1、BRITISH STANDARD BS 5766-14: 1991 ISO 6654:1991 Methods for Analysis of animal feeding stuffs Part 14: Determination of urea contentBS5766-14:1991 This British Standard, having been prepared under the directionof the Agriculture andFood Standards Policy Committee, was published underthe authority of
2、 the Standards Board and comes into effect on 31July1991 BSI 12-1999 The following BSI references relate to the work on this standard: Committee reference AFC/10 Draft for comment 89/52841 DC ISBN 0 580 19898 7 Committees responsible for this British Standard The preparation of this British Standard
3、 was entrusted by the Agriculture and Food Standards Policy Committee (AFC/-) to Technical Committee AFC/10, upon which the following bodies were represented: Association of Public Analysts Department of Trade and Industry (Laboratory of the Government Chemist) Grain and Feed Trade Association Insti
4、tute of Trading Standards Administration Ministry of Agriculture, Fisheries and Food National Farmers Union Natural Resources Institute Pet Food Manufacturers Association Royal Association of British Dairy Farmers United Kingdom Agricultural Supply Trade Association Ltd United Kingdom Renderers Asso
5、ciation Ltd Amendments issued since publication Amd. No. Date CommentsBS5766-14:1991 BSI 12-1999 i Contents Page Committees responsible Inside front cover National foreword ii 1 Scope 1 2 Normative reference 1 3 Definition 1 4 Principle 1 5 Reagents 1 6 Apparatus 1 7 Sampling 1 8 Preparation of the
6、test sample 1 9 Procedure 1 10 Expression of results 2 11 Test report 2 Publication(s) referred to Inside back coverBS5766-14:1991 ii BSI 12-1999 National foreword This Part of BS5766 has been prepared under the direction of the Agriculture and Food Standards Policy Committee. It is identical with I
7、SO6654:1991 “Animal feeding stuffs Determination of urea content” published by the International Organization for Standardization (ISO), in the preparation of which the United Kingdom played a full part. Cross-reference. The Technical Committee has reviewed the provisions of ISO6498:1983, referred t
8、o in clause8, and has decided that they are acceptable for use in conjunction with this standard. The United Kingdom did not approve ISO6498 but, in the present context, test samples prepared in accordance with either ISO6498 or BS5766 “Methods for analysis of animal feeding stuffs” Part10 “Preparat
9、ion of test samples” are equally acceptable. Additional information. With reference to clause5, water complying with grade3 of BS3978 “Specification for water for laboratory use” is suitable. A British Standard does not purport to include all the necessary provisions of a contract. Users of British
10、Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages1 and 2, an inside back cover and a back cover. T
11、his standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.BS5766-14:1991 BSI 12-1999 1 1 Scope This International Standard specifies a spectrometric method for the determination of the urea con
12、tent of animal feeding stuffs. 2 Normative reference The following standard contains provisions which, through reference in this text, constitute provisions of this International Standard. At the time of publication, the edition indicated was valid. All standards are subject to revision, and parties
13、 to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent edition of the standard indicated below. Members of IEC and ISO maintain registers of currently valid International Standards. ISO 6498:1983, Animal feeding stuffs Preparatio
14、n of test samples. 3 Definition For the purposes of this International Standard, the following definition applies. urea content the mass fraction of substances determined using the procedure specified in this International Standard it is expressed as a percentage by mass 4 Principle Suspension in wa
15、ter of the test portion in the presence of a decolorant. Stirring of the suspension, then filtration. Addition to the filtrate of4-dimethyl-amino-benzaldehyde (4-DMAB) and spectrometric measurement at420nm of the absorbance of the solution thus obtained. 5 Reagents All reagents shall be of recognize
16、d analytical grade. The water used shall be distilled water or water of at least equivalent purity. 5.1 Activated carbon, which does not adsorb urea. 5.2 4-dimethyl-amino-benzaldehyde (4-DMAB), solution prepared as follows. Dissolve1,6g of 4-DMAB in100ml of96% (V/V) ethanol, add10ml of concentrated
17、hydrochloric acid ( 20= 1,19g/ml) and mix. This solution may be stored for a maximum of2weeks. 5.3 Carrez I solution Dissolve in water24g of zinc acetate dihydrate Zn(CH 3 COO) 2 2H 2 O and3g of glacial acetic acid. Make up to100ml with water and mix. 5.4 Carrez II solution Dissolve in water10,6g of
18、 potassium hexacyanoferrate(II) trihydrate (potassium ferrocyanide trihydrate) K 4 Fe(CN) 6 3H 2 O. Make up to100ml with water and mix. 5.5 Urea, standard solution corresponding to1g of urea per litre. 6 Apparatus Usual laboratory apparatus and, in particular, the following. 6.1 Rotary shaker, capab
19、le of being operated at a rotational frequency of about30min 1to40min 1 . 6.2 Spectrometer, suitable for measuring absorbance at a wavelength of420nm, and equipped with cells of thickness10mm. 6.3 Test tubes, 160mm 16mm, fitted with ground glass stoppers. 6.4 Volumetric flasks, of100ml and500ml capa
20、city. 6.5 Water-bath, capable of being controlled at20 C. 7 Sampling Sampling will be the subject of a future International Standard. 8 Preparation of the test sample Prepare the test sample in accordance with ISO6498. 9 Procedure 9.1 Test portion Weigh, to the nearest1mg, about2g of the test sample
21、 (clause8). For urea contents greater than3% (m/m), reduce the test portion to1g or dilute the test solution (see9.2) so that it does not exceed a concentration of50mg of urea per500ml. For low urea contents, the test portion may be increased provided that the filtrate remains clear and colourless.B
22、S5766-14:1991 2 BSI 12-1999 9.2 Preparation of the test solution 9.2.1 Transfer the test portion (9.1) together with1g of the activated carbon (5.1) into a500ml volumetric flask (6.4). Add400ml of water,5ml of the Carrez I solution (5.3) and5ml of the Carrez II solution (5.4). Mix for30min using a r
23、otary shaker(6.1). Make up to the mark with water, mix and filter on a dense, slow, qualitative filter paper. 9.2.2 If the filtrate is coloured, prepare a fresh test solution in accordance with9.2.1 but increase the quantity of activated carbon added. 9.3 Colour development Transfer, by means of a p
24、ipette,5ml of the clear colourless filtrate (9.2) into a test tube (6.3) and add, by means of a pipette,5ml of the 4-DMAB solution(5.2). Mix and leave to stand for15min in a water-bath (6.5) controlled at20 C. 9.4 Blank test Carry out a blank test in parallel with the determination using the same pr
25、ocedure and the same quantities of all reagents, but omitting the test portion. 9.5 Preparation of the calibration graph 9.5.1 Pipette into a series of five100ml volumetric flasks (6.4), 1ml, 2ml, 4ml, 5ml and10ml of the urea standard solution (5.5). Make each flask up to the mark with water. One mi
26、llilitre of the standard solutions contains104g, 204g, 404g, 504g and1004g of urea respectively. 9.5.2 Pipette into a series of five test tubes (6.3) 5ml of each of these solutions (9.5.1) (one dilution per test tube). Add to each test tube, by means of a pipette, 5ml of the 4-DMAB solution (5.2) an
27、d mix. Transfer the solutions to spectrometer cells and measure their absorbances at420nm, using the spectrometer (6.2), against a compensation solution containing5ml of4-DMAB and5ml of water. 9.5.3 Plot the calibration graph, with the absorbance values on the ordinate and the corresponding concentr
28、ations of urea, in micrograms per millilitre, on the abscissa. 9.6 Spectrometric measurement Transfer the solution obtained in9.3 to a spectrometer cell and measure its absorbance at420nm, using the spectrometer (6.2), against the blank test (9.4). NOTE 1If the sample contains simple nitrogenous com
29、pounds, such as amino acids, carry out the measurement of absorbance at a wavelength of435nm. 9.7 Number of determinations Carry out two determinations on test portions taken from the same test sample. 10 Expression of results The urea content, expressed as a percentage by mass, or the sample is equ
30、al to where 11 Test report The test report shall specify the method used and the result obtained. It shall also mention all operating details not specified in this International Standard, or regarded as optional, together with details of any incidents which may have influenced the result. The test r
31、eport shall include all information necessary for the complete identification of the sample. c is the urea content, in micrograms per millilitre, of the filtrate of the test solution, determined from the calibration graph (9.5.3); m is the mass, in grams, of the test portion (9.1). c 20m -BS5766-14:
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