOC) and/or total organic carbon (TOC);
— colour or turbidity;
— suspended particular matter (SPM) content.
During the validation or characterization study, it is up to the laboratory to:

— define, for its practice, the characteristic ranges associated with each of the above parameters;

— justify, if applicable, the lack of influence thereof on the characterized method;

— complement this list with other characteristic parameters based on the methods and the source of

the samples analysed, using for example Annex A or Annex C.
5.2 Water intended for consumption

Water intended for human and livestock consumption is water considered to be fit for drinking.

Drinking water belongs to this category. It includes groundwater that has been chlorinated in the

resource.
The minimum additional characteristics to be included for this category are:

— disinfectant presence and content (distributed waters or groundwater chlorinated in the resource);

— CO content (natural mineral water), if relevant to subsequent specified analysis requirements.

5.3 Natural waters

Natural waters are waters taken from the natural environment not undergoing to any treatment other

than the addition of reagents for analyte preservation.

Surface waters and groundwater belong to this category. Brackish waters with salinity lower than

30 g/l are incorporated in this category.

Rainwater, which is generally not intended for consumption, are incorporated in this category.

5.4 Waste waters

Waste waters can originate from any combination of household, industrial or commercial activities.

They include collected run-offs and those from any spillage or infiltration from the waste water

collection system, including the contents of storm water tanks or ponds, discharged into collection

systems or into the environment.
NOTE 1 Waste waters can be collected in common systems or in separate systems.

NOTE 2 For the purposes of this document, the definition of waste water also includes untreated sanitary

waters.

NOTE 3 National or local regulations can include lists of substances of concern in relation to sewer discharges.

Annex C gives a list of examples of additional characteristics associated with some sectors of activity.

Some waste waters may have a high salinity.
5.5 Marine waters

Sea water consists of a large number of compounds distributed over the following categories: gases,

particulate matter, colloids, and dissolved elements (see Reference [7]).
6 © ISO 2019 – All rights reserved
---------------------- Page: 14 ----------------------
SIST-TS ISO/TS 21231:2019
ISO/TS 21231:2019(E)

The dissolved elements consist of 92 natural chemical elements, approximately two-thirds of which

are present in ultra-trace amounts and are difficult to detect. Sea water is characterized in that the

[8]

relative proportions of its 11 main constituents are substantially constant (Dittmar's law ) within

1 %. Dittmar's law can thus be used to determine the salinity of sea water by measuring only one of its

components.

The average salinity of sea water is 35 g/kg. It is generally between 30 g/kg (North Atlantic) and 40 g/

kg (Red Sea) but exhibits extreme values in closed or semi-closed seas (6 g/kg in the Baltic Sea, 330 g/

kg in the Dead Sea). The pH of sea water is approximately 8,2.
5.6 Recreational waters

Recreational waters are bathing, swimming pool, thermal bath and spa waters. They may be sourced

from natural waters or waters intended for human consumption and are characterized, in addition to

the influence parameters defined in 5.2, by the potential presence of specific disinfection products and

by-products, and the potential presence of sulfur compounds.
6 Selection of characteristic parameters of a matrix
6.1 General

For the purposes of characterization of the applicability and the performances of an analytical method

to a matrix, the laboratory shall describe the limits of the ranges associated with the characteristic

parameters discussed in this clause.
6.2 All waters
The parameters are those defined in 5.1.
6.3 Waters intended for consumption

In addition to the characteristics listed in 5.1, waters intended for consumption are characterized by:

— their free and total chlorine content;
— the nature and content of disinfection reagents and by-products;
— their CO content, if relevant.

Refer to Annex A for more detailed characterization of waters intended for human consumption.

6.4 Natural waters

In addition to the characteristics listed in 5.1, natural waters are characterized by:

— the sampling location, including the sampling depth;
— the identified surrounding anthropic pressures.

In the case of groundwater used as drinking water resources, which are treated in situ, free and total

chlorine content should be verified.
6.5 Waste waters

In addition to the characteristics listed in 5.1, waste waters are characterized by:

— the original activity sector (see Annex C);
© ISO 2019 – All rights reserved 7
---------------------- Page: 15 ----------------------
SIST-TS ISO/TS 21231:2019
ISO/TS 21231:2019(E)

— the connected activity sectors in the case of municipal waste water treatment plants (MWWTP)

discharges.
6.6 Marine waters

In addition to the characteristics listed in 5.1, marine waters are characterized by:

— the sampling location, including sampling depth;
— their salinity.
6.7 Recreational waters

In addition to the characteristics listed in 5.1, recreational waters are characterized by:

— the sampling location;
— the nature and content of disinfection reagents and by products.
7 Available materials
7.1 General

The laboratory shall select study matrices for one or more of the above water types from, in order of

preference:
— reference materials if the matrix is sufficiently characterized;

— supernumerary material from interlaboratory tests if stable and sufficiently characterized;

— material obtained by spiking with the real matrix free from the analytes of interest;

— material obtained by spiking a reasonable dilution of a real matrix, after adjusting the characteristics

modified by the dilution;

— material obtained by spiking of an artificial matrix based on a recipe (see Annex B).

At least three different representative samples of each water type should be studied to provide a

realistic evaluation of performance of the method on the selected water type. Wherever possible, the

method performances shall be characterized on a non-artificial sample.
7.2 Material obtained by reasonable dilution of a real matrix

When the laboratory cannot select a real matrix free from analyte(s) of interest, but it is possible to

select a real matrix containing the analyte(s) of interest at a concentration lower than 10× the limit

of quantification (LOQ) defined for the method under examination, a representative matrix can be

prepared by diluting the low-concentration real matrix, so as to lower the concentration of analyte(s) of

interest to less than the LOQ defined for the method.

The dilution factor, f, shall be lower than 10. For this dilution, a water free from analyte(s) of interest

having a similar composition to the chosen matrix (major elements and influence factors) shall be used.

Before dilution, the selected matrix shall be characterized on the basis of the influence parameters

chosen for the study. After dilution, these parameters shall be readjusted if required using solid state

reagents or stock solutions of solid state reagents so that the value of each influence parameter remains

within the scope defined by the laboratory.
8 © ISO 2019 – All rights reserved
---------------------- Page: 16 ----------------------
SIST-TS ISO/TS 21231:2019
ISO/TS 21231:2019(E)
7.3 Artificial material

Artificial materials can be prepared according to Annex B, after adjusting the influence parameters

selected based on a bibliographic study, and/or on Annex C, within the concentration range defining the

scope of the method.
7.4 Analyte-specific blank values in matrices

For some analytes, such as heavy metals, no analyte-free natural or artificial matrix can be obtained.

After proper justification, the laboratory should study LOQ as follows.
— Determine LOQ on ultrapure water.

— Calculate LOQ by correcting LOQ using the recovery of the analyte in the intended matric,

water i MQ
i.e. water by using Formula (1):
LOQ
LOQ = (1)
water i
water i
where
LOQ is the LOQ of the method for the analyte in water type i;
water i
LOQ is the LOQ of the method for the analyte in ultra pure water;
is the mean recovery of the method for the analyte in water type i.
...

SLOVENSKI STANDARD
oSIST-TS ISO/TS 21231:2019
01-maj-2019
Kakovost vode - Karakterizacija analiznih metod - Smernice za izbiro
reprezentativnega matriksa

Water quality - Characterization of analytical methods - Guidelines for the selection of a

representative matrix

Qualité de l'eau - Caractérisation des méthodes d'analyses - Lignes directrices pour la

sélection d'une matrice représentative
Ta slovenski standard je istoveten z: ISO/TS 21231:2019
ICS:
13.060.50 3UHLVNDYDYRGHQDNHPLþQH Examination of water for
VQRYL chemical substances
oSIST-TS ISO/TS 21231:2019 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
oSIST-TS ISO/TS 21231:2019
---------------------- Page: 2 ----------------------
oSIST-TS ISO/TS 21231:2019
TECHNICAL ISO/TS
SPECIFICATION 21231
First edition
2019-02
Water quality — Characterization of
analytical methods — Guidelines for
the selection of a representative matrix
Reference number
ISO/TS 21231:2019(E)
ISO 2019
---------------------- Page: 3 ----------------------
oSIST-TS ISO/TS 21231:2019
ISO/TS 21231:2019(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2019

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: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2019 – All rights reserved
---------------------- Page: 4 ----------------------
oSIST-TS ISO/TS 21231:2019
ISO/TS 21231:2019(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Principle ........................................................................................................................................................................................................................ 4

5 Influence parameters ...................................................................................................................................................................................... 5

5.1 Common parameters for all matrices .................................................................................................................................. 5

5.2 Water intended for consumption ............................................................................................................................................ 6

5.3 Natural waters ......................................................................................................................................................................................... 6

5.4 Waste waters ............................................................................................................................................................................................ 6

5.5 Marine waters .......................................................................................................................................................................................... 6

5.6 Recreational waters ............................................................................................................................................................................ 7

6 Selection of characteristic parameters of a matrix .......................................................................................................... 7

6.1 General ........................................................................................................................................................................................................... 7

6.2 All waters ..................................................................................................................................................................................................... 7

6.3 Waters intended for consumption ......................................................................................................................................... 7

6.4 Natural waters ......................................................................................................................................................................................... 7

6.5 Waste waters ............................................................................................................................................................................................ 7

6.6 Marine waters .......................................................................................................................................................................................... 8

6.7 Recreational waters ............................................................................................................................................................................ 8

7 Available materials ............................................................................................................................................................................................ 8

7.1 General ........................................................................................................................................................................................................... 8

7.2 Material obtained by reasonable dilution of a real matrix ................................................................................ 8

7.3 Artificial material .................................................................................................................................................................................. 9

7.4 Analyte-specific blank values in matrices........................................................................................................................ 9

8 Report .............................................................................................................................................................................................................................. 9

Annex A (informative) Characterization of waters intended for human consumption and

mineral waters .....................................................................................................................................................................................................10

Annex B (informative) Examples of preparation of artificial matrices and representative

characteristics ......................................................................................................................................................................................................11

Annex C (informative) Occurrence of chemical substances in waste water, by industrial

activity sector ........................................................................................................................................................................................................23

Annex D (informative) Leachate .............................................................................................................................................................................32

Bibliography .............................................................................................................................................................................................................................33

© ISO 2019 – All rights reserved iii
---------------------- Page: 5 ----------------------
oSIST-TS ISO/TS 21231:2019
ISO/TS 21231:2019(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 147, Water quality, Subcommittee SC 2,

Physical, chemical and biochemical methods.

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 2019 – All rights reserved
---------------------- Page: 6 ----------------------
oSIST-TS ISO/TS 21231:2019
ISO/TS 21231:2019(E)
Introduction

This document has been prepared for the validation of analytical methods applied to the water quality

field. It enables a laboratory to determine the characteristics of a material suitable for determination of

the performances of an analytical method itself.

It is not intended to provide an exhaustive inventory of all published recipes, but to propose a selection

of recipes supporting the characterization of the performances of analytical methods used by a

laboratory. For this reason, a restricted number of recipes are proposed. References giving access to

other recipes are available in the Bibliography.

This document includes four recipes for preparing marine waters and five recipes for waste waters

with controlled characteristics.
© ISO 2019 – All rights reserved v
---------------------- Page: 7 ----------------------
oSIST-TS ISO/TS 21231:2019
---------------------- Page: 8 ----------------------
oSIST-TS ISO/TS 21231:2019
TECHNICAL SPECIFICATION ISO/TS 21231:2019(E)
Water quality — Characterization of analytical methods —
Guidelines for the selection of a representative matrix
1 Scope

This document specifies representative materials suitable for the determination of the performance

characteristics, including uncertainty, during the initial assessment of a quantitative method, used in a

laboratory, for physico-chemical water analysis.
This document focuses on five main types of water:
— waters intended for consumption (5.2);
— natural waters (5.3);
— waste waters (5.4);
— marine waters (5.5);
— recreational waters (5.6).

NOTE Other more specific or less common types of water can be incorporated in any of the above types

provided appropriate justifications. The characteristics of the standard matrix are compatible with the

characteristics of the samples handled.
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 5667-3, Water quality — Sampling — Part 3: Preservation and handling of water samples

ISO 6107 (all parts), Water quality — Vocabulary
3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 6107 (all parts) and the

following apply.

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/
3.1 General vocabulary
3.1.1
matrix
set of constituents of the test sample, except the analyte (3.2.1)

Note 1 to entry: By extension, a matrix defines a group of waters characterized by similar analytical behaviour in

relation to the analytical method used.
© ISO 2019 – All rights reserved 1
---------------------- Page: 9 ----------------------
oSIST-TS ISO/TS 21231:2019
ISO/TS 21231:2019(E)
3.1.2
accepted reference value

value that serves as an agreed-upon reference for comparison, and which is derived as:

a) a theoretical or established value, based on scientific principles;

b) an assigned or certified value, based on experimental work of some national or international

organization;

c) a consensus or certified value, based on collaborative experimental work under the auspices of a

scientific or engineering group;

d) when a), b) and c) are not available, the expectation of the (measurable) quantity, i.e. the mean of a

specified population of measurements

Note 1 to entry: In the specific context of this document, the accepted reference value (or conventionally true

value) of the sample is provided according to possibilities by:
— the value from a certified reference material certificate,
— the consensus value obtained from an inter-laboratory comparison,

— the arithmetic mean of the repeated measurement values according to the reference method,

— the target value by adding analyte to a representative matrix of the scope in question.

[SOURCE: ISO 5725-1:1994, 3.5]
3.1.3
reference material

material, sufficiently homogeneous and stable with respect to one or more specified properties, which

has been established to be fit for its intended use in a measurement process
[SOURCE: ISO Guide 35:2017, 3.1]
3.1.4
certified reference material

reference material (3.1.3), accompanied by a certificate, one or more of whose property values are

certified by a procedure which establishes traceability to an accurate realization of the unit in which

the property values are expressed, and for which each certified value is accompanied by an uncertainty

at a stated level of confidence
[SOURCE: ISO/TS 13530:2009, 3.2.7]
3.1.5
assessment procedure

procedure related to the establishment of the specifications for the performance of a new method and/

or experimental verification that a method meets theoretically derived quality criteria

3.2 Terms related to analytical methods
3.2.1
analyte
subject of the analytical method
3.2.2
analytical method

unambiguously written procedure describing all details required to carry out the analysis of the analyte

(3.2.1), namely: scope and field of application, principle and/or reactions, definitions, reagents, apparatus,

analytical procedures, calculations and presentation of results, performance data and test report

[SOURCE: ISO/TS 16489:2006, 3.3]
2 © ISO 2019 – All rights reserved
---------------------- Page: 10 ----------------------
oSIST-TS ISO/TS 21231:2019
ISO/TS 21231:2019(E)
3.2.3
quantitative analytical method

analytical method for measuring the quantity of analyte (3.2.1)contained in the test sample

Note 1 to entry: The result can consist of a quantity in a given quantity of test sample.

3.2.4
limit of detection

output signal or value above which it can be affirmed, with a stated level of confidence, for example

95 %, that a sample is different from a blank sample containing no determinand of interest, and which

could be estimated by different means and shall be verified in the intended matrix

[SOURCE: ISO 6107-2:2006, 60, modified — “and which could be estimated by different means and shall

be verified in the intended matrix” has been added.]
3.2.5
limit of quantification
LOQ

lowest value of a determinand that can be determined with an acceptable level of accuracy, which could

be estimated by different means and shall be verified in the intended matrix

Note 1 to entry: For each matrix, this limit is related to the pair [analyte (3.2.1), method].

3.2.6
reasonable dilution

dilution conditions for reducing the concentration of a substance in a matrix without substantially

modifying the intrinsic characteristics of the matrix
3.2.7
matrix blank values

values of a given parameter obtained using a test conducted on a matrix giving rise to a result below the

limit of detection (3.2.4) for the analyte (3.2.1) in question
3.2.8
scope of the analytical method

combination of the various types of matrix and the analyte (3.2.1) concentration range covered, to

which the analytical method applies

Note 1 to entry: In addition to an indication of all the satisfactory performance conditions for each factor, the

scope of the analytical method may also include warnings in respect of known interferences from other analytes,

or inapplicability to some matrices or conditions.
3.3 Terms related to matrix
3.3.1
influence parameter

intrinsic characteristic of the matrix, independent of the analyte (3.2.1) concentration, a variation of

which is liable to modify the analytical result
3.3.2
representative matrix

sample for which all the intrinsic characteristics are characteristic of a type of water or the source of a

group of samples
3.3.3
salinity

mass in grams of solid substances contained in one kilogram of sea water, when the bromide and iodide

ions are replaced by their chloride equivalent, carbonates converted into oxides and all the organic

matter oxidized
© ISO 2019 – All rights reserved 3
---------------------- Page: 11 ----------------------
oSIST-TS ISO/TS 21231:2019
ISO/TS 21231:2019(E)
3.3.4
leachate

water which has percolated through tipped refuse or other specified permeable material

Note 1 to entry: See Annex D.
[SOURCE: ISO 6107-7:2006, 23]
4 Principle

The purpose of this document is to specify the concept of a representative matrix and its characteristics

with a view to studying the performance of an analytical method.

For each analyte under test, the scope of an analytical method includes all the matrices under test,

their descriptive parameters, and the concentration ranges of the influence parameters for which the

method is applicable. The laboratory should define its requirements beforehand in respect of the scope

of the analytical method, selecting the materials most in line with requirements.

WARNING — The definition of the scope is entirely dependent on the analyst (the validation or

characterization study manager) and their knowledge acquired while developing the method.

It is sometimes preferable to segment a scope rather than seek to validate an overly general

method. In this case, a validation file should be compiled for each scope.
See Figure 1.
4 © ISO 2019 – All rights reserved
---------------------- Page: 12 ----------------------
oSIST-TS ISO/TS 21231:2019
ISO/TS 21231:2019(E)
Figure 1 — Summary flow chart
5 Influence parameters
5.1 Common parameters for all matrices

The following influence parameters are liable to have an impact on analysis procedures. They shall help

classify the types of water on which the laboratory has validated its method or determined performance

characteristics.
— pH;
— ion composition and/or conductivity;
© ISO 2019 – All rights reserved 5
---------------------- Page: 13 ----------------------
oSIST-TS ISO/TS 21231:2019
ISO/TS 21231:2019(E)
— salinity;
— dissolved organic carbon (DOC) and/or total organic carbon (TOC);
— colour or turbidity;
— suspended particular matter (SPM) content.
During the validation or characterization study, it is up to the laboratory to:

— define, for its practice, the characteristic ranges associated with each of the above parameters;

— justify, if applicable, the lack of influence thereof on the characterized method;

— complement this list with other characteristic parameters based on the methods and the source of

the samples analysed, using for example Annex A or Annex C.
5.2 Water intended for consumption

Water intended for human and livestock consumption is water considered to be fit for drinking.

Drinking water belongs to this category. It includes groundwater that has been chlorinated in the

resource.
The minimum additional characteristics to be included for this category are:

— disinfectant presence and content (distributed waters or groundwater chlorinated in the resource);

— CO content (natural mineral water), if relevant to subsequent specified analysis requirements.

5.3 Natural waters

Natural waters are waters taken from the natural environment not undergoing to any treatment other

than the addition of reagents for analyte preservation.

Surface waters and groundwater belong to this category. Brackish waters with salinity lower than

30 g/l are incorporated in this category.

Rainwater, which is generally not intended for consumption, are incorporated in this category.

5.4 Waste waters

Waste waters can originate from any combination of household, industrial or commercial activities.

They include collected run-offs and those from any spillage or infiltration from the waste water

collection system, including the contents of storm water tanks or ponds, discharged into collection

systems or into the environment.
NOTE 1 Waste waters can be collected in common systems or in separate systems.

NOTE 2 For the purposes of this document, the definition of waste water also includes untreated sanitary

waters.

NOTE 3 National or local regulations can include lists of substances of concern in relation to sewer discharges.

Annex C gives a list of examples of additional characteristics associated with some sectors of activity.

Some waste waters may have a high salinity.
5.5 Marine waters

Sea water consists of a large number of compounds distributed over the following categories: gases,

particulate matter, colloids, and dissolved elements (see Reference [7]).
6 © ISO 2019 – All rights reserved
---------------------- Page: 14 ----------------------
oSIST-TS ISO/TS 21231:2019
ISO/TS 21231:2019(E)

The dissolved elements consist of 92 natural chemical elements, approximately two-thirds of which

are present in ultra-trace amounts and are difficult to detect. Sea water is characterized in that the

[8]

relative proportions of its 11 main constituents are substantially constant (Dittmar's law ) within

1 %. Dittmar's law can thus be used to determine the salinity of sea water by measuring only one of its

components.

The average salinity of sea water is 35 g/kg. It is generally between 30 g/kg (North Atlantic) and 40 g/

kg (Red Sea) but exhibits extreme values in closed or semi-closed seas (6 g/kg in the Baltic Sea, 330 g/

kg in the Dead Sea). The pH of sea water is approximately 8,2.
5.6 Recreational waters

Recreational waters are bathing, swimming pool, thermal bath and spa waters. They may be sourced

from natural waters or waters intended for human consumption and are characterized, in addition to

the influence parameters defined in 5.2, by the potential presence of specific disinfection products and

by-products, and the potential presence of sulfur compounds.
6 Selection of characteristic parameters of a matrix
6.1 General

For the purposes of characterization of the applicability and the performances of an analytical method

to a matrix, the laboratory shall describe the limits of the ranges associated with the characteristic

parameters discussed in this clause.
6.2 All waters
The parameters are those defined in 5.1.
6.3 Waters intended for consumption

In addition to the characteristics listed in 5.1, waters intended for consumption are characterized by:

— their free and total chlorine content;
— the nature and content of disinfection reagents and by-products;
— their CO content, if relevant.

Refer to Annex A for more detailed characterization of waters intended for human consumption.

6.4 Natural waters

In addition to the characteristics listed in 5.1, natural waters are characterized by:

— the sampling location, including the sampling depth;
— the identified surrounding anthropic pressures.

In the case of groundwater used as drinking water resources, which are treated in situ, free and total

chlorine content should be verified.
6.5 Waste waters

In addition to the characteristics listed in 5.1, waste waters are characterized by:

— the original activity sector (see Annex C);
© ISO 2019 – All rights reserved 7
---------------------- Page: 15 ----------------------
oSIST-TS ISO/TS 21231:2019
ISO/TS 21231:2019(E)

— the connected activity sectors in the case of municipal waste water treatment plants (MWWTP)

discharges.
6.6 Marine waters

In addition to the characteristics listed in 5.1, marine waters are characterized by:

— the sampling location, including sampling depth;
— their salinity.
6.7 Recreational waters

In addition to the characteristics listed in 5.1, recreational waters are characterized by:

— the sampling location;
— the nature and content of disinfection reagents and by products.
7 Available materials
7.1 General

The laboratory shall select study matrices for one or more of the above water types from, in order of

preference:
— reference materials if the matrix is sufficiently characterized;

— supernumerary material from interlaboratory tests if stable and sufficiently characterized;

— material obtained by spiking with the real matrix free from the analytes of interest;

— material obtained by spiking a reasonable dilution of a real matrix, after adjusting the characteristics

modified by the dilution;

— material obtained by spiking of an artificial matrix based on a recipe (see Annex B).

At least three different representative samples of each water type should be studied to provide a

realistic evaluation of performance of the method on the selected water type. Wherever possible, the

method performances shall be characterized on a non-artificial sample.
7.2 Material obtained by reasonable dilution of a real matrix

When the laboratory cannot select a real matrix free from analyte(s) of interest, but it is possible to

select a real matrix containing the analyte(s) of interest at a concentration lower than 10× the limit

of quantification (LOQ) defined for the method under examination, a representative matrix can be

prepared by diluting the low-concentration real matrix, so as to lower the concentration of analyte(s) of

interest to less than the LOQ defined for the method.

The dilution factor, f, shall be lower than 10. For this dilution, a water free from analyte(s) of interest

having a similar composition to the chosen matrix (major elements and influence factors) shall be used.

Before dilution, the selected matrix shall be characterized on the basis of the influence parameters

chosen for the study. After dilution, these parameters shall be readjusted if required using solid state

reagents or stock solutions of solid state reagents so that the value of each influence parameter remains

within the scope defined by the laboratory.
8 © ISO 2019 – All rights reserved
---------------------- Page: 16 ----------------------
oSIST-TS ISO/TS 21231:2019
ISO/TS 21231:2019(E)
7.3 Artificial material

Artificial materials can be prepared according to Annex B, after adjusting the influence parameters

selected based on a bibliographic study, and/or on Annex C, within the concentration range defining the

scope of the method.
7.4 Analyte-specific blank values in matrices

For some analytes, such as heavy metals, no analyte-free natural or artificial matrix can be obtained.

After proper justification, the laboratory should study LOQ as follows.
— Determine LOQ on ultrapure water.

— Calculate LOQ by correcting LOQ using the recovery of the analyte in the intended matric,

water i MQ
i.e. water by using Formula (1):
LOQ
LOQ = (1)
water i
water i
where
LOQ is the LOQ of the method for the analyte in water type i;
water i
LOQ is the LOQ of the method for the analyte in ultra pure water;
is the mean recovery of t
...

Questions, Comments and Discussion

Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.