ISO 5379:2013

Starches and derived products — Determination of sulfur dioxide content — Acidimetric method and nephelometric method

ISO 5379:2013 specifies two methods (an acidimetric method and a nephelometric method) for the determination of the sulfur dioxide content of starches and derived products.

Amidons, fécules et produits dérivés — Détermination de la teneur en dioxyde de soufre — Dosage acidimétrique et dosage par néphélémétrie

General Information

• Status: Published
• Publication Date: 18-Aug-2013
• ICS: 67.180.20 - Starch and derived products
• Technical Committee: ISO/TC 93 - Starch (including derivatives and by-products)
• Drafting Committee: ISO/TC 93 - Starch (including derivatives and by-products)
• Current Stage: 9093 - International Standard confirmed
• Start Date: 10-Aug-2021
• Completion Date: 13-Dec-2025

Relations

• Revises: ISO 5379:1983 - Starches and derived products — Determination of sulfur dioxide content — Acidimetric method and nephelometric method
• Effective Date: 28-Feb-2009

Overview

ISO 5379:2013 - "Starches and derived products - Determination of sulfur dioxide content - Acidimetric method and nephelometric method" specifies two validated analytical procedures for measuring sulfur dioxide (SO2) in starches and starch-derived products. The standard (second edition, 2013) defines the scope, required reagents and apparatus, stepwise procedures, calculation of results, quality checks and reporting rules for routine laboratory determinations.

Key topics and technical requirements

• Two methods specified
  • Acidimetric (entrainment + titration): SO2 is displaced from the sample by acid and nitrogen entrainment, absorbed in hydrogen peroxide, converted to sulfuric acid and titrated with standardized NaOH (or determined by iodine titration as a check).
  • Nephelometric: Used when titrant volumes are very small (practical limit thresholds specified); detects sulfate/barium sulfate turbidity using barium chloride/PVP reagent and measurement at 650 nm.
• Essential reagents and purity
  • Reagents must be analytical quality and sulfate-free (water, hydrogen peroxide solutions, hydrochloric acid, indicators, standardized NaOH and iodine solutions, Na2S2O5/EDTA standard).
  • Nephelometric reagents include polyvinylpyrrolidone (PVP), barium chloride and a mixed reagent with ethanol and sulfuric acid.
• Apparatus
  • Entrainment apparatus (Lieb/Zaccheri type) with round-bottom flask, condenser and two bubblers; ground-glass joints recommended.
  • Standard volumetric glassware, burettes, analytical balance, magnetic stirrer with heating, water bath (20 ±1 °C) and a spectrometer at 650 nm for nephelometry.
• Sampling and test portion
  • Test portion mass depends on expected SO2 (table provided). For high contents adjust to contain ≤10 mg SO2.
• Quality control
  • Check tests for entrainment apparatus and titration accuracy; minimize oxidation of standards (EDTA use).
  • Repeatability: difference between two determinations by same analyst ≤ 5% of mean. Reproducibility between labs ≤ 10% (ISO 5725-2 referenced).
• Decision rule
  • If titrant volume V < 5 mL (with 10 mmol/L NaOH) or < 0.5 mL (with 0.1 mol/L NaOH), the nephelometric method must be used. (For 100 g sample, 5 mL corresponds to ~16 mg SO2/kg.)

Applications and users

• Quality control and compliance testing in the starch production and food ingredient industries.
• Contract testing and food analysis laboratories monitoring sulfite/sulfur dioxide residues in starches, flours, dextrins and derived products.
• Regulatory bodies and R&D groups developing analytical protocols for food safety and labeling where SO2 limits apply.
• Useful for troubleshooting manufacturing processes where sulfiting agents are used.

Related standards

• ISO 1042 (volumetric flasks), ISO 648 (pipettes), ISO 385 (burettes), ISO 5725-2 (repeatability/reproducibility) - all cited within ISO 5379:2013 for equipment and precision guidance.

Keywords: ISO 5379:2013, sulfur dioxide determination, starches, acidimetric method, nephelometric method, SO2 analysis, entrainment apparatus, nephelometry, titration, food quality control.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 5379
Second edition
2013-09-01
Starches and derived products —
Determination of sulfur dioxide
content — Acidimetric method and
nephelometric method
Amidons, fécules et produits dérivés — Détermination de la teneur
en dioxyde de soufre — Dosage acidimétrique et dosage par
néphélémétrie
Reference number
©
ISO 2013
© ISO 2013
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
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Published in Switzerland
ii © ISO 2013 – All rights reserved

Contents Page
Foreword .iv
1 Scope . 1
2 Acidimetric method . 1
2.1 Reagents. 1
2.2 Apparatus . 2
2.3 Procedure . 4
2.4 Expression of results . 6
3 Nephelometric method . 6
3.1 Reagents. 6
3.2 Apparatus . 7
3.3 Procedure . 7
3.4 Expression of results . 8
4 Test report . 8
Bibliography . 9
Foreword
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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.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2. www.iso.org/directives
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. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received. www.iso.org/patents
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
The committee responsible for this document is ISO/TC 93, Starch (including derivatives and by-products).
This second edition cancels and replaces ISO 5379:1983, of which it constitutes a minor revision.
iv © ISO 2013 – All rights reserved

INTERNATIONAL STANDARD ISO 5379:2013(E)
Starches and derived products — Determination of
sulfur dioxide content — Acidimetric method and
nephelometric method
1 Scope
This International Standard specifies two methods (an acidimetric method and a nephelometric method)
for the determination of the sulfur dioxide content of starches and derived products.
2 Acidimetric method
2.1 Reagents
WARNING — All chemicals shall be handled with care. Consult the appropriate material safety
data sheet for proper handling and disposal procedures.
All reagents shall be of recognized analytical quality and be sulfate-free.
2.1.1 Water, distilled water or water of at least equivalent purity, recently boiled.
2.1.2 Nitrogen, oxygen-free.
2.1.3 Hydrogen peroxide, solution containing approximately 9 g to 10 g of H O per litre
2 2
{c(H O ) = 0,265 to 0,294 mol/l}.
2 2
Place 150 ml of 20 volumes (6 wt %, 2,08 mol/l) hydrogen peroxide solution or 30 ml of 110 volumes (30 wt %,
10,4 mol/l) hydrogen peroxide solution in a 1 l one-mark volumetric flask. Dilute to the mark with water.
This solution should be freshly prepared.
2.1.4 Hydrochloric acid.
To 500 ml of water in a 1 l beaker, slowly add 150 ml of concentrated hydrochloric acid (ρ 1,18 g/ml;
12 mol/l; 37 wt %) with stirring. Transfer this qualitatively to a 1 l volumetric flask and dilute to the mark.
CAUTION — Never add water to concentrated acid.
2.1.5 Bromophenol blue indicator solution.
Dissolve 100 mg of bromophenol blue [alternative names are α, α-bis(3,5-dibromo-4-hydroxyphenyl)
toluene-2, α–sulfone or 3, 3’, 5, 5’-tetrabromophenol sulfonephthalein] in 100 ml of 20 % (V/ V) ethanol.
2.1.6 Tashiro indicator solution.
Dissolve 30 mg of methyl red {2-[[4-(dimethylamino)phenyl ]-azo] benzoic acid} and 50 mg of methylene
blue [3,7-bis(dimethylamino)phenothiazin-5-ium chloride] in 120 ml of 90 % (V/ V) ethanol. Dilute to
200 ml with water, mix and filter if necessary.
NOTE The Tashiro indicator can only be used with the titrimetric method (2.3.4). The bromophenol blue
indicator is appropriate for the titrimetric method and does not hinder the further use of the nephelometric
method (see Clause 3). Nevertheless, with this indicator, it is more difficult to detect the end-point.
2.1.7 Sodium hydroxide, standard volumetric solution, c(NaOH) = 0,1 mol/l; or sodium hydroxide,
standard volumetric solution, c(NaOH) = 10 mmol/l.
In order to obtain a sharp end-point, prepare this solution using carbon-dioxide-free water obtained by
cooling boiled distilled water (2.1.1) under a flow of nitrogen (2.1.2).
The use of sodium hydroxide, standard volumetric solution, c(NaOH) = 0,1 mol/l is recommended and a
piston-burette is useful for small volumes. If necessary, increase the mass of the test portion.
2.1.8 Iodine, standard volumetric solution, c(I ) = 10 mmol/l. Potassium iodate (KIO ) at the
2 3
appropriate concentration is a suitable substitute.
2.1.9 Starch, 5 g/l solution.
Dissolve 0,5 g of Lintner starch or similar in 100 ml of water. Heat to boiling while stirring. Add 20 g of
sodium chloride, stir and boil until dissolution is complete. Allow to cool to ambient temperature before use.
2.1.10 Sodium metabisulfite (c(SO ) = 7,8 mmol/l) and ethylenediaminetetraacetic acid (EDTA),
1)
disodium salt (c(EDTA) = 0,5 mmol/l).
Dissolve in water 0,74 g of sodium metabisulfite (Na S O ) and 0,20 g of ethylenediaminetetraacetic
2 2 5
acid disodium salt dihydrate (Na H EDTA·2H O). Transfer the solution quantitatively to a 1 l volumetric
2 2 2
flask and make up to the mark with water. For accurate results, minimize exposure of this solution to
the atmosphere.
2.2 Apparatus
Glass apparatus should preferably be fitted with ground glass joints. Use ordinary laboratory apparatus,
and in particular, the following. See Figure 1.
2.2.1 One-mark volumetric flasks, of capacity 1 l, complying with the requirements of ISO 1042, class A.
2.2.2 One-mark pipettes, of capacities 0,1 −1 −2 −3 −5 and 20 ml, complying with the requirements of
ISO 648, class A.
2.2.3 Burettes, with capacities of 10 ml, 25 ml and 50 ml, complying with ISO 385, smallest scale
division, accuracy class A or AS.
2.2.4 Analytical balance, capable of weighing to the nearest 10 mg.
2.2.5 Magnetic stirrer, efficient, with heating, for use with the flask (A) (see Figure 1).
2.2.6 Entrainment apparatus, as shown in the Figure 1, or equivalent equipment for ensuring the
displacement and entrainment of sulfur dioxide and its absorption in a solution of hydrogen peroxide.
Avoid making connections with tubes between the condenser and the bubblers as this could lead to
absorption of sulfur dioxide.
1) EDTA is used to retard any oxidation of sulfite by air in the presence of trace amounts of copper ion.
2 © ISO 2013 – All rights reserved

Dimensions in millimetres
Key
A round-bottom flask, of capacity 250 ml or greater, with a ground tubular allowing the introduction of a
thermometer
B vertical condenser of high efficiency, to fit the flask (A)
C separating funnel, fitted to the flask (A)
D nitrogen inlet with an absorber containing an alkaline solution of pyrog
...