Milk, milk products, infant formula and adult nutritionals - Determination of minerals and trace elements - Inductively coupled plasma mass spectrometry (ICP-MS) method (ISO 21424:2018)

This document specifies a method for the quantitative determination of calcium (Ca), copper (Cu), iron (Fe), magnesium (Mg), manganese (Mn), phosphorus (P), potassium (K), sodium (Na), zinc (Zn), chromium (Cr), molybdenum (Mo) and selenium (Se) using inductively coupled plasma and mass spectrometry (ICP-MS).
The method is applicable for the determination of all 12 elements in infant formula and adult nutritional products. The method is also applicable for milk, milk powder, whey powder, butter and cheese excluding the determination of Cr, because all Cr results were below the quantification limit and reproducibility could not be determined in these matrices[1]. The present method is an extension of ISO 20649 | IDF 235 (AOAC 2011.19[2]) which was validated only for Cr, Mo and Se in infant formula and adult nutritional products.

Milch, Milcherzeugnisse, Säuglingsnahrung und Nahrungsergänzungsmittel für Erwachsene - Bestimmung von Mineralien und Spurenelementen - Verfahren mit induktiv gekoppelter Plasma-Massenspektrometrie (ICP-MS) (ISO 21424:2018)

Dieses Dokument legt ein Verfahren für die quantitative Bestimmung von Calcium (Ca), Kupfer (Cu), Eisen (Fe), Magnesium (Mg), Mangan (Mn), Phosphor (P), Kalium (K), Natrium (Na), Zink (Zn), Chrom (Cr), Molybdän (Mo) und Selen (Se) mittels Massenspektrometrie mit induktiv gekoppeltem Plasma (ICP MS) fest.
Das Verfahren ist für die Bestimmung aller 12 Elemente in Säuglingsnahrung und Nahrungs-ergänzungsmitteln für Erwachsene anwendbar. Das Verfahren ist auch für Milch, Milchpulver, Molkepulver, Butter und Käse anwendbar, allerdings mit Ausnahme der Bestimmung von Cr, weil sämtliche Cr Ergebnisse unterhalb der Quantifizierungsgrenze lagen und die Vergleichpräzision in diesen Matrices nicht bestimmt werden konnte [1]. Bei dem vorliegenden Verfahren handelt es sich um eine Erweiterung von ISO 20649 | IDF 235 (AOAC 2011.19 [2]), die nur für Cr, Mo und Se in Säuglingsnahrung und Nahrungsergänzungsmitteln für Erwachsene validiert wurde.
Die in Tabelle 1 angegebenen Bereiche werden abgedeckt (siehe auch Tabelle A.1).
[Tabelle 1 - Analytische Bereiche]

Lait, produits laitiers, formules infantiles et produits nutritionnels pour adultes - Détermination de la teneur en minéraux et en oligo-éléments - Méthode par spectrométrie de masse avec plasma à couplage inductif (ICP-SM) (ISO 21424:2018)

Le présent document spécifie une méthode de détermination quantitative de la teneur en calcium (Ca), cuivre (Cu), fer (Fe), magnésium (Mg), manganèse (Mn), phosphore (P), potassium (K), sodium (Na), zinc (Zn), chrome (Cr), molybdène (Mo) et sélénium (Se) par spectrométrie de masse avec plasma à couplage inductif (ICP-SM).
La méthode est applicable pour la détermination de la totalité des 12 éléments dans les formules infantiles et les produits nutritionnels pour adultes. La méthode est également applicable au lait, au lait en poudre, au lactosérum en poudre, au beurre et au fromage, à l'exclusion de la détermination du Cr, car tous les résultats de Cr étaient inférieurs à la limite de quantification et la reproductibilité n'a pas pu être établie dans ces matrices.[1] La présente méthode est une extension de l'ISO 20649 | FIL 235 (AOAC 2011.19[2]) qui n'a été validée que pour le Cr, le Mo et le Se dans les formules infantiles et les produits nutritionnels pour adultes.

Mleko, mlečni proizvodi, hrana za dojenčke in prehranska dopolnila za odrasle - Določevanje mineralov in elementov v sledovih - Masna spektrometrija z induktivno sklopljeno plazmo (ICP-MS) (ISO 21424:2018)

General Information

Status
Published
Public Enquiry End Date
19-Mar-2020
Publication Date
18-Jun-2020
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
11-Jun-2020
Due Date
16-Aug-2020
Completion Date
19-Jun-2020

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SLOVENSKI STANDARD
SIST EN ISO 21424:2020
01-julij-2020
Mleko, mlečni proizvodi, hrana za dojenčke in prehranska dopolnila za odrasle -
Določevanje mineralov in elementov v sledovih - Masna spektrometrija z
induktivno sklopljeno plazmo (ICP-MS) (ISO 21424:2018)

Milk, milk products, infant formula and adult nutritionals - Determination of minerals and

trace elements - Inductively coupled plasma mass spectrometry (ICP-MS) method (ISO

21424:2018)
Milch, Milcherzeugnisse, Säuglingsnahrung und Nahrungsergänzungsmittel für
Erwachsene - Bestimmung von Mineralien und Spurenelementen - Verfahren mit
induktiv gekoppelter Plasma-Massenspektrometrie (ICP-MS) (ISO 21424:2018)

Lait, produits laitiers, formules infantiles et produits nutritionnels pour adultes -

Détermination de la teneur en minéraux et en oligo-éléments - Méthode par
spectrométrie de masse avec plasma à couplage inductif (ICP-SM) (ISO 21424:2018)
Ta slovenski standard je istoveten z: EN ISO 21424:2020
ICS:
67.050 Splošne preskusne in General methods of tests and
analizne metode za živilske analysis for food products
proizvode
67.100.10 Mleko in predelani mlečni Milk and processed milk
proizvodi products
67.230 Predpakirana in pripravljena Prepackaged and prepared
hrana foods
SIST EN ISO 21424:2020 en

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

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SIST EN ISO 21424:2020
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SIST EN ISO 21424:2020
EN ISO 21424
EUROPEAN STANDARD
NORME EUROPÉENNE
June 2020
EUROPÄISCHE NORM
ICS 67.100.10
English Version
Milk, milk products, infant formula and adult nutritionals -
Determination of minerals and trace elements -
Inductively coupled plasma mass spectrometry (ICP-MS)
method (ISO 21424:2018)

Lait, produits laitiers, formules infantiles et produits Milch, Milcherzeugnisse, Säuglingsnahrung und

nutritionnels pour adultes - Détermination de la teneur Nahrungsergänzungsmittel für Erwachsene -

en minéraux et en oligo-éléments - Méthode par Bestimmung von Mineralien und Spurenelementen -

spectrométrie de masse avec plasma à couplage Verfahren mit induktiv gekoppelter Plasma-

inductif (ICP-SM) (ISO 21424:2018) Massenspektrometrie (ICP-MS) (ISO 21424:2018)
This European Standard was approved by CEN on 10 May 2020.

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

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

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

member.

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

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

Centre has the same status as the official versions.

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

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

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

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

© 2020 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 21424:2020 E

worldwide for CEN national Members.
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SIST EN ISO 21424:2020
EN ISO 21424:2020 (E)
Contents Page

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

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SIST EN ISO 21424:2020
EN ISO 21424:2020 (E)
European foreword

The text of ISO 21424:2018 has been prepared by Technical Committee ISO/TC 34 "Food products” of

the International Organization for Standardization (ISO) and has been taken over as EN ISO 21424:2020

by Technical Committee CEN/TC 302 “Milk and milk products - Methods of sampling and analysis” the

secretariat of which is held by NEN.

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

identical text or by endorsement, at the latest by December 2020, and conflicting national standards

shall be withdrawn at the latest by December 2020.

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

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

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

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

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

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

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

United Kingdom.
Endorsement notice

The text of ISO 21424:2018 has been approved by CEN as EN ISO 21424:2020 without any modification.

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SIST EN ISO 21424:2020
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SIST EN ISO 21424:2020
INTERNATIONAL ISO
STANDARD 21424
IDF 243
First edition
2018-11
Milk, milk products, infant formula and
adult nutritionals — Determination
of minerals and trace elements —
Inductively coupled plasma mass
spectrometry (ICP-MS) method
Lait, produits laitiers, formules infantiles et produits nutritionnels
pour adultes — Détermination de la teneur en minéraux et en oligo-
éléments — Méthode par spectrométrie de masse avec plasma à
couplage inductif (ICP-SM)
Reference numbers
ISO 21424:2018(E)
IDF 243:2018(E)
ISO and IDF 2018
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SIST EN ISO 21424:2020
ISO 21424:2018(E)
IDF 243:2018(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO and IDF 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 International Dairy Federation
CP 401 • Ch. de Blandonnet 8 Silver Building • Bd Auguste Reyers 70/B
CH-1214 Vernier, Geneva B-1030 Brussels
Phone: +41 22 749 01 11 Phone: +32 2 325 67 40
Fax: +41 22 749 09 47 Fax: +32 2 325 67 41
Email: copyright@iso.org Email: info@fil-idf.org
Website: www.iso.org Website: www.fil-idf.org
Published in Switzerland
ii © ISO and IDF 2018 – All rights reserved
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SIST EN ISO 21424:2020
ISO 21424:2018(E)
IDF 243:2018(E)
Contents Page

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

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

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

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

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

5 Reagents ........................................................................................................................................................................................................................ 2

6 Preparation of standards and solutions ...................................................................................................................................... 3

6.1 Surfactant solution (optional, approximately 5 %) ................................................................................................. 3

6.2 Nitric acid rinse solution for autosampler rinse port, 2 % ............................................................................... 3

6.3 P/A factor tuning working solution ...................................................................................................................................... 3

6.4 Calibration blank (Cal Blk) and preparation blank (PB) solution .............................................................. 3

6.5 Calibration standard solution set............................................................................................................................................ 4

7 Apparatus ..................................................................................................................................................................................................................... 4

8 Preparation of test sample ......................................................................................................................................................................... 5

9 Determination ......................................................................................................................................................................................................... 6

10 Calculation .................................................................................................................................................................................................................. 7

11 Precision data .......................................................................................................................................................................................................... 8

11.1 General ........................................................................................................................................................................................................... 8

11.2 Repeatability ............................................................................................................................................................................................. 8

11.3 Reproducibility ....................................................................................................................................................................................... 8

12 Test report ................................................................................................................................................................................................................... 8

Annex A (informative) Precision data ................................................................................................................................................................. 9

Bibliography .............................................................................................................................................................................................................................31

© ISO and IDF 2018 – All rights reserved iii
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SIST EN ISO 21424:2020
ISO 21424:2018(E)
IDF 243:2018(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 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 34, Food products, Subcommittee SC 5,

Milk and milk products and the International Dairy Federation (IDF), in collaboration with AOAC

INTERNATIONAL.

It is being published jointly by ISO and IDF and separately by AOAC INTERNATIONAL. The method

described in this document is equivalent to the AOAC Official Method 2015.06: Minerals and Trace

Elements in Infant Formula.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www .iso .org/members .html.
iv © ISO and IDF 2018 – All rights reserved
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SIST EN ISO 21424:2020
ISO 21424:2018(E)
IDF 243:2018(E)

IDF (the International Dairy Federation) is a non-profit private sector organization representing the

interests of various stakeholders in dairying at the global level. IDF members are organized in National

Committees, which are national associations composed of representatives of dairy-related national

interest groups including dairy farmers, dairy processing industry, dairy suppliers, academics and

governments/food control authorities.

ISO and IDF collaborate closely on all matters of standardization relating to methods of analysis

and sampling for milk and milk products. Since 2001, ISO and IDF jointly publish their International

Standards using the logos and reference numbers of both organizations.

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

patent rights. IDF 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.

This document was prepared by the IDF Standing Committee on Analytical Methods for Composition

and ISO Technical Committee ISO/TC 34, Food products, Subcommittee SC 5, Milk and milk products, in

collaboration with AOAC INTERNATIONAL.

It is being published jointly by ISO and IDF and separately by AOAC INTERNATIONAL. The method

described in this document is equivalent to the AOAC Official Method 2015.06: Minerals and Trace Elements

in Infant Formula. All work was carried out by the ISO/IDF Action Team on C40 of the Standing Committee

on Analytical Methods for Composition under the aegis of its project leader, Mr. H. Cruijsen (NL).

© ISO and IDF 2018 – All rights reserved v
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SIST EN ISO 21424:2020
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SIST EN ISO 21424:2020
ISO 21424:2018(E)
INTERNATIONAL STANDARD
IDF 243:2018(E)
Milk, milk products, infant formula and adult
nutritionals — Determination of minerals and
trace elements — Inductively coupled plasma mass
spectrometry (ICP-MS) method
1 Scope

This document specifies a method for the quantitative determination of calcium (Ca), copper (Cu),

iron (Fe), magnesium (Mg), manganese (Mn), phosphorus (P), potassium (K), sodium (Na), zinc (Zn),

chromium (Cr), molybdenum (Mo) and selenium (Se) using inductively coupled plasma and mass

spectrometry (ICP-MS).

The method is applicable for the determination of all 12 elements in infant formula and adult

nutritional products. The method is also applicable for milk, milk powder, whey powder, butter and

cheese excluding the determination of Cr, because all Cr results were below the quantification limit and

[1]

reproducibility could not be determined in these matrices . The present method is an extension of

[2]

ISO 20649 | IDF 235 (AOAC 2011.19 ) which was validated only for Cr, Mo and Se in infant formula and

adult nutritional products.
The ranges given in Table 1 are in scope (see also Table A.1).
Table 1 — Analytical ranges
Ca Cu Fe Mg Mn P K Na Zn Cr Se Mo
Lower
analytical
3 0,002 0,04 0,7 0,002 3 3 2 0,07 0,002 0,000 6 0,000 2
range , in
mg/100 g
Upper
analytical
1 280 1,2 20 110 1,0 800 2 000 850 18 0,16 0,05 0,10
range , in
mg/100 g
Concentrations apply to

— milk and ”ready-to-feed” liquid as-is, using a typical sample size of 1 g per final analytical solution volume of 50 ml, and

— reconstituted milk powder, reconstituted infant formula powder and reconstituted adult nutritional powder (25 g into

200 g of water), using a typical sample size of 1,8 g of the reconstituted slurry per final analytical solution volume of 50 ml.

Ranges for non-reconstituted dairy ingredients (butter, cheese, whey powder, whey protein concentrate) are adjusted

proportionally upward from these values based upon the sample size used for the ingredient. For example, if 0,3 g of cheese

is digested the ranges will be 1 g/ 0,3 g = 3,3 × higher.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
No terms and definitions are listed in this document.

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
© ISO and IDF 2018 – All rights reserved 1
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SIST EN ISO 21424:2020
ISO 21424:2018(E)
IDF 243:2018(E)
— IEC Electropedia: available at http: //www .electropedia .org/
4 Principle

Nitric acid, internal standard, and hydrogen peroxide are added to the sample in microwave vessels

and the samples are digested at 200 °C using a pre-programmed temperature control digestion. The

addition of hydrogen peroxide helps reduce carbon and nitrous oxide levels in the digestate. The

presence of carbon in the samples causes signal enhancement of Se. Therefore, to matrix match the

samples, carbon in the form of methanol is added to both the standard solutions and the digestate

before analysis. An ionization buffer is not necessary because the multielement standards and samples

always contain significant amounts of the easily ionized elements. Germanium (Ge, for 11 elements) and

tellurium (Te just for Se) are used as internal standards. Analysis is performed by ICP-MS. Polyatomic

interferences on the low mass elements are reduced or eliminated by analysing in He collision mode

using kinetic energy discrimination (KED). For Se measurements the H gas mode is preferred for

increased sensitivity. Quantitation of 12 elements is achieved essentially simultaneously by comparing

the analyte/internal standard response ratios in the unknown samples to a standard curve constructed

from response ratios of calibration standards.
5 Reagents

WARNING — The use of this document can involve hazardous materials, operations and reagents.

This standard does not propose to address all the safety problems associated with its use. It is

the responsibility of the user of this document to establish safety and health practices.

5.1 Methanol, purity ≥ 99,99 %, analytical reagent grade.
5.2 Nitric acid (HNO ), concentrated, ultrapure reagent grade.
5.3 Nitric acid (HNO ), concentrated, trace metal grade.
5.4 H O , with a volume fraction of 30 %, ACS reagent grade.
2 2

5.5 Laboratory water, metal-free, organic-free, pyrogen-free, filtered 18 MΩ-cm quality.

5.6 Surfactant, for example, Tergitol® Type 15-S-9, Sigma or equivalent (optional).

5.7 Argon gas, purity ≥ 99,996 %.
5.8 Helium gas, purity ≥ 99,999 9 %.
5.9 Hydrogen gas, purity ≥ 99,999 5 %, for Se analyses (recommended).
5.10 Multi-element standard stock solution.

NIST or NIST-traceable containing Se at mass concentration ρ = 20 µg/l; Cr and Mo at 40 µg/l; Mn and

Cu at 0,25 mg/l; Zn at 1 mg/l; Fe at 2,5 mg/l; Mg at 10 mg/l; P at 25 mg/l; Ca and K at 50 mg/l and Na at

25 mg/l in 2 % HNO + trace hydrofluoric acid (HF). This stock standard solution expires on the date

given by the manufacturer.

1) Tergitol® is an example of a suitable product available commercially. This information is given for the

convenience of users of this document and does not constitute an endorsement by ISO or IDF of the product named.

2 © ISO and IDF 2018 – All rights reserved
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SIST EN ISO 21424:2020
ISO 21424:2018(E)
IDF 243:2018(E)
5.11 Multi-element internal standard stock solution (ISTD stock).

NIST or NIST-traceable containing Ge and Te at 5 mg/l in 2 % HNO + trace HF. This stock standard

solution expires on the date given by the manufacturer.
5.12 Tuning and pulse/analogue (P/A) factor tuning stock solutions.

NIST or NIST-traceable containing various elements at concentration levels recommended by the

manufacturer. Since this method determines the major elements at relatively high concentrations

for an ICP-MS, it is important to understand the solutions needed and the procedure to obtain high

quality calibration curves in which the detector is used in both pulse counting and analogue modes. A

properly calibrated instrument will deliver the linearity requirements of the method; for example, that

calibration residuals are < 4 %, see Clause 9.
5.13 Quality control sample (QCS).

Standard Reference Material (SRM)® 1849a milk-based hybrid infant/adult nutritional powder with

certified values for Ca, Cu, Cr, Fe, Mg, Mn, Mo, P, K, Se, Na, and Zn. Supplied as a unit of 10 packets each

containing approximately 10 g of material. This is the recommended control material for this analysis,

but other suitable SRMs could be substituted.
6 Preparation of standards and solutions
6.1 Surfactant solution (optional, approximately 5 %)

Add about 700 ml laboratory water to a 1 l plastic bottle containing a polytetrafluoroethylene

(PTFE)-coated stirring bar. Place the bottle on a magnetic stirrer and begin stirring at a moderate

speed. Slowly add 50 ml surfactant from a graduated cylinder. When the surfactant is dissolved, fill

the bottle to approximately 1 000 ml with laboratory water. Transfer to 1 l plastic bottle fitted with a

PTFE-constructed dispenser with adjustable volume from 1 ml to 10 ml. This solution is added to the

autosampler rinse solution to minimize residue build-up in the spray chamber. It does not otherwise

affect the analysis. Expiration: 6 months. Store at room temperature.
6.2 Nitric acid rinse solution for autosampler rinse port, 2 %

Mix 20 ml of concentrated nitric acid (5.2) with 20 ml surfactant solution (6.1) and laboratory water to

prepare a total volume of 1 000 ml. Expiration: 3 months. Store at room temperature.

6.3 P/A factor tuning working solution

Dilute and/or combine P/A factor tuning stock solutions (or equivalent) to the manufacturer’s

recommended dilution level with laboratory water for use at the instrument. Expiration: 6 months.

Store at room temperature.
6.4 Calibration blank (Cal Blk) and preparation blank (PB) solution

Add approximately 15 ml laboratory water to a 50 ml volumetric flask. Dispense (using bottle dispenser

or pipet) 5 ml nitric acid (5.2) into the same volumetric flask. Pipet (using calibrated digital pipet) 0,5 ml

of the ISTD stock and 0,5 ml of methanol (5.1). Dilute to volume with laboratory water. This solution

serves as both the calibration blank (Cal Blk) and preparation blank (PB). Use same lots of reagent for

samples. Expiration: 2 days. Store at room temperature.

2) SRM 1849a is the trade name of a product supplied by the National Institute of Standards and Technology (NIST).

This information is given for the convenience of users of this document and does not constitute an endorsement by

ISO or IDF of the product named. Equivalent products may be used if they can be shown to lead to the same results.

© ISO and IDF 2018 – All rights reserved 3
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SIST EN ISO 21424:2020
ISO 21424:2018(E)
IDF 243:2018(E)
6.5 Calibration standard solution set

Prepare Cal Blk, Cal Std 1, Cal Std 2, Cal Std 3, and Cal Std 4 standard solutions by pipetting with a

volumetric pipet (7.10) 0 ml, 1,00 ml, 5,00 ml, 20,00 ml and 40,00 ml, respectively, of the multi-element

standard stock solution into separate 50 ml volumetric flasks or sample tubes. Add 0,5 ml of the ISTD

with a volumetric pipet (7.10) or digital pipet calibrated at point-of-use to 0,8 % accuracy), 5 ml (using

repipetter or PTFE bottle dispenser) of nitric acid (5.2), and 0,5 ml of methanol (5.1) to each flask. Fill

the flasks to volume with laboratory water. Expiration: 2 days. Store at room temperature. The analyte

and ISTD concentrations in the calibration standard solutions are shown in Table 2.

Table 2 — Concentrations of standards and ISTD in calibration standard solutions
Calibration Calibration Calibration Calibration Calibration
ISTD
Blank Standard 1 Standard 2 Standard 3 Standard 4
Na, mg/l 0 0,500 2,50 10,0 20,0 Ge
Mg, mg/l 0 0,200 1,00 4,00 8,00 Ge
P, mg/l 0 0,500 2,50 10,0 20,0 Ge
K, mg/l 0 1,00 5,00 20,0 40,0 Ge
Ca, mg/l 0 1,00 5,00 20,0 40,0 Ge
Cr, µg/l 0 0,800 4,00 16,0 32,0 Ge
Mn, mg/l 0 0,005 00 0,025 0 0,100 0,200 Ge
Fe, mg/l 0 0,050 0 0,250 1,00 2,00 Ge
Cu, mg/l 0 0,005 00 0,025 0 0,100 0,200 Ge
Zn, mg/l 0 0,020 0 0,100 0,400 0,800 Ge
Se, µg/l 0 0,400 2,00 8,00 16,0 Te
Mo, µg/l 0 0,800 4,00 16,0 32,0 Ge
Internal standard (ISTD) added at 50 µg/l.
7 Apparatus
7.1 Inductively coupled plasma mass spectrometer.

It shall contain a quartz spray chamber, quartz torch, Ni/Pt sample cone, Ni/Pt skimmer cone,

autosampler and printer. The ICP mass spectrometer shall have collision reaction cells (CRCs). In two

separate interlaboratory studies, four different model ICP-MS instruments from three major vendors

[1][2]
delivered equivalent performance .
7.2 Microwave oven.

Commercial microwave designed for laboratory use at 0 °C to 300 °C, with closed vessel system and

controlled temperature ramping capability. Use vessels recommended by the manufacturer. In the

[1]

interlaboratory study, five different microwave designs delivered equivalent performance .

CAUTION — Microwave operation involves hot pressurized acid solution. Use appropriate face

protection and laboratory clothing.
7.3 Hydrogen generator, recommended for better Se sensitivity.

On-demand supply of > 99,999 % pure hydrogen at > 150 ml/min. Alternatively, a high pressure cylinder

(99,999 % purity) may be used.
7.4 Magnetic stir plate and PTFE-coated magnetic stir bars.
7.5 Analytical balance.
4 © ISO and IDF 2018 – All rights reserved
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SIST EN ISO 21424:2020
ISO 21424:2018(E)
IDF 243:2018(E)
7.6 Fume hood.
7.7 Common laboratory glassware/plasticware.
7.8 Repipetter, 50 ml.
7.9 Bottle top dispenser, PTFE, adjustable volume 0,5 ml to 5 ml.
[3]
7.10 Volumetric pipets, Class A in accordance with ISO 1042 , assorted sizes.

7.11 Digital pipets, 1 ml, adjustable, to deliver 500 µl with accuracy tolerance of better than 0,8 % and

precision of better than 0,2 % relative standard deviation (RSD).
8 Preparation of test sample
Make a single sample preparation to determine all 12 elements.
[4]

NOTE ISO 20649 | IDF 235 for Cr, Mo, and Se requires duplicate samples to be taken and their results

averaged, but comparable reproducibility was obtained in a second interlaboratory study with the 12-element

[1]
method described in this document in which only a single sample was analysed .

In sample vessels, weigh test portions to the nearest 0,000 1 g. For liquid products (including milk),

the test portion size is 1,0 g. Liquid samples shall be thoroughly shaken (5 min in a mechan

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