BS ISO 20620:2021 pdf download – Fertilizers and soil conditioners — Determination of total nitrogen by combustion 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 14820-2:2016, Fertilizers and liming materials — Sampling and sample preparation — Part 2:Sample preparation No terms and definitions are listed in this document. ISO and IEC maintain terminology 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/ 4 Principle The sample is combusted at a high temperature of 900 °C or above in the presence of oxygen. Following the reduction of formed nitrogen oxides to elemental nitrogen and the removal of any interfering products of combustion, nitrogen is measured with a thermal-conductivity detector. 5 Apparatus 5.1 Automatic nitrogen analyser, based on combustion methods. 5.2 Analytical balance. The accuracy of the balance is a function of the analyser used and the required weighed portions. The resolution should be 0,1 % or better of the weighed portion. 5.3 Auxiliary devices for sample preparation, for example: been obtained for the same sample material when analysed in succession when the sample has been sufficiently prepared. Different types of apparatus are available on the market. Operation and performance criteria should be based on the respective operation manuals. 7.2 Reference curve Perform calibration as required for the specific type of analyser and according to the respective operation manuals (e.g. after replacement of the combustion tube, reagent or similar) by performing measurements as described in 7.4. Weigh in an appropriate amount of standard substances repeatedly as appropriate for the respective types of apparatus to obtain a reference curve. 7.3 Inspection and calibration Use an appropriate standard substance or in-house secondary standard to review the good working order of the apparatus and the reference curve. Preferably, a certified standard should be used. Frequency of inspection is a function of the analyser used. Use of quality control charts is also advised to monitor trends in instrument performance. 7.4 Measurement Weigh a portion of the sample in a suitable holder as specified for the type of nitrogen analyser used. The amount should be such that the absolute amount...
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