BS ISO 20921 pdf free download

BS ISO 20921-2019 pdf free download.Textiles – Determination of stable nitrogen isotope ratio in cotton fibres.
7 Preparation
7.1 Sampling of test specimen
Cotton fibre samples are taken from fabricated textiles and prepared as test specimens.
7.2 Pretreatment of test specimen
Cotton fibre samples are immersed with 100 ml distilled waters for 3 mm and oven-dried at 80 °C for
24 h. Dried samples are chopped, homogeneously ground into a very fine powder using a ball-mill and
used in triplicate for ISN analysis.
8 Test procedure
8.1 Weighing of aliquot
8.1.1 Determination of weighing amount needed
Each finely ground test specimen is weighed with a tin capsule (or can) using a microbalance (readability: at least 1 pg).
Provide between (100 -4 200) pg of nitrogen for each aliquot of the test specimen to meet EA-IRMS detection limits.
However, the minimum amount needed for accurate and precise analysis of &5N is typically about 100 pg of nitrogen.
A simple formula to determine the amount of an aliquot to weigh for the EA-IRMS measurements is given as Formula (1):
where
ma is the dry mass of an aliquot needed for EA-IRMS measurements (mg); mN is the dry mass of nitrogen needed (pg);
Wp is the mass fraction percentage of nitrogen in the test specimen (%).
For example, if the test specimen has 1 % nitrogen and 100 pg of nitrogen for the IRMS measurements is provided, then an aliquot that weighs 10 mg shall be prepared. For samples with unknown % nitrogen, it is recommended to determine the % nitrogen of the test specimen before making isotope analysis.
In general, the optimal mass of an aliquot for the IRMS measurements is 33 mg to 56 mg for cotton products (cotton fibres in yarns or textiles), since cotton products typically contain between 0,18 and 0,30) % nitrogen.
8.1.2 General weighing procedure
a) Clean the plate and tools using lint-free papers or equivalents moistened with alcohol or acetone.
b) Clean the microbalance with a brush.
c) Turn on the microbalance and wait for the microbalance to stabilize.
d) Use the tweezer to grab an empty tin capsule by the edge and place on top of the balance.
e) Push the TARE button to re-zero the mass.
1] Carefullyscoopout a smallaliquot oftest specimen into the tin capsule byadding in small increments.
g) Remove the tin capsule from the microbalance.
Ii) Fold the tin capsules several times into a small cube or sphere with the tweezers to make sure the openings are closed.
i) Place the cube into your sample tray such as 96-well tray for delivery or shipping.
j) Clean the spatula between each weighing to avoid contamination.
When finished, clean the microbalance and tools before turning off the microbalance.
8.2 Natural 15N abundance analysis
8.2.1 Instrumentation
Continuous-type EA-IRMS is used for the determination of 15N 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 N2 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 N2) during each sample run, and the resulting sample’s 6’5N 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 02 to complete oxidation.
c) Perform EA-IRMS measurements and check the isotopic nitrogen composition of gas relative to that of the standard gas (atmospheric N2) 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 (b’5N) relative to that of atmospheric N2.BS ISO 20921 pdf download.