EN ISO 3188:1994

SLOVENSKI STANDARD
01-november-1998
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Starches and derived products - Determination of nitrogen content by the Kjeldahl
method - Titrimetric method (ISO 3188:1978)
Stärken und Stärkederivate - Bestimmung des Stickstoffgehaltes nach dem Kjeldahl-
Verfahren - Volumetrisches Verfahren (ISO 3188:1978)
Amidons, fécules et produits dérivés - Dosage de l'azote selon la méthode de Kjeldahl -
Méthode titrimétrique (ISO 3188:1978)
Ta slovenski standard je istoveten z: EN ISO 3188:1994
ICS:
67.180.20 Škrob in izdelki iz njega Starch and derived products
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

INTERNATIONAL STANDARD
INTERNATIONAL ORGANIZATION FOR STANDARDIZATIONWlEIKJjYHAPO,QHAR OPrAHM3AL&lR fl0 CTAH~APTM3AL&WWORGANISATION INTERNATIONALE DE NORMALISATION
Starches and derived products - Determination of nitrogen
content by the Kjeldahl method - Titrimetric method
Amidons, fdcules et produits d&iv& - Dosage de l’azote selon Ia methode de Kjeldahl - Mt!thode titrimetrique
First edition - 1978-08-15
Ei
-
UDC 664.2 : 546.17 : 543.24
Ref. No. ISO 3188-1978 (E)
Descriptors : starches, Chemical analysis, determination of content, nitrogen, volumetric analysis, Kjeldahl method.
Price based on 3 pages
FOREWORB
ISO (the International Organization for Standardization) is a worldwide federation
of national Standards institutes (ISO member bodies). The work of deweloping
International Standards is carried out through ISO technical committees. Ewery
member body interested in a subject for which a technical committee has been set
up 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.
Draft International Standards adopted by the technical committees are circulated
to the member bodies for approval before their acceptance as International
Standards by the ISO Council.
International Standard ISO 3188 was developed by Technicai Committee
ISO/TC 93, Starch (including derivatives and by-products), and was circulated
to the member bodies in August 1975.
lt has been approved by the member bodies of the following countries :
Australia 1 ran Thailand
Czechoslovakia Netherlands Turkey
France Poland United Kingdom
Germany Romania Yugoslavia
Hungary South Africa, Rep. of
The member body of the following country expressed d isapprova I of the docume nt
on technical grounds :
U.S.A.
@ International Organisation for Standard ization, 9 978 l
Printed in Switzerland
ISO 31884978 (E)
INTERNATIONAL STANDARD
Starches and derived products - Determination of nitrogen
content by the Kjeldahl method - Titrimetric method
5 REAGENTS
1 SCOPE AND FIELD OF APPLICATION
The reagents shall be of recognized analytical quality.
This International Standard specifies a titrimetric method
Ammonia-free distilled water or water of at least equivalent
for the determination, by the Kjeldahl method, of the
purity shall be used.
nitrogen content of starch and its derived products whose
presumed nitrogen content is greater than 0,Ol % (mlm)? )
5.1 Sulphuric acid, concentrated, p20 1,84 g/ml [96 %
NOTE - In starches and derived products to which nitrogenous
(mhd].
materials have not been added, the nitrogen is present essentially
in the form of Protein and/or amino acids.
5.2 Sodium hydroxide, solution 30 % (mlm), p20
1,33 g/ml.
2 REFERENCES
NOTE - This Solution may be more concentrated.
ISO 1227fAdd. 2, Starch, including derivatives and by-
products - Vocabulary.
5.3 Boric acid, 20 g/ solution.3)
ISO 1871, Agricultural food products - General directions
for the determination of nitrogen by the Kjeldahlmethod.
5.4 Compound catalyst4), consisting of, for example :
ISO 5378, Starches and derived products - Determination
- potassium sulphate : 97 g;
of nitrogen content by the Kjeldahl method - Spectro-
- copper( II) sulphate, anhydrous : 3 g.
pho tome tric me thod,
5.5 Sulphuric acid,
approximately 0,02 N or 0,l N
-
3 DEFINITION
Standard volumetric Solution,
nitrogen content : The value found using the procedure
5.6 Colorimetric indicator, prepared by mixing 2 Parts
specified. lt includes the nitrogen content of free amino
by volume of a cold saturated Solution of neutral methyl
acids, of compounds producing amino acids on hydrolysis
red in 50 % (WV) ethanol with 1 part by volume of a
and of ammonium compounds. lt does not include the
0,25 g/l Solution of methylene blue in 50 % (VW) ethanol.
nitrogen of nitrate and nitrite radicals, the nitrogen
attached directly to another nitrogen atom or the nitrogen
Store the indicator in a brown glass bottle.
attached to an Oxygen atom.
6 APPARATUS
4 PRINCIPLE
Usual laboratory equipment, and in particular
Destruction of organic matter by sulphuric acid in the
presence of a compound catalyst*), alkalization of the 6.1 Kjeldahl flask, of suitable capacity, usually 500 to
800 ml, preferably with a ground glass joint, and provided
reaction products, distillation of the Iiberated ammonia
with a pear-shaped glass bulb fitting loosely in the top of
and collection in a boric acid Solution, followed by
the neck of the flask.
titration with a Standard volumetric sulphuric acid Solution.
1) For products whose presumed nitrogen content is less than 0,025 % (m/m), see ISO 5378.
2) See ISO 1871.
3) For anticipated low nitrogen contents, a less concentrated Solution may be needed in Order to obtain greater accuracy.
4) See ISO 1871, sub-clause 5.2,
ISO
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