EN ISO 5378:1994

Starches and derived products - Determination of nitrogen content by the Kjeldahl method - Spectrophotometric method (ISO 5378:1978)

Destruction of organic matter by sulphuric acid in the presence of a compound catalyst (see ISO 1871), alkalization of the reaction products, destillation of the liberated ammonia and collection in a sulphuric acid solution, followed by measuring of the ammonium salt formed after the addition of Nessler reagent. The method is provided for contents less than 0,025 % (m/m). For greater contents, see ISO 3188.

Stärke und Stärkederivate - Bestimmung des Stickstoffgehalts nach dem Kjeldahl-Verfahren - Spektrometrisches Verfahren (ISO 5378:1978)

Diese Internationale Norm legt ein spektralphotometrisches Verfahren zur Bestimmung des Stickstoffgehalts nach dem Kjeldahl-Verfahren fest. Das Verfahren ist bei Stärke und Stärkeerzeugnissen anwendbar, deren Stickstoffgehalt voraussichtlich weniger als 0,025% (Massenanteil) beträgt.

Amidons, fécules et produits dérivés - Dosage de l'azote selon la méthode de Kjeldahl - Méthode spectrophotométrique (ISO 5378:1978)

La présente Norme internationale spécifie une méthode spectrophotométrique de dosage de l'azote selon la méthode de Kjeldahl, dans les amidons, fécules et leurs produits dérivés, dont la teneur présumée en azote est inférieure à 0,025 % (m/m).1)NOTE - Dans les amidons, fécules et dérivés n'ayant pas reçu d'adjonctions azotées, l'azote est présent essentiellement sous forme de protides et/ou d'amino-acides.

Škrobi in škrobni derivati - Določevanje dušika po Kjeldahlovi metodi - Spektrofotometrijska metoda (ISO 5378:1978)

General Information

• Status: Published
• Publication Date: 24-Aug-1994
• Withdrawal Date: 27-Feb-1995
• ICS: 67.180.20 - Starch and derived products
• Technical Committee: CEN/SS C10 - Starch
• Drafting Committee: CEN/SS C10 - Starch
• Current Stage: 9093 - Decision to confirm - Review Enquiry
• Start Date: 13-Oct-1999
• Completion Date: 13-Oct-1999
• Ref Project: SIST EN ISO 5378:1998 - Starches and derived products - Determination of nitrogen content by the Kjeldahl method - Spectrophotometric method (ISO 5378:1978)

Overview

EN ISO 5378:1994 specifies a spectrophotometric method for determining nitrogen content in starches and derived products through the Kjeldahl method. This international standard, developed by CEN in alignment with ISO 5378:1978, provides a precise procedure suitable for nitrogen contents below 0.025% (m/m). It involves the destruction of organic matter using sulphuric acid and a compound catalyst, followed by alkalization, distillation of liberated ammonia, and measurement via spectrophotometry using Nessler reagent.

This method is critical for accurate nitrogen analysis in food and agricultural products where protein and amino acid nitrogen content is essential and serves as a foundation for quality control and regulatory compliance in starch-related industries.

Key Topics

• Scope and Application
  Designed for starches and related products with nitrogen content below 0.025% (m/m), focusing on protein and amino acid nitrogen while excluding nitrate, nitrite, and other nitrogen forms. For higher nitrogen contents, ISO 3188 is referenced.

• Principle
  Organic nitrogen compounds are digested by concentrated sulphuric acid in the presence of a catalyst. Ammonia produced is distilled and trapped in sulphuric acid, then reacted with Nessler reagent to form an ammonium salt measured spectrophotometrically at 430 nm.

• Reagents and Equipment

  • Concentrated sulphuric acid and sodium hydroxide solutions
  • Compound catalyst (potassium sulphate and copper(II) sulphate)
  • Nessler reagent (mercuroiodide-potassium iodide-potassium hydroxide solution)
  • Kjeldahl digestion and distillation apparatus
  • Spectrophotometer adjustable to 430 nm wavelength and appropriate cells

• Analytical Procedure

  1. Sample preparation, including grinding and sieving as needed
  2. Digestion of the sample with sulphuric acid and catalyst
  3. Alkalization and steam distillation of ammonia
  4. Ammonia absorption into sulphuric acid
  5. Addition of Nessler reagent and spectrophotometric measurement
  6. Use of calibration curves from known ammonium salt standards
  7. Blank and check tests to verify accuracy

• Calculation and Expression of Results
  Nitrogen content is calculated as a percentage of sample mass using absorbance data and calibration standards. The method requires duplicate determinations to ensure reliability.

Applications

• Food Industry

  • Quality control and nutritional analysis of starch-based products
  • Protein content verification in food formulations
  • Compliance with food labeling and safety regulations

• Agricultural Laboratories

  • Analysis of starch derivatives and bioproducts for nitrogen content
  • Monitoring raw material quality in starch production

• Research and Development

  • Studying nitrogen metabolism and protein presence in starch materials
  • Developing new starch-based products with defined nutritional profiles

EN ISO 5378:1994 provides a reliable, standardized approach for nitrogen determination essential to maintaining product quality, safety, and integrity in starch-related industries.

Related Standards

• ISO 1871 – General directions for nitrogen determination using the Kjeldahl method
• ISO 3188 – Determination of nitrogen content in starches and derivatives by the Kjeldahl method using a titrimetric approach for samples with nitrogen content greater than 0.025%
• ISO 1227/Add. 2 – Vocabulary related to starch and derived products
• ISO 1042 – Specifications for volumetric laboratory glassware such as flasks and pipettes
• ISO 565 – Specifications for sieves used in sample preparation
• ISO 648 – Specifications for laboratory pipettes

These complementary standards ensure comprehensive analytical consistency and support broad application of Kjeldahl nitrogen determination techniques in food and agricultural product testing.

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Keywords: EN ISO 5378, Kjeldahl method, nitrogen determination, starch analysis, spectrophotometric method, Nessler reagent, sulphuric acid digestion, ammonia distillation, food quality control, starch derivatives, nitrogen content standard.

Standards Content (Sample)

SLOVENSKI STANDARD
01-november-1998
âNURELLQãNUREQLGHULYDWL'RORþHYDQMHGXãLNDSR.MHOGDKORYLPHWRGL
6SHNWURIRWRPHWULMVNDPHWRGD,62
Starches and derived products - Determination of nitrogen content by the Kjeldahl
method - Spectrophotometric method (ISO 5378:1978)
Stärke und Stärkederivate - Bestimmung des Stickstoffgehalts nach dem Kjeldahl-
Verfahren - Spektrometrisches Verfahren (ISO 5378:1978)
Amidons, fécules et produits dérivés - Dosage de l'azote selon la méthode de Kjeldahl -
Méthode spectrophotométrique (ISO 5378:1978)
Ta slovenski standard je istoveten z: EN ISO 5378:1994
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 STANDARDIZATION.MEXaYHAPOnHAPO~HAR OPf-AHM3ALWlR fl0 CTAH~APTI43AlJMM.ORGANISATlON INTERNATIONALE DE NORMALISATIOf’!
Starches and derived products - Determination of nitrogen
content by the Kjeldahl method - Spectrophotometric
method
Amidons, fbules et produits derr’ves - Dosage de l’azote selon Ia methode de Kjeldahl - Mbhode
spectropho tom&rique
First edition - 1978-06-15
UDC 664.2 : 543.846 : 543.42 Ref. No. ISO 5378-1978 (E)
determination of content, nitrogen,
Descriptors : food products, starches, Chemical analysis, spectrophotometric analysis.
Price based on 3 pages
FOREWORD
ISO (the International Organization for Standardization) is a worldwide federation
of national Standards institutes (ISO member bodies). The work of developing
International Standards is carried out through ISO technical committees. Every
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 5378 was developed by Technical Committee
ISO/TC 93, Starch (including derivatives and by-products), and was circulated
to the member bodies in March 1976.
It has been approved by the member bodies of the following countries :
Australia Germany Romania
Austria Hungary Spain
Chile I reland Turkey
Czechoslovakia Mexico United Kingdom
Finland Netherlands Yugoslavia
France Philippines
The member body of the following country expressed disapproval of the document
on technical grounds :
Poland
@ International Organkation for Standardkation, 1978 l
Printed in Switzerland
INTERNATIONAL STANDARD ISO 5378-1978 (E)
Starches and derived products - Determination of nitrogen
content by the Kjeldahl method - Spectrophotometric
method
1 SCOPE AND FIELD OF APPLICATION 5 REAGENTS
This International Standard specifies a spectrophotometric The reagents shall be of recognized analytical quality.
method for the determination, by the Kjeldahl method, Ammonia-free distilled water or water of at least equivalent
purity shall be used.
of the nitrogen content of starch and its derived products
whose presumed nitrogen content is less than 0,025 %
(m/m).l)
5.1 Sulphuric acid, concentrated, p2c 1,84 g/ml 196 %
(mhd]-
NOTE - In starches and their derived products to which nitrogen-
ous materials have not been added, the nitrogen is present essen-
tially in the form of Protein and/or amino acids.
5.2 Sodium hydroxide, Solution 30 % (mlm), p20
1,33 glml.
2 REFERENCES NOTE - This solution may be more concentrated.
ISO 1227/Add. 2, Starch, including derivatives and by-
5.3 Compound catalyst3) , consisting of, for example
Vocabulary, Addend.
products -
- potassium sulphate : 97 g;
ISO 1871, Agricultural food products - General directions
for the determination of nitrogen by the Kjeldahl method.
-
copper( II) sulphate, anhydrous : 3 g.
ISO 3 188, Starches and derived products - Determination
of nitrogen content by the Kjeldahl method - Titrimetric
5.4 Ammonium sulphate, ammonium oxalate or am-
method.
monium chloride.
5.5 Sulphuric acid, approximately 0,l N Standard volu-
3 DEFINITION
metric Solution.
nitrogen content : The value found using the procedure
specified. lt includes the nitrogen content of free amino
5.6 Nessler reagent, prepared as follows at least 2 days
acids, of compounds producing amino acids on hydrolysis
before use :
and of ammonium compounds. lt does not include the
nitrogen of nitrate and nitrite radicals, the nitrogen at-
Dissolve 100 g of mercury(I 1) iodide and 70 g of potassium
tached directly to another nitrogen atom or the nitrogen
iodide in 100 ml of water. Dissolve 224 g of potassium
attached to an Oxygen atom.
hydroxide in 700 ml of water in a 1 000 ml one-mark
volumetric flask and allow to cool to ambient tempera-
ture. Add the mercury( II) iodide/potassium iodide Solution
4 PRINCIPLE
slowly, with stirring, to the potassium hydroxide Solution.
Dilute to the mark with water and mix. Allow to stand for
Destruction of organic matter by sulphuric acid in the
at least 2 days before using.
presence of a compound catalyst*), alkalization of the
reaction products, distillation of the liberated ammonia
NOTE - The reagent should be kept in a brown glass bottle. If it is
and collection in a sulphuric acid Solution, followed by
kept in an air-tight bottle and in the shade, it tan be used even after
spectrophotometry, of the ammonium salt formed after
1 year if care is taken to leave the Sediments undisturbed when it is
the addition of the Nessler reagent. re-used.
1) For products whose presumed nitrogen content is greater than 0,Ol % (m/m), see ISO 3188.
2) See ISO 1871.
3) See ISO 1871. sub-clause 5.2.
ISO 5378-1978 (E)
7.2 Test portion
6 APPARATUS
Usual laboratory equipment and, in particular : Weigh, to the nearest 0,001 g, 2 to 5 g (mass m,) of the
test Sample (7.1), according to the presumed nitrogen
content, and transfer to the predried Kjeldahl flask (6.1),
6.1 Kjeldahl flask, of suitable capacity, usually 500 po
taking care that none of the product adheres to the inner
800 ml, preferably with a ground glass joint, and provided
wall of the neck of the flask.
with a pear-shaped glass bulb fitting Ioosely in the top of
the neck of the flask.
In the case of a viscous liquid or a product in Paste form,
the test Portion may be weighed in a small glass Container
6.2 Digestion stand, on which the Kjeldahl flask (6.1)
or on a sheet of aluminium, Paper or plastics which does
tan be heated in an inclined Position in such a way that
not yield nitrogen, or whose nitrogen content is known,
heat is applied only to
...