UGANDA STANDARD
 
      US ISO 5522
First Edition
2009-mm-dd
 
 Reference numbe r
    US ISO 5522:1981
© UNBS 2009
  
Fruits, vegetables and derived products — Determination of 
total sulphur dioxide content 
 US ISO 5522:1981 
 
© UNBS  2009 – All rights reserved 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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The Executive Director 
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P.O. Box 6329 
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Uganda 
Tel: 256 41 505 995 
Fax: 256 41 286 123 
E-mail: unbs@infocom.co.ug  
      US ISO 5522:1981  
© UNBS  2009 - All rights reserved 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 Uganda.  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 5522:1981, Fruits, vegetables and derived products — Determination of total 
sulphur dioxide content, is identical with and  has been reproduced from an International Standard ISO 5522:
1981,  Fruits, vegetables and derived products — Determination of total sulphur dioxide content, and adopted
as a Uganda Standard . 
 
This standard was developed by the Food and agricu lture Standards Technical Committee, UNBS/TC 2. 
Wherever the words, "International Standard" a ppear, they should be replaced by "Uganda Standard." international Standard 
INTERNATIONAL ORGANIZATION FOR STANDARDIZATION.ME)I(L1YHAPO~HAfl OPI-AHH3AWR 00 CTAH~APTH3AI#lH~RGANISATION INTERNATIONALE DE NORMALISATION 
Fruits, vegetables and derived products - Determination 
of total sulphur dioxide content 
Fruits, kgumes et produits dhriv& - Dbtermination de Ia teneur en dioxyde de soufre total 
First edition - 1981-09-01 
UDC 634/635: 543.846 Ref. No. ISO 55224981 (EI 
Descriptors : agricultural products, fruit and vegetable products, fruits, vegetables, Chemical analysis, determination of content, sulphur dioxide. 
Price based on 7 pages Foreword 
ISO (the international Organization for Standardization) is a worldwide federation of 
national Standards institutes (ISO member bedies). The work of developing lnter- 
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 5522 was developed by Technical Committee ISO /TC 34, 
Agricuftural 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 
Netherlands 
No member body expressed disapproval of the document. 
0 International Organkation for Standardkation, 1981 New Zealand 
Peru 
Philippines 
Poland 
Portugal 
Romania 
South Africa, Rep. of 
Spain 
Thailand 
Turkey 
Y ugoslavia 
Printed in Switzerland INTERNATIONAL STANDARD ISO 5522-1981 (E) 
Fruits, vegetables and derived products - Determination 
of total sulphur dioxide content 
1 Scope and field of application 
This International Standard specifies a method for the deter- 
mination of the total sulphur dioxide content of fruits, 
vegetables and derived products, whatever the sulphur dioxide 
content. 
2 Principle 
Acidification and heating of a test Portion, then entrainment, in 
a current of nitrogen, of the sulphur dioxide Iiberated. Absorp- 
tion and Oxidation of the sulphur dioxide by bubbling it through 
a neutral, dilute hydrogen peroxide Solution. Determination of 
the sulphuric acid thus formed using Standard volumetric 
sodium hydroxide Solution. 
Verification of the determination by precipitation of 
sulphate from the resulting Solution, and, according 
sulphur dioxide content : 
- weighing of the barium sulphate (annex A); or 
- nephelometric determination (annex B). barium 
to the 
3 Reagents 
All reagents shall be of recognized analytical quality. The water 
used shall be distilled water or water of at least equivalent 
purity, recently boiled. 
3.1 Nitrogen, Oxygen free. 
3.2 Hydrogen Peroxide, 9,1 g/l Solution, free from sulphate 
ions. 
3.3 Hydrochlorit acid, 100 g/l Solution. 
Dilute 1 volume of concentrated hydrochloric acid, 
@20 = 1,19 g/ml, with 3 volumes of water. 3.4 Indicator solution. 
Dissolve 100 mg of bromophenol bluel) in 100 ml of 
20 % ( vl v) ethanol. 
3.5 Sodium hydroxide, Standard volumetric Solution, 
c(NaOH) = 0,l moW, free from sulphate ions; or 
3.6 Sodium hydroxide, Standard volumetric Solution, 
c(NaOH) = 0,Ol mol/l3), free from sulphate ions. 
3.7 lodine, Standard volumetric Solution, 
c(l/2 12) = 0,02 mol/14). 
3.8 Starch, 5 g/l Solution containing 200 g of sodium 
chloride (as preservative) per Iitre. 
Maintain the Solution at boiling Point for 10 min during prepara- 
tion. 
3.9 Potassium metabisulphite/EDTA Solution. 
Dissolve in a little water 1,20 g of potassium metabisulphite 
(K2S205) and 0,20 g of the disodium salt of ethylenedinitrilo- 
tetraacetic acid? Transfer the Solution quantitatively to a 
1 000 ml one-mark volumetric flask. Make up to the mark with 
water and mix. 
3.10 Sucrose, 100 g/l Solution. 
4 Apparatus 
Usual laboratory apparatus not otherwise specified, and in par- 
ticular : 
4.1 Measuring cylinders. 
4.2 Pipettes. 
1) This indicator has been Chosen because it does not give rise to interference in nephelometric determinations. 
2) Hitherto expressed as “OJ N Standard volumetric solution”. 
3) Hitherto expressed as “0,Ol N Standard volumetric solution”. 
4) Hitherto expressed as “0,02 N Standard volumetric solution”. 
5) This product is intended to protect the sulphite ion from Oxidation by air by complexing the traces of topper ion. 
1 ISO 55224981 (El 
4.3 Semi-microburette, of capacity 10 ml. 
4.4 Burette, of capacity 25 ml. 
4.5 Blender. 
4.6 Entrainment apparatus, such as that shown in the 
figurei), or equivalent apparatus ensuring the displacement and 
the entrainment of sulphur dioxide and its absorption in the 
hydrogen peroxide solution. 
4.6.1 Construction of the apparatus 
A: 
8 : 
c: 
D: 
E and E 
F: 
NOTE - Between tests, if the entrainment is sufficiently 
tle, only the flask (A) need be cleaned. round-bottom flask, of capacity 250 ml or more. 
reflux condenser, of high efficiency, capable of be- 
ing fitted to the flask (AI. 
dropping funnel, capable of being adapted to the 
flask (AI. 
nitrogen inlet. 
2 bubblers, in series, capable of being fitted to the 
condenser I B). 
disk, of sheet-iron or asbestos, diameter 150 mm, 
having a central hole of diameter 40 mm. This disk is 
intended to prevent any pyrogenation, particularly of 
the extractable matter in the product. 
slow and gen- 
4.6.2 Check tests 
The apparatus shall satisfy the following three check tests : 
4.6.2.1 lntroduce into the flask (A) 100 ml of water and 5 ml 
of the hydrochloric acid Solution (3.3). Heat the flask under 
reflux, while passing a current of nitrogen, for 1 h, with the 
bubblers (E and E’ 1 each containing 5 ml of water and 0,l ml of 
the indicator Solution (3.4). 
The contents of each bubbler shall remain neutral. 
4.6.2.2 Introduce into the flask (AI 20 ml of the sucrose solu- 
tion (3.10). Heat the flask under reflux, while passing a current 
of nitrogen, for 1 h. 
The sucrose Solution shall remain colourless, and there shall be 
no deposition of caramel on the Walls of the flask. (The test is 
intended to check the intensity of heating.) 
~-~ 
1) Apparatus of 
2) the Lieb and Zaccherl tYPe- 4.6.2.3 Carry out the following two operations : 
a) By means of a pipette t4.2), introduce into the flask (A) 
20 ml of the potassium metabisulphite/EDTA Solution (3.9) 
and 5 ml of the hydrochloric acid Solution (3.3). Carry out 
the entrainment and determination of sulphur dioxide under 
the same conditions as the determination proper, but 
without adding hydrochloric acid Solution (i.e. as specified 
in 5.3.1, 5.3.2, 5.3.5 and 5.4). 
b) Introduce into a 100 ml conical flask, 20 ml of the 
potassium metabisulphite/EDTA Solution (3.9), and add 
5 ml of the hydrochloric acid Solution (3.3) and 1 ml of the 
starch Solution (3.8). 
Titrate, using the burette (4.4) containing the iodine solu- 
tion (3.7) until the first appearance of a blue colour. 
I ne sulphur dioxide content obtained in a) shall be within 
+ 1 % of that obtained in b). 
Procedure b) shall not be carried out more than 15 min after 
terminating procedure a), in Order to avoid a possible Change in 
the sulphur dioxide content of the metabisulphite Solution. 
4.7 Balance. 
5 Proeedure 
51 . Preparation of test Sample 
Remove seeds and hard seed-cavity 
blend the Sample carefully. Walls if necessary, and 
Allow frozen or deep-frozen products to thaw in a closed 
Container, and add the liquid formed during this process to the 
product before blending. 
5.2 Test Portion 
Weigh, to the nearest 0,Ol g, 10 to 100 g of the test Sample 
(5.11, according to the expected sulphur dioxide content, so 
that the test Portion contains not more than 10 mg of sulphur 
dioxide; transfer the test Portion to the flask (A) of the entrain- 
ment apparatus (4.6). 
5.3 Entrainment 
53.1 Place in each bubbler (E and E’ ) 3 ml2) of the hydrogen 
peroxide Solution (3.2) and 0,l ml of the indicator Solution 
(3.4), and neutralize the hydrogen peroxide Solution with the 
0,Ol mol/1 sodium hydroxide Solution (3.6). 
This quantity is theoretically sufficient to oxidize 51 mg of sulphur dioxide, but an excess is essential. 
2 ISO 5522-1981 (Ei 
5.3.2 Connect the dropping funnel KZ), the reflux condenser 
(B) and the bubblers (E and E’ ) to the flask (A); pass a current 
of nitrogen to drive out the air from the flask (A) and the whole 
of the apparatus. 
5.3.3 Place 100 ml of water and 5 ml of the hydrochloric acid 
Solution (3.3) in the dropping funnel (CL 
5.3.4 Allow the dilute hydrochloric acid Solution contained in 
the dropping funnel (C) to run into the flask (A) (if necessary, 
interrupting the nitrogen current momentarily). 
5.3.5 Bring the contents of the flask slowly to the boil, and 
maintain at the boiling Point, allowing the nitrogen to circulate 
regularly throughout to give one or two bubbles per second, for 
about 30 min. 
5.4 Titration 
Transfer the contents of the second bubbler (E’ ) to the first and 
titrate the sulphuric acid formed with the 0’01 mol/1 (3.6) or 
0’1 mol/1 (3.5) sodium hydroxide solution, according to the 
expected sulphur dioxide content. 
5.5 Verification 
5.5.1 If the volume Vof 0’01 mol/1 sodium hydroxide Solution 
required exceeds 10 ml (or 1 ml in the case of 0’1 mol/1 sodium 
hydroxide solution), carry out the gravimetric determination 
specified in annex A. 
5.5.2 If the volume V is less than 10 ml, carry out the 
nephelometric determination specified in annex B. 
If the volume V is less than 5 ml, only the nephelometric 
method may be used. For a test Portion of 100 g, this 5 ml limit 
corresponds to a sulphur dioxide content of 16 mg/kg. 
Above this limit, the acidimetric determination is sufficient. 
5.6 Number of determinations 
Carry out two determinations on the same test Sample (5.1). 6 Expression of results 
6.1 Method of calculation and formula 
The sulphu r dioxide content, expressed in milligrams per 
kilogram of product, is given by the formula 1) 
V V 
0’32 x - x 103 = 320 x - 
m m 
m is the mass, in grams, of the test Portion (5.2); 
V is the volume, in millilitres, of the 0’01 mol/1 sodium 
hydroxide Solution (3.6) used for the titration (5.4); 
0’32 is the mass, in milligrams, of sulphur dioxide cor- 
responding to 1 ml of 0’01 mol/1 sodium hydroxide 
Solution. 
6.2 Repeatability 
The differente between the results of two determinations, car- 
ried out simultaneously or in rapid succession by the same 
analyst, shali not exceed + 5 % of the mean value. 
7 Test report 
The test report shall show the method used and the result ob- 
tained. It 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 result. 
The test repot-t shall include 
identification of the Sample. all details required for complete 
1) If the 0,l mol/1 sodium hydroxide Solution (3.5) is used, replace the coefficient 320 by 3 200. ISO5522-1981 (El 
(D) 
(Al (9) 
m 
c I 
- 
\ 
I . Dimensions in millimetres 
(E) 
NOTE - The internal diameters of the four concentric tubes which serve as the condenser are 45, 34, 27 and IO mm, respectively. lt is advantageous 
to replace the two ground conical surfaces by spherical ones. 
Figure - Schematic diagram of an apparatus for entrainment 
4 ISO 5522-1981 (E) 
Annex A 
Gravimetric verification of the acidimetric determination 
of the sulphate ion formed 
A.1 Reagents 
All reagents shall be of recognized analytical quality. The water 
used shall be distilled water or water of at least equivalent 
purity, recently boiled. 
A.l.l Barium chloride, 100 g/l solution. 
A.1.2 Concentrated hydrochloric acid, 
@20 = 1,19 g/ml. 
A.1.3 Washing Solution for the barium sulphate 
precipitate. 
Dissolve in water, in a 1 000 ml one-mark volumetric flask, 
26 mg of barium chloride dihydrate (BaC12-2H20), add 1 ml of 
the concentrated hydrochloric acid (A.l.2) and dilute to the 
mark with water. 
A.2 Apparatus 
Usual laboratory apparatus not otherwise specified, and in par- 
ticular : 
A.2.1 
A.2.2 
A.2.3 
A.2.4 
A.2.5 
A.2.6 Conical flasks, of capacity 50 ml. 
Volumetric pipettes, of appropriate capacities. 
Ash-less filter Paper. 
Oven, capable of being controlled at 800 + 25 OC. - 
Incineration dishes. 
Desiccator, containing an efficient desiccant (other 
than sulphuric acid). 
A.2.7 Analytical balance. 
A.3 Procedure 
A.3.1 After the titration (see 5.41, transfer the contents of 
the bubbler (EI, and the water used for washing, to a conical 
flask (A.2.1); the total volume shall be approximately 25 ml. 
Add 1 ml of the concentrated hydrochloric acid (A.1.2) and 
bring to the boil. 
Add, drop by drop, 2 ml of the barium chloride Solution 
(A.l.l), stir, then allow to cool and stand for 12 h. Quan- 
titatively collect the precipitate formed, on the filter Paper 
(A.2.31, previously moistened with boiling water. Wash the precipitate once with 20 ml of tepid distilled water, then five 
times with 20 ml portions of tepid washing Solution (A.l.3). 
Drain and dry. 
Place the filter Paper and precipitate in the incineration dish 
(A.2.5)’ previously dried and tared to the nearest 1 mg, and in- 
cinerate in the oven (A.2.4)’ controlled at 800 + 25 OC, for 2 h. 
Remove from the oven. After cooling in the desiccator (A.2.61, 
weigh the dish and its contents to the nearest 1 mg. 
Determine by differente the mass of barium sulphate obtained. 
A.3.2 Carry out gravimetric verifications of both the deter- 
minations specified in 5.6. 
A.4 Expression of results 
A.4.1 Method of calculation and formula 
The sulphur dioxide content, expressed in milligrams per 
kilogram of product, is given by the formula 
0,274 5 ml x 103 m 
where 
ml is the mass, in milligrams, of barium sulphate ob- 
tained (see A.2.6); 
m has the same meaning as in 6.1; 
0,274 5 is the mass, in milligrams, of sulphur dioxide cor- 
responding to 1 mg of barium sulphate. 
Take as the result the arithmetic mean of the two determina- 
tions, provided that the requirement for repeatability (see 
A.4.2) is satisfied. 
A.4.2 Repeatability 
The differente between the results of the two determinations, 
carried out simultaneously or in rapid succession by the same 
analyst, shall not exceed + 5 % of their mean value. 
A.5 Agreement of results 
The result obtained shall not differ by more than 5 % from that 
obtained using the acidimetric method. 
In the case where the differente in results obtained by the 
acidimetric method and the gravimetric method is greater than 
5 %, only the result obtained by the gravimetric method shall 
be reported. 
5 ISO 5522-1981 (E) 
Annex B 
Nephelometric verification of the acidimetric determination 
of the sulphate ion formed 
B.l Reagents 
B.l .l Sulphuric acid, Standard Solution. 
Place 31,2 ml of Standard volumetric sulphuric acid solution, 
c(l/2 H2SOd) = 0,l mol/lt), in a 1 000 ml one-mark volumetric 
flask, and make up to the mark with water. 
1 ml of this Solution corresponds to 0’1 mg of S02. 
B.1.2 Polyvinyl pyrolidone, 50 g/l solution, free from 
sulphate ions (mean relative molecular mass 85 000). 
B.1.3 Barium chloride and polyvinyl pyrolidone, mixed 
Solution. 
Mix 80 ml of IQ0 g/l barium chloride Solution with 20 ml of the 
polyvinyl pyrolidone Solution (B.1.2). 
BA.4 Hydrochlorit acid Solution (sec 3.3). 
B.1.5 Indicator Solution (sec 3.4). 
B.2 Apparatus 
B.2.1 One-mark volumetric flasks, of capacity 50 ml, 
complying with the requirements of ISO 1042. 
B.2.2 Pipettes, or burettes, to deliver 2 - 4 - 8 - 12 - 
16 and 25 ml. 
B.2#3: Spectrophotometer, suitable for measurements at a 
wavelength of 650 nm. 
B.3 Procedure 
B.3.1 Preparation of the calibration curve 
Into a series of six 50 ml one-mark volumetric flasks (B.2.1)’ 
place 0 - 2 - 4 - 8 - 12 and 16 ml of the Standard sulphuric 
acid Solution (B.l .l), 20 ml of water, 0,l ml of the indicator 
Solution (B.1.5), 1 ml of the hydrochloric acid Solution (B.1.4) 
and 5 ml of the mixed Solution (B.1.3). Make up to the mark 
with water and mix. 
1) Hitherto expressed as “0,l N Standard volumetric solution”. The solutions obtained correspond respectively to 0 - 0’2 - 
0’4 - 0’8 - 1’2 and 1,6 mg of sulphur dioxide. 
After 15 to 20 min of having added the mixed Solution (B. 1.3)’ 
measure the absorbance of each Solution at 650 nm using the 
spectrophotometer (B.2.3). 
Plot the calibration curve of absorbance as a function of the 
sulphur dioxide content, in milligrams per Iitre. 
B.3.2 Determination 
B.3.2.1 Case where the volume V of 0,Ol mol/1 sodium 
hydroxide solution is less than 5 ml 
After the titration (see 5.41, transfer the contents of the bubbler 
(E), and the water used for washing, to a 50 ml one-mark 
volumetric flask (B.2.1). Add 1 ml of the hydrochloric acid sol- 
ution (B.1.4) and 5 ml of the mixed Solution (B.1.3). Make up 
to the mark with water and mix. 
After the titration (sec 5.4)’ transfer the contents of the bubbler 
(EI, and the water used for washing, to a 50 ml one-mark 
volumetric flask (B.2.1). Make up to the mark with water and 
mix. 
B.3.2.2 Case where the volume V of 0,Ol mol/1 sodium 
hydroxide solution is between 5 and 10 ml 
After the titration (sec 5.41, transfer the contents of the bubbler * 
(EI, and the water used for washing, to a 50 ml one-mark 
volumetric flask (8.2.1). Make up to the mark with water and 
mix. 
Transfer 25 ml of this Solution to another 50 ml one-mark 
volumetric flask (B.2.1). Add 1 ml of the hydrochloric acid sol- 
ution (B.1.4) and 5 ml of the mixed Solution (B.1.3). Make up 
to the mark with water and mix. 
After 15 to 20 min of having added the mixed Solution (B.1.3)’ 
measure the absorbance of the Solution at 650 nm using the 
spectrophotometer (8.2.3). 
B.3.3 Number of determinations 
Carry out nephelometric verifications of both the determina- 
tions specified in 5.6. ISO 55224981 (El 
8.4 Expression of results 
B.4.1 If verification was carried out in accordance 
with B.3.2.1, the sulphur dioxide content, expressed in 
milligrams per kilogram of product, is given by the formula 
1 000 
cx- 
m 
c is the sulphur dioxide concentration, in milligrams per 
litre, read from the calibration curve (B.3.1) and 
corresponding to the absorbance measured in B.3.2.1; 
m has the same meaning as in 6.1. 
B.4.2 If verification was carried out in accordance 
with B.3.2.2, the sulphur dioxide content, expressed in 
milligrams per kilogram of product, is given by the formula 
‘Ooox2 cx- 
m where 
c has the same meaning as in B.4.1 
the absorbance measured in 8.3.2.2; 
m has the same meaning as in 6.1. I and corresponds to 
B.4.3 Take as the result the arithmetic mean of the two 
determinations, provided that the requirement for repeatability 
(see 6.2) is satisfied. 
8.5 Agreement of results 
The result obta ined shall not differ by more 
obtained using the acidimetric method. than 5 % from that 
In the case where the differente in results obtained by the 
acidimetric method and the nephelometric method is greater 
than 5 %, only the result of the nephelometric method shall be 
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