ISO INTERNATIONAL STANDARD 6654 First edition 1991-03-15 ANsi Intermat Doc Sec Animal feeding stuffs -- Determination of urea content Aliments des animaux -- Determination de la teneur en uree Referencenumber ISO 6654:1991(E) Not for Resale ISO 6654:1991(E) Foreword IsO (the International Organization for Standardization) is a worldwide federation of national standards bodies (isO member bodies). The work of preparing International Standards is normally carried out through iso technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. Internationat organizations, govern- mental and non-governmental, in liaison with isO, also take part in the work. Iso collaborates closely with the International Electrotechnical Commission (lEC) on all matters of'electrotechnical standardization. Draft International Standards adopted by the technical committees are national Standard requires approval by at least 75 % of the member bodies casting a vote. International Standard IsO 6654 was prepared by Technical Committee IsO/TC 34, Agricultural food products. IsO 1991 or by any means, electronic or mechanlcal, including photocopying and microfilm, without permission in writing from the publlsher. International Organization for Standardization CasePostale 56.CH-1211Genéve20·Switzeriand Printed in Switzerland ii Copyright International Organization for Standardization NotforResa ISO 6654:1991(E) INTERNATIONAL STANDARD Animal feeding stuffs --. Determination of urea content Scope Reagents 5 This International Standard specifies a spectro- All reagents shall be of recognized analytical grade. metric method for the determination of the urea The water used shall be distilled water or water of content of animal feeding stuffs. at least equivalent purity. 5.1 Actlvated carbon, which does not adsorb urea. 2 Normative reference 5.2 4-dlmethyl-amino-benzaidehyde (4-DMAB), sol- ution prepared as follows. The following standard contains provisions which, through reference in this text, constitute provisions Dissolve 1,6 g of 4-DMAB in 100 ml of 96 % (V/V) of this International Standard. At the time of publi- ethanol, add 10 ml of concentrated hydrochloric acid cation, the edition indicated was valid. All standards (p20 = 1,19 g/ml) and mix. are subject to revision, and parties to agreements based on this International Standard are encour- This solution may be stored for a maximum of aged to investigate the possibility of applying the 2 weeks. most recent edition of the standard indicated below. Members of IEC and ISO maintain registers of cur- 5.3 Carrez I solution. rently valid international Standards. Dissolve in water 24 g of zinc acetate dihydrate 1so 6498:1983, Animal feeding stuffs -- Preparation [Zn(CH,COO)2:2H,O] and 3 g of glacial acetic acid. of test samples. Make up to 100 mi with water and mix. 5.4 Carrez Il solution. 3 Definition Dissolve in water 10,6 g of potassium hexa- cyanoferrate(ll) trihydrate (potassium ferrocyanide For the purposes of this International Standard, the trihydrate) (K4[Fe(CN)]-3H,O). Make up to 100 ml following definition applies. with water and mix. urea content: The mass fraction of substances de- 5.5 Urea, standard solution corresponding to 1 g termined using the procedure specified in this Inter- of urea per litre. national Standard. It is expressed as a percentage by mass. Apparatus 6 Usuat laboratory apparatus and, in particular, the following. Principle 4 6.1 Rotary shaker, capable of being operated at a Suspension in water of the test portion in the pres- rotational frequency of about 30 min-1 to 40 min-1. ence of a decolorant. Stirring of the suspension, thefiltrate thenfiltration. Additionto (4-DMAB) 4-dimethyl-amino-benzaldehyde 6.2 Spectrometer, suitable and for measuring measurement at 420nm wavelength of 420 nm, and spectrometric of the absorbance a absorbance of the solution thus obtained. equipped