Water quality - Determination of arsenic(III) and arsenic(V) species - Method using high performance liquid chromatography (HPLC) with detection by inductively coupled plasma mass spectrometry (ICP-MS) or hydride generation atomic fluorescence spectrometry (HG-AFS)

This document specifies a method primarily developed for the determination of inorganic arsenic
species (arsenite (As(III)) and arsenate (As(V)) dissolved in a sample after a preservation process
in waters with a low total organic carbon content such as potable water, tap water, surface waters,
ground waters and rain waters. Information is provided on the determination of potentially relevant
organo-arsenic species such as methylarsonic acid (MMA) and dimethylarsinic acid (DMA) which may
be encountered at very low levels in natural surface waters.
The linear working dynamic range depends on the operating conditions and the method of detection
used; under standard conditions, it typically ranges from 0,5 μg/l to 50 μg/l for each species. Samples
containing arsenic at concentrations higher than the linear dynamic range can be analysed after
suitable dilution.
This method is based on high performance liquid chromatography separation of arsenic species with
either inductively coupled mass spectrometry (ICP-MS) or hydride generation atomic fluorescence
spectrometry (HG-AFS) as a method of detection.
The sensitivity of this method depends on the method of detection and the instrumental operating
conditions selected. The limit of quantification (LOQ) of the method also depends on the operating
conditions of the analytical system used and the extent of the calibration range used. LOQ examples for
As(III) and As(V) are provided; LOQs are generally less than 1 μg/l.
This document does not apply to arsenobetaine and other organic arsenic species which are not present
in natural water samples.

Qualité de l'eau - Détermination des formes chimiques (III) et (V) d'arsenic - Méthode par chromatographie en phase liquide à haute performance (HPLC) avec détection par spectrométrie de masse par torche à plasma (ICP-MS) ou génération d'hydrure fluorescence atomique (HG-AFS)

Kakovost vode - Določevanje arzena (III) in arzena (V) - Metoda tekočinske kromatografije visoke ločljivosti (HPLC) z masno spektrometrijo z induktivno sklopljeno plazmo (ICP/MS) ali atomsko fluorescenčno spektrometrijo s hidridno tehniko (HG/AFS)

Ta dokument določa metodo, razvito predvsem za določevanje anorganskih arzenovih vrst (arzenita (As(III)) in arzenata (As(V)), raztopljenih v vzorcu po postopku shranjevanja v vodah z nizkim skupnim deležem organskega ogljika, kot so pitna voda, površinske vode, podtalnice in deževnice. Podane so informacije o določevanju potencialno ustreznih organo-arzenovih vrst, kot sta metilarzonska kislina (MMA) in dimetilarzinska kislina (DMA), ki ju je mogoče najti na zelo nizkih ravneh v naravnih površinskih vodah.
Linearno delovno dinamično območje je odvisno od delovnih pogojev in uporabljene metode zaznavanja; pod standardnimi pogoji območje običajno zajema od 0,5 μg/l do 50 μg/l za posamezno vrsto. Vzorce s koncentracijami arzena, ki presegajo linearno dinamično območje, je mogoče analizirati po ustreznem redčenju.
Ta metoda temelji na visokoločljivostnem tekočinskem kromatografskem ločevanju arzenovih vrst z induktivno sklopljeno masno spektrometrijo (ICP-MS) ali atomsko fluorescenčno spektrometrijo s hibridno tehniko (HG-AFS) kot metodo zaznavanja.
Občutljivost te metode je odvisna od metode zaznavanja in izbranih instrumentalnih delovnih pogojev. Meja kvantifikacije (LOQ) metode je odvisna tudi od delovnih pogojev uporabljenega analitičnega sistema in obsega uporabljenega kalibracijskega območja. Podani so primeri meje kvantifikacije za arzenit in arzenat; meje kvantifikacije so običajno nižje od 1 μg/l.
Ta dokument se ne uporablja za arzenobetain in druge organske arzenove vrste, ki niso prisotne v naravnih vzorcih vode.

General Information

Status
Published
Public Enquiry End Date
02-Jul-2018
Publication Date
09-Jul-2018
Technical Committee
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
22-Jun-2018
Due Date
27-Aug-2018
Completion Date
10-Jul-2018

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ISO/TS 19620:2018 - Water quality -- Determination of arsenic(III) and arsenic(V) species -- Method using high performance liquid chromatography (HPLC) with detection by inductively coupled plasma mass spectrometry (ICP-MS) or hydride generation atomic fluorescence spectrometry (HG-AFS)
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TECHNICAL ISO/TS
SPECIFICATION 19620
First edition
2018-01
Water quality — Determination of
arsenic(III) and arsenic(V) species
— Method using high performance
liquid chromatography (HPLC) with
detection by inductively coupled
plasma mass spectrometry (ICP-
MS) or hydride generation atomic
fluorescence spectrometry (HG-AFS)
Qualité de l'eau — Détermination des formes chimiques (III) et (V)
d'arsenic — Méthode par chromatographie en phase liquide à haute
performance (HPLC) avec détection par spectrométrie de masse
par torche à plasma (ICP-MS) ou génération d'hydrure fluorescence
atomique (HG-AFS)
Reference number
ISO/TS 19620:2018(E)
ISO 2018
---------------------- Page: 1 ----------------------
ISO/TS 19620:2018(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2018

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, Switzerland
Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
Published in Switzerland
ii © ISO 2018 – All rights reserved
---------------------- Page: 2 ----------------------
ISO/TS 19620:2018(E)
Contents Page

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

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

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

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

3 Terms and definitions ..................................................................................................................................................................................... 2

4 Principle ........................................................................................................................................................................................................................ 3

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

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

7 Reagents and standards ................................................................................................................................................................................ 4

8 Sampling, preservation and storage of samples .................................................................................................................. 6

9 Procedure..................................................................................................................................................................................................................... 6

9.1 HPLC instrument optimization ................................................................................................................................................. 6

9.2 Calibration .................................................................................................................................................................................................. 7

9.3 Sample measurement ........................................................................................................................................................................ 7

10 Expression of results ........................................................................................................................................................................................ 7

11 Test report ................................................................................................................................................................................................................... 8

Annex A (normative) Detection using inductively coupled plasma mass spectrometry (ICP-MS) ......9

Annex B (normative) Detection using hydride generation atomic fluorescence (HG-AFS) ......................20

Annex C (informative) Determination of organic arsenic species ......................................................................................27

Annex D (informative) Storage and preservation of arsenic species in water samples ...............................29

Bibliography .............................................................................................................................................................................................................................40

© ISO 2018 – All rights reserved iii
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ISO/TS 19620:2018(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.
iv © ISO 2018 – All rights reserved
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ISO/TS 19620:2018(E)
Introduction

In the environment, metals and metalloids are found in the form of various chemical species. Chemical

speciation makes it possible to identify and quantify these different species. For the same metal or

metalloid, given that the toxicity of each compound may vary significantly, it can be useful to quantify

each of the species present in a given sample. For arsenic, the toxicity of the various species varies

considerably; inorganic species are recognized as being more toxic than organic species and, for

example, the toxicity of As(III) is greater than that of As(V). This method is primarily applicable to the

determination of arsenite (As(III)) and arsenate (As(V)) as these are the main species of interest and

are the predominant species found in potable water samples from the underlying geological strata in

many parts of the world. Arsenic speciation measurements are important to establish and select the

best water treatment technology for arsenic removal from raw waters containing significant levels of

arsenic.
© ISO 2018 – All rights reserved v
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TECHNICAL SPECIFICATION ISO/TS 19620:2018(E)
Water quality — Determination of arsenic(III) and
arsenic(V) species — Method using high performance liquid
chromatography (HPLC) with detection by inductively
coupled plasma mass spectrometry (ICP-MS) or hydride
generation atomic fluorescence spectrometry (HG-AFS)

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

This document is not intended to cover any safety problems associated with its use, if applicable.

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 primarily developed for the determination of inorganic arsenic

species (arsenite (As(III)) and arsenate (As(V)) dissolved in a sample after a preservation process

in waters with a low total organic carbon content such as potable water, tap water, surface waters,

ground waters and rain waters. Information is provided on the determination of potentially relevant

organo-arsenic species such as methylarsonic acid (MMA) and dimethylarsinic acid (DMA) which may

be encountered at very low levels in natural surface waters.

The linear working dynamic range depends on the operating conditions and the method of detection

used; under standard conditions, it typically ranges from 0,5 µg/l to 50 µg/l for each species. Samples

containing arsenic at concentrations higher than the linear dynamic range can be analysed after

suitable dilution.

This method is based on high performance liquid chromatography separation of arsenic species with

either inductively coupled mass spectrometry (ICP-MS) or hydride generation atomic fluorescence

spectrometry (HG-AFS) as a method of detection.

The sensitivity of this method depends on the method of detection and the instrumental operating

conditions selected. The limit of quantification (LOQ) of the method also depends on the operating

conditions of the analytical system used and the extent of the calibration range used. LOQ examples for

As(III) and As(V) are provided; LOQs are generally less than 1 µg/l.

This document does not apply to arsenobetaine and other organic arsenic species which are not present

in natural water samples.
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 2018 – All rights reserved 1
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ISO/TS 19620:2018(E)

ISO 17294-1, Water quality — Application of inductively coupled plasma mass spectrometry (ICP-MS) —

Part 1: General guidelines
3 Terms and definitions
For the purposes of this document, the following terms and definitions 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
analyte
substance to be determined
[SOURCE: ISO/TS 28581:2012, 3.1]
3.2
blank calibration solution

solution prepared in the same way as the calibration solution but leaving out the analyte

[SOURCE: ISO 17294-1:2004, 3.3]
3.3
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]
3.4
stock solution

solution with accurately known analyte concentration(s), prepared from suitably pure chemicals

[SOURCE: ISO 17294-1:2004, 3.30]
3.5
determination

entire process from preparing the test sample solution up to and including measurement and calculation

of the final result
[SOURCE: ISO 17294-1:2004, 3.6]
3.6
limit of quantification
LOQ

lowest concentration of an analyte that can be determined with a specified degree of accuracy and

precision
3.7
limit of detection
LOD

lowest concentration of an analyte that can be detected with a specified degree of accuracy and

precision
2 © ISO 2018 – All rights reserved
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ISO/TS 19620:2018(E)
4 Principle

The different arsenic species are separated using a specific column in a high performance liquid

chromatograph (HPLC). The separation of arsenic species in natural water is typically achieved using

strong anion exchange ion chromatography. The species can be separated using isocratic conditions

however faster more efficient separations can be achieved using gradient elution.

This method permits the use of ICP-MS (see Annex A) or HG-AFS (see Annex B) for individual detection

of the various arsenic species.
Annex C provides information on the determination of organic arsenic species.

Annex D provides information on the stability of arsenic species using different storage and

preservations.
5 Interferences

Retention time shift may occur for some water samples, especially when they are enriched with

significant levels of various water matrix ions. These ions compete with the active sites on the column.

Sample spikes using each of the arsenic species should therefore be used to confirm species identity if

a retention time shift is observed. The sample may also be diluted to overcome this effect or a smaller

injection volume may be used with an inferior LOQ. The co-elution of organic arsenic species with

arsenite (As(III)) and arsenate (As(V)) may cause a positive interference; therefore, the separation

conditions should be well proven and established.
To detect ICP-MS interferences, follow the procedure specified in Annex A.
To detect HG-AFS interferences, follow the procedure specified in Annex B.
6 Apparatus

Due to significant differences between the various instrument models and brands available, it is not

possible to give detailed instructions on their operation. The operator shall thus refer to the instructions

provided by the manufacturer of each instrument.
Usual laboratory glassware and equipment and, in particular, the following:

6.1 High performance liquid chromatograph (HPLC), including a column for analyte separation

and optionally a chromatographic guard column.

The HPLC system may be equipped with an autosampler, in-line degassing system and auto injection

system for introducing the sample. In most cases, an isocratic pump can be used; although, the use of

gradient pumps to provide optimal separation times is permitted.

NOTE Various column/eluent pairings can be used for separating arsenic species. A strong anion exchange

column is typically used. Some examples are provided in Annexes A and B.
6.2 Vacuum filtration system, for filtering the eluent and reagents prepared.

6.3 pH meter, for adjusting pH of eluent to one decimal place between 1,0 and 14,0.

6.4 Inductively coupled plasma mass spectrometer (ICP-MS).
See Annex A.
6.5 Hydride generation atomic fluorescence spectrometer (HG-AFS).
See Annex B.
© ISO 2018 – All rights reserved 3
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ISO/TS 19620:2018(E)
7 Reagents and standards
7.1 General requirements

All reagents shall be of known analytical grade. The concentration of the analyte or interfering

substances in the reagents and water should be negligible compared to the lowest concentration to be

determined.

NOTE Standard stock solutions are commercially available or can be prepared using chemicals of known

analytical purity.

Any reagents used in the preparation of the mobile phases of the HPLC procedure are column and

instrument specific and are not included here.
7.2 Water, grade 1, as defined in ISO 3696.
7.3 HPLC grade water.

HPLC grade water is used to prepare the mobile phase and the calibration solutions and to produce the

sample dilutions. It can be prepared by suitably purifying water (7.2).
7.4 Sodium hydroxide.
7.5 Sodium hydroxide solution, 1 mol/l.

Weigh 4 g of sodium hydroxide pellets (7.4) and add them to a 100 ml beaker. Then add approximately

50 ml de-ionized water and stir until the pellets have dissolved. Transfer to a 100 ml volumetric flask

and make up to the mark with de-ionized water (7.2)
7.6 Hydrochloric acid, mass fraction 35 % to 37 %.
7.7 Hydrochloric acid preservation solution for HG-AFS, approximately 6 mol/l.

Carefully add 500 ml of hydrochloric acid (7.6) to 250 ml of water (7.2). Make up to a final volume of

1 000 ml with water (7.2).
7.8 Nitric acid, mass fraction, 68 % to 72 %.
7.9 Nitric acid preservation solution for ICP-MS, approximately 6 mol/l.

Carefully add 365 ml of nitric acid (7.8) to 250 ml of water (7.2). Make up to a final volume of 1 000 ml

with water (7.2).
7.10 Standard substances
As(III): Arsenious oxide As O (CAS No. 1327-53-3);
2 3
As(V): Di-sodium hydrogen arsenate Na HAsO ·7H O (CAS No. 10048-95-0);
2 4 2
DMA: Dimethylarsinic acid, refer to Annex C;
MMA: Methylarsonic acid acid, refer to Annex C.
7.11 Stock solutions 1 000 mg/l

For each of the species, As(III) and As(V), prepare a stock solution with a concentration of 1 000 mg/l

expressed as As.
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ISO/TS 19620:2018(E)
These solutions are prepared from the standard substances (7.10).

In 100 ml volumetric flasks, dissolve the appropriate mass of each substance (7.10) as shown in Table 1.

Commercially available As(III) and As(V) stock solutions of the required concentration can also be used.

Table 1 — Preparation guidelines for 1 000 mg/l arsenic standards
Species Mass Final volume
g ml
As(III) 0,132 4 ml of 1 mol/l NaOH (7.5)
made up to 100 ml with water (7.2)
As(V) 0,416 100 ml in water (7.2)

These solutions, when stored protected from light and at 4 °C, are considered to be stable for one year.

7.12 Single component stock solutions 10 mg/l

Pipette 1 ml of 1 000 mg/l stock solution (7.11) and dilute to 100 ml in a volumetric flask.

The 10 mg/l single-component working solutions are also stable for one year if they are stored protected

from light and at 4 °C and stabilized in 0,04 mol/l NaOH (7.5) for As(III).
7.13 Calibration solutions

The calibration solutions are prepared from the 1 000 mg/l stock solutions (7.12). Tables 2 and 3 are

given as examples. The method is primarily for As(III) and As(V). It may be necessary to include DMA

and MMA standards to prove that the chromatographic separation is acceptable. Additional guidance is

provided in Annex C. Working standards should be prepared daily.
Table 2 — Preparation guidelines for working arsenic standards

Concentration Volume of each stock solution Solution for dilution HPLC grade water

µg/l µl (7.3)
1 000 100 µl of each stock solution 1 000 mg/l (7.11) 100 ml
As(III), As(V)
5 500 µl 1 000 µg/l 100 ml
10 1 000 µl 1 000 µg/l 100 ml
25 2 500 µl 1 000 µg/l 100 ml
50 5 000 µl 1 000 µg/l 100 ml

To prepare standard solutions below 5 µg/l use the 10 mg/l intermediate stock to produce a mixed

standard of 100 µg/l. Table 3 is given as an example.
Table 3 — Preparation guidelines for working arsenic standards

Concentration Volume of each working solution Solution for dilution HPLC grade water

µg/l µl (7.3)
100 1 000 µl of each solution 10 mg/l (7.12) 100 ml
As(III), As(V)
0,2 200 µl 100 µg/l 100 ml
0,5 500 µl 100 µg/l 100 ml
1,0 1 000 µl 100 µg/l 100 ml
2,0 2 000 µl 100 µg/l 100 ml
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ISO/TS 19620:2018(E)
7.14 Eluents

Various eluents can be used and the choice depends on the type of separation column chosen. The eluent

compositions described in Annex A and Annex B and in the associated tables are given as examples.

Given the number of possible eluents that can be used, this document does not provide guidance on how

to prepare these eluents.
7.15 HPLC trace analysis grade methanol.
8 Sampling, preservation and storage of samples

During the elaboration of this document, the stability of dissolved arsenic species was studied using

various methods of storage and preservation. A summary of the findings of this work is provided in

Annex D. Given the possible transformation of arsenate (As(V)) and arsenite (As(III)) species, it is

imperative that all laboratories using this document conduct their own investigations to demonstrate

that their selected storage and preservation approach is suitable for the water samples that their

laboratory may analyse.

This document is based on the preservation of dissolved arsenic species contained in the sample.

Depending on the type of sample, filtering at 0,45 µm, preferably on-site, is recommended followed by

acid stabilization, particularly in the case of ground waters and surface waters.

In the case of samples of water intended for human consumption with turbidity levels < 2 NFU, filtering

at 0,45 µm is not required.

If filtration and subsequent stabilization with acid are not feasible on-site, to minimize variations in

terms of speciation, these procedures shall be carried out on receipt in the laboratory and within not

more than 48 h of sampling. Sample preservation with acid shall always be carried out after filtration.

For HG-AFS, samples should be preserved by the addition of 300 µl of 6 mol/l HCl (7.7) per 100 ml of

sample. This equates to a final concentration of 0,018 mol/l HCl.
40 35 75

For ICP-MS, nitric acid stabilization can be used to avoid polyatomic Ar Cl interference for As. This

stabilization approach has not been fully tested; therefore, additional verification is strongly advised.

In this case, samples should be preserved by the addition of 300 µl of 6 mol/l HNO per 100 ml of sample.

This equates to a final concentration of 0,018 mol/l HNO .

Samples may be shipped at room temperature but should be stored in the laboratory at 4 °C until they

are analysed.

Additional guidance on stability, preservation and storage is provided in Annex D and in the

Bibliography.

In general terms, sampling shall be performed in accordance with ISO 5667-1 and ISO 5667-3, using

suitable sampling containers that have been validated for the stability and storage of arsenic species.

9 Procedure
9.1 HPLC instrument optimization
Use the instrument under the manufacturer's standard conditions.

Start up the HPLC system, set the pump flow rate and couple the column outlet to the detection system.

Ensure that the baseline is stable and the eluent has sufficiently flushed the column.

Before running the calibration, check that the chromatographic conditions selected enable satisfactory

separation with minimum resolution between each peak for the highest concentration of standard

solutions.
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ISO/TS 19620:2018(E)

Independent from the detection system, identify the analyte by comparing the retention times for the

samples and reference standards. The minimum requirements for identification are retention times

within ±0,1 min and relative retention times within ±0,5 % over the total run of a chromatogram.

A retention time shift may occur for some samples, especially when they are enriched with significant

levels of various water matrix ions. Sample spikes of each arsenic species should therefore be used to

confirm the species identity if the retention shift observed is greater than ±0,2 min. The sample may be

diluted to overcome this effect or a smaller injection volume may be used with an inferior LOQ.

Annex A provides more detailed information on HPLC-ICP-MS using different separations.

Annex B provides more detailed information on HPLC-HG-AFS using different separations.

Annex C provides information on the separation of organic arsenic species.

Annex D provides information on sample storage, preservation and stability of arsenic species.

9.2 Calibration
As a general rule, proceed as follows.

— Prepare and measure the blank calibration solution and the calibration solutions prepared in 7.13.

— Prepare a calibration graph in accordance with the manufacturer's instructions according to the

processing software used for signal acquisition in coupling mode.
9.3 Sample measurement

The water samples can be injected with or without dilution depending on the arsenic concentrations

measured previously.

The preliminary arsenic analysis of the filtered sample provides information on any dilution required

prior to injecting the sample and serves to check the consistency of the results. It is important to ensure

that the sum of the species measured remains less than or equal to the total arsenic value measured.

Regulatory total arsenic measurements are based on unfiltered samples and, therefore, may provide a

significantly higher result than total dissolved arsenic.
10 Expression of results

The results obtained are expressed as µg/l As, applying the dilution factors used for each sample. Give

the results to a maximum of two significant digits.
© ISO 2018 – All rights reserved 7
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ISO/TS 19620:2018(E)
EXAMPLE
Arsenic(III) 1,2 µg/l
Arsenic(V) 0,5 µg/l
11 Test report
The test report shall contain at least the following information:

a) the test method used, together with a reference to this document, i.e. ISO/TS 19620;

b) the instrumental and separation conditions used;
c) complete identification of the sample;
d) expression of the results according to Clause 10;

e) any details not specified in this document or considered to be optional, and any particular factor

liable to have affected the results.
8 © ISO 2018 – All rights reserved
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ISO/TS 19620:2018(E)
Annex A
(normative)
Detection using inductively coupled plasma mass spectrometry
(ICP-MS)
A.1 Principle

For ICP-MS, the eluted species are entrained in an argon plasma by means of a nebulizer and a

nebulization chamber. The arsenic compounds contained in the sample are atomized and ionized in the

plasma. The ions produced are introduced into the mass spectrometer chamber where they are routed

via a series of charged lenses and separated by a quadrupole, to be ultimately captured by a detector.

The concentration of an element with a specific mass is determined by comparing the quantities of ions

detected in the sample and in the calibration solutions.
A.2 Interferences

For ICP-MS, the interferences encountered for the arsenic assay essentially consist of interferences

caused by polyatomic species formation. Non-specific interferences (or the matrix effects) are

described in ISO 17294-1. Polyatomic ions are formed by concordance of gaseous compounds in the

plasma, reagents and the sample matrix (for example, interference with the relative mass of 75As by

40Ar35Cl and 40Ca35Cl). This interference is particularly important for the element arsenic. The mass

corresponding to the polyatomic ion ClO having a mass 51 should be monitored if the matrix under

analysis contains a high concentration of chloride ions. The chromatographic separation system

frequently provides for the separation of chloride ions from the species under analysis.

The impact of this effect on the measurement is dependent on the system used; this impact shall be

known. If mathematical corrections are used, the fact that the extent of the interference depends on

the plasma setting (oxide formation rate, for example) and the mass concentration of the interfering

element, which is, in general, a variable component of the sample solution, shall be taken into account.

Using a reaction/collision chamber after the skimmer cone makes it possible to reduce the polyatomic

interference caused by the molecular species 40Ar35Cl formed. Regardless of the interference reduction

system used, chloride ion related interference shall be controlled in accordance with ISO 17294-1.

NOTE An internal standard can be used to check instrumental drift. For example, a solution containing

10 µg/l of germanium can be injected.
A.3 Apparatus

Due to significant differences between the various instrument models and brands available, it is not

possible to give detailed instructions on their operation. The operator shall thus refer to the instructions

provided by the manufacturer of each instrument.
A.3.1 Mass spectrometer, with argon plasma as an ion source (ICP-MS).
Depending on the instruments used, the mass
...

SLOVENSKI STANDARD
SIST-TS ISO/TS 19620:2018
01-september-2018
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Water quality - Determination of arsenic(III) and arsenic(V) species - Method using high

performance liquid chromatography (HPLC) with detection by inductively coupled plasma

mass spectrometry (ICP-MS) or hydride generation atomic fluorescence spectrometry

(HG-AFS)

Qualité de l'eau - Détermination des formes chimiques (III) et (V) d'arsenic - Méthode par

chromatographie en phase liquide à haute performance (HPLC) avec détection par
spectrométrie de masse par torche à plasma (ICP-MS) ou génération d'hydrure
fluorescence atomique (HG-AFS)
Ta slovenski standard je istoveten z: ISO/TS 19620:2018
ICS:
13.060.50 3UHLVNDYDYRGHQDNHPLþQH Examination of water for
VQRYL chemical substances
71.040.50 Fizikalnokemijske analitske Physicochemical methods of
metode analysis
SIST-TS ISO/TS 19620:2018 en,fr

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

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SIST-TS ISO/TS 19620:2018
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SIST-TS ISO/TS 19620:2018
TECHNICAL ISO/TS
SPECIFICATION 19620
First edition
2018-01
Water quality — Determination of
arsenic(III) and arsenic(V) species
— Method using high performance
liquid chromatography (HPLC) with
detection by inductively coupled
plasma mass spectrometry (ICP-
MS) or hydride generation atomic
fluorescence spectrometry (HG-AFS)
Qualité de l'eau — Détermination des formes chimiques (III) et (V)
d'arsenic — Méthode par chromatographie en phase liquide à haute
performance (HPLC) avec détection par spectrométrie de masse
par torche à plasma (ICP-MS) ou génération d'hydrure fluorescence
atomique (HG-AFS)
Reference number
ISO/TS 19620:2018(E)
ISO 2018
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SIST-TS ISO/TS 19620:2018
ISO/TS 19620:2018(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2018

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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Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
Published in Switzerland
ii © ISO 2018 – All rights reserved
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SIST-TS ISO/TS 19620:2018
ISO/TS 19620:2018(E)
Contents Page

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

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

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

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

3 Terms and definitions ..................................................................................................................................................................................... 2

4 Principle ........................................................................................................................................................................................................................ 3

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

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

7 Reagents and standards ................................................................................................................................................................................ 4

8 Sampling, preservation and storage of samples .................................................................................................................. 6

9 Procedure..................................................................................................................................................................................................................... 6

9.1 HPLC instrument optimization ................................................................................................................................................. 6

9.2 Calibration .................................................................................................................................................................................................. 7

9.3 Sample measurement ........................................................................................................................................................................ 7

10 Expression of results ........................................................................................................................................................................................ 7

11 Test report ................................................................................................................................................................................................................... 8

Annex A (normative) Detection using inductively coupled plasma mass spectrometry (ICP-MS) ......9

Annex B (normative) Detection using hydride generation atomic fluorescence (HG-AFS) ......................20

Annex C (informative) Determination of organic arsenic species ......................................................................................27

Annex D (informative) Storage and preservation of arsenic species in water samples ...............................29

Bibliography .............................................................................................................................................................................................................................40

© ISO 2018 – All rights reserved iii
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SIST-TS ISO/TS 19620:2018
ISO/TS 19620:2018(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.
iv © ISO 2018 – All rights reserved
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SIST-TS ISO/TS 19620:2018
ISO/TS 19620:2018(E)
Introduction

In the environment, metals and metalloids are found in the form of various chemical species. Chemical

speciation makes it possible to identify and quantify these different species. For the same metal or

metalloid, given that the toxicity of each compound may vary significantly, it can be useful to quantify

each of the species present in a given sample. For arsenic, the toxicity of the various species varies

considerably; inorganic species are recognized as being more toxic than organic species and, for

example, the toxicity of As(III) is greater than that of As(V). This method is primarily applicable to the

determination of arsenite (As(III)) and arsenate (As(V)) as these are the main species of interest and

are the predominant species found in potable water samples from the underlying geological strata in

many parts of the world. Arsenic speciation measurements are important to establish and select the

best water treatment technology for arsenic removal from raw waters containing significant levels of

arsenic.
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SIST-TS ISO/TS 19620:2018
TECHNICAL SPECIFICATION ISO/TS 19620:2018(E)
Water quality — Determination of arsenic(III) and
arsenic(V) species — Method using high performance liquid
chromatography (HPLC) with detection by inductively
coupled plasma mass spectrometry (ICP-MS) or hydride
generation atomic fluorescence spectrometry (HG-AFS)

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

This document is not intended to cover any safety problems associated with its use, if applicable.

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 primarily developed for the determination of inorganic arsenic

species (arsenite (As(III)) and arsenate (As(V)) dissolved in a sample after a preservation process

in waters with a low total organic carbon content such as potable water, tap water, surface waters,

ground waters and rain waters. Information is provided on the determination of potentially relevant

organo-arsenic species such as methylarsonic acid (MMA) and dimethylarsinic acid (DMA) which may

be encountered at very low levels in natural surface waters.

The linear working dynamic range depends on the operating conditions and the method of detection

used; under standard conditions, it typically ranges from 0,5 µg/l to 50 µg/l for each species. Samples

containing arsenic at concentrations higher than the linear dynamic range can be analysed after

suitable dilution.

This method is based on high performance liquid chromatography separation of arsenic species with

either inductively coupled mass spectrometry (ICP-MS) or hydride generation atomic fluorescence

spectrometry (HG-AFS) as a method of detection.

The sensitivity of this method depends on the method of detection and the instrumental operating

conditions selected. The limit of quantification (LOQ) of the method also depends on the operating

conditions of the analytical system used and the extent of the calibration range used. LOQ examples for

As(III) and As(V) are provided; LOQs are generally less than 1 µg/l.

This document does not apply to arsenobetaine and other organic arsenic species which are not present

in natural water samples.
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

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ISO 17294-1, Water quality — Application of inductively coupled plasma mass spectrometry (ICP-MS) —

Part 1: General guidelines
3 Terms and definitions
For the purposes of this document, the following terms and definitions 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
analyte
substance to be determined
[SOURCE: ISO/TS 28581:2012, 3.1]
3.2
blank calibration solution

solution prepared in the same way as the calibration solution but leaving out the analyte

[SOURCE: ISO 17294-1:2004, 3.3]
3.3
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]
3.4
stock solution

solution with accurately known analyte concentration(s), prepared from suitably pure chemicals

[SOURCE: ISO 17294-1:2004, 3.30]
3.5
determination

entire process from preparing the test sample solution up to and including measurement and calculation

of the final result
[SOURCE: ISO 17294-1:2004, 3.6]
3.6
limit of quantification
LOQ

lowest concentration of an analyte that can be determined with a specified degree of accuracy and

precision
3.7
limit of detection
LOD

lowest concentration of an analyte that can be detected with a specified degree of accuracy and

precision
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4 Principle

The different arsenic species are separated using a specific column in a high performance liquid

chromatograph (HPLC). The separation of arsenic species in natural water is typically achieved using

strong anion exchange ion chromatography. The species can be separated using isocratic conditions

however faster more efficient separations can be achieved using gradient elution.

This method permits the use of ICP-MS (see Annex A) or HG-AFS (see Annex B) for individual detection

of the various arsenic species.
Annex C provides information on the determination of organic arsenic species.

Annex D provides information on the stability of arsenic species using different storage and

preservations.
5 Interferences

Retention time shift may occur for some water samples, especially when they are enriched with

significant levels of various water matrix ions. These ions compete with the active sites on the column.

Sample spikes using each of the arsenic species should therefore be used to confirm species identity if

a retention time shift is observed. The sample may also be diluted to overcome this effect or a smaller

injection volume may be used with an inferior LOQ. The co-elution of organic arsenic species with

arsenite (As(III)) and arsenate (As(V)) may cause a positive interference; therefore, the separation

conditions should be well proven and established.
To detect ICP-MS interferences, follow the procedure specified in Annex A.
To detect HG-AFS interferences, follow the procedure specified in Annex B.
6 Apparatus

Due to significant differences between the various instrument models and brands available, it is not

possible to give detailed instructions on their operation. The operator shall thus refer to the instructions

provided by the manufacturer of each instrument.
Usual laboratory glassware and equipment and, in particular, the following:

6.1 High performance liquid chromatograph (HPLC), including a column for analyte separation

and optionally a chromatographic guard column.

The HPLC system may be equipped with an autosampler, in-line degassing system and auto injection

system for introducing the sample. In most cases, an isocratic pump can be used; although, the use of

gradient pumps to provide optimal separation times is permitted.

NOTE Various column/eluent pairings can be used for separating arsenic species. A strong anion exchange

column is typically used. Some examples are provided in Annexes A and B.
6.2 Vacuum filtration system, for filtering the eluent and reagents prepared.

6.3 pH meter, for adjusting pH of eluent to one decimal place between 1,0 and 14,0.

6.4 Inductively coupled plasma mass spectrometer (ICP-MS).
See Annex A.
6.5 Hydride generation atomic fluorescence spectrometer (HG-AFS).
See Annex B.
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7 Reagents and standards
7.1 General requirements

All reagents shall be of known analytical grade. The concentration of the analyte or interfering

substances in the reagents and water should be negligible compared to the lowest concentration to be

determined.

NOTE Standard stock solutions are commercially available or can be prepared using chemicals of known

analytical purity.

Any reagents used in the preparation of the mobile phases of the HPLC procedure are column and

instrument specific and are not included here.
7.2 Water, grade 1, as defined in ISO 3696.
7.3 HPLC grade water.

HPLC grade water is used to prepare the mobile phase and the calibration solutions and to produce the

sample dilutions. It can be prepared by suitably purifying water (7.2).
7.4 Sodium hydroxide.
7.5 Sodium hydroxide solution, 1 mol/l.

Weigh 4 g of sodium hydroxide pellets (7.4) and add them to a 100 ml beaker. Then add approximately

50 ml de-ionized water and stir until the pellets have dissolved. Transfer to a 100 ml volumetric flask

and make up to the mark with de-ionized water (7.2)
7.6 Hydrochloric acid, mass fraction 35 % to 37 %.
7.7 Hydrochloric acid preservation solution for HG-AFS, approximately 6 mol/l.

Carefully add 500 ml of hydrochloric acid (7.6) to 250 ml of water (7.2). Make up to a final volume of

1 000 ml with water (7.2).
7.8 Nitric acid, mass fraction, 68 % to 72 %.
7.9 Nitric acid preservation solution for ICP-MS, approximately 6 mol/l.

Carefully add 365 ml of nitric acid (7.8) to 250 ml of water (7.2). Make up to a final volume of 1 000 ml

with water (7.2).
7.10 Standard substances
As(III): Arsenious oxide As O (CAS No. 1327-53-3);
2 3
As(V): Di-sodium hydrogen arsenate Na HAsO ·7H O (CAS No. 10048-95-0);
2 4 2
DMA: Dimethylarsinic acid, refer to Annex C;
MMA: Methylarsonic acid acid, refer to Annex C.
7.11 Stock solutions 1 000 mg/l

For each of the species, As(III) and As(V), prepare a stock solution with a concentration of 1 000 mg/l

expressed as As.
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These solutions are prepared from the standard substances (7.10).

In 100 ml volumetric flasks, dissolve the appropriate mass of each substance (7.10) as shown in Table 1.

Commercially available As(III) and As(V) stock solutions of the required concentration can also be used.

Table 1 — Preparation guidelines for 1 000 mg/l arsenic standards
Species Mass Final volume
g ml
As(III) 0,132 4 ml of 1 mol/l NaOH (7.5)
made up to 100 ml with water (7.2)
As(V) 0,416 100 ml in water (7.2)

These solutions, when stored protected from light and at 4 °C, are considered to be stable for one year.

7.12 Single component stock solutions 10 mg/l

Pipette 1 ml of 1 000 mg/l stock solution (7.11) and dilute to 100 ml in a volumetric flask.

The 10 mg/l single-component working solutions are also stable for one year if they are stored protected

from light and at 4 °C and stabilized in 0,04 mol/l NaOH (7.5) for As(III).
7.13 Calibration solutions

The calibration solutions are prepared from the 1 000 mg/l stock solutions (7.12). Tables 2 and 3 are

given as examples. The method is primarily for As(III) and As(V). It may be necessary to include DMA

and MMA standards to prove that the chromatographic separation is acceptable. Additional guidance is

provided in Annex C. Working standards should be prepared daily.
Table 2 — Preparation guidelines for working arsenic standards

Concentration Volume of each stock solution Solution for dilution HPLC grade water

µg/l µl (7.3)
1 000 100 µl of each stock solution 1 000 mg/l (7.11) 100 ml
As(III), As(V)
5 500 µl 1 000 µg/l 100 ml
10 1 000 µl 1 000 µg/l 100 ml
25 2 500 µl 1 000 µg/l 100 ml
50 5 000 µl 1 000 µg/l 100 ml

To prepare standard solutions below 5 µg/l use the 10 mg/l intermediate stock to produce a mixed

standard of 100 µg/l. Table 3 is given as an example.
Table 3 — Preparation guidelines for working arsenic standards

Concentration Volume of each working solution Solution for dilution HPLC grade water

µg/l µl (7.3)
100 1 000 µl of each solution 10 mg/l (7.12) 100 ml
As(III), As(V)
0,2 200 µl 100 µg/l 100 ml
0,5 500 µl 100 µg/l 100 ml
1,0 1 000 µl 100 µg/l 100 ml
2,0 2 000 µl 100 µg/l 100 ml
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SIST-TS ISO/TS 19620:2018
ISO/TS 19620:2018(E)
7.14 Eluents

Various eluents can be used and the choice depends on the type of separation column chosen. The eluent

compositions described in Annex A and Annex B and in the associated tables are given as examples.

Given the number of possible eluents that can be used, this document does not provide guidance on how

to prepare these eluents.
7.15 HPLC trace analysis grade methanol.
8 Sampling, preservation and storage of samples

During the elaboration of this document, the stability of dissolved arsenic species was studied using

various methods of storage and preservation. A summary of the findings of this work is provided in

Annex D. Given the possible transformation of arsenate (As(V)) and arsenite (As(III)) species, it is

imperative that all laboratories using this document conduct their own investigations to demonstrate

that their selected storage and preservation approach is suitable for the water samples that their

laboratory may analyse.

This document is based on the preservation of dissolved arsenic species contained in the sample.

Depending on the type of sample, filtering at 0,45 µm, preferably on-site, is recommended followed by

acid stabilization, particularly in the case of ground waters and surface waters.

In the case of samples of water intended for human consumption with turbidity levels < 2 NFU, filtering

at 0,45 µm is not required.

If filtration and subsequent stabilization with acid are not feasible on-site, to minimize variations in

terms of speciation, these procedures shall be carried out on receipt in the laboratory and within not

more than 48 h of sampling. Sample preservation with acid shall always be carried out after filtration.

For HG-AFS, samples should be preserved by the addition of 300 µl of 6 mol/l HCl (7.7) per 100 ml of

sample. This equates to a final concentration of 0,018 mol/l HCl.
40 35 75

For ICP-MS, nitric acid stabilization can be used to avoid polyatomic Ar Cl interference for As. This

stabilization approach has not been fully tested; therefore, additional verification is strongly advised.

In this case, samples should be preserved by the addition of 300 µl of 6 mol/l HNO per 100 ml of sample.

This equates to a final concentration of 0,018 mol/l HNO .

Samples may be shipped at room temperature but should be stored in the laboratory at 4 °C until they

are analysed.

Additional guidance on stability, preservation and storage is provided in Annex D and in the

Bibliography.

In general terms, sampling shall be performed in accordance with ISO 5667-1 and ISO 5667-3, using

suitable sampling containers that have been validated for the stability and storage of arsenic species.

9 Procedure
9.1 HPLC instrument optimization
Use the instrument under the manufacturer's standard conditions.

Start up the HPLC system, set the pump flow rate and couple the column outlet to the detection system.

Ensure that the baseline is stable and the eluent has sufficiently flushed the column.

Before running the calibration, check that the chromatographic conditions selected enable satisfactory

separation with minimum resolution between each peak for the highest concentration of standard

solutions.
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ISO/TS 19620:2018(E)

Independent from the detection system, identify the analyte by comparing the retention times for the

samples and reference standards. The minimum requirements for identification are retention times

within ±0,1 min and relative retention times within ±0,5 % over the total run of a chromatogram.

A retention time shift may occur for some samples, especially when they are enriched with significant

levels of various water matrix ions. Sample spikes of each arsenic species should therefore be used to

confirm the species identity if the retention shift observed is greater than ±0,2 min. The sample may be

diluted to overcome this effect or a smaller injection volume may be used with an inferior LOQ.

Annex A provides more detailed information on HPLC-ICP-MS using different separations.

Annex B provides more detailed information on HPLC-HG-AFS using different separations.

Annex C provides information on the separation of organic arsenic species.

Annex D provides information on sample storage, preservation and stability of arsenic species.

9.2 Calibration
As a general rule, proceed as follows.

— Prepare and measure the blank calibration solution and the calibration solutions prepared in 7.13.

— Prepare a calibration graph in accordance with the manufacturer's instructions according to the

processing software used for signal acquisition in coupling mode.
9.3 Sample measurement

The water samples can be injected with or without dilution depending on the arsenic concentrations

measured previously.

The preliminary arsenic analysis of the filtered sample provides information on any dilution required

prior to injecting the sample and serves to check the consistency of the results. It is important to ensure

that the sum of the species measured remains less than or equal to the total arsenic value measured.

Regulatory total arsenic measurements are based on unfiltered samples and, therefore, may provide a

significantly higher result than total dissolved arsenic.
10 Expression of results

The results obtained are expressed as µg/l As, applying the dilution factors used for each sample. Give

the results to a maximum of two significant digits.
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SIST-TS ISO/TS 19620:2018
ISO/TS 19620:2018(E)
EXAMPLE
Arsenic(III) 1,2 µg/l
Arsenic(V) 0,5 µg/l
11 Test report
The test report shall contain at least the following information:

a) the test method used, together with a reference to this document, i.e. ISO/TS 19620;

b) the instrumental and separation conditions used;
c) complete identification of the sample;
d) expression of the results according to Clause 10;

e) any details not specified in this document or considered to be optional, and any particular factor

liable to have affected the results.
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Annex A
(normative)
Detection using inductively coupled plasma mass spectrometry
(ICP-MS)
A.1 Principle

For ICP-MS, the eluted species are entrained in an argon plasma by means of a nebulizer and a

nebulization chamber. The arsenic compounds contained in the sample are atomized and ionized in the

plasma. The ions produced are introduced into the mass spectrometer chamber where they are routed

via a series of charged lenses and separated by a quadrupole, to be ultimately captured by a detector.

The concentration of an element with a specific mass is determined by comparing the quantities of ions

detected in the sample and in the calibration solutions.
A.2 Interferences

For ICP-MS, the interferences encountered for the arsenic assay essentially consist of interferences

caused by polyatomic species formation. Non-specific interferences (
...

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