ISO 23637:2021

FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 23637
ISO/TC 34/SC 4
Cereals — Determination of cadmium
Secretariat: SAC
content by graphite furnace atomic
Voting begins on:
2021-09-29 absorption spectrometry with diluted
nitric acid extraction
Voting terminates on:
2021-11-24
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ISO/FDIS 23637:2021(E)
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ISO/FDIS 23637:2021(E)
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ISO/FDIS 23637:2021(E)
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Reagents and solution .1
6 Apparatus and equipment . 2
7 Procedure .2
7.1 General . 2
7.2 Sampling . 2
7.3 Preparation of the test samples. 3
7.4 Extraction . 3
7.4.1 General . 3
7.4.2 Reagent blank . 3
7.5 Sample analysis . . 3
7.5.1 General . 3
7.5.2 Operating conditions . 3
7.5.3 Calibration graph . 3
7.5.4 Determination . 4
7.5.5 Application of matrix-modifier . 4
7.6 Analytical quality control . 4
8 Calculation . 4
9 Precision . 4
9.1 General . 4
9.2 Repeatability . 5
9.3 Reproducibility . 5
9.4 Critical difference, D . 5
9.4.1 General . 5
9.4.2 Comparison of two groups of measurements in one laboratory . 5
9.4.3 Comparison of two groups of measurements in two laboratories . 5
10 Test report . 6
Annex A (informative) Results of interlaboratory tests . 7
Bibliography .10
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© ISO 2021 – All rights reserved

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ISO/FDIS 23637:2021(E)
Foreword
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different types of ISO documents should be noted. This document was drafted in accordance with the
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This document was prepared by Technical Committee ISO/TC 34, Food products, Subcommittee SC 4,
Cereals and pulses.
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.
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FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 23637:2021(E)
Cereals — Determination of cadmium content by graphite
furnace atomic absorption spectrometry with diluted
nitric acid extraction
1 Scope
This document specifies a method for the determination of cadmium (Cd) in cereals.
It is applicable to rice, brown rice, wheat and maize by graphite furnace atomic absorption spectrometry
(GFAAS) after extraction with diluted nitric acid (HNO ). The limit of quantification is 0,002 mg/kg; it
3
is approximate and dependent on the sample matrix as well as on the instrument conditions.
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
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
— IEC Electropedia: available at https:// www .electropedia .org/
4 Principle
Cadmium (Cd) is extracted from the cereals using diluted nitric acid and then determined by graphite
furnace atomic absorption spectrometry (GFAAS).
5 Reagents and solution
During the analysis, unless otherwise stated, use only reagents of recognized analytical purity and only
water of grade 1 in accordance with ISO 3696.
5.1 Nitric acid (HNO ), not less than 65 % (mass fraction) of approximately ρ(HNO ) = 1,4 g/ml.
3 3
5.2 Nitric acid solution (0,5 %, volume fraction), mix 0,5 volume parts of HNO (5.1) and 100 ml
3
volume parts of water.
5.3 Nitric acid solution (50 %, volume fraction), mix HNO (5.1) and water in equal volume.
3
5.4 Palladium nitrate hydrate (Pd(NO ) , 99,9 % purity).
3 2
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ISO/FDIS 23637:2021(E)
5.5 Palladium nitrate (Pd(NO ) ) solution, c(Pd(NO ) ) = 100 mg/l, dissolve 0,1 g Pd(NO ) (5.4)
3 2 3 2 3 2
and dilute to 1 000 ml with HNO (5.2). Other matrix modifiers may also be used if their applicability is
3
proven.
5.6 Cadmium standard solution.
5.6.1 Cadmium stock standard solution, with a cadmium mass concentration of 1 000 mg/l or
500 mg/l.
5.6.2 Cadmium standard solution, stepwise dilute cadmium stock solution (5.6.1) into concentration
of 2 μg /l with HNO (5.2).
3
5.6.3 Cadmium calibration solutions, pipette suitable volumes of cadmium standard solution
(5.6.2), e.g. 2 ml, 4 ml, 6 ml, 8 ml and 10 ml, into, for example, a 10 ml volumetric flask (6.7) and dilute
to the mark with diluted nitric acid solution (5.2). The concentration of cadmium in the calibration
solutions should cover the range of 0,4 μg /l to 2,0 μg/l.
6 Apparatus and equipment
All glassware shall be cleaned several times with water after being soaked overnight with HNO (5.3)
3
and rinsed three times with ultrapure water before use.
6.1 Grinding mill, grinder suitable to obtain the particle sizes of 0,25 mm and 0,40 mm.
6.2 Atomic absorption spectrometer, equipped with graphite furnace, autosampler and background
correction capability, such as Zeeman background correction.
6.3 Cadmium hollow cathode lamp, with wavelength 228,8 nm and stable lamp energy.
6.4 Centrifuge, with positions for 10 ml centrifuge tubes and 3 000 r/min of speed.
6.5 Analytical balance, accurate to 1 mg.
6.6 Sieve, with aperture sizes of 0,25 mm and 0,40 mm.
6.7 Plastic centrifuge tube, 10 ml.
7 Procedure
7.1 General
The measurement should be performed as soon as possible after extraction.
7.2 Sampling
A representative sample should be sent to the laboratory. It should not h
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