ISO 20921:2019

INTERNATIONAL ISO
STANDARD 20921
First edition
2019-02
Textiles — Determination of stable
nitrogen isotope ratio in cotton fibres
Textiles — Détermination du rapport isotopique stable de l'azote
dans les fibres de coton
Reference number
©
ISO 2019
© ISO 2019
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ii © ISO 2019 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Reagent . 2
6 Apparatus . 2
7 Preparation . 3
7.1 Sampling of test specimen . 3
7.2 Pre-treatment of test specimen . 3
8 Test procedure . 3
8.1 Weighing of aliquot . 3
8.1.1 Determination of weighing amount needed . 3
8.1.2 General weighing procedure . 3
8.2 Natural N abundance analysis . 4
8.2.1 Instrumentation . 4
8.2.2 General analytical procedure . 4
9 Precision . 5
10 Test report . 5
Annex A (normative) Identification procedure of organic raw cotton fibres by using stable
nitrogen isotope ratios . 6
Annex B (informative) Analytical results of cotton fibres of various origin and process stage .8
Bibliography .10
Foreword
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iv © ISO 2019 – All rights reserved

Introduction
Nitrogen (N) is the most essential element for cotton fibre production, since cotton crops require large
amounts of N to sustain their growth and productivity. For this purpose, considerable amounts of
nitrogen are applied to the soil as chemical fertilizers (e.g. urea) or organic fertilizers (e.g. composted
manure).
The nitrogen applied in the form of a chemical fertilizer or a composted manure is absorbed from the
soil to cotton crops through their root systems during cultivation, leaving a fertilizer-specific nitrogen
isotopic signature in cotton tissues (particularly in cotton fibres). The inerasable nitrogen isotopic
fingerprint engraved in cotton fibres remains unchanged during manufacturing of yarns, textiles and
fabrics.
This document employs the principle of nitrogen isotope discrimination that fractionates against N
15 15
(heavier nitrogen isotope), resulting in N-enriched reactants and N-depleted products. In general,
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composted manure has a much higher δ N (natural N abundance, defined hereinafter) than chemical
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fertilizer due to faster NH (ammonia) volatilization of the lighter nitrogen isotope ( N) than N during
the composting process. In contrast, chemical fertilizers (e.g. urea) are produced from the atmospheric
N via the Haber-Bosch process, resulting in low δ N values close to atmospheric N , which means that
2 2
similar isotopic nitrogen compositions of chemical fertilizers to the atmospheric N .
Organic farming strictly bans the use of genetically modified crops (GMO), synthetic pesticides, and
chemical fertilizers. Therefore, the use of chemical fertilizer during organic cotton production can be
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detected by determining δ N of cotton fibres, since the difference in δ N values between the two
isotopically different nitrogen inputs (chemical vs. organic fertilizers) leaves a fertilizer-specific
isotopic fingerprint in cotton fibres that can thereafter provide a forensic evidence for organic cotton
fibre production.
INTERNATIONAL STANDARD ISO 20921:2019(E)
Textiles — Determination of stable nitrogen isotope ratio
in cotton fibres
1 Scope
This document specifies the determination of the ratio of nitrogen isotopes in cotton fibres that are
used for textile production. It applies not only to cotton textiles but also to raw cotton taken from
cotton fields.
2 Normative references
There are no normative references in this document.
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
stable isotope
atom whose nucleus contains the same number of protons but a different number of neutrons
Note 1 to entry: Stable isotopes do not decay into other elements, while radioactive isotopes are unstable and
will decay into other elements.
3.2
isotope-ratio mass spectrometry
IRSM
specialization of mass spectrometry, in which mass spectrometric methods are used to measure the
relative abundance of isotopes in given sample
Note 1 to entry: The analysis of isotopes is normally related to measuring isotopic variations caused by mass-
dependent isotopic fractionation in natural systems.
3.3
isotopic fractionation
isotopic discrimination
process that affect the relative abundance of isotopes
Note 1 to entry: Normally, the focus is on stable isotopes (3.1) of the same element. Isotopic fractionation in the
natural environment can be measured by isotope analysis, using isotope-ratio mass spectrometry, to separate
different element isotopes on the basis of their mass-to-charge ratios.
Note 2 to entry: Both heavy and light stable isotopes participate freely in biochemical reactions and in
geochemical processes, but the rate at which heavy and light stable isotopes react differs. As a result, the lighter
isotopes react faster than the heavier isotopes leading to isotopic fractionation between reactant and product in
the reactions.
3.4
natural N abundance
relative amount of the isotopes of nitrogen, as it occurs in nature
Note 1 to entry: Natural N abundance is expressed in parts per thousand (‰, per mil) deviations from the
atmospheric N (a standard).
4 Principle
Isotope-ratio mass spectrometry (IRMS) measures the relative abundance of stable isotopes (e.g. N
and N for nitrogen) in a cotton fibre sample. The abundance of stable isotopes varies according to
physical, physiological and biochemical isotopic fractionation processes. Consequently, variations in
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the isotopic ratio of nitrogen (i.e. N/ N) can be used both as fingerprints of the nitrogen source and
to track the fate and transformation of nitrogen-containing compounds.
Nitrogen (N) is the most essential element that can increase the production of cotton fibres that are
used to manufacture cotton yarns, textiles and fabrics. To ensure cotton fibre production, sufficient
amount of nitrogen should be supplied as fertilizers (chemical or organic fertilizers) to the soil to meet
the nitrogen demand for the growth and productivity of cotton crops.
Since most of fertilizer-nitrogen released into the soil is absorbed through root systems, translocated,
and stored in the cotton fibres during cultivation, the isotopic nitrogen composition of the cotton fibre,
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expressed as δ N, reflects the type of fertilizer from which it originated. In general, δ N of chemical
fertilizers is close to 0 ‰, ranging from −3,9 ‰ to +0,5 ‰, while that of composted manure is much
higher, ranging between +15,4 ‰ and +19,4 ‰. Cotton fibres harvested are processed to produce cotton
yarns, textiles, and fabrics. Therefore, it is believed that δ N of a cotton fibre that contains information
about the type of nitrogen fertilizers can serve as an isotopic fingerprint to identify authenticity and
trace origin of cotton products, such as yarns, textiles and fabrics.
An accurate measurement of δ N of an aliquot of the dried cotton fibres can be obtained by using a
continuous-flow type isotope ratio mass spectrometer linked to an elemental analyser (EA-IRMS). An
aliquot of the test sample is washed, dried, ground to very fine powders using a ball-mill, weighed in a
tin capsule on a microbalance, and then analysed for cotton-δ N.
In particular, the use of chemical fertiliz
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