UGANDA STANDARD
 
        US ISO 5523
First Edition
2009-mm-dd
 
Reference numbe r 
     US ISO 5523:1981
 © UNBS 2009
  
Liquid fruit and vegetable products — Determination of sulphur 
dioxide content (Routine method) 
 US ISO 5523: 1981 
 
© UNBS  2009 – All rights reserved ii Compliance with this standard does not, of itself confer immunity from legal obligations 
A Uganda Standard does not purport to include all necessary provisions of a contract. Users are 
responsible for its correct application  
© UNBS 2009 
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       US ISO 5523:1981  
© UNBS  2009 - All rights rese rved                iii National foreword 
Uganda National Bureau of Standards (UNBS) is a parastatal under the Ministry  of Tourism, Trade and 
Industry established under Cap 327, of the Laws of U ganda. UNBS is mandated to co-ordinate the elaboration 
of standards and is  
(a) a member of International Organisation for Standardisation (ISO) and  
(b) a contact point for the WHO/FAO Codex A limentarius Commission on Food Standards, and  
(c) the National Enquiry Point on TBT/SPS Agr eements of the World Trade Organisation (WTO). 
The work of preparing Uganda Standards is carried out through Technical Committees. A Technical 
Committee is established to deliberate on standards in a gi ven field or area and consists of representatives of 
consumers, traders, academician s, manufacturers, governme nt and other stakeholders. 
Draft Uganda Standards adopted by the Technical Committ ee are widely circulated to stakeholders and the 
general public for comments. The committee reviews the comments before recommending the draft standards 
for approval and declaration as Uganda Standards by the National Standards Council. 
This Uganda Standard, US ISO 5523, Liquid fruit and vegetable products — Determination of sulphur dioxide
content (Routine method),  is identical with and has been reproduced from an International Standard, ISO
5523:1981, Liquid fruit and vegetable products — Determination of sulphur dioxide content (Routine 
method), and adopted  as a Uganda Standard.  
This standard was developed under the subcommittee on fruits and vegetables by the Food and agriculture 
Standards Technical Committee (UNBS/TC 2). 
Wherever the words, "International Standard" a ppear, they should be replaced by "Uganda Standard." 
 w - 
ii International Standard 
INTERNATIONAL ORGANIZATION FOR STANDARDIZATION.MEIK~YHAPO~HAR OPrAHM3ALWfl I-IO CTAH~APTM3ALWlWORGANISATION INTERNATIONALE DE NORMALISATION 
Liquid fruit and vegetable products - Determination of 
sulphur dioxide content (Routine method) 
Produits liquides d&iv& des fruits et &gumes - Determination de Ia teneur en dioxyde de soufre (Methode pratique) 
First edition - 1981-08-01 
M 
UDC 634/635 : 543.845 Ref. No. ISO 5523-1981 (EI 
Descriptors : fruit and vegetable products, beverages, Chemical analysis, determination of content, sulphur dioxide. 
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 Inter- 
national 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 5523 was developed by Technical Committee ISO/TC 34, 
Agricultuml food products, and was circulated to the member bodies in July 1979. 
lt has been approved by the member bodies of the following countries : 
Australia 
Austria 
Brazil 
Bulgaria 
Canada 
Chile 
Cyprus 
Czechoslovakia 
Egypt, Arab Rep. of 
Ethiopia 
France Germany, F. R. 
Hungary 
India 
Indonesia 
Israel 
Italy 
Kenya 
Korea, Rep. of 
Libyan Arab Jamahiriya 
Malaysia 
Mexico Netherlands 
Poland 
Portugal 
Romania 
South Africa, Rep. of 
Spain 
Thailand 
Turkey 
Y ugoslavia 
The member body of the following country expressed disapproval of the document on 
technical grounds : 
New Zealand 
0 International Organization for Standardization, 1981 
Printed in Switzerland INTERNATIONALSTANDARD ISO 5523-1981 (E) 
Liquid fruit and vegetable products - Determination of 
sulphur dioxide content (Routine method) 
0 Introduction 
This method, which was developed for the determination of the 
sulphur dioxide content of wines, has been found to be suitable 
for liquid fruit and vegetable products, and tan be used as a 
rapid method. 
In the case of more precise analyses, or in cases of dispute, the 
method specified in ISO 5522 shall be used. 
1 Scope and field of application 
This International Standard specifies a routine method for the 
determination of the sulphur dioxide content of liquid fruit and 
vegetable products. 
2 References 
ISO/R 385, Burettes. 
ISO 648, Laboratory glassware - One-mark pipettes. 
ISO 1773, Laboratory glassware - Boiling flasks fnarrow- 
necked). 
I SO 5522, Fruits, vegetables and derived products - Deter- 
mination of total sulphur dioxide content. 
3 Definitions 
3.1 free sulphur dioxide : Sulphur dioxide as such or as 
inorganic combinations of <H2S03, HS03 and SO;-. 
3.2 bound sulphur dioxide content : The differente be- 
tween the total sulphur dioxide content and the free sulphur 
dioxide con tent . 4 Principle 
4.1 Free sulphur dioxide 
Direct iodometric titration of the product at a pH between 0,7 
and 1, followed by a blank titration of the same product, freed 
from sulphur dioxide by boiling under reflux or by binding its 
free sulphur dioxide content with an excess of acetaldehyde 
(ethanal) or propionaldehyde (propanal). 
4.2 Bound sulphur dioxide 
After titration of the free sulphur dioxide, rendering of the pro- 
duct alkaline and titration of the sulphur dioxide liberated by 
this hydrolysis with iodine in an acid medium. 
A second iodometric titration after a second alkali hydrolysis 
permits titration of the sulphur dioxide which may have recom- 
bined, after the first hydrolysis, with any acetaldehyde present 
in the product. 
5 Reagents 
All reagents shall be of recognized analytical quality and in par- 
ticular shall not contain impurities which could be determined 
as sulphur dioxide. The water used shall be distilled water or 
water of at least equivalent purity, recently boiled. 
5.1 Sodium hydroxide, approximately 4 mol/1 solution.1) 
Dissolve 160 g of sodium hydroxide in water and dilute to 
1 000 ml. 
5.2 Sulphuric acid, 10 % (WV) Solution (180 g of H2S04 
per litre) . 
5.3 Starch, 5 g/l Solution containing 200 g of sodium 
chloride (as preservative) per litre. 
Maintain the Solution at boiling Point for 10 min during prepara- 
tion. 
1) Hitherto expressed as “approximately 4 N solution”. ISO 55234981 (E) 
5.4 lodine, Standard volumetric Solution, 
c(1/2 12) = 0,05 mol/lJ 
5.5 Sodium thiosulphate, Standard volumetric Solution, 
c(Na&03.5H20) = 0,005 moM.2) 
5.6 Acetaldehyde, 7 g/l Solution; or 
5.7 Propionaldehyde, 10 g/l Solution. 
6 Apparatus 
Usual laboratory 
particular : apparatus, not otherwise specif ied, and in 
6.1 Conical boiling flasks, of capacity 500 ml, complying 
with the requirements of ISO 1773. 
6.2 One-mark pipettes, of capacity 5 - 10 - 20 and 50 ml, 
complying with the requirements of ISO 648. 7.3.2 Add 8 ml of the sodium hydroxide Solution (5.1). Swirl 
once only and allow to stand for 5 min. With a Single move- 
ment and whilst swirling the flask vigorously, pour in 10 ml of 
the sulphuric acid Solution (5.2) from a beaker. Immediately 
titrate with the iodine Solution (5.4) (sec 9.1) until the mixture 
turns blue (sec 9.2). Decolourize with the minimum volume 
necessary of the sodium thiosulphate Solution (5.5). Subtract 
one tenth of the volume of this Solution from the volume of the 
iodine Solution used. 
7.3.3 Add 20 ml of the sodium hydroxide Solution (5.1). Swirl 
once only and allow to stand for 5 min. 
Dilute with 200 ml of water at a temperature close to 0 OC. 
With a Single movement and whilst swirling the flask 
vigorously, pour in 30 ml of the sulphuric acid Solution (5.2) 
from a beaker. Immediately titrate the sulphur dioxide thus 
liberated with the iodine Solution (5.4) (sec 9.1) until the 
mixture turns blue (see 9.2). Decolourize with the minimum 
volume necessary of the sodium thiosulphate Solution (5.5). 
Subtract one tenth of the volume of this Solution from the 
volume of the iodine Solution used. 
6.3 Burettes, of capacity 50 ml, 
requirements of ISO/R 385, class A. complying with the 
7.3.4 Blank titration 
6.4 Device for illuminating the bottom of the boiling flask 
with a vertical, yellow light beam obtained from a sodium 
vapour lamp, or from an ordinary lamp, the white light of which 
is filtered through a potassium chromate solution. 
6.5 Distillation apparatus, consisting of a 500 ml boiling 
flask and a reflux condenser. 
7 Procedure 
7.1 Preparation of test Sample 
Render the Sample homogeneous. 
7.2 Test Portion 
Transfer, by means of a pipette (6.2), 50 ml of the test Sample 
to a 500 ml boiling flask (6.1). 
7.3 Determination 
7.3.1 Add 3 ml of the sulphuric acid Solution (5.2) and 5 ml of 
the starch solution (5.3) to the contents of the boiling flask. Im- 
mediately titrate with the iodine Solution (5.4) (sec 9.1) until the 
mixture turns blue (see 9.2). Decolourize with the minimum 
volume necessary of the sodium thiosulphate Solution (5.5). 
Subtract one tenth of the volume of this Solution from the 
volume of the iodine Solution used. 
1) Hitherto expressed as “0,05 N Standard volumetric solution”. 
2) Hitherto expressed as “0,005 N Standard volumetric solution”. Some substances (especially ascorbic acid), present in a natura1 
state or added to a product, are oxidized by iodine in acid 
medium. This leads to a false value for the iodometric titration 
and, in such cases, the determinations shall be carried out on a 
test Sample desulphurized by one of the following procedures. 
7.3.4.1 Desulphurization by boiling under reflux 
Place 100 ml of the product to be analysed in the 500 ml boiling 
flask of the distillation apparatus (6.5) fitted with the reflux con- 
denser, and boil vigorously for at least 30 min. 
The condenser shall be sufficiently short and wide to enable the 
sulphur dioxide to escape by diffusion at a sufficient rate. Allow 
to cool before removing the condenser. Transfer 50 ml of the 
liquid thus freed from sulphur dioxide into a 500 ml boiling flask 
(6.1). 
7.3.4.2 Desulphurization by combination with an aldehyde 
Place 50 ml of the product to be analysed in a 500 ml boiling 
flask (6.1) and add 5 ml of the acetaldehyde Solution (5.6) or 
5 ml of the propionaldehyde Solution (5.7). Stopper the flask, 
and allow to stand for at least 30 min. 
7.3.4.3 Titration 
Proceed as specified in 7.3.1 using 50 ml of the desulphurized 
product (7.3.4.1 or 7.3.4.2). 
2 ISO 5523-1981 (E) 
7.4 Number of determinations 
Carry out two determinations on the same test Sample (7.1). 
8 Expression of results 
8.1 Method of calculation and formulae 
The free sulphur dioxide content, expressed in milligrams per 
litre of product, is given by the formulal) 
1,6 x 1000 
5. ( V. - VS) = 32 ( V. - VS) 
The total sulphur dioxide content, expressed in milligrams per 
litre of product, is given by the formulal) 
32 ( V. + V, + V2 - VS) 
The bound sulphur dioxide content, expressed in milligrams per 
litre of product, is given by the formulal) 
32 ( V, + V2) 
where 
V0 is the corrected volume, in millilitres, of iodine Solution 
used in 7.3.1; 
VI is the corrected volume, in millilitres, of iodine Solution 
used in 7.3.2; 
V2 is the corrected volume, in millilitres, of iodine Solution 
used in 7.3.3; 
V3 is the corrected volume, in millilitres, of iodine solution 
used in 7.3.4.3; 1,6 is the mass, in milligrams, of sulphur dioxide cor- 
responding to 1 ml of 0,05 mol/1 iodine Solution. 
NOTE - If the product 
general, 5to 15 % of VI. 
8.2 Repeatability 
To be added later. contains acetaldehyde, V’2 represents, in 
9 Notes on procedure 
9.1 For products having low sulphur dioxide contents, it is 
preferable to use a more dilute iodine Solution, for example a 
Solution of concentration c( 1/2 12) = 0,02 mol/l. 
9.2 For highly coloured products, it is more advantageous to 
use the device producing a yellow light beam (6.4) for 
illuminating the bottom of the flask containing the test Portion. 
Operate in a dark room and observe the transparency of the 
product, which becomes opaque when the starch changes 
colour. 
10 Test report 
The test report shall show the method used and the results 
obtained. lt shall also mention any operating conditions not 
specified in this International Standard, or regarded as op- 
tional, as weil as any circumstances that may have influenced 
the results. 
The report shall include all 
identification of the Sample. details required for complete 
1) If iodine Solution of concentration c( 1/2 12) = 0,OZ mol/1 was used, replace the coefficient 32 by 12,8. This page intentionally left blank This page intentionally lef? blank This page intentionally left blank