SIST EN ISO 8968-2:2002

Milk - Determination of nitrogen content - Part 2: Block-digestion method (Macro method) (ISO 8968-2:2001)

ISO 8968-2|IDF 20-2:2001 specifies a method for the determination of the nitrogen content of liquid milk, whole or skimmed, by the block-digestion principle.

Milch - Bestimmung des Stickstoffgehaltes - Teil 2: Blockaufschluss-Verfahren (Makroverfahren) (ISO 8968-2:2001)

Dieser Teil von ISO 8968/IDF 20 legt ein Blockaufschluss-Verfahren zur Bestimmung des Stickstoffgehaltes von flüssiger Vollmilch oder entrahmter Milch fest.

Lait - Détermination de la teneur en azote - Partie 2: Méthode de minéralisation en bloc (Méthode macro) (ISO 8968-2:2001)

L'ISO 8968-2|FIL 20-2:2001 spécifie une méthode pour la détermination de la teneur en azote du lait liquide, entier ou écrémé, selon le principe de la minéralisation en bloc.

Mleko - Določevanje dušika - 2. del: Metoda razkroja v električnem bloku (Makro metoda) (ISO 8968-2:2001)

General Information

• Status: Withdrawn
• Publication Date: 31-May-2002
• Withdrawal Date: 12-Mar-2014
• ICS: 67.100.10 - Milk and processed milk products
• Technical Committee: KŽP - Agricultural food products
• Current Stage: 9900 - Withdrawal (Adopted Project)
• Start Date: 13-Mar-2014
• Due Date: 05-Apr-2014
• Completion Date: 13-Mar-2014
• Ref Project: EN ISO 8968-2:2001 - Milk - Determination of nitrogen content - Part 2: Block-digestion method (Macro method) (ISO 8968-2:2001)

Relations

• Replaced By: SIST EN ISO 8968-1:2014 - Milk and milk products - Determination of nitrogen content - Part 1: Kjeldahl principle and crude protein calculation (ISO 8968-1:2014)
• Effective Date: 01-Apr-2014

Standards Content (Sample)

SLOVENSKI STANDARD
SIST EN ISO 8968-2:2002
01-junij-2002
0OHNR'RORþHYDQMHGXãLNDGHO0HWRGDUD]NURMDYHOHNWULþQHPEORNX0DNUR
PHWRGD,62
Milk - Determination of nitrogen content - Part 2: Block-digestion method (Macro method)
(ISO 8968-2:2001)
Milch - Bestimmung des Stickstoffgehaltes - Teil 2: Blockaufschluss-Verfahren
(Makroverfahren) (ISO 8968-2:2001)
Lait - Détermination de la teneur en azote - Partie 2: Méthode de minéralisation en bloc
(Méthode macro) (ISO 8968-2:2001)
Ta slovenski standard je istoveten z: EN ISO 8968-2:2001
ICS:
67.100.10 0OHNRLQSUHGHODQLPOHþQL Milk and processed milk
SURL]YRGL products
SIST EN ISO 8968-2:2002 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 8968-2:2002

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SIST EN ISO 8968-2:2002
EUROPEAN STANDARD
EN ISO 8968-2
NORME EUROPÉENNE
EUROPÄISCHE NORM
December 2001
ICS 67.100.10
English version
Milk - Determination of nitrogen content - Part 2: Block-digestion
method (Macro method) (ISO 8968-2:2001)
Lait - Détermination de la teneur en azote - Partie 2: Milch - Bestimmung des Stickstoffgehaltes - Teil 2:
Méthode de minéralisation en bloc (Méthode macro) (ISO Blockaufschluss-Verfahren (Makroverfahren) (ISO 8968-
8968-2:2001) 2:2001)
This European Standard was approved by CEN on 15 December 2001.
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, 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
© 2001 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 8968-2:2001 E
worldwide for CEN national Members.

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SIST EN ISO 8968-2:2002
EN ISO 8968-2:2001 (E)
CORRECTED  2002-03-13
Foreword
This document (ISO 8968-2:2001) 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 June 2002, and conflicting national
standards shall be withdrawn at the latest by June 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,
Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and the United Kingdom.
Endorsement notice
The text of the International Standard ISO 8968-2:2001 has been approved by CEN as a
European Standard without any modifications.
2

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SIST EN ISO 8968-2:2002



INTERNATIONAL ISO
STANDARD 8968-2
IDF
20-2
First edition
2001-12-15


Milk — Determination of nitrogen
content —
Part 2:
Block-digestion method (Macro method)
Lait — Détermination de la teneur en azote —
Partie 2: Méthode de minéralisation en bloc (Méthode macro)




Reference numbers
ISO 8968-2:2001(E)
IDF 20-2:2001(E)
©
 ISO and IDF 2001

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SIST EN ISO 8968-2:2002
ISO 8968-2:2001(E)
IDF 20-2:2001(E)
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©  ISO and IDF 2001
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 address below.
ISO copyright office International Dairy Federation
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Printed in Switzerland

ii © ISO and IDF 2001 – All rights reserved

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SIST EN ISO 8968-2:2002
ISO 8968-2:2001(E)
IDF 20-2:2001(E)
Contents Page
Foreword.iv
1 Scope.1
2 Normative reference.1
3 Term and definition .1
4 Principle.1
5 Reagents.2
6 Apparatus.3
7 Sampling.3
8 Preparation of test sample.3
9 Procedure.4
9.1 Test portion and pretreatment .4
9.2 Determination.4
9.3 Blank test.5
9.4 Recovery tests.6
10 Calculation and expression of results.7
10.1 Calculation of nitrogen content .7
10.2 Calculation of crude protein content.7
11 Precision.8
11.1 Interlaboratory test.8
11.2 Repeatability.8
11.3 Reproducibility.8
12 Test report.8
Bibliography.9


© ISO and IDF 2001 – All rights reserved iii

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SIST EN ISO 8968-2:2002
ISO 8968-2:2001(E)
IDF 20-2:2001(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 part of ISO 8968IDF 20 may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights.
International Standard ISO 8968-2IDF 20-2 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.
ISO 8968IDF 20 consists of the following parts, under the general title Milk — Determination of nitrogen content:
— Part 1: Kjeldahl method
— Part 2: Block-digestion method (Macro method)
— Part 3: Block-digestion method (Semi-micro rapid routine method)
— Part 4: Determination of the non-protein-nitrogen content
— Part 5: Determination of the protein-nitrogen content

iv © ISO and IDF 2001 – All rights reserved

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SIST EN ISO 8968-2:2002
ISO 8968-2:2001(E)
IDF 20-2:2001(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 8968-2IDF 20-2 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, under the aegis of its
project leader, Mr D.M. Barbano (US).

© ISO and IDF 2001 – All rights reserved v

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SIST EN ISO 8968-2:2002

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SIST EN ISO 8968-2:2002
ISO 8968-2:2001(E)
INTERNATIONAL STANDARD
IDF 20-2:2001(E)

Milk — Determination of nitrogen content —
Part 2:
Block digestion method (Macro method)
WARNING — The use of this part of ISO 8968IDF 20 may involve the use of hazardous materials,
operations, and equipment. This standard does not purport to address all the safety risks associated with
its use. It is the responsibility of the user of this standard to establish appropriate safety and healthy
practices and determine the applicability of local regulatory limitations prior to use.
1 Scope
This part of ISO 8968IDF 20 specifies a method for the determination of the nitrogen content of liquid milk, whole
or skimmed, by the block-digestion principle.
2 Normative reference
The following normative document contains provisions which, through reference in this text, constitute provisions of
this part of ISO 8968IDF 20. For dated references, subsequent amendments to, or revisions of, any of these
publications do not apply. However, parties to agreements based on this part of ISO 8968IDF 20 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 385-1, Laboratory glassware — Burettes — Part 1: General requirements
3 Term and definition
For the purposes of this part of ISO 8968IDF 20, the following term and definition apply.
3.1
nitrogen content
mass fraction of substances determined by the procedure specified in this part of ISO 8968IDF 20
NOTE The nitrogen content is expressed as a percentage by mass.
4 Principle
A test portion is digested by using a block-digestion apparatus with a mixture of concentrated sulfuric acid and
potassium sulfate, using copper(II) sulfate as a catalyst to thereby convert organic nitrogen present to ammonium
sulfate. The function of the potassium sulfate is to elevate the boiling point of the sulfuric acid and to provide a
stronger oxidizing environment. Excess sodium hydroxide is added to the cooled digest to liberate ammonia. The
liberated ammonia is steam distilled, using either a manual or semi-automatic steam distillation unit, into an excess
of boric acid solution then titrated with hydrochloric acid. The nitrogen content is calculated from the amount of
ammonia produced.
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SIST EN ISO 8968-2:2002
ISO 8968-2:2001(E)
IDF 20-2:2001(E)
5 Reagents
Use only reagents of recognized analytical grade, unless otherwise specified, and distilled or demineralized water
or water of equivalent purity.
5.1 Potassium sulfate (K SO ), nitrogen free.
2 4
5.2 Copper(II) sulfate solution, c(CuSO ) = 5,0 g per 100 ml.
4
Dissolve 5,0 g of copper(II) sulfate pentahydrate (CuSO ⋅5H O) in water in a 100 ml one-mark volumetric flask.
4 2
Dilute to the mark with water and mix.
5.3 Sulfuric acid (H SO ), with a mass faction of between 95 % to 98 %, nitrogen free (ρ = 1,84 g/ml
2 4 20
approximately).
5.4 Sodium hydroxide solution (NaOH), nitrogen free, containing 50 g of sodium hydroxide per 100 g of solution.
A 40 % sodium hydroxide solution may be used instead of a 50 %, if plugging of the flow system in an automatic
distillation unit is a problem.
5.5 Indicator solution
Dissolve 0,1 g of methyl red in 95 % (volume fraction) ethanol. Dilute to 50 ml with the ethanol. Dissolve 0,5 g of
bromocresol green in 95 % (volume fraction) ethanol. Dilute to 250 ml with the ethanol. Mix amounts of one part of
the methyl red solution with five parts of the bromocresol green solution or combine and mix all of both solutions.
5.6 Boric acid solution, c(H BO ) = 40,0 g/l.
3 3
Dissolve 40,0 g of boric acid in 1 litre of hot water in a 1 000 ml one-mark volumetric flask. Allow the flask and its
contents to cool to 20 °C. Dilute to the mark with water, add 3 ml of the indicator solution (5.5) and mix. Store the
solution, which will be light orange in colour, in a borosilicate glass bottle. Protect the solution from light and
sources of ammonia fumes during storage.
If using the electronic pH endpoint titration, the addition of the indicator solution to the boric acid solution may be
omitted. On the other hand, the change in colour may also be used as a check of proper titration procedures.
5.7 Hydrochloric acid standard volumetric solution, c(HCl) = (0,1 ± 0,000 5) mol/l.
It is recommended that this material be purchased prestandardized by the manufacturer to meet or exceed the
above specification.
NOTE Often systematic errors (which can be avoided) introduced by an analyst diluting a concentrated stock acid and then
determining the molarity of the acid can reduce the reproducibility of the method. The analyst should not use solution for titration
that has a higher concentration than 0,1 mol/l, because this will reduce the total titration volume per sample and the uncertainty
in readability of the burette will become a larger percentage of the value. This will have a negative impact on the repeatability
and reproducibility of the method. The same issues and additional sources of error arise when another acid (e.g., sulfuric acid)
is substituted for hydrochloric acid. Thus, these substitutions are not recommended.
5.8 Ammonium sulfate [(NH ) SO ], minimum assay 99,9 % (mass fraction) on dried material.
4 2 4
Immediately before use, dry the ammonium sulfate at 102 °C ± 2 °C for not less than 2 h. Cool to room temperature
in a desiccator.
5.9 Tryptophan (C H N O ) or lysine hydrochloride (C H CIN O ), minimum assay 99 % (mass fraction).
11 12 2 2 6 15 2 2
Do not dry the reagents in an oven before use.
5.10 Sucrose, with a nitrogen content of not more than 0,002 % (mass fraction).
Do not dry the sucrose in an oven before use.
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SIST EN ISO 8968-2:2002
ISO 8968-2:2001(E)
IDF 20-2:2001(E)
6 Apparatus
Usual laboratory apparatus and, in particular, the following.
6.1 Water bath, capable of being maintained at 38 °C ± 2 °C.
6.2 Analytical balance, capable of weighing to the nearest 0,1 mg.
6.3 Digestion block, aluminium alloy block or equivalent block, fitted with an adjustable temperature control and
device for measuring the temperature of the block.
6.4 Digestion tubes, of capacity 250 ml, suitable for use with the digestion block (6.3).
6.5 Exhaust manifold, suitable for use with the digestion tubes (6.4).
6.6 Centrifugal scrubber apparatus or filter pump or aspirator, constructed of acid-resistant material, for use
with mai
...