SIST EN ISO 14637:2007

SLOVENSKI STANDARD
SIST EN ISO 14637:2007
01-marec-2007
0OHNR'RORþHYDQMHVHþQLQH(Q]LPVNDPHWRGDQDSRGODJLVSUHPHPEYS+
UHIHUHQþQDPHWRGD,62
Milk - Determination of urea content - Enzymatic method using difference in pH
(Reference method) (ISO 14637:2004)
Milch - Bestimmung des Harnstoffgehaltes - Enzymatisches Verfahren mit pH-Änderung
(Referenzverfahren) (ISO 14637:2004)
Lait - Détermination de la teneur en urée - Méthode enzymatique par mesurage de pH
différentiel (Méthode de référence) (ISO 14637:2004)
Ta slovenski standard je istoveten z: EN ISO 14637:2006
ICS:
67.100.10 0OHNRLQSUHGHODQLPOHþQL Milk and processed milk
SURL]YRGL products
SIST EN ISO 14637:2007 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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EUROPEAN STANDARD
EN ISO 14637
NORME EUROPÉENNE
EUROPÄISCHE NORM
December 2006
ICS 67.100.10

English Version
Milk - Determination of urea content - Enzymatic method using
difference in pH (Reference method) (ISO 14637:2004)
Lait - Détermination de la teneur en urée - Méthode Milch - Bestimmung des Harnstoffgehaltes -
enzymatique par mesurage de pH différentiel (Méthode de Enzymatisches Verfahren mit pH-Änderung
référence) (ISO 14637:2004) (Referenzverfahren) (ISO 14637:2004)
This European Standard was approved by CEN on 13 November 2006.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national
standards may be obtained on application to the Central Secretariat or to any CEN member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CEN member into its own language and notified to the Central Secretariat has the same status as the official
versions.
CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,
Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania,
Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36  B-1050 Brussels
© 2006 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 14637:2006: E
worldwide for CEN national Members.

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EN ISO 14637:2006 (E)






Foreword



The text of ISO 14637:2004 has been prepared by Technical Committee ISO/TC 34 "Agricultural
food products” of the International Organization for Standardization (ISO) and has been taken
over as EN ISO 14637:2006 by Technical Committee CEN/TC 302 "Milk and milk products -
Methods of sampling and analysis", the secretariat of which is held by NEN.

This European Standard shall be given the status of a national standard, either by publication of
an identical text or by endorsement, at the latest by June 2007, and conflicting national
standards shall be withdrawn at the latest by June 2007.

According to the CEN/CENELEC Internal Regulations, the national standards organizations of
the following countries are bound to implement this European Standard: Austria, Belgium,
Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary,
Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland,
Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.



Endorsement notice

The text of ISO 14637:2004 has been approved by CEN as EN ISO 14637:2006 without any
modifications.

2

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INTERNATIONAL ISO
STANDARD 14637
IDF
195
First edition
2004-10-15

Milk — Determination of urea content —
Enzymatic method using difference in pH
(Reference method)
Lait — Détermination de la teneur en urée — Méthode enzymatique
utilisant les fluctuations du pH (Méthode de référence)




Reference numbers
ISO 14637:2004(E)
IDF 195:2004(E)
©
ISO and IDF 2004

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ISO 14637:2004(E)
IDF 195:2004(E)
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©  ISO and IDF 2004
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,
electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO or IDF at the respective
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Published in Switzerland

ii © ISO and IDF 2004 – All rights reserved

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ISO 14637:2004(E)
IDF 195:2004(E)
Contents Page
Foreword. iv
1 Scope. 1
2 Terms and definitions. 1
3 Principle. 1
4 Reagents. 1
5 Apparatus. 2
6 Sampling. 3
7 Preparation of test sample. 3
8 Procedure. 3
8.1 General. 3
8.2 Blank determination. 3
8.3 Calibration. 4
8.4 Checking the calibration. 5
8.5 Determination. 5
8.6 Checking the stability. 5
8.7 Checking the contamination of the electrodes. 5
8.8 Cleaning procedure. 5
9 Maintenance of the electrodes . 5
9.1 Regeneration. 5
9.2 Strong regeneration. 6
10 Calculation and expression of results . 6
10.1 Calculation. 6
10.2 Expression of results. 6
11 Precision. 6
11.1 Interlaboratory tests. 6
11.2 Repeatability. 6
11.3 Reproducibility. 7
12 Test report. 7
Annex A (informative) Differential pH apparatus. 8
Annex B (informative) Interlaboratory tests. 9
Bibliography . 11

© ISO and IDF 2004 – All rights reserved iii

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ISO 14637:2004(E)
IDF 195:2004(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, International organizations, governmental
and non-governmental, in liaison with ISO, also take part in the work, ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization,
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2,
The main task of technical committees is to prepare International Standards, Draft International Standards
adopted by the technical committee are circulated to the member bodies for voting, Publication as an
International standard requires approval by at least 75 % of the member bodies casting a vote,
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights, ISO shall not be held responsible for identifying any or all such patent rights,
International Standard ISO 14637|IDF 195 was prepared by Technical Committee ISO/TC 34, Food products,
Subcommittee SC 5, Milk and milk products, and the International Dairy Federation (IDF), in collaboration with
AOAC International. It is being published jointly by ISO and IDF and separately by AOAC International.

iv © ISO and IDF 2004 – All rights reserved

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ISO 14637:2004(E)
IDF 195:2004(E)
Foreword
IDF (the International Dairy Federation) is a worldwide federation of the dairy sector with a National
Committee in every member country, Every National Committee has the right to be represented on the IDF
Standing Committees carrying out the technical work, IDF collaborates with ISO and AOAC International in
the development of standard methods of analysis and sampling for milk and milk products,
Draft International Standards adopted by the Action Teams and Standing Committees are circulated to the
National Committees for voting, Publication as an International Standard requires approval by at least 50% of
IDF National Committees casting a vote,
International Standard ISO 14637|IDF 195 was prepared by Technical Committee ISO/TC 34, Food products,
Subcommittee SC 5, Milk and milk products, and the International Dairy Federation (IDF), in collaboration with
AOAC International. It is being published jointly by ISO and IDF and separately by AOAC International.
All work was carried out by the Joint ISO/IDF/AOAC Action Team, Nitrogen compounds, of the Standing
Committee on Main components of milk, under the aegis of its project leader, Mr Ph. Trossat (FR).

© ISO and IDF 2004 – All rights reserved v

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ISO 14637:2004(E)
INTERNATIONAL STANDARD
IDF 195:2004(E)

Milk — Determination of urea content — Enzymatic method
using difference in pH (Reference method)
1 Scope
This International Standard specifies an enzymatic method for the determination of the urea content of milk by
measurement of the difference in pH.
2 Terms and definitions
For the purpose of this document, the following terms and definitions apply.
2.1
urea content
mass fraction of substances determined by the procedure specified in this International Standard
NOTE The urea content is expressed in milligrams per litre.
3 Principle
Urease is added to the test sample to split urea into ammonia and carbon dioxide. At pH 6,7, ammonia
immediately hydrolyses thereby releasing hydroxyl ions, and carbon dioxide liberates protons that partly
neutralize these hydroxyl ions. The balance between the ammonia and carbon dioxide hydrolysis and the
resulting neutralization induces a change in pH. The pH change varies as a function of the urea content of the
sample and is measured by using a differential pH analyser.
4 Reagents
Use only reagents of recognized analytical grade, unless otherwise specified, and distilled or demineralized
water or water of equivalent purity.
4.1 Reagents for urea determination.
4.1.1 Buffer solution, pH 6,7.
Dissolve 1,777 g of potassium monohydrogenphosphate (K HPO ), 1,388 g of potassium dihydrogen-
2 4
phosphate (KH PO ), 7,600 g of potassium chloride (KCl), 1,00 g of sodium azide (NaN ), 0,010 g of
2 4 3
acetazolamide (5-acetamido-1,3,4-thiadiazole-2-sulfonamide), 1,040 g of magnesium chloride hexahydrate
1)
(MgCl◊6H O), 2 g of Triton X100, 1 g of Brij 35 and 20 ml of LM1 in a 1 000 ml volumetric flask (5.5). Dilute
2 2
to the mark with water and mix.

1) This detergent is available from Valetudo S.r.l., BG, Italy, and is an example of a suitable product available
commercially. This information is given for the convenience of users of this International Standard and does not constitute
an endorsement by ISO or IDF of this product.
© ISO and IDF 2004 – All rights reserved 1

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ISO 14637:2004(E)
IDF 195:2004(E)
The buffer solution may be kept for 6 months if stored at 4 °C.
4.1.2 Urease enzyme solution.
Dissolve 360 mg of lyophilized urease (EC 3.5.1.5) in 1 ml of a 50 % (volume fraction) aqueous solution of
2)
glycerol. The activity of the obtained urease enzyme solution shall be 2 100 units/ml ± 300 units/ml .
The urease enzyme solution may be kept for 6 months if stored at 4 °C.
4.1.3 Urea s
...