Water quality -- Determination of perfluoroalkyl and polyfluoroalkyl substances (PFAS) in water -- Method using solid phase extraction and liquid chromatography-tandem mass spectrometry (LC-MS/MS)

This document specifies a method for the determination of selected perfluoroalkyl and polyfluoroalkyl substances (PFAS) in non‑filtrated waters, for example drinking water, natural water (fresh water and sea water) and waste water containing less than 2 g/l solid particulate material (SPM) using liquid chromatography-tandem mass spectrometry (LC‑MS/MS). The compounds monitored by this method are typically the linear isomers. The group of compounds determined by this method are representative of a wide variety of PFAS. The analytes specified in Table 1 can be determined by this method. The list can be modified depending on the purpose for which the method is intended. The lower application range of this method can vary depending on the sensitivity of the equipment used and the matrix of the sample. For most compounds to which this document applies ≥0,2 ng/l as limit of quantification can be achieved. Actual levels can depend on the blank levels realized by individual laboratory. The applicability of the method to further substances, not listed in Table 1, or to further types of water is not excluded, but is intended to be validated separately for each individual case. NOTE 1 PFAS is used in this document to describe the analytes monitored. Many of the compounds in Table 1 are perfluoroalkyl and are also considered polyfluoroalkyl substances. NOTE 2 The linear PFAS isomers are specified in this document. The branched isomers can be present in environmental samples, especially for PFOS. Annex E provides an example of an analytical approach to the chromatographic and spectroscopic separation of individual isomers.

Qualité de l'eau -- Détermination des substances d'alkyle perfluorés et polyfluorés (SPFA) dans l'eau -- Méthode par extraction en phase solide et chromatographie liquide et spectrométrie de masse en tandem (CL-SM/SM)

Kakovost vode - Določevanje perfluoroalkil in polifluoroalkil spojin (PFAS) v vodi - Metoda z ekstrakcijo na trdni fazi in s tekočinsko kromatografijo-tandemsko masno spektrometrijo (LC-MS/MS)

Ta dokument določa metodo za določevanje izbranih perfluoroalkilnih in polifluoroalkilnih spojin (PFAS) v nefiltrirani vodi, na primer pitni vodi, naravni vodi (sladka in morska voda) ter odpadni vodi, ki vsebuje manj kot 2 g/l trdnih delcev (SPM) z uporabo tekočinske kromatografije-tandemske masne spektrometrije (LC-MS/MS). Spojine, ki jih nadzira ta metoda, so običajno linearni izomeri. Skupine spojin, določene s to metodo, so reprezentativne za najrazličnejše spojine PFAS. S to metodo je mogoče določiti analite, opredeljene v preglednici 1. Seznam je mogoče spremeniti glede na namen, za katerega je metoda namenjena. Spodnje področje uporabe te metode se lahko razlikuje glede na občutljivost uporabljene opreme in matrico vzorca. Za večino spojin, za katere se uporablja ta dokument, je mogoče doseči mejo količinskega določanja ≥ 0,2 ng/l. Dejanske ravni so lahko odvisne od slepih ravni, ki jih doseže posamezen laboratorij. Uporabnost metode za druge spojine, ki niso navedene v preglednici 1, ali za druge vrste vode ni izključena, vendar naj bi jo posebej potrdili za vsak posamezen primer.

General Information

Status
Published
Publication Date
25-Oct-2019
Current Stage
6060 - International Standard published
Start Date
05-Sep-2019
Completion Date
26-Oct-2019

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INTERNATIONAL ISO
STANDARD 21675
First edition
2019-10
Water quality — Determination of
perfluoroalkyl and polyfluoroalkyl
substances (PFAS) in water — Method
using solid phase extraction and
liquid chromatography-tandem mass
spectrometry (LC-MS/MS)
Qualité de l'eau — Détermination des substances d'alkyle perfluorés
et polyfluorés (SPFA) dans l'eau — Méthode par extraction en phase
solide et chromatographie liquide et spectrométrie de masse en
tandem (CL-SM/SM)
Reference number
ISO 21675:2019(E)
ISO 2019
---------------------- Page: 1 ----------------------
ISO 21675:2019(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
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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
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ISO 21675:2019(E)
Contents Page

Foreword ..........................................................................................................................................................................................................................................v

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

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

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

4 Principle ........................................................................................................................................................................................................................ 2

5 Interferences ............................................................................................................................................................................................................ 3

5.1 Interferences with sampling and extraction ................................................................................................................. 3

5.2 Interferences with LC-MS/MS.................................................................................................................................................... 4

6 Reagents ........................................................................................................................................................................................................................ 4

7 Apparatus ..................................................................................................................................................................................................................... 7

8 Sampling ........................................................................................................................................................................................................................ 8

9 Procedure..................................................................................................................................................................................................................... 8

9.1 Solid-phase extraction ...................................................................................................................................................................... 8

9.1.1 General...................................................................................................................................................................................... 8

9.1.2 Sample preparation ....................................................................................................................................................... 8

9.1.3 Conditioning of the solid-phase extraction material ........................................................................ 9

9.1.4 Sample extraction ........................................................................................................................................................... 9

9.1.5 Elution ....................................................................................................................................................................................... 9

9.2 LC-MS/MS operating conditions ...........................................................................................................................................10

9.3 Blank determination .......................................................................................................................................................................12

9.4 Identification .........................................................................................................................................................................................12

10 Calibration ...............................................................................................................................................................................................................13

10.1 General requirements ....................................................................................................................................................................13

10.2 Calibration using an external standard ...........................................................................................................................13

10.3 Calibration using an internal standard ...........................................................................................................................14

11 Calculation ...............................................................................................................................................................................................................15

11.1 Use of a calibration curve to determine concentration .....................................................................................15

11.2 Calculation of concentration using calibration with external standards ...........................................15

11.3 Calculation of concentration using calibration with internal standards ...........................................16

11.4 Treatment of results outside the calibration range ..............................................................................................16

12 Determination of analyte recovery ................................................................................................................................................16

12.1 Recovery ....................................................................................................................................................................................................16

12.2 Recovery of internal standards ..............................................................................................................................................17

13 Expression of results .....................................................................................................................................................................................18

14 Test report ................................................................................................................................................................................................................18

Annex A (informative) Examples of suitable sorbents ....................................................................................................................19

Annex B (informative) Examples of suitable LC columns .............................................................................................................20

Annex C (informative) Examples of suitable LC-MS/MS conditions ..................................................................................21

Annex D (normative) Filtration and extraction of suspended matter in the sample ......................................25

Annex E (informative) Examples of chromatographic separation of individual linear and

branched PFAS isomers ..............................................................................................................................................................................27

Annex F (informative) Rapid method by direct injection ............................................................................................................31

Annex G (informative) Rapid method by online solid phase extraction LC-MS/MS .........................................32

Annex H (informative) Performance data by DIN 38407-42 for selected PFAS .....................................................35

© ISO 2019 – All rights reserved iii
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ISO 21675:2019(E)

Annex I (informative) Performance data ......................................................................................................................................................37

Bibliography .............................................................................................................................................................................................................................43

iv © ISO 2019 – All rights reserved
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ISO 21675:2019(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.
© ISO 2019 – All rights reserved v
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INTERNATIONAL STANDARD ISO 21675:2019(E)
Water quality — Determination of perfluoroalkyl and
polyfluoroalkyl substances (PFAS) in water — Method
using solid phase extraction and liquid chromatography-
tandem mass spectrometry (LC-MS/MS)

WARNING — Persons using this document should be familiar with normal laboratory practice.

This document does not purport to address all of the safety problems, if any, associated with its

use. It is the responsibility of the user to establish appropriate safety and health practices.

IMPORTANT — It is absolutely essential that tests conducted in accordance with this document

be carried out by suitably qualified staff.
1 Scope

This document specifies a method for the determination of selected perfluoroalkyl and polyfluoroalkyl

substances (PFAS) in non-filtrated waters, for example drinking water, natural water (fresh water and

sea water) and waste water containing less than 2 g/l solid particulate material (SPM) using liquid

chromatography-tandem mass spectrometry (LC-MS/MS). The compounds monitored by this method

are typically the linear isomers. The group of compounds determined by this method are representative

of a wide variety of PFAS. The analytes specified in Table 1 can be determined by this method. The list

can be modified depending on the purpose for which the method is intended. The lower application

range of this method can vary depending on the sensitivity of the equipment used and the matrix of the

sample. For most compounds to which this document applies ≥0,2 ng/l as limit of quantification can be

achieved. Actual levels can depend on the blank levels realized by individual laboratory.

The applicability of the method to further substances, not listed in Table 1, or to further types of water

is not excluded, but is intended to be validated separately for each individual case.

NOTE 1 PFAS is used in this document to describe the analytes monitored. Many of the compounds in Table 1

are perfluoroalkyl and are also considered polyfluoroalkyl substances.

NOTE 2 The linear PFAS isomers are specified in this document. The branched isomers can be present in

environmental samples, especially for PFOS. Annex E provides an example of an analytical approach to the

chromatographic and spectroscopic separation of individual isomers.
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 3696, Water for analytical laboratory use — Specification and test methods

ISO 5667-1, Water quality — Sampling — Part 1: Guidance on the design of sampling programmes and

sampling techniques

ISO 5667-3, Water quality — Sampling — Part 3: Preservation and handling of water samples

ISO 21253-1, Water quality — Multi-compound class methods — Part 1: Criteria for the identification of

target compounds by gas and liquid chromatography and mass spectrometry
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
© ISO 2019 – All rights reserved 1
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ISO 21675:2019(E)

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
perfluoroalkyl and polyfluoroalkyl substances
PFAS

commonly used international abbreviation for organic compounds with replacement of most or all

hydrogen atoms by fluorine in the aliphatic chain structure

Note 1 to entry: The term is used in the broader sense for per- and polyfluoroalkyl substances (PFAS), and per-

and polyfluorinated compounds (PFC) as well.
4 Principle

The analytes listed in Table 1 are extracted from the water sample by solid-phase extraction

using a weak anion exchange sorbent followed by solvent elution and determination by liquid

chromatography-tandem mass-spectrometry.

The user should be aware that each analyte has its own specific optimum conditions and therefore

modification of the analyte list could require the specification of additional conditions for each

additional parameter.
Table 1 — Analytes determinable by this method
a b
Analyte IUPAC name Formula Abbreviation CAS-RN
Perfluoro-n- 1,1,2,2,3,3,4,4,4-Nonafluorobutane-1-sul- C HF O S PFBS 375-73-5
4 9 3
butanesulfonic acid fonic acid
Perfluoro-n- 1,1,2,2,3,3,4,4,5,5,6,6,6-Tridecafluorohex- C HF O S PFHxS 355-46-4
6 13 3
hexanesulfonic acid ane-1-sulfonic acid
Perfluoro-n- 1,1,2,2,3,3,4,4,5,5,6,6,7,7,7-Pentade- C HF O S PFHpS 375-92-8
7 15 3
heptanesulfonic acid cafluoroheptane-1-sulfonic acid
Perfluoro-n- 1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-Heptade- C HF O S PFOS 1763-23-1
8 17 3
octanesulfonic acid cafluorooctane-1-sulfonic acid

Perfluoro-n- 1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-Hen- C HF O S PFDS 335-77-3

10 21 3
decanesulfonic acid icosafluorodecane-1-sulfonic acid

Perfluorooctanesulfo- 1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-Heptade- C H F NO S FOSA 754-91-6

8 2 17 2
namide cafluoro-1-octanesulfonamide

N-methyl 1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-Heptade- C H F NO S N-MeFOSA 31506-32-8

9 4 17 2
perfluorooctanesulfo- cafluoro-N-methyl-1-octanesulfonamide
namide

N-ethyl N-Ethyl-1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-he C H F NO S N-EtFOSA 4151-50-2

10 6 17 2
perfluorooctanesulfo- ptadecafluorooctane-1-sulfonamide
namide

N-methyl 2-[1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-Hepta- C H F NO S N-MeFOSAA 2355-31-9

11 6 17 4
perfluorooctanesulfon- decafluorooctylsulfonyl(methyl)amino]
amidoacetic acid acetic acid

N-ethyl 2-[Ethyl(1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8,8 C H F NO S N-EtFOSAA 2991-50-6

12 8 17 4
perfluorooctanesulfon- -heptadecafluorooctylsulfonyl)amino]
amidoacetic acid acetic acid

6:2 Fluorotelomer sul- 3,3,4,4,5,5,6,6,7,7,8,8,8-Tridecafluorooc- C H F O S 6:2 FTSA 27619-97-2

8 5 13 3
fonic acid tane-1-sulfonic acid

8:2 Fluorotelomer sul- 3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-Heptade- C H F O S 8:2 FTSA 39108-34-4

10 5 17 3
fonic acid cafluorodecane-1-sulfonic acid
IUPAC: International Union of Pure and Applied Chemistry.
CAS-RN: Chemical Abstract Services Registry Number.
2 © ISO 2019 – All rights reserved
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ISO 21675:2019(E)
Table 1 (continued)
a b
Analyte IUPAC name Formula Abbreviation CAS-RN

9-Chlorohexade- 2-(6-Chloro-1,1,2,2,3,3,4,4,5,5,6,6-do- C HClF O S 9Cl-PF3ONS 73606-19-6

8 16 4
cafluoro-3-oxanon- decafluorohexoxy)-1,1,2,2-tetrafluo-
ane-1-sulfonic acid roethanesulfonic acid
Perfluoro-n-butanoic 2,2,3,3,4,4,4-Heptafluorobutanoic acid C HF O PFBA 375-22-4
4 7 2
acid
Perfluoro-n- 2,2,3,3,4,4,5,5,5-Nonafluoropentanoic acid C HF O PFPeA 2706-90-3
5 9 2
pentanoic acid
Perfluoro-n- 2,2,3,3,4,4,5,5,6,6,6-Undecafluorohexa- C HF O PFHxA 307-24-4
6 11 2
hexanoic acid noic acid
Perfluoro-n- 2,2,3,3,4,4,5,5,6,6,7,7,7-Tridecafluorohep- C HF O PFHpA 375-85-9
7 13 2
heptanoic acid tanoic acid
Perfluoro-n- 2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-Pentadecafluo- C HF O PFOA 335-67-1
8 15 2
octanoic acid rooctanoic acid
Perfluoro-n- 2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,9-Heptade- C HF O PFNA 375-95-1
9 17 2
nonanoic acid cafluorononanoic acid
Perfluoro-n- 2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-Non- C HF O PFDA 335-76-2
10 19 2
decanoic acid adecafluorodecanoic acid
Perfluoro-n- 2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10, C HF O PFUnDA 2058-94-8
11 21 2
undecanoic acid 11,11,11-Henicosafluoroundecanoic acid
Perfluoro-n- 2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10, C HF O PFDoDA 307-55-1
12 23 2
dodecanoic acid 11,11,12,12,12-Tricosafluorododecanoic
acid
Perfluoro-n- 2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10, C HF O PFTrDA 72629-94-8
13 25 2
tridecanoic acid 11,11,12,12,13,13,13-Pentacosafluorotri-
decanoic acid
Perfluoro-n- 2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10, C HF O PFTeDA 376-06-7
14 27 2
tetradecanoic acid 11,11,12,12,13,13,14,14,14-Hepta-
cosafluorotetradecanoic acid
Perfluoro-n- 2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10, C HF O PFHxDA 67905-19-5
16 31 2
hexadecanoic acid 11,11,12,12,13,13,14,14,15,15,16,16,
16-Hentriacontafluorohexadecanoic acid
Perfluoro-n- 2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10, C HF O PFOcDA 16517-11-6
18 35 2
octadecanoic acid 11,11,12,12,13,13,14,14,15,15,16,16,
17,17,18,18,18-Pentatriacontafluoroocta-
decanoic acid

8:2 Fluorotelomer 3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-Hexade- C H F O 8:2 FTUCA 70887-84-2

10 2 16 2
unsaturated carboxylic cafluorodec-2-enoic acid
acid

8:2 Polyfluoroalkyl Bis(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-he C H F O P 8:2 diPAP 678-41-1

20 9 34 4
phosphate diester ptadecafluorodecyl) hydrogen phosphate

Hexafluoropropylene 2,3,3,3-Tetrafluoro-2-(1,1,2,2,3,3,3- C HF O HFPO-DA 13252-13-6

6 11 3
oxide dimer acid heptafluoropropoxy)propanoic acid

4,8-Dioxa-3H-perfluor- 2,2,3-Trifluoro-3-[1,1,2,2,3,3-hex- C H F O DONA 919005-14-4

7 2 12 4
ononanoic acid afluoro-3-(trifluoromethoxy)propoxy]
propanoic acid
IUPAC: International Union of Pure and Applied Chemistry.
CAS-RN: Chemical Abstract Services Registry Number.
5 Interferences
5.1 Interferences with sampling and extraction

Sample bottles (7.1) shall consist of materials that do not contaminate or change the composition of the

sample during sample storage. All types of fluoropolymer plastics, including polytetrafluoroethylene

(PTFE) and fluoroelastomer materials, shall be avoided during sampling, sample storage and extraction.

© ISO 2019 – All rights reserved 3
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ISO 21675:2019(E)

Sample bottles (7.1) shall be checked for possible background contamination before use. If background

contamination is suspected or detected in sample bottles (7.1), then wash sample bottles (7.1) with

water (6.1) and methanol (6.6) prior to use. To avoid cross contamination, the sample bottles (7.1) should

only be used once. The use of intermediate sample tubes (7.6) and vials (7.10) should be limited in the

overall process to avoid contamination of loss by sorption. To avoid losses resulting from adsorption of

target analytes to the wall of sample bottle (7.1) and reservoir column (7.4), extract all of the sample

from the sample bottle (7.1) and rinse the wall of sample bottle (7.1) and reservoir column (7.4) with

methanol (6.6).

Commercially available adsorbent materials often vary in quality or activity. Considerable batch-

to-batch differences in quality and selectivity of these materials are possible. The recovery of a

single substance may also vary with respect to its concentration. Therefore, check analyte recovery

periodically at different concentrations and whenever new batches/lots of reagents or labware are

used (12.1).
5.2 Interferences with LC-MS/MS

Substances with similar retention times that can produce ions with similar mass to charge ratios (m/z)

to those produced by the analytes of interest may interfere with the determination.

These interferences may lead to incompletely resolved signals and/or additional signals in the mass

chromatograms of target substances. Depending on their levels in the sample, such substances may

affect the accuracy and precision of the results. The chromatographic separation is different with the

LC column (see Annex C for examples). As long as the peak of interest can be separately integrated from

interferences, it may be used.

Matrix interferences may be caused by contaminants that are co-extracted from the samples. The extent

of matrix interferences varies considerably, depending on the nature of the samples. In drinking water

and ground water, matrix interferences are usually negligible, whereas waste water and sea water

matrices can be affected by matrix interferences that lead to ionization suppression or enhancement

resulting in bias or reduced sensitivity of the method. As long as the required limits of quantification

can be achieved in samples, samples can be diluted to minimize matrix effects.

Interferences arising directly from analytical instruments can be significant for unmodified commercial

LC systems because many parts are made of PTFE and other fluoropolymers. It is necessary to check

for possible blank contamination from the individual parts, such as tubing, solvent inlet filters, valve

seals and the degassing equipment, and replace these with materials such as stainless steel and

polyetheretherketone (PEEK), where possible.

NOTE Background contamination can arise from within the instrument. A delay column can be attached

between the solvent mixer and injection valve to chromatographically resolve these background contaminants

from the instrument and/or mobile phases from the target analytes.

The LC-vial caps shall be free of fluoropolymer material. Efforts should be taken to minimize background

levels in procedural blank materials such that the procedural blank, including the instrumental blank,

is at least 10-fold below the reporting limit.
6 Reagents

Whenever possible, use certified or analytical-grade reagents or residue free-analytical grade

reagents stored in glass or polypropylene containers with metal or polypropylene lined caps. Avoid

using reagents with fluoropolymer lined caps and check contamination levels of target substances

using repeated blank determinations. Carry out additional cleaning or conditioning steps to ensure

background levels are minimized, if necessary.

6.1 Water, blank-value free, e.g. complying with grade 1 as specified in ISO 3696.

Purified laboratory water can be used, but should be confirmed to be free of PFAS. The quality of water

is checked by the same procedure given in 9.3.
4 © ISO 2019 – All rights reserved
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ISO 21675:2019(E)
6.2 Acetic acid, w(CH COOH) = 99,9 % mass fraction (999 g/kg).
6.3 Acetonitrile, CH CN.
6.4 Ammonia solution, w(NH ) = 25 % mass fraction (250 g/kg).
6.5 Ammonium acetate, w(CH COONH ) = 97 % mass fraction (970 g/kg).
3 4
6.6 Methanol, CH OH, blank-value free.

NOTE The quality of methanol is checked by evaporating 10 ml of methanol with a gentle stream of nitrogen

gas (6.13) to 0,5 ml and determining levels according to this document.
6.7 Reference substances, see Table 1.

Reference substances are analytical standards used for quantitative determination of the method

analytes. Use only reference substances or solutions, where the content of linear isomers is at least

95 %. Make sure that the individual reference substances do not contain detectable concentrations of

other target analytes to be determined by analysing alternate lots or second sources.

NOTE Solutions of reference substances are commercially available.
6.8 Internal standard substances, see Table 3.

Internal standard substances are labelled forms of the reference substances to be used in the analytical

procedure to correct for recovery due to losses of analyte or changes in analytical conditions that could

result in bias. Make sure that the internal standard substances do not contain detectable concentrations

of the analytes to be determined by analysing new lots using this document.
NOTE Solutions of internal standard substances are commercially available.
6.9 Preparation of the solutions

Calculate the concentration of all reference substances and internal standard solutions with regard to

the anion content.

Store the solutions at (5 ± 3) °C in the dark, protected against evaporation. Bring them to room

temperature prior to use (i.e. before dilution or spiking or injection).
6.9.1 Individual stock solutions of the reference substances

Stock solutions of the individual reference substances (6.7) in methanol (6.6) or acetonitrile (6.3) should

be of mass concentration to enable dilution to the desired range, e.g. 50 μg/ml each.

6.9.2 Individual stock solutions of internal standard substances

Stock solutions of the individual internal standard substances (6.8) in methanol (6.6) or acetonitrile (6.3)

should be of mass concentration to enable dilution to the desired range, e.g. 50 μg/ml each.

6.9.3 Native stock solution (reference substances)

Prepare a solution of the reference substances with a mass concentration of, for example, 0,1 μg/ml each.

Fill, for example, 1 ml of each solution of the individual reference substances, for example 50 μg/ml

(6.9.1), into a 500 ml volumetric flask (7.7) and make the solution up to the mark with methanol (6.6).

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ISO 21675:2019(E)
6.9.4 Labelled stock solution (internal standard substances)

Prepare a solution of the labelled internal standard substances with a mass concentration of, for

example, 0,1 μg/ml each.

Fill, for example, 1 ml of each solution of the individual internal standard substances, e.g. 50 μg/ml

(6.9.2), into a 500 ml volumetric flask (7.7) and make the solution up to the mark with methanol (6.6).

6.9.5 Spiking solution (reference substances)

Prepare a solution of the reference substances with a mass concentration of, for example, 10 ng/ml each.

Fill, for example, 1 ml of the native stock solution e.g. 0,1 μg/ml (6.9.3) into a 10 ml volumetric flask (7.7)

and make the solution up to the mark with methanol (6.6).
This solution is used for recovery samples (see 12.1).
6.9.6 Spiking solution (in
...

SLOVENSKI STANDARD
SIST ISO 21675:2019
01-december-2019

Kakovost vode - Določevanje perfluoroalkil in polifluoroalkil spojin (PFAS) v vodi -

Metoda z ekstrakcijo na trdni fazi in s tekočinsko kromatografijo-tandemsko
masno spektrometrijo (LC-MS/MS)

Water quality - Determination of perfluoroalkyl and polyfluoroalkyl substances (PFAS) in

water - Method using solid phase extraction and liquid chromatography-tandem mass

spectrometry (LC-MS/MS)

Qualité de l'eau - Détermination des substances d'alkyle perfluorés et polyfluorés (SPFA)

dans l'eau - Méthode par extraction en phase solide et chromatographie liquide et

spectrométrie de masse en tandem (CL-SM/SM)
Ta slovenski standard je istoveten z: ISO 21675:2019
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 ISO 21675:2019 en,fr,de

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

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SIST ISO 21675:2019
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SIST ISO 21675:2019
INTERNATIONAL ISO
STANDARD 21675
First edition
2019-10
Water quality — Determination of
perfluoroalkyl and polyfluoroalkyl
substances (PFAS) in water — Method
using solid phase extraction and
liquid chromatography-tandem mass
spectrometry (LC-MS/MS)
Qualité de l'eau — Détermination des substances d'alkyle perfluorés
et polyfluorés (SPFA) dans l'eau — Méthode par extraction en phase
solide et chromatographie liquide et spectrométrie de masse en
tandem (CL-SM/SM)
Reference number
ISO 21675:2019(E)
ISO 2019
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SIST ISO 21675:2019
ISO 21675:2019(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
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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
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SIST ISO 21675:2019
ISO 21675:2019(E)
Contents Page

Foreword ..........................................................................................................................................................................................................................................v

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

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

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

4 Principle ........................................................................................................................................................................................................................ 2

5 Interferences ............................................................................................................................................................................................................ 3

5.1 Interferences with sampling and extraction ................................................................................................................. 3

5.2 Interferences with LC-MS/MS.................................................................................................................................................... 4

6 Reagents ........................................................................................................................................................................................................................ 4

7 Apparatus ..................................................................................................................................................................................................................... 7

8 Sampling ........................................................................................................................................................................................................................ 8

9 Procedure..................................................................................................................................................................................................................... 8

9.1 Solid-phase extraction ...................................................................................................................................................................... 8

9.1.1 General...................................................................................................................................................................................... 8

9.1.2 Sample preparation ....................................................................................................................................................... 8

9.1.3 Conditioning of the solid-phase extraction material ........................................................................ 9

9.1.4 Sample extraction ........................................................................................................................................................... 9

9.1.5 Elution ....................................................................................................................................................................................... 9

9.2 LC-MS/MS operating conditions ...........................................................................................................................................10

9.3 Blank determination .......................................................................................................................................................................12

9.4 Identification .........................................................................................................................................................................................12

10 Calibration ...............................................................................................................................................................................................................13

10.1 General requirements ....................................................................................................................................................................13

10.2 Calibration using an external standard ...........................................................................................................................13

10.3 Calibration using an internal standard ...........................................................................................................................14

11 Calculation ...............................................................................................................................................................................................................15

11.1 Use of a calibration curve to determine concentration .....................................................................................15

11.2 Calculation of concentration using calibration with external standards ...........................................15

11.3 Calculation of concentration using calibration with internal standards ...........................................16

11.4 Treatment of results outside the calibration range ..............................................................................................16

12 Determination of analyte recovery ................................................................................................................................................16

12.1 Recovery ....................................................................................................................................................................................................16

12.2 Recovery of internal standards ..............................................................................................................................................17

13 Expression of results .....................................................................................................................................................................................18

14 Test report ................................................................................................................................................................................................................18

Annex A (informative) Examples of suitable sorbents ....................................................................................................................19

Annex B (informative) Examples of suitable LC columns .............................................................................................................20

Annex C (informative) Examples of suitable LC-MS/MS conditions ..................................................................................21

Annex D (normative) Filtration and extraction of suspended matter in the sample ......................................25

Annex E (informative) Examples of chromatographic separation of individual linear and

branched PFAS isomers ..............................................................................................................................................................................27

Annex F (informative) Rapid method by direct injection ............................................................................................................31

Annex G (informative) Rapid method by online solid phase extraction LC-MS/MS .........................................32

Annex H (informative) Performance data by DIN 38407-42 for selected PFAS .....................................................35

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Annex I (informative) Performance data ......................................................................................................................................................37

Bibliography .............................................................................................................................................................................................................................43

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SIST ISO 21675:2019
ISO 21675:2019(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.
© ISO 2019 – All rights reserved v
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SIST ISO 21675:2019
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SIST ISO 21675:2019
INTERNATIONAL STANDARD ISO 21675:2019(E)
Water quality — Determination of perfluoroalkyl and
polyfluoroalkyl substances (PFAS) in water — Method
using solid phase extraction and liquid chromatography-
tandem mass spectrometry (LC-MS/MS)

WARNING — Persons using this document should be familiar with normal laboratory practice.

This document does not purport to address all of the safety problems, if any, associated with its

use. It is the responsibility of the user to establish appropriate safety and health practices.

IMPORTANT — It is absolutely essential that tests conducted in accordance with this document

be carried out by suitably qualified staff.
1 Scope

This document specifies a method for the determination of selected perfluoroalkyl and polyfluoroalkyl

substances (PFAS) in non-filtrated waters, for example drinking water, natural water (fresh water and

sea water) and waste water containing less than 2 g/l solid particulate material (SPM) using liquid

chromatography-tandem mass spectrometry (LC-MS/MS). The compounds monitored by this method

are typically the linear isomers. The group of compounds determined by this method are representative

of a wide variety of PFAS. The analytes specified in Table 1 can be determined by this method. The list

can be modified depending on the purpose for which the method is intended. The lower application

range of this method can vary depending on the sensitivity of the equipment used and the matrix of the

sample. For most compounds to which this document applies ≥0,2 ng/l as limit of quantification can be

achieved. Actual levels can depend on the blank levels realized by individual laboratory.

The applicability of the method to further substances, not listed in Table 1, or to further types of water

is not excluded, but is intended to be validated separately for each individual case.

NOTE 1 PFAS is used in this document to describe the analytes monitored. Many of the compounds in Table 1

are perfluoroalkyl and are also considered polyfluoroalkyl substances.

NOTE 2 The linear PFAS isomers are specified in this document. The branched isomers can be present in

environmental samples, especially for PFOS. Annex E provides an example of an analytical approach to the

chromatographic and spectroscopic separation of individual isomers.
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 3696, Water for analytical laboratory use — Specification and test methods

ISO 5667-1, Water quality — Sampling — Part 1: Guidance on the design of sampling programmes and

sampling techniques

ISO 5667-3, Water quality — Sampling — Part 3: Preservation and handling of water samples

ISO 21253-1, Water quality — Multi-compound class methods — Part 1: Criteria for the identification of

target compounds by gas and liquid chromatography and mass spectrometry
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
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ISO 21675:2019(E)

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
perfluoroalkyl and polyfluoroalkyl substances
PFAS

commonly used international abbreviation for organic compounds with replacement of most or all

hydrogen atoms by fluorine in the aliphatic chain structure

Note 1 to entry: The term is used in the broader sense for per- and polyfluoroalkyl substances (PFAS), and per-

and polyfluorinated compounds (PFC) as well.
4 Principle

The analytes listed in Table 1 are extracted from the water sample by solid-phase extraction

using a weak anion exchange sorbent followed by solvent elution and determination by liquid

chromatography-tandem mass-spectrometry.

The user should be aware that each analyte has its own specific optimum conditions and therefore

modification of the analyte list could require the specification of additional conditions for each

additional parameter.
Table 1 — Analytes determinable by this method
a b
Analyte IUPAC name Formula Abbreviation CAS-RN
Perfluoro-n- 1,1,2,2,3,3,4,4,4-Nonafluorobutane-1-sul- C HF O S PFBS 375-73-5
4 9 3
butanesulfonic acid fonic acid
Perfluoro-n- 1,1,2,2,3,3,4,4,5,5,6,6,6-Tridecafluorohex- C HF O S PFHxS 355-46-4
6 13 3
hexanesulfonic acid ane-1-sulfonic acid
Perfluoro-n- 1,1,2,2,3,3,4,4,5,5,6,6,7,7,7-Pentade- C HF O S PFHpS 375-92-8
7 15 3
heptanesulfonic acid cafluoroheptane-1-sulfonic acid
Perfluoro-n- 1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-Heptade- C HF O S PFOS 1763-23-1
8 17 3
octanesulfonic acid cafluorooctane-1-sulfonic acid

Perfluoro-n- 1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-Hen- C HF O S PFDS 335-77-3

10 21 3
decanesulfonic acid icosafluorodecane-1-sulfonic acid

Perfluorooctanesulfo- 1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-Heptade- C H F NO S FOSA 754-91-6

8 2 17 2
namide cafluoro-1-octanesulfonamide

N-methyl 1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-Heptade- C H F NO S N-MeFOSA 31506-32-8

9 4 17 2
perfluorooctanesulfo- cafluoro-N-methyl-1-octanesulfonamide
namide

N-ethyl N-Ethyl-1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-he C H F NO S N-EtFOSA 4151-50-2

10 6 17 2
perfluorooctanesulfo- ptadecafluorooctane-1-sulfonamide
namide

N-methyl 2-[1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-Hepta- C H F NO S N-MeFOSAA 2355-31-9

11 6 17 4
perfluorooctanesulfon- decafluorooctylsulfonyl(methyl)amino]
amidoacetic acid acetic acid

N-ethyl 2-[Ethyl(1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8,8 C H F NO S N-EtFOSAA 2991-50-6

12 8 17 4
perfluorooctanesulfon- -heptadecafluorooctylsulfonyl)amino]
amidoacetic acid acetic acid

6:2 Fluorotelomer sul- 3,3,4,4,5,5,6,6,7,7,8,8,8-Tridecafluorooc- C H F O S 6:2 FTSA 27619-97-2

8 5 13 3
fonic acid tane-1-sulfonic acid

8:2 Fluorotelomer sul- 3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-Heptade- C H F O S 8:2 FTSA 39108-34-4

10 5 17 3
fonic acid cafluorodecane-1-sulfonic acid
IUPAC: International Union of Pure and Applied Chemistry.
CAS-RN: Chemical Abstract Services Registry Number.
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Table 1 (continued)
a b
Analyte IUPAC name Formula Abbreviation CAS-RN

9-Chlorohexade- 2-(6-Chloro-1,1,2,2,3,3,4,4,5,5,6,6-do- C HClF O S 9Cl-PF3ONS 73606-19-6

8 16 4
cafluoro-3-oxanon- decafluorohexoxy)-1,1,2,2-tetrafluo-
ane-1-sulfonic acid roethanesulfonic acid
Perfluoro-n-butanoic 2,2,3,3,4,4,4-Heptafluorobutanoic acid C HF O PFBA 375-22-4
4 7 2
acid
Perfluoro-n- 2,2,3,3,4,4,5,5,5-Nonafluoropentanoic acid C HF O PFPeA 2706-90-3
5 9 2
pentanoic acid
Perfluoro-n- 2,2,3,3,4,4,5,5,6,6,6-Undecafluorohexa- C HF O PFHxA 307-24-4
6 11 2
hexanoic acid noic acid
Perfluoro-n- 2,2,3,3,4,4,5,5,6,6,7,7,7-Tridecafluorohep- C HF O PFHpA 375-85-9
7 13 2
heptanoic acid tanoic acid
Perfluoro-n- 2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-Pentadecafluo- C HF O PFOA 335-67-1
8 15 2
octanoic acid rooctanoic acid
Perfluoro-n- 2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,9-Heptade- C HF O PFNA 375-95-1
9 17 2
nonanoic acid cafluorononanoic acid
Perfluoro-n- 2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-Non- C HF O PFDA 335-76-2
10 19 2
decanoic acid adecafluorodecanoic acid
Perfluoro-n- 2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10, C HF O PFUnDA 2058-94-8
11 21 2
undecanoic acid 11,11,11-Henicosafluoroundecanoic acid
Perfluoro-n- 2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10, C HF O PFDoDA 307-55-1
12 23 2
dodecanoic acid 11,11,12,12,12-Tricosafluorododecanoic
acid
Perfluoro-n- 2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10, C HF O PFTrDA 72629-94-8
13 25 2
tridecanoic acid 11,11,12,12,13,13,13-Pentacosafluorotri-
decanoic acid
Perfluoro-n- 2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10, C HF O PFTeDA 376-06-7
14 27 2
tetradecanoic acid 11,11,12,12,13,13,14,14,14-Hepta-
cosafluorotetradecanoic acid
Perfluoro-n- 2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10, C HF O PFHxDA 67905-19-5
16 31 2
hexadecanoic acid 11,11,12,12,13,13,14,14,15,15,16,16,
16-Hentriacontafluorohexadecanoic acid
Perfluoro-n- 2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10, C HF O PFOcDA 16517-11-6
18 35 2
octadecanoic acid 11,11,12,12,13,13,14,14,15,15,16,16,
17,17,18,18,18-Pentatriacontafluoroocta-
decanoic acid

8:2 Fluorotelomer 3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-Hexade- C H F O 8:2 FTUCA 70887-84-2

10 2 16 2
unsaturated carboxylic cafluorodec-2-enoic acid
acid

8:2 Polyfluoroalkyl Bis(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-he C H F O P 8:2 diPAP 678-41-1

20 9 34 4
phosphate diester ptadecafluorodecyl) hydrogen phosphate

Hexafluoropropylene 2,3,3,3-Tetrafluoro-2-(1,1,2,2,3,3,3- C HF O HFPO-DA 13252-13-6

6 11 3
oxide dimer acid heptafluoropropoxy)propanoic acid

4,8-Dioxa-3H-perfluor- 2,2,3-Trifluoro-3-[1,1,2,2,3,3-hex- C H F O DONA 919005-14-4

7 2 12 4
ononanoic acid afluoro-3-(trifluoromethoxy)propoxy]
propanoic acid
IUPAC: International Union of Pure and Applied Chemistry.
CAS-RN: Chemical Abstract Services Registry Number.
5 Interferences
5.1 Interferences with sampling and extraction

Sample bottles (7.1) shall consist of materials that do not contaminate or change the composition of the

sample during sample storage. All types of fluoropolymer plastics, including polytetrafluoroethylene

(PTFE) and fluoroelastomer materials, shall be avoided during sampling, sample storage and extraction.

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Sample bottles (7.1) shall be checked for possible background contamination before use. If background

contamination is suspected or detected in sample bottles (7.1), then wash sample bottles (7.1) with

water (6.1) and methanol (6.6) prior to use. To avoid cross contamination, the sample bottles (7.1) should

only be used once. The use of intermediate sample tubes (7.6) and vials (7.10) should be limited in the

overall process to avoid contamination of loss by sorption. To avoid losses resulting from adsorption of

target analytes to the wall of sample bottle (7.1) and reservoir column (7.4), extract all of the sample

from the sample bottle (7.1) and rinse the wall of sample bottle (7.1) and reservoir column (7.4) with

methanol (6.6).

Commercially available adsorbent materials often vary in quality or activity. Considerable batch-

to-batch differences in quality and selectivity of these materials are possible. The recovery of a

single substance may also vary with respect to its concentration. Therefore, check analyte recovery

periodically at different concentrations and whenever new batches/lots of reagents or labware are

used (12.1).
5.2 Interferences with LC-MS/MS

Substances with similar retention times that can produce ions with similar mass to charge ratios (m/z)

to those produced by the analytes of interest may interfere with the determination.

These interferences may lead to incompletely resolved signals and/or additional signals in the mass

chromatograms of target substances. Depending on their levels in the sample, such substances may

affect the accuracy and precision of the results. The chromatographic separation is different with the

LC column (see Annex C for examples). As long as the peak of interest can be separately integrated from

interferences, it may be used.

Matrix interferences may be caused by contaminants that are co-extracted from the samples. The extent

of matrix interferences varies considerably, depending on the nature of the samples. In drinking water

and ground water, matrix interferences are usually negligible, whereas waste water and sea water

matrices can be affected by matrix interferences that lead to ionization suppression or enhancement

resulting in bias or reduced sensitivity of the method. As long as the required limits of quantification

can be achieved in samples, samples can be diluted to minimize matrix effects.

Interferences arising directly from analytical instruments can be significant for unmodified commercial

LC systems because many parts are made of PTFE and other fluoropolymers. It is necessary to check

for possible blank contamination from the individual parts, such as tubing, solvent inlet filters, valve

seals and the degassing equipment, and replace these with materials such as stainless steel and

polyetheretherketone (PEEK), where possible.

NOTE Background contamination can arise from within the instrument. A delay column can be attached

between the solvent mixer and injection valve to chromatographically resolve these background contaminants

from the instrument and/or mobile phases from the target analytes.

The LC-vial caps shall be free of fluoropolymer material. Efforts should be taken to minimize background

levels in procedural blank materials such that the procedural blank, including the instrumental blank,

is at least 10-fold below the reporting limit.
6 Reagents

Whenever possible, use certified or analytical-grade reagents or residue free-analytical grade

reagents stored in glass or polypropylene containers with metal or polypropylene lined caps. Avoid

using reagents with fluoropolymer lined caps and check contamination levels of target substances

using repeated blank determinations. Carry out additional cleaning or conditioning steps to ensure

background levels are minimized, if necessary.

6.1 Water, blank-value free, e.g. complying with grade 1 as specified in ISO 3696.

Purified laboratory water can be used, but should be confirmed to be free of PFAS. The quality of water

is checked by the same procedure given in 9.3.
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6.2 Acetic acid, w(CH COOH) = 99,9 % mass fraction (999 g/kg).
6.3 Acetonitrile, CH CN.
6.4 Ammonia solution, w(NH ) = 25 % mass fraction (250 g/kg).
6.5 Ammonium acetate, w(CH COONH ) = 97 % mass fraction (970 g/kg).
3 4
6.6 Methanol, CH OH, blank-value free.

NOTE The quality of methanol is checked by evaporating 10 ml of methanol with a gentle stream of nitrogen

gas (6.13) to 0,5 ml and determining levels according to this document.
6.7 Reference substances, see Table 1.

Reference substances are analytical standards used for quantitative determination of the method

analytes. Use only reference substances or solutions, where the content of linear isomers is at least

95 %. Make sure that the individual reference substances do not contain detectable concentrations of

other target analytes to be determined by analysing alternate lots or second sources.

NOTE Solutions of reference substances are commercially available.
6.8 Internal standard substances, see Table 3.

Internal standard substances are labelled forms of the reference substances to be used in the analytical

procedure to correct for recovery due to losses of analyte or changes in analytical conditions that could

result in bias. Make sure that the internal standard substances do not contain detectable concentrations

of the analytes to be determined by analysing new lots using this document.
NOTE Solutions of internal standard substances are commercially available.
6.9 Preparation of the solutions

Calculate the concentration of all reference substances and internal standard solutions with regard to

the anion content.

Store the solutions at (5 ± 3) °C in the dark, protected against evaporation. Bring them to room

temperature prior to use (i.e. before dilution or spiking or injection).
6.9.1 Individual stock solutions of the reference substances

Stock solutions of the individual reference substances (6.7) in methanol (6.6) or acetonitrile (6.3) should

be of mass concentration to enable dilution to the desired range, e.g. 50 μg/ml each.

6.9.2 Individual stock solutions of internal standard substances
Stock solutions of the indivi
...

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