SIST EN ISO 14891:2002

SLOVENSKI STANDARD
SIST EN ISO 14891:2002
01-september-2002
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Milk and milk products - Determination of nitrogen content - Routine method using
combustion according to the Dumas principle (ISO 14891:2002)
Milch und Milchprodukte - Bestimmung des Stickstoffgehaltes - Verbrennungsverfahren
nach Dumas (Routineverfahren) (ISO 14891:2002)
Lait et produits laitiers - Détermination de la teneur en azote - Méthode pratique par
combustion selon le principe de Dumas (ISO 14891:2002)
Ta slovenski standard je istoveten z: EN ISO 14891:2002
ICS:
67.100.01 0OHNRLQPOHþQLSURL]YRGLQD Milk and milk products in
VSORãQR general
SIST EN ISO 14891:2002 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 14891:2002

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SIST EN ISO 14891:2002
EUROPEAN STANDARD
EN ISO 14891
NORME EUROPÉENNE
EUROPÄISCHE NORM
March 2002
ICS 67.100.01
English version
Milk and milk products - Determination of nitrogen content -
Routine method using combustion according to the Dumas
principle (ISO 14891:2002)
Lait et produits laitiers - Détermination de la teneur en Milch und Milchprodukte - Bestimmung des
azote - Méthode pratique par combustion selon le principe Stickstoffgehaltes - Verbrennungsverfahren nach Dumas
de Dumas (ISO 14891:2002) (Routineverfahren) (ISO 14891:2002)
This European Standard was approved by CEN on 1 March 2002.
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 Management Centre 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 Management Centre has the same status as the official
versions.
CEN members are the national standards bodies of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece,
Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal, 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
© 2002 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 14891:2002 E
worldwide for CEN national Members.

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SIST EN ISO 14891:2002
EN ISO 14891:2002 (E)
CORRECTED  2002-04-17
Foreword
This document (ISO 14891:2002) has been prepared by Technical Committee ISO/TC 34
"Agricultural food products" in collaboration with 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 September 2002, and conflicting
national standards shall be withdrawn at the latest by September 2002.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of
the following countries are bound to implement this European Standard: Austria, Belgium,
Czech Republic, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy,
Luxembourg, Malta, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and the
United Kingdom.
Endorsement notice
The text of the International Standard ISO 14891:2002 has been approved by CEN as a
European Standard without any modifications.
NOTE  Normative references to International Standards are listed in annex ZA (normative).
2

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SIST EN ISO 14891:2002
EN ISO 14891:2002 (E)
Annex ZA
(normative)
Normative references to International Publicationswith their relevant
European publications
This European Standard incorporates by dated or undated reference, provisions from other
publications. These normative references are cited at the appropriate places in the text, and the
publications are listed hereafter. For dated references, subsequent amendments to or revisions
of any of these publications apply to this European Standard only when incorporated in it by
amendment or revision. For undated references the latest edition of the publication referred to
applies (including amendments).
NOTE  Where an International Publication has been modified by common modifications,
indicated by (mod.), the relevant EN/HD applies.
Publication Year Title EN/HD Year
ISO 8968-1 2001 Milk - Determination of nitrogen content - Part EN ISO 8968-1 2001
1: Kjeldahl method
3

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SIST EN ISO 14891:2002

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SIST EN ISO 14891:2002



INTERNATIONAL ISO
STANDARD 14891
IDF
185
First edition
2002-03-01


Milk and milk products — Determination of
nitrogen content — Routine method using
combustion according to the Dumas
principle
Lait et produits laitiers — Détermination de la teneur en azote — Méthode
pratique par combustion selon le principe de Dumas





Reference numbers
ISO 14891:2002(E)
IDF 185:2002(E)
©
ISO and IDF 2002

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SIST EN ISO 14891:2002
ISO 14891:2002(E)
IDF 185:2002(E)
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ii © ISO and IDF 2002 – All rights reserved

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SIST EN ISO 14891:2002
ISO 14891:2002(E)
IDF 185:2002(E)
Contents Page
Foreword.iv, vi
1 Scope .1
2 Normative reference.1
3 Term and definition .1
4 Principle.1
5 Reagents.1
6 Apparatus .2
7 Sampling.3
8 Preparation of test sample.3
8.1 General.3
8.2 Liquid test samples .3
9 Procedure .4
9.1 General.4
9.2 Test portion .4
9.3 Control of oxygen demand .4
9.4 Calibration .4
9.5 Determination.4
9.6 Detection and integration .5
10 Calculation and expression of results.5
10.1 Calculation .5
10.2 Expression of results .5
11 Precision.6
11.1 Interlaboratory test.6
11.2 Repeatability .6
11.3 Reproducibility.7
12 Test report .7
Annex A (informative) Flowchart for the basic design of a Dumas apparatus.8
Annex B (informative) Schemes of suitable types of Dumas apparatus.9
Annex C (informative) Equipment calibration .11
Annex D (informative) Comparison of results using the Dumas method with those obtained by the
Kjeldahl method.13
Bibliography.14

© ISO and IDF 2002 – All rights reserved iii

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SIST EN ISO 14891:2002
ISO 14891:2002(E)
IDF 185:2002(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 3.
The main task of technical committees is to prepare International Standards. Draft International Standards adopted
by the technical committees 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 International Standard may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights.
International Standard ISO 14891ΩIDF 185 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.
Annexes A, B, C and D are for information only.
iv © ISO and IDF 2002 – All rights reserved

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SIST EN ISO 14891:2002
ISO 14891:2002(E)
IDF 185:2002(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 National
Committees casting a vote.
International Standard ISO 14891/IDF 185 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, Main compounds of milk, under the aegis of its project leader, Prof. H. Frister (DE).

© ISO and IDF 2002 – All rights reserved v

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SIST EN ISO 14891:2002

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SIST EN ISO 14891:2002
ISO 14891:2002(E)
INTERNATIONAL STANDARD
IDF 185:2002(E)

Milk and milk products — Determination of nitrogen content —
Routine method using combustion according to the Dumas
principle
1 Scope
This International Standard specifies a routine method for the determination of the total nitrogen content of milk and
milk products.
2 Normative reference
The following normative document contains provisions which, through reference in this text, constitute provisions of
this International Standard. For dated references, subsequent amendments to, or revisions of, any of these
publications do not apply. However, parties to agreements based on this International Standard are encouraged to
investigate the possibility of applying the most recent edition of the normative document indicated below. For
undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC
maintain registers of currently valid International Standards.
ISO 8968-1ΩIDF 20-1, Milk — Determination of nitrogen content — Part 1: Kjeldahl method
3 Term and definition
For the purposes of this International Standard, the following term and definition apply.
3.1
nitrogen content
mass fraction of the total nitrogen determined by the procedure specified in this International Standard
NOTE  The nitrogen content is expressed as a percentage by mass.
4 Principle
A test portion is heated to destruction in a combustion tube at high temperature (900 °C to 1 200 °C) in an oxygen
atmosphere according to the Dumas principle. All interfering components are removed from the resulting gas
mixture. The nitrogen compounds in the test portion are converted to molecular nitrogen, followed by quantitative
determination using a thermal conductivity detector. The nitrogen content is calculated using a microprocessor.
5 Reagents
Use only reagents of recognized analytical grade, or reagents of equivalent purity as specified by instrument
manufacturers.
5.1 Carrier gases: use one of the following.
© ISO and IDF 2002 – All rights reserved 1

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SIST EN ISO 14891:2002
ISO 14891:2002(E)
IDF 185:2002(E)
5.1.1 Carbon dioxide (CO ), purity 99,9 % (volume fraction) for samples with moderate nitrogen contents;
2
99,995 % (volume fraction) for samples with low nitrogen contents.
5.1.2 Helium (He), purity 99,996 % (volume fraction).
5.2 Oxygen (O ), purity 99,995 % (volume fraction).
2
5.3 Absorbent for SO , e.g. lead chromate to eliminate any sulfur compounds from the combustion products.
2
5.4 Copper oxide platinum catalyst (as filling material for the post-combustion tube).
Platinum catalyst (5 % of Pt on Al O ) is blended with CuO at a ratio of 1 to 7, 8 or 9 parts.
2 3
To prevent separation as result of the different bulk densities of the two materials, it is not recommended to prepare
the mixture before filling the tube. It is advisable to pour the platinum catalyst and copper oxide simultaneously into
the post-combustion tube using a suitable funnel.
5.5 Silver wool.
Silver wool should be desegregated before being inserted in the post-combustion or reduction tube.
5.6 Silica (quartz) or glass wool.
5.7 Copper or tungsten (wire, cuttings or powder), suitable for filling the reduction tube.
To improve the precision of analytical results for low nitrogen contents, the use of copper or tungsten wire is
recommended.
5.8 Phosphorus pentoxide (P O ) or granulated magnesium perchlorate [Mg(ClO ) ], or another suitable
2 5 4 2
support material, to fill the drying tubes.
5.9 Hollow corundum spheres or aluminium oxide pellets, suitable for filling the combustion tube.
5.10 Copper oxide (CuO), suitable as a filling material for the combustion tube.
5.11 Sodium hydroxide (NaOH), on a support material.
5.12 Standard nitrogen compounds, e.g. aspartic acid (C H NO), ethylenediaminetetraacetic acid
4 7 4
(C H N O ) (see annex C), or other suitable reference reagents with known constant nitrogen content (e.g. urea,
10 16 2 8
tyrosine, phenylalanine); minimum assay should be 99 %.
For calibration purposes (see 9.4), use a standard nitrogen compound to prepare a standard series with a nitrogen
content of 4 mg to 100 mg in equal steps of about 5 mg nitrogen. Prepare a second standard series with a nitrogen
content of 10 mg to 200 mg in equal steps of about 10 mg nitrogen.
6 Apparatus
Usual laboratory equipment and, in particular, the following.
6.1 Analytical balance, capable of weighing to 0,000 1 g.
6.2 Drying oven, capable of maintaining a temp
...