BS ISO 20921:2019 pdf download.Textiles — Determination of stable nitrogen isotope ratio in cotton fibres.
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.
8.2 Natural 15 N abundance analysis
8.2.1 Instrumentation Continuous-type EA-IRMS is used for the determination of 15 N in a gas sample that is introduced into IRMS through the elemental analyser (EA). The EA-IRMS is equipped with an ion-source for ionizing the incoming sample gases, a permanent magnet and an electromagnet for steering the ions, and the Faraday cups collecting N 2 gas travelling with the different mass-to-charge ratios. The isotopic nitrogen composition of the sample gas is compared to that of standard gas (atmospheric N 2 ) during each sample run, and the resulting sample’s δ 15 N value is calculated using Formula (1).
8.2.2 General analytical procedure a) Place packed tin capsules continuously into a carousel (auto-sampler unit) for automatic analysis. b) Drop packed tin capsules sequentially into the oxidation reactor (980 approximately 1 080) °C and then combust them with excess O 2 to complete oxidation. c) Perform EA-IRMS measurements and check the isotopic nitrogen composition of gas relative to that of the standard gas (atmospheric N 2 ) from a compressed cylinder with known or predetermined isotope ratio at every measurement. d) During each run, check the precision of isotope analysis with an internationally accepted reference material. e) Calculate and report the final isotopic value (δ 15 N) relative to that of atmospheric N 2 .
9 Precision
The accuracy and reproducibility of the analytical procedure can be checked by reference materials.
10 Test report
The test report shall at least include the following items:
a) a reference to this document, i.e. ISO 20921:2019;
b) sample number;
c) cotton-δ 15 N and nitrogen content;
d) mean and standard deviation of the reference material.BS ISO 20921 pdf download.