Coal - Determination of nitrogen - Semi-micro Kjeldahl method. Kol - Bestämning av kvävehalt - Semimicrometod enligt Kjeldahl

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1 Coal - Determination of nitrogen - Semi-micro Kjeldahl method Kol - Bestämning av kvävehalt - Semimicrometod enligt Kjeldahl The International Standard ISO 333:1996 has the status of a Swedish Standard. This document contains the official English version of ISO 333:1996. Swedish Standards corresponding to documents referred to in this Standard are listed in Catalogue of Swedish Standards, annually issued by SIS. The Catalogue lists, with reference number and year of Swedish approval, International and European Standards approved as Swedish Standards as well as other Swedish Standards. Den internationell standarden ISO 333:1996 gäller som svensk standard. Detta dokument innehåller den officiella engelska versionen av ISO 333:1996. Motsvarigheten och aktualiteten i svensk standard till de publikationer som omnämns i denna standard framgår av Katalog över svensk standard, som årligen ges ut av SIS. I katalogen redovisas internationellaoch europeiska standarder som fastställts som svenska standarder och övriga gällande svenska standarder.

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3 Coal Determination of nitrogen Semi-micro Kjeldahl method 1 Scope This International Standard specifies a method of determining the nitrogen content of hard coal, brown coal and lignite by the semi-micro Kjeldahl method. 2 Normative references The following standards contain provisions which, through reference in this text, constitute provisions of this International Standard. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. Members of IEC and ISO maintain registers of currently valid International Standards. ISO 331:1983, Coal Determination of moisture in the analysis sample Direct gravimetric method. ISO 1015:1992, Brown coals and lignites Determination of moisture content Direct volumetric method. ISO 1170:1977, Coal and coke Calculation of analyses to different bases. ISO 1988:1975, Hard coal Sampling. ISO 5068:1983, Brown coals and lignites Determination of moisture content Indirect gravimetric method. ISO :1983, Brown coals and /ignites Principles of sampling Part 2: Sample preparation for determination of moisture content and for general analysis. 3 Principle A known mass of the sample is heated with concentrated sulfuric acid in the presence of a mixed catalyst to convert the nitrogen into ammonium sulfate, from which the ammonia, released by steam distillation from alkaline solution, is absorbed in boric acid and determined by titration with sulfuric acid. 4 Reagents WARNING Care should be exercised when handling reagents, many of which are toxic and corrosive. During the analysis, unless otherwise stated, use only reagents of recognized analytical grade and only distilled water, or water of equivalent purity. 4.1 Mixed catalyst, containing by mass: 90 parts of anhydrous potassium sulfate; 2 parts of selenium powder; 5 parts of vanadium pentoxide. Grind the above reagents in a mortar and mix them thoroughly. 4.2 Sucrose. 4.3 Sulfuric acid, concentrated, approximately 98 % (m/m). 4.4 Boric acid solution, saturated. Dissolve 60 g of boric acid in 1 Iitre of hot water, cool and allow to stand for 3 d before decanting the clear solution.

4 4.5 Sodium hydroxide, 400 g/1 solution. Dissolve 400 g of sodium hydroxide in water, dilute to 1 Iitre and mix thoroughly. NOTE 1 It is advisable to stir the mixture frequently while dissolving in order to dissipate the heat of solution. 4.6 Sulfuric acid, standard volumetric solution, C(H 2 SO 4 ) = 0,005 mol/ Mixed indicator solution Solution A. Dissolve 0,125 g of 2-(4dimethylaminophenylazo) benzoic acid, sodium salt (methyl red) in 60 ml of ethanol and dilute to 100 ml with water Solution B. Dissolve, 0,083 g of 3,7-bis(dimethylamino) phenothiazin-5-ylium chloride (methylene blue) in 100 ml of water. Store in a dark bottle Mixed solution. Mix equal volumes of solution A and solution B. Store in a dark bottle. Discard the mixed solution after 1 week. 5 Apparatus 5.1 Analytical balance, capable of weighing to the nearest 0,1 mg. 5.2 Graduated glassware, conforming to the requirements for Grade A in the International Standards prepared by lso/tc 48, Laboratory glassware and related apparatus. 5.3 Digestion flask, of borosilicate glass, of bulb capacity 50 ml, preferably pistol-shaped, with a light blown bulb of borosilicate glass which is a loose fit in the neck of the flask, to prevent loss of acid. 5.4 Distillation apparatus, comprising a suitable water/steam distillation flask of borosilicate glass, fitted with a splash head to arrest the passage of any entrained sodium hydroxide from the distillation flask and a condenser. An example of a suitable distillation apparatus is illustrated in figure Receiver, a wide-necked, flat-bottomed conical flask, of capacity 100 ml. 5.6 Heating apparatus, capable of heating one or more digestion flasks while supporting it at an angle of 35 from the vertical. An electric heating unit or a gas microburner may be used. An example of a suitable electric heating unit, capable of heating several flasks simultaneously, is shown in figure 2. 6 Preparation of the test sample Prepare the test sample for general analysis in accordance with ISO 1988, or ISO , as appropriate. Ensure that the moisture content of the sample is in equilibrium with the laboratory atmosphere, exposing it, if necessary, in a thin layer for the minimum time required to achieve equilibrium. Before commencing the determination, thoroughly mix the test sample for at least 1 min, preferably by mechanical means. If the results are to be calculated other than on an "air-dried" basis (see clause 9), after weighing the test portion, determine the moisture content using a further portion of the test sample by the method described in ISO 331, ISO 1015 or ISO 5068, as appropriate. 7 Procedure 7.1 Digestion Weigh, to the nearest 0,1 mg, about 0,1 g of the test sample and transfer it quantitatively to the digestion flask (5.3). Add 2 g of the mixed catalyst (4.1) and shake to mix. Add 4 ml of the sulfuric acid (4.3) and mix again. Switch on the electric heating unit (5.6) at approximately half load for 20 min, and then at maximum load for 10 min before placing the flask on the unit. Alternatively, with gas heating, place the digestion flask over the fully aerated flame of a microburner and adjust the flame so that clearing of the solution is effected in 7 min to 10 min, for example by using a flame 50 mm high with the lowest part of the bulb of the flask 40 mm above the top of the burner. After the solution become clear (see note 2), continue boiling for a further 20 min, in order to complete the conversion of the nitrogenous compounds into ammonium sulfate.

5 Figure 1 Suitable distillation apparatus

6 Figure 2 Electric digestion unit suitable for semi-micro Kjeldahl method

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