UGANDA STANDARD
 
        US ISO 6636-3
First Edition
2009-mm-dd
 
Reference numbe r 
    US ISO 6636-3:1983
 © UNBS 2009
  
Fruit and vegetable products — Determination of zinc content - 
Part 3: Dithizone spectrometric method 
 US ISO 6636-3: 1983 
 
© 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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The Executive Director 
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       US ISO 6636-3:1983  
© 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 6636-3, Fruit and vegetable products — Determination of zinc content —
Part 3: Dithizone spectrometric method,  is identical with and has been reproduced from an International 
Standard, ISO 6636-3:1983, Fruit and vegetable products — Dete rmination of zinc content — Part 3: 
Dithizone spectrometric 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." 
 International Standard 663613 
INTERNATIONAL ORGANIZATION FOR STANDARDIZATIONWlE~~YHAPO~HAR OPrAHM3AlJklR fl0 CTAHAAPTl43ALWWORGANISATION INTERNATIONALE DE NORMALISATION 
Fruit and vegetable products - Determination of zinc 
content - 
Part 3 : Dithizone spectrometric method 
Produits d&ivt% des fruits et lt+gumes - Dbtermination de Ia teneur en zinc - Partie 3 : Mbthode spectrom&rique a Ia dithizone 
First edition - 1983-12-01 
Ul - sa 0) UDC 634.V635.6 : 543.42 : 646.47 Ref. No. ISO 6636/3-1983 (E) 
Descriptors : fruit and vegetable products, tests, determination of content, zinc, spectrophotometric analysis. 
Price based on 3 pages Foreword 
ISO (the International Organization for Standardization) is a worldwide federation of 
national Standards bodies (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 authorized 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 6636/3 was developed by Technical Committee 
ISO/TC 34, Agricultural food products, and was circulated to the member bodies in 
April 1982. 
lt has been approved by the member bodies of the following countries : 
Austria 
Canada 
Czechoslovakia 
Germany, F. R. 
Hungary 
India 
Iran 
Iraq 
The member bodies of 
on technical grounds : the following countries expressed disapproval of the document Kenya Romania 
Korea, Dem. P. Rep. of South Africa, Rep. of 
Malaysia Spain 
New Zealand Sri Lanka 
Peru Tanzania 
Philippines Turkey 
Poland USSR 
Portugal Y ugoslavia 
Netherlands 
0 International Organkation for Standardkation, 1983 l 
Printed in Switzerland INTERNATIONAL STANDARD ISO 6636/3-1983 (EI 
Fruit and vegetable products - Determination of zinc 
content - 
Part 3 : Dithizone spectrometric method 
1 Scope and field of application 
This part of ISO 6696 specifies a dithizone spectrometric 
method for the determination of the zinc content of fruit and 
vegetable products. 
2 Ref erence 
ISO 5515, Fruits, vegetables and derived products - Decom- 
Position of organic matter Prior to analysis - Wet method. 
3 Principle 
Decomposition of organic matter, neutralization of the Solution 
obtained and addition sf dithizone (15diphenylthiocarbazone) 
Solution. Extraction of the zinc complex thus formed with 
chloroform and spectrometric measurement of the absorbance 
of the extract at a wavelength of 538 nm. 
4 Reagents 
All reagents shall be of recognized analytical quality and, with 
the exception of the Standard zinc solutions (4.8 and 4.91, shall, 
in particular, be free from zinc. The water used shall be double- 
distilled water or water of at least equivalent purity. 
4.1 Sulfuric acid, 25 % (Vl V) solution. 
4.2 Ammonia, 25 % (Vl V) Solution. 
4.3 Phenol red, indicator Solution. 
Dissolve, in a mortar, 0,l g of phenolsulfonephthalein in 
2,85 ml of 0,l mol/1 sodium hydroxide solution and dilute to 
100 ml with water. 
4.4 Sodium acetate trihydrate, 100 g/l Solution. 
4.5 Sodium thiosulfate, 250 g/l Solution. 
4.6 Hydrochlorit acid, concentrated, Q~ = 1,19 g/ml. 
4.7 Chloroform. 4.8 Zinc, Standard Solution corresponding to 500 pg of zinc 
per millilitre. 
In a 1 000 ml volumetric flask, dissolve 0,500 g of pure 
granulated zinc in 20 ml of the concentrated hydrochloric acid 
(4.61, and dilute to the mark with water. 
4.9 Zinc, Standard Solution corresponding to 5 pg of zinc per 
millilitre. 
In a 1 000 ml volumetric flask, dilute 10 ml of the Standard zinc 
Solution (4.8) to the mark with the 0,04 mol/1 hydrochloric acid 
Solution (4. IO). 
Prepare this Solution at the time of use. 
4.10 Hydrochlorit acid, 0,04 mol/1 Solution. 
4.11 1,5-diphenylthiocarbazone (dithizone), Solution. 
Dissolve 0,2 g of dithizone in 100 ml of the chloroform (4.7). 
4.12 1,5-diphenylthiocarbazone (dithizone), extraction 
Solution. 
Dilute 1,O ml of the dithizone solution (4.11) to 100 ml with the 
chloroform (4.7). 
5 Apparatus 
NOTE - Contamination may lead to high values in the blank test and 
the apparatus used should, therefore, be rinsed with the dithizone solu- 
tion. 
Usual laboratory apparatus, and 
5.1 One-mark volumetric flasks, of capacities 15, 50, 100, 
500 and 1000 ml. 
5.2 Separating funnels, of capacity 250 mI. 
5.3 Spectrometer, suitable for making measurements at a 
wavelength of 538 nm, equipped with cells of Optical path 
length 1 cm. 
1 ISO 6636/3-1983 (El 
6 Procedure 6.5 Blank test 
Simultaneously with each set of determinations, carry out a 
blank test by replacing the digested Sample Solution with 10 ml 
of the sulfuric acid Solution (4.1) and proceeding as described 
in 6.4. 61 . Preparation of the test Sample 
Homogenize the laboratory Sample thoroughly before taking 
the test Portion. Allow frozen and deep-frozen products to 
thaw in a closed vessel and mix the liquid formed during this 
process with the product during homogenization. 6.6 Preparation of the calibration graph 
Into a series of four separating funnels, introduce 1 - 2 - 4 
and 5 ml of the Standard zinc Solution (4.9) and dilute to 10 ml 
with the sulfuric acid Solution (4.1). Then add the reagents and 
carry out the dilution with the chloroform as specified in 6.4. 6.2 Test Portion 
Weigh, to the nearest 0,Ol g, 5 to 10 g of the test Sample (6.11, 
according to the expected zinc content. 
These solutions contain 5 - 10 - 20 and 25 1.19 of zinc, respec- 
tively. 6.3 Destruction of organic matter 
Use the procedure specified in ISO 5515. Measure the absorbances of these calibration solutions using 
the spectrometer following the procedure specified in 6. 4. 
NOTE - Milling and sieving of the Sample, if necessary, should be car- 
ried out in equipment free from zinc and/or topper alloys before the 
destruction of organic matter. Check the calibration graph regularly each day, as the specific 
absorbance values may vary according to the actual concen- 
tration of the dithizone solution. 
6.4 Determination 
NOTE - If the digested Sample Solution is not diluted (sec the note to 
6.41, place 0,2 - 0,4 - 0,6 and 0,8 ml of the Standard zinc solution 
(4.9) in the separating funnels, and then add the reagents specified in 
6.4. These solutions contain 1 - 2 - 3 and 4 c(g of zinc, respectively. 
Measure the absorbances of these calibration solutions using the spec- 
trometer following the procedure specified in 6.4. According to the expected zinc content, dilute the Solution 
obtained (see 6.3) to 50 or 100 ml in a volumetric flask. Place 1 
to 10 ml of this Solution in one of the separating funnels (5.2) 
and dilute to 20 ml with water. 
Carry out the following Steps in subdued light. 
6.7 Number of determinations 
Add 2 drops of the Phenol red indicator (4.3) and make the 
Solution alkaline by addition of the ammonia Solution (4.2) until 
the colour turns from yellow to red (PH 7,8 to 8,3). Cool the 
warm Solution under a stream of water, loosening and replac- 
ing the stopper of the separating funnel from time to time. Carry out two determinations on the same test 
the destruction of organic matter (sec 6.1). Sample taken for 
7 . Expression of results 
Add to the cooled Solution, 1 ml of the sodium thiosulfate solu- 
tion (4.5) and 15 ml of the sodium acetate Solution (4.4). Add, 
drop by drop, 3 ml of the dithizone extraction Solution (4.12). 
Shake vigorously for 3 min after the addition of the dithizone. 7.1 Method of calculation and formulae 
7.1.1 Calculation of specific absorbance 
Allow the phases to separate, If the organic Phase is white, the 
extraction is complete. If the organic Phase is red, continue 
adding, drop by drop, the dithizone extraction Solution until the 
organic Phase becomes white. Shake vigorously for 3 min. 
Allow the phases to separate. From the absorbances of the calibration solutions (sec 6.61, 
calculate the individual specif ic absorbances from the formulae 
El - Eo A, = 5 NOTE - If a large amount of the dithizone extraction Solution is added 
at one time the organic Phase will become green and the Sample will be 
unusable. E2 - Eo 
A2=7j- 
Collect the organic Phase in a dried 15 ml one-mark volumetric 
flask, dilute to the mark with the chloroform (4.7) and mix 
thoroughly. E3 - Eo A, = 20 
Measure the absorbance of the Solution using the spectrometer 
(5.3) set at a wavelength of 538 nm, using attenuated light and 
pure chloroform as the reference liquid. E4 - Eo A, = 25 
where NOTE - If the digested Sample Solution contains less than 5 pg of 
zinc, the dilution described in the first Paragraph of 6.4 may be omit- 
ted. This fact should be taken into account, however, when preparing 
the calibration graph. Al, 4, 4 and 4 are the individual specific absor- 
bances; 
2 ISO 6636/3-1963 (EI 
El, E2, E3 and Fs are the absorbances determined as 
described in 6.6; 
&, is the absorbance of the blank test Solution. 
Caiculate the Overall specific absorbance, A, from the formula 
A A, + A2 + A3 + A4 i= 4 
7.1.2 Calculation of tinc contept 
The zinc content, 
duct, is equal to expressed in milligrams 
E x V. 
AxmxV, 
where 
E is the absorbance of the ,test solytion; 
A is the Overall specific absorbance; V. is the total volume, in millilitres, of the diluted digested 
Sample solution (50 or 160 ml) (sec 6.4); 
VI is the volume, in millilitres, of the aliquot Portion of 
digested Sample Solution transferred to the separating fun- 
nel; 
is the mass, in grams, of the test Portion. 
7.2 Repeatability 
The differente between the results of two determinations car- 
ried out simultaneously OP in rapid succession by the same 
analyst on the same test sample shall not exceed 5 % of the 
mean value. 
8 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 part of ISO 6636, or in the International 
Standard to which reference is made, or regarded as optional, 
as weil as any circumstances which may haye influenced the 
result. 
The test report shall give all the details 
plete identification of the Sample. for the comt This page intentionally left blank This page intentionally left blank This page intentionally left blank