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1、Ei - INTERNATIONAL STANDARD INTERNATIONAL ORGANIZATION FOR STANDARDIZATIONWlEIKJjYHAPO,QHAR OPrAHM3AL - copper( II) sulphate, anhydrous : 3 g. 5.5 Sulphuric acid, approximately 0,02 N or 0,l N - Standard volumetric Solution, 5.6 Colorimetric indicator, prepared by mixing 2 Parts by volume of a cold
2、saturated Solution of neutral methyl red in 50 % (WV) ethanol with 1 part by volume of a 0,25 g/l Solution of methylene blue in 50 % (VW) ethanol. Store the indicator in a brown glass bottle. 6 APPARATUS Usual laboratory equipment, and in particular 6.1 Kjeldahl flask, of suitable capacity, usually
3、500 to 800 ml, preferably with a ground glass joint, and provided with a pear-shaped glass bulb fitting loosely in the top of the neck of the flask. 1) For products whose presumed nitrogen content is less than 0,025 % (m/m), see ISO 5378. 2) See ISO 1871. 3) For anticipated low nitrogen contents, a
4、less concentrated Solution may be needed in Order to obtain greater accuracy. 4) See ISO 1871, sub-clause 5.2, 1 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/27/2007 01:09:02 MDTNo re
5、production or networking permitted without license from IHS -,-,- ISO 31884978 (E) 6.2 Digestion stand, on which the Kjeldahl flask (6.1) tan be heated in an inclined Position in such a way that heat is applied only to that part of the flask wall which is below the liquid level at all stages. 6.3 Di
6、stillation or steam distillation apparatus, with a 200 ml graduated dropping funnel and an efficient splash head, the latter connecting the Kjeldahl flask (6.1) to the condenser. Any apparatus that satisfies the control tests given in ISO 1871 is permitted. 6.4 Burette, 25 ml with 0,05 ml graduation
7、s, or 10 ml with 0,Ol ml graduations. 6.5 Mechanical grinder or mortar. 6.6 Sieve, with nominal mesh openings of 0,6 mm, complying with the requirements of ISO 565. 6.7 Analytical balance. 7 PROCEDURE 7.1 Preparation of the test Sample Mix the Sample thoroughly and rapidly by shaking or stirring wit
8、h a spatula in the Sample container? If the Sample Container is too small for this purpose, transfer the entire Sample to another predried Container of a suitable size to facilitate mixing. lt may be necessary to grind the Sample, in which case it shall all pass through the sieve (6.6) without leavi
9、ng any residue. 7.2 Test Portion Weigh, to the nearest 0,001 g, up to IO g (mass m) of the test Sample (7.1), according to the presumed nitrogen content, and transfer to the predried Kjeldahl flask (6.1), taking care that none of the product adheres to the inner wall of the neck of the flask. In the
10、 case of a viscous liquid or a product in Paste form, the test Portion may be weighed in a small glass Container or on a sheet of aluminium, Paper or plastics which does not yield nitrogen, or whose nitrogen content is known, and which is left in the flask. In the case of a Container which yields ni
11、trogen, this should be taken into account in the blank test (7.6). 7.3 Destruction of organic matter -. Add 10 g of the compound catalyst (5.4) and, using a suitable measuring cylinder, add- the appropriate. volume, in millilitres, of the concentrated sulphuric acid (5.1), calculated by the formula
12、20 + 4 m, in such a way that the acid rinses the inner wall of the neck of the flask. Mix the contents of the flask by swirling the flask gently until the mixture is free from lumps and the test Portion is completely wetted. In Order to avoid super-heating, add a boiling aid (for example glass beads
13、). Insert the pear-shaped glass bulb (see 6.1) in the neck of the flask and place it in an inclined Position on the digestion stand (6.2). Heat with care until the liquid in the flask boils gently. Continue to heat for 1 h after the liquid becomes clear. In the case of digestion apparatus heated by
14、gas, ensure that the flame does not extend beyond the part of the flask filled with liquid, in Order to avoid loss of nitrogen. 7.4 Distillation and titration Allow the contents of the flask to cool and rinse the pear-shaped glass bu!b and the inner neck of the flask with a few millilitres of water,
15、 allowing the rinsings to run into the flask. Add, with care, between 50 and 200 ml of water (according to the apparatus used), whilst swirling the contents of the flask. Connect the flask to the distillation or steam distillation apparatus (6.3), previously freed from ammonia by steaming. Adjust th
16、e Iower end of the condenser so that it just touches the bottom of a 500 ml conical flask containing a known volume (varying between 25 and 50 ml) of the boric acid Solution (5.3) and 3 to 5 drops of the titration indicator (5.6). Render the digestion liquid alkaline by slowly adding, through the gr
17、aduated separating funnel (See 6.3) placed in the neck of the flask, between 150 and 200 ml of the sodium hydroxide Solution (5.2), ensuring that the stem of the funnel does not become empty. Mix weil, then turn on the condenser water and Start heating; the ammonia then begins to be carried over. Th
18、e indicator contained in the flask turns immediately to its alkaline colour. During distillation, ensure that steam generation is kept constant. Distillation is complete when 200 ml of liquid have been collected in 20 to 30 min. Turn off the heat and lower the conical flask. Allow the condenser to d
19、rip for a few minutes into the flask and rinse the tip of the condenser with water, collecting the rinsings in the conical flask. The liquid contained in the flask should be green. Titrate the contents of the flask with either 0,02 N or 0,l N sulphuric acid Solution (5.5), using a IO ml or 25 ml bur
20、ette (6.4) as appropriate, until the colour of the contents turns reddish violet. 7.5 Number of determinations Carry out two determinations on the same test Sample (7.1). 1) In the case of glucose syrup, remove the surface layer (about 5 mm) before mixing. 2 Copyright International Organization for
21、Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/27/2007 01:09:02 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 3188-1978 (E) 7.6 Blank test Carry out a blank test on the reagents only. If the tes
22、t por- tion has been weighed in a Container which yields nitrogen (see 7.2), carry out the blank test using an identical Container. V, is the volume, in millilitres, of the sulphuric acid Solution used in the blank test (7.6); V, is the volume, in millilitres, of the sulphuric acid Solution used in
23、the determination (7.4); 7.7 Check tests Carry out the check tests specified in ISO 1871. 8 EXPRESSION OF RESULTS The nitrogen content is given, as a percentage by mass, by the formula 100 0,01401 xTx(V, -V,) x- m 1,401 T(V, - V,) = m where The test report shall indicate the method used and the resu
24、lts obtained. lt shall also mention all operating conditions that are not specified in this International Standard, or are regarded as optional, as weil as any circumstances that may have influenced the results. T is the normality sf the sulphuric acid Solution (5.5) The test report shall include al
25、l used in the two titrations; complete identification of the Sample. m is the mass, in grams, of the test Portion (7.2). Express the result as the arithmetic mean of the two determinations if the volumes of the sulphuric acid Solution used do not differ by more than 0,l ml. Otherwise, repeat the det
26、erminations on the same test Sample. 9 TEST REPORT details required for Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/27/2007 01:09:02 MDTNo reproduction or networking permitted withou
27、t license from IHS -,-,- This page intentionally left blank Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/27/2007 01:09:02 MDTNo reproduction or networking permitted without license fr
28、om IHS -,-,- This page intentionally left blank Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/27/2007 01:09:02 MDTNo reproduction or networking permitted without license from IHS -,-,- This page intentionally left blank Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/27/2007 01:09:02 MDTNo reproduction or networking permitted without license from IHS -,-,-