SIST EN ISO 21253-1:2020

Water quality - Multi-compound class methods - Part 1: Criteria for the identification of target compounds by gas and liquid chromatography and mass spectrometry (ISO 21253-1:2019)

This International Standard gives criteria for mass spectrometric identification of target compounds in water. This document is a guideline for the identification of molecules <1 200 Da. For identification of larger molecules additional investigations are recommended.
This standard shall be used in conjunction with standards developed for the determination of the specific compounds. If the standards for analysing specific compounds give criteria for identification, those criteria shall be followed.

Wasserbeschaffenheit - Gemeinsam erfassbare Stoffgruppen - Teil 1: Kriterien für die Identifizierung von Zielverbindungen mittels Gaschromatographie und Flüssigchromatographie mit Massenspektrometrie-Kopplung (ISO 21253-1:2019)

Dieses Dokument legt Kriterien für die massenspektrometrische Identifizierung von Zielverbindungen in Wasserproben fest und ist im Allgemeinen auf Umweltproben anwendbar. Dieses Dokument ist für die Anwendung in Verbindung mit einer Norm vorgesehen, die für die Bestimmung bestimmter Verbindungen entwickelt wurde. Wenn ein genormtes Verfahren für die Analyse bestimmter Verbindungen Kriterien für die Identifizierung enthält, dann sind diese Kriterien zu befolgen.

Qualité de l'eau - Méthodes d'analyse de composés multi-classes - Partie 1: Critères pour l'identification des composées cibles par chromatographie en phase gazeuse et liquide et spectrométrie de masse (ISO 21253-1:2019)

Le présent document spécifie des critères pour l'identification par spectrométrie de masse de composés cibles dans des échantillons d'eau et est applicable aux échantillons environnementaux en général. Le présent document est destiné à être utilisé en association avec des normes élaborées pour permettre la détermination de composés spécifiques. Si une méthode normalisée d'analyse de composés spécifiques inclut des critères d'identification, ces critères sont appliqués.

Kakovost vode - Metode za več spojin - 1. del: Merila za identifikacijo ciljnih spojin s plinsko in tekočinsko kromatografijo ter masno spektrometrijo (ISO 21253-1:2019)

Ta mednarodni standard podaja merila za identifikacijo ciljnih spojin v vodi na podlagi masne spektrometrije. Ta dokument je smernica za identifikacijo molekul < 1200 Da. Za identifikacijo večjih molekul so priporočene dodatne preiskave. Ta standard se uporablja skupaj s standardi, pripravljenimi za določanje specifičnih spojin. Če standardi za analizo določenih spojin podajajo merila za identifikacijo, je treba ta merila upoštevati.

General Information

• Status: Published
• Public Enquiry End Date: 02-Jan-2019
• Publication Date: 02-Dec-2019
• ICS: 13.060.50 - Examination of water for chemical substances
• ICS: 71.040.50 - Physicochemical methods of analysis
• Technical Committee: KAV - Water quality
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 11-Nov-2019
• Due Date: 16-Jan-2020
• Completion Date: 03-Dec-2019
• Ref Project: EN ISO 21253-1:2019 - Water quality - Multi-compound class methods - Part 1: Criteria for the identification of target compounds by gas and liquid chromatography and mass spectrometry (ISO 21253-1:2019)

Standards Content (Sample)

SLOVENSKI STANDARD
SIST EN ISO 21253-1:2020
01-januar-2020

Kakovost vode - Metode za več spojin - 1. del: Merila za identifikacijo ciljnih spojin

s plinsko in tekočinsko kromatografijo ter masno spektrometrijo (ISO 21253-
1:2019)

Water quality - Multi-compound class methods - Part 1: Criteria for the identification of

target compounds by gas and liquid chromatography and mass spectrometry (ISO 21253

-1:2019)

Wasserbeschaffenheit - Gemeinsam erfassbare Stoffgruppen - Teil 1: Kriterien für die

Identifizierung von Zielverbindungen mittels Gaschromatographie und
Flüssigchromatographie mit Massenspektrometrie-Kopplung (ISO 21253-1:2019)

Qualité de l'eau - Méthodes d'analyse de composés multi-classes - Partie 1: Critères

pour l'identification des composées cibles par chromatographie en phase gazeuse et

liquide et spectrométrie de masse (ISO 21253-1:2019)
Ta slovenski standard je istoveten z: EN ISO 21253-1:2019
ICS:
13.060.50 Preiskava vode na kemične Examination of water for
snovi chemical substances
71.040.50 Fizikalnokemijske analitske Physicochemical methods of
metode analysis
SIST EN ISO 21253-1:2020 en,fr,de

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

---------------------- Page: 1 ----------------------
SIST EN ISO 21253-1:2020
---------------------- Page: 2 ----------------------
SIST EN ISO 21253-1:2020
EN ISO 21253-1
EUROPEAN STANDARD
NORME EUROPÉENNE
October 2019
EUROPÄISCHE NORM
ICS 13.060.50
English Version
Water quality - Multi-compound class methods - Part 1:
Criteria for the identification of target compounds by gas
and liquid chromatography and mass spectrometry (ISO
21253-1:2019)

Qualité de l'eau - Méthodes d'analyse de composés Wasserbeschaffenheit - Gemeinsam erfassbare

multi-classes - Partie 1: Critères pour l'identification Stoffgruppen - Teil 1: Kriterien für die Identifizierung

des composées cibles par chromatographie en phase von Zielverbindungen mittels Gaschromatographie und

gazeuse et liquide et spectrométrie de masse (ISO Flüssigchromatographie mit Massenspektrometrie-

21253-1:2019) Kopplung (ISO 21253-1:2019)
This European Standard was approved by CEN on 9 August 2019.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this

European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references

concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN

member.

This European Standard exists in three official versions (English, French, German). A version in any other language made by

translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management

Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,

Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,

Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and

United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels

© 2019 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 21253-1:2019 E

worldwide for CEN national Members.
---------------------- Page: 3 ----------------------
SIST EN ISO 21253-1:2020
EN ISO 21253-1:2019 (E)
Contents Page

European foreword ....................................................................................................................................................... 3

---------------------- Page: 4 ----------------------
SIST EN ISO 21253-1:2020
EN ISO 21253-1:2019 (E)
European foreword

This document (EN ISO 21253-1:2019) has been prepared by Technical Committee ISO/TC 147 "Water

quality" in collaboration with Technical Committee CEN/TC 230 “Water analysis” the secretariat of

which is held by DIN.

This European Standard shall be given the status of a national standard, either by publication of an

identical text or by endorsement, at the latest by April 2020, and conflicting national standards shall be

withdrawn at the latest by April 2020.

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. CEN shall not be held responsible for identifying any or all such patent rights.

According to the CEN-CENELEC Internal Regulations, the national standards organizations of the

following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,

Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,

Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of

North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the

United Kingdom.
Endorsement notice

The text of ISO 21253-1:2019 has been approved by CEN as EN ISO 21253-1:2019 without any

modification.
---------------------- Page: 5 ----------------------
SIST EN ISO 21253-1:2020
---------------------- Page: 6 ----------------------
SIST EN ISO 21253-1:2020
INTERNATIONAL ISO
STANDARD 21253-1
First edition
2019-08
Water quality — Multi-compound
class methods —
Part 1:
Criteria for the identification of
target compounds by gas and
liquid chromatography and mass
spectrometry
Qualité de l'eau — Méthodes d'analyse de composés multi-classes —
Partie 1: Critères pour l'identification de composées cibles par
chromatographie en phase gazeuse ou liquide et spectrométrie de
masse
Reference number
ISO 21253-1:2019(E)
ISO 2019
---------------------- Page: 7 ----------------------
SIST EN ISO 21253-1:2020
ISO 21253-1:2019(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: [phone]
Fax: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii © ISO 2019 – All rights reserved
---------------------- Page: 8 ----------------------
SIST EN ISO 21253-1:2020
ISO 21253-1:2019(E)
Contents Page

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

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

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

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

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

4 Abbreviated terms .............................................................................................................................................................................................. 2

5 Principle ........................................................................................................................................................................................................................ 3

6 Apparatus ..................................................................................................................................................................................................................... 3

7 Identification of target compounds .................................................................................................................................................. 4

7.1 Procedure for identification of organic compounds with chromatography-mass

spectrometry ............................................................................................................................................................................................ 4

7.2 Step 1: Chromatographic separation ................................................................................................................................... 5

7.3 Step 2: Mass spectrometric evaluation .............................................................................................................................. 6

7.3.1 Mass spectrometric detection .............................................................................................................................. 6

7.3.2 Selection of diagnostic ions .................................................................................................................................... 6

7.3.3 Assigning identification points ............................................................................................................................ 7

7.4 Step 3: Additional analytical confirmation evaluation ......................................................................................... 8

7.5 Reporting the presence of target compounds .............................................................................................................. 9

7.5.1 Identification ....................................................................................................................................................................... 9

7.5.2 Indication ............................................................................................................................................................................... 9

7.5.3 Absence of the target compounds (

8 Test report ................................................................................................................................................................................................................... 9

Annex A (informative) Recommendations for the most commonly used techniques ....................................10

Annex B (normative) Criteria for full scan measurement ...........................................................................................................12

n n

Annex C (informative) Diagnostic ions to be used for identification using GC-MS and LC-MS .........13

Annex D (informative) Examples of calculating identification points ............................................................................14

Bibliography .............................................................................................................................................................................................................................21

© ISO 2019 – All rights reserved iii
---------------------- Page: 9 ----------------------
SIST EN ISO 21253-1:2020
ISO 21253-1:2019(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 on 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 the following

URL: 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.
A list of all parts in the ISO 21253 series can be found on the ISO website.

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: 10 ----------------------
SIST EN ISO 21253-1:2020
ISO 21253-1:2019(E)
Introduction

The use of gas chromatography (GC) and liquid chromatography (LC) in combination with mass

spectrometric (MS) detection is common in many analytical standards. This detector is a powerful tool

provided it is properly used. This document gives the criteria for the identification of target compounds

in various types of water. This document shall be used in combination with specific analytical standards

or in combination with any GC-MS and LC-MS procedure. The result of the procedure described is

identified, indicated or absent.
NOTE See Annex A for recommendations for the most commonly used techniques.
[5]
This document is generally based on ISO 22892 .
© ISO 2019 – All rights reserved v
---------------------- Page: 11 ----------------------
SIST EN ISO 21253-1:2020
---------------------- Page: 12 ----------------------
SIST EN ISO 21253-1:2020
INTERNATIONAL STANDARD ISO 21253-1:2019(E)
Water quality — Multi-compound class methods —
Part 1:
Criteria for the identification of target compounds by gas
and liquid chromatography and mass spectrometry
1 Scope

This document specifies the criteria for mass spectrometric identification of target compounds in water

samples and is applicable to environmental samples in general. This document is intended to be used

in conjunction with standards developed for the determination of specific compounds. If a standard

method for analysing specific compounds includes criteria for identification, those criteria are followed.

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 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
diagnostic ion

selected fragment ion, molecular ion or other characteristic ion from the mass spectrum of the target

compound (3.7) with the highest possible specificity
[SOURCE: ISO 22892:2006, 3.6]
3.2
identification point

result of mass spectrometric investigation or other investigations/information to identify a component

in environmental matrices
[SOURCE: ISO 22892:2006, 3.7]
3.3
relative retention time

ratio between the retention time of the target compound (3.7) and the retention time of the retention

time standard (3.4)
[SOURCE: ISO 22892:2006, 3.4]
© ISO 2019 – All rights reserved 1
---------------------- Page: 13 ----------------------
SIST EN ISO 21253-1:2020
ISO 21253-1:2019(E)
3.4
retention time standard

compound that is added to the sample (or to the sample extract) and to the calibration standard solution,

and used to calculate the relative retention times (3.3) of the target compounds (3.7)

[SOURCE: ISO 22892:2006, 3.3]
3.5
selected ion monitoring
SIM
measurement of the intensity of selected diagnostic ions (3.1) only
3.6
standard compound

target compound (3.7) with the highest possible purity, which can be used as a reference during the

analysis

Note 1 to entry: Any impurities should not have influence on the mass spectrum of the standard compound.

[SOURCE: ISO 22892:2006, 3.2]
3.7
target compound
selected component, the presence or absence of which is being established

Note 1 to entry: This definition can also apply to a derivative of the original compound which is formed during an

intentional derivatization procedure.
[SOURCE: ISO 22892:2006, 3.1]
3.8
calibration standard

solution prepared from a secondary standard and/or stock solutions and used to calibrate the response

of the instrument with respect to analyte concentration
[SOURCE: ISO 18073:2004, 3.1.2]
3.9
calibration solution

solution used to calibrate the instrument, prepared from (a) stock solution(s) or from a certified

standard
[SOURCE: ISO 17294-1:2004, 3.4]
4 Abbreviated terms
APCI atmospheric pressure chemical ionization
CI chemical ionization
Da Dalton
ECD electron capture detector
EI electron ionization
EI-GC-MS electron ionization-gas chromatography-mass spectrometry
ESI electrospray ionization
2 © ISO 2019 – All rights reserved
---------------------- Page: 14 ----------------------
SIST EN ISO 21253-1:2020
ISO 21253-1:2019(E)
FWHM full width at half maximum
GC gas chromatography
GC-MS gas chromatography-mass spectrometry
HRMS high resolution mass spectrometry
LC liquid chromatography
LC-MS liquid chromatography-mass spectrometry
mDa milliDalton
MRM multiple reaction monitoring
MS mass spectrometry
MS mass spectrometry
MTBE methyl tertiary-butyl ether
m/z mass to charge ratio
NPD nitrogen-phosphorus detector
OCP organo chlorine pesticides
PFPD pulsed flame photometric detector
PID photoionization detector
SIM selected ion monitoring
S/N signal to noise ratio
SRM selected reaction monitoring
TAME tertiary amyl methyl ether
UV/Vis ultraviolet – visible spectroscopy
5 Principle

A target compound is identified if the measured values meet the criteria specified in this document or in

the standard in which the procedures are described to analyse the target compound. Criteria are based

on the relative retention times and the intensity ratio of diagnostic ions, and other relevant factors.

Additional information regarding diagnostic ions from specific international standards on the analysis

of the target compound can be used. The principle of identification points is used (see Annex D).

6 Apparatus

As this document is complementary to other standards using GC-MS and LC-MS, it is assumed that the

instrumentation used meets the requirements of those standards and a detailed description is not

within the scope of this document. The minimum acquisition requirements for low resolution and high

resolution mass spectrometry are summarized in Tables 1 and 2.
© ISO 2019 – All rights reserved 3
---------------------- Page: 15 ----------------------
SIST EN ISO 21253-1:2020
ISO 21253-1:2019(E)
Table 1 — Minimum acquisition requirements for low resolution mass spectrometry

Mass range: Peaks (masses) with a S/N < 3 are not taken into consideration and the lower

end of the scan range is limited to 35 (to avoid the measurement of oxygen and
nitrogen) to the highest mass of the target compound +10 unified atomic mass
units (u) in full scan measurements.
Scan rate: Minimum of 7 scans per peak.
Scan mode: Full scan or SIM.

Mass resolution: To be tuned on nominal resolution, the peak width at half-height of every tune

mass should not exceed 0,7 DA.
Table 2 — Minimum acquisition requirements for high resolution mass spectrometry
Scan rate: Minimum of 7 scans per peak.

Mass resolution: The resolution shall be greater the 10 000 FWHM for the used mass range.

Mass accuracy: The mass accuracy should be ≤5 ppm.
7 Identification of target compounds

IMPORTANT — The equipment shall be operated, and the determination shall be carried out by

suitably trained staff.
7.1 Procedure for identification of organic compounds with chromatography-mass
spectrometry

The procedure to qualify a component consists of three steps (see the flow scheme in Figure 1).

7.1.1 Step 1

Chromatographic evaluation (see 7.2): the relative retention time shall fulfil the specified criteria.

Proceed to step 2 only if step 1 is positive.
7.1.2 Step 2

Mass spectrometric evaluation (see 7.3): gathering identification points using mass spectrometric data.

[1]

For qualification, the principle of identification points is used (see EN 16693 ).

Identification points can be obtained from mass spectrometric data, but also using other analytical

information.
7.1.3 Step 3
Additional analytical confirmation evaluation (see 7.4).
The following classification can be obtained.

a) Identified (see 7.5.1): The target compound is present in the analysed extract if at least

3 identification points are obtained.

b) Indicated (see 7.5.2): The target compound may be present if only 1 or 2 identification points are

obtained.

c) Absent (below the detection limit) (see 7.5.3): No identification points are obtained using mass

spectrometry.

In case the classification result "indication" is unwanted, then any result with less than 3 identification

points shall be regarded as not identified.
4 © ISO 2019 – All rights reserved
---------------------- Page: 16 ----------------------
SIST EN ISO 21253-1:2020
ISO 21253-1:2019(E)

Figure 1 — Flow scheme for the identification of a target compound using three steps

7.2 Step 1: Chromatographic separation

For GC-MS procedures, the gas chromatographic separation shall be carried out using capillary or a

packed column. For LC-MS procedures, the chromatographic separation shall be carried out using a

© ISO 2019 – All rights reserved 5
---------------------- Page: 17 ----------------------
SIST EN ISO 21253-1:2020
ISO 21253-1:2019(E)

suitable LC column. The minimum acceptable retention time for the analyte under examination shall

be twice the retention time corresponding to the void volume of the column. The (relative) retention

time of the analyte in the sample shall match the (relative) retention time of the calibration standard

within a specified retention time window. The retention time window shall be commensurate with the

resolving power of the chromatographic system. The ratio of the chromatographic retention time of

the analyte to that of the retention time standard, i.e. the relative retention time of the analyte, shall

correspond to that of the calibration solution at a tolerance of ±2,5 % for LC and ±0,5 % for GC.

NOTE If specific retention time criteria are given in another standard, these can be followed.

7.3 Step 2: Mass spectrometric evaluation
7.3.1 Mass spectrometric detection

Mass spectrometric detection shall be carried out by employing MS-techniques such as recording of full

mass spectra (full scan) or selected ion monitoring (SIM), as well as MS techniques such as selected

reaction monitoring (SRM), multiple reaction monitoring (MRM) or other suitable MS or MS techniques

in combination with appropriate ionization modes. In high-resolution mass spectrometry (HRMS), the

resolution shall typically be greater than 10 000 FWHM for the entire mass range.

a) Full scans: When mass spectrometric determination is performed by the recording of full scan

spectra, the presence of all measured diagnostic ions (the molecular ion, characteristics adducts of

the molecular ion, characteristic fragment ions and isotope ions) with a relative intensity of more

than 10 % in the reference spectrum of the calibration standard is obligatory. In HRMS, a partial

scan (of limited mass range) may be adequate to yield sufficient diagnostic ions for identification.

b) SIM: When mass spectrometric determination is performed by fragmentation, the molecular

ion can be one of the selected diagnostic ions (the molecular ion, characteristics adducts of the

molecular ion, characteristic fragment ions and the isotope ions). Whenever possible, the selected

diagnostic ions should be independent from each other, for example not exclusively originate from

the same part of the molecule, nor exclusively be isotope ions. The S/N ratio for each diagnostic ion

shall be ≥ 3:1.

c) Full scan and SIM: The relative intensities of the detected ions, expressed as a percentage of the

intensity of the most intense ion or transition, shall correspond to those of the calibration standard,

either from calibration standard solutions or from spiked samples, at comparable concentrations,

measured under the same conditions, within the tolerances given in Table 3.

Table 3 — Maximum permitted tolerances for relative ion intensities using a range of mass

spectrometric techniques
Maximum allowed tolerance in Maximum allowed tolerance
Relative intensity
n n n
EI-GC-MS CI-GC-MS, CI-GC-MS , EI-GC-MS , LC-MS, LC-MS
>50 % to 100 % ±10 %
>20 % to 50 % ±15 % ±30 %
>10 % to 20 % ±20 %
≤10 % ±50 % ±50 %
7.3.2 Selection of diagnostic ions

If available, three diagnostic ions shall be selected for each target compound. Their intensities shall be

determined in the calibration standard solution either from a calibration standard solution or from

spiked samples at comparable concentrations measured under the same conditions, as the peak area

or peak height of the corresponding extracted ion current chromatograms. Their intensities shall be

determined using at least three injections. The relative intensities are calculated as the ratio of the

determined peak heights (or areas) and the peak height (or area) of the most intensive diagnostic ion.

NOTE Due to overloading, the ratios of the diagnostic ions can change.
6 © ISO 2019 – All rights reserved
---------------------- Page: 18 ----------------------
SIST EN ISO 21253-1:2020
ISO 21253-1:2019(E)

Diagnostic ions may also be specified in the standard method being used. It is not always possible to

obtain three diagnostic ions (for instance for polycyclic aromatic hydrocarbons). In that case, select the

[5]

available ions. Diagnostic ions should have a high “uniqueness value” (see ISO 22892 ). Annex C gives

selection criteria for diagnostic ions.

Co-eluting substances may influence the peak shape. As long as the peak of interest can be separately

integrated, it may be used.

Criteria for the retention time of the selected diagnostic ions are related to the peak maxima of the

extracted ion current chromatograms.

Diagnostic ions should originate from the analyte under investigation only. This implies that,

theoretically, all diagnostic ions belonging to one and the same analyte have the same retention time. If

the retention time of one selected diagnostic ion differs from the retention times of the other diagnostic

ions from the same analyte, a co-eluting substance or a partly-separated substance giving the same

mass may be present. In this case, the particular diagnostic ion cannot be used.

The accuracy of the retention time depends on the number of scans within the chromatographic peak

and hence, on the scan rate. Because the scan rate is limited, small differences in the retention times

of the diagnostic ions should be allowed. A suitable criterion for the allowed difference in retention

times of the diagnostic ions of an analyte shall not be greater than 40 % of the peak width at half the

peak height in a single run. Therefore, the differences in retention times of the peak maxima of all the

selected diagnostic ions in the extracted ion current chromatograms belonging to the same analyte

shall not be greater than 40 % of the peak width at half the peak height. For most analyses, whether GC

or LC, this means an acceptable difference of 1 s. These criteria apply for both the calibration standard

solution and the sample.
7.3.3 Assigning identification points

The qualification of the results is different depending on the mass spectrometric technique used.

When full scan spectra are recorded, a minimum of three ions shall be present with a relative intensity

of ≥10 % of the base peak. The molecular ion shall be included if it is present in the re

...