UGANDA STANDARD
 
        US ISO 6561-1
First Edition
2009-mm-dd
 
Reference numbe r 
     US ISO 6561-1:2005
 © UNBS 2009
  
Fruits, vegetables and derived products — Determination of 
cadmium content — Part 1: Method using graphite furnace 
atomic absorption spectrometry 
 US ISO 6561-1: 2005 
 
© 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 
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilised in any 
form or by any means, electronic or mechanical, in cluding photocopying and microfilm, without prior written 
permission from UNBS. 
Requests for permission to reproduce this document should be addressed to 
The Executive Director 
Uganda National Bureau of Standards 
P.O. Box 6329 
Kampala  
Uganda 
Tel: 256 41 505 995 
Fax: 256 41 286 123 
E-mail: unbs@infocom.co.ug
Web: www.unbs.go.ug  
       US ISO 6561-1: 2005  
© 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 6561-1, Fruits, vegetables and derived products — Determination
of cadmium content — Part 1: Method using graphite furnace atomic absorption spectrometry,  is identical
with and has been reproduced from  an International Standard, ISO 6561-1:2005, Fruits, vegetables
and derived products — Determination of cadmium content — Part 1: Method using graphite furnace 
atomic absorption spectrometry, 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." 
  
 
 
  
 Reference numbe r
ISO 6561-1:2005(E)
© ISO 2005
  
 INTERNATIONAL 
STANDARD  ISO
6561-1
First edition
2005-02-01
Fruits, vegetables and derived 
products — Determination of cadmium content — 
Part 1: 
Method using graphite furnace atomic 
absorption spectrometry 
Fruits, légumes et produits dérivés — Détermination de la teneur en 
cadmium — 
Partie 1: Méthode par spectrométrie d'absorption atomique avec four en 
graphite 
 ISO 6561-1:2005(E) 
PDF disclaimer 
This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed b ut 
shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editin g. In 
downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Se cretariat 
accepts no liability in this area. 
Adobe is a trademark of Adobe Systems Incorporated. 
Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-cr eation 
parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bod ies. In 
the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below. 
 
©   ISO 2005 
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by an y means, 
electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address be low or 
ISO's member body in the country of the requester. 
ISO copyright office 
Case postale 56 • CH-1211 Geneva 20 
Tel.  + 41 22 749 01 11 
Fax  + 41 22 749 09 47 
E-mail  copyright@iso.org Web  www.iso.org 
Published in Switzerland 
 
ii © ISO 2005 – All rights reserved
  ISO 6561-1:2005(E) 
© ISO 2005 – All rights reserved  iii
 Foreword 
ISO (the International Organization for Standardization) is a worldwide federation of national standards 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. 
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of technical committees is to prepare International Standards. Draft International Standards 
adopted by the technical committees are circulated to the member bodies for voting. Publication as an 
International Standard requires approval by at least 75 % of the member bodies casting a vote. 
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. 
ISO 6561-1 was prepared by Technical Committee ISO/TC 34, Food products , Subcommittee SC 3, Fruit and 
vegetable products . 
This first edition of ISO 6561-1, together with ISO 6561-2:2004, cancels and replaces ISO 6561:1983, which 
has been technically revised. 
ISO 6561 consists of the following parts, under the general title Fruits, vegetables and derived products — 
Determination of cadmium content : 
 Part 1: Method using graphite furnace atomic absorption spectrometry 
 Part 2: Method using flame atomic absorption spectrometry 
 INTERNATIONAL STANDARD ISO 6561-1:2005(E)
 
© ISO 2005 – All rights reserved  1
 Fruits, vegetables and derived products — Determination of 
cadmium content — 
Part 1: 
Method using graphite furnace atomic absorption spectrometry 
1 Scope 
This part of ISO 6561 specifies a graphite furnace atomic absorption spectrometric method for the 
determination of the cadmium content of fruits, vegetables and derived products. 
2 Normative references 
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced 
document (including any amendments) applies. 
ISO 5515:1979, Fruits, vegetables and derived products — Decomposition of organic matter prior to 
analysis — Wet method  
3 Principle 
Organic matter is decomposed by a wet method and the dissolved cadmium is determined by graphite furnace 
atomic absorption spectrometry. 
4 Reagents 
Use only reagents of recognized analytical grade, and which, with the exception of the cadmium sulfate 
hydrate (4.8) and the cadmium standard solutions (4.9 and 4.10), shall be free from cadmium. Use only water 
which has been double-distilled in borosilicate glass apparatus, or water of at least equivalent purity. 
4.1 Sulfuric acid , concentrated, ρ20 = 1,84 g/ml. 
4.2 Nitric acid , ρ20 = 1,38 g/ml. 
4.3 Perchloric acid , ρ20 = 1,67 g/ml. 
4.4 Sulfuric acid , dilute, 10 % (volume fraction). 
4.5 EDTA (ethylenediaminetetraacetic acid, disodium salt) , 0,20 mol/l solution. 
4.6 Buffer solution , pH 9. 
Dissolve 5,4 g of ammonium chloride in water and transfer to a 100 ml one-mark volumetric flask. Add 35 ml 
of 25 % (volume fraction) ammonia solution and make up to the mark with water. ISO 6561-1:2005(E) 
2 © ISO 2005 – All rights reserved
 4.7 Eriochrome black T , 1 % (mass fraction) mixture with sodium chloride. 
4.8 Cadmium sulfate hydrate  (3CdSO4·8H2O). 
The titre of the cadmium sulfate shall be verified as follows. 
Weigh exactly 102,6 mg of cadmium sulfate hydrate, transfer quantitatively to a conical flask with water and 
shake until dissolved. Add 5 ml of the buffer solution (4.6) and about 20 mg of the eriochrome black T mixture (4.7). Titrate with the EDTA solution (4.5) until the end point is reached as indicated by a change of colour to blue. 
The volume of EDTA used shall be 20 ml. If the volume differs slightly, correct the mass of cadmium sulfate 
used to prepare the standard cadmium solution (4.9) accordingly. 
4.9 Cadmium standard solution , corresponding to 1,0 mg of cadmium per mililitre. 
4.10 Cadmium standard solution , containing 0,05 mg of cadmium per litre. 
Transfer, by means of a pipette, 10 ml of the cadmium standard solution (4.9) to 1 000 ml one-mark volumetric 
flask and dilute to the mark with water. Transfer 5 ml of this solution to another 1 000 ml one-mark volumetric flask and dilute to the mark with the dilute sulfuric acid (4.4). 
1 ml of this standard solution contains 0,05 µg of cadmium. 
5 Apparatus 
The glassware used shall be washed beforehand with hot concentrated nitric acid and rinsed with water. Usual laboratory apparatus and, in particular, the following. 
5.1 Round-bottom flasks , of capacity 1 000 ml. 
5.2 One-mark volumetric flasks , of capacity 50 ml. 
5.3 One-mark pipettes  or graduated pipettes , of appropriate capacities. 
5.4 Funnels  and ashless filter papers . 
5.5 Conical flask . 
5.6 Burette , of capacity 25 ml, graduated in 0,1 ml divisions. 
5.7 Atomic absorption spectrometer , with a graphite furnace, a background corrector, a 
multipotentiometric recorder and a hollow-cathode cadmium lamp, suitable for measurements at a wavelength 
of 228,8 nm. 
5.8 Eppendorf micropipettes , of capacities 5 µl, 10 µl, 20 µl, 25 µl and 50 µl, having standard colourless 
Eppendorf tips. 
Some Eppendorf micropipettes are inaccurate by 10 % or more. Unless they have been especially calibrated 
for this procedure, it is recommended that the same pipette be used with the test solution, blank test solution and calibration solutions. 
5.9 Analytical balance . 
5.10 Mechanical grinder , the internal lining and blades of which are of polytetrafluoroethylene (PTFE). ISO 6561-1:2005(E) 
© ISO 2005 – All rights reserved  3
 6 Sampling 
A representative sample should have been sent to the laboratory. It should not have been damaged or 
changed during transport or storage. 
Sampling is not part of the method specified in this part of ISO 6561. If there is no specific International 
Standard dealing with the product concerned, it is recommended that the parties concerned come to an 
agreement on the subject. 
7 Procedure 
7.1 Preparation of the test sample 
Mix the laboratory sample well. If necessary, first remove stones, stalks and hard seed-cavity walls and pass the laboratory sample through the mechanical grinder (5.10). 
Allow frozen or deep-frozen products to thaw in a closed vessel and add the liquid formed during this process 
to the product before mixing. 
7.2 Test portion 
7.2.1 Liquid products 
Take, by means of pipette, 10 ml of the test sample (7.1). 
It is also possible to take the test portion by mass by weighing a quantity of the test sample to the nearest 
0,01 g. 
7.2.2 Semi-solid and solid products 
Weigh, to the nearest 0,01 g, a quantity of the test sample (7.1) corresponding to approximately 10 g of 
product. 
7.3 Decomposition 
Transfer the test portion (7.2) to a round-bottom flask (5.1). If the test portion is liquid (7.2.1) and contains ethanol, first eliminate ethanol by boiling and then allow to cool. Add 10 ml of nitric acid (4.2), heat and then 
carefully add 5 ml of concentrated sulfuric acid (4.1) Proceed as described in ISO 5515:1979, 6.3.1, from the 
second paragraph to the eighth paragraph. 
When decomposition is complete, filter the sample solution, diluted with a few millilitres of water, through an 
ashless filter paper (5.4) that has been previously rinsed with hydrochloric acid and water. Collect the filtrate in a 50 ml one-mark volumetric flask (5.2), rinsing the round-bottom flask (5.1) and the filter paper with a few millilitres of water and collecting the rinsing in the same volumetric flask. Shake, allow to cool, and dilute to the 
mark. Mix by shaking. 
7.4 Blank test 
Carry out a blank test by repeating the decomposition (7.3), replacing the test portion by 10 ml of water. ISO 6561-1:2005(E) 
4 © ISO 2005 – All rights reserved
 7.5 Determination 
7.5.1 Furnace programme 
The furnace shall allow four independent thermal stages: a) drying the solution; b) thermal decomposition; c) atomization; d) increase to maximum temperature to purge the furnace. The proposed conditions are as follows: 
 drying at 100 °C for 25 s; 
 instantaneous change to the stage of thermal decomposition at 450 °C for 30 s; 
 atomization in 7 s at 1 900 °C, after a progressive increase to this temperature. During this stage, the 
apparatus shall record the maximum absorbance and the variation in absorbance. The duration over which atoms exist in the furnace may be increased by decreasing the rate of circulation of nitrogen (“mini 
flow”) or by stopping it altogether (“gas stop”); 
 increase to the maximum temperature (2 700 °C) to purge the furnace with nitrogen at the end of the 
procedure. 
7.5.2 Preparation of the calibration graph 
Prepare calibration solutions having cadmium concentrations of 5 µg/l, 10 µg/l and 20 µg/l by suitably diluting 
the cadmium standard solution (4.10). Inject successively into the furnace, programmed in accordance with 7.5.1, by means of micropipette (5.8) fitted with a tip, 50 µl of each of these calibration solutions. Determine the absorbance from the heights of the peaks registered. Calculate the mean value of the absorbance from the results of three injections into the furnace. The absorbances thus determined correspond, respectively, to 
0,000 25 µg, 0,000 5 µg and 0,001 µg of cadmium. Plot a calibration graph having, for example, the values of 
absorbances as ordinates and the corresponding cadmium concentrations as abscissae. 
7.5.3 Determination of test solution 
Inject successively into the furnace, programmed in accordance with 7.5.1, by means of a micropipette (5.8) 
fitted with a tip, three times the adequate volume of the decomposed sample solution obtained in 7.3. Note the corresponding absorbances. Calculate the mean value of the absorbance and, from the calibration graph, 
read the quantity of cadmium contained in the 50 µl of injected test solution. 
7.5.4 Determination of the blank test solution 
Inject successively into the furnace, programmed in accordance with 7.5.1, by means of a micropipette (5.8) 
fitted with a tip, three times the adequate volume of the blank test solution (7.4). The absorbance shall be zero or less than 0,005. If necessary, subtract the mean of the three values of absorbance of the blank test solution from the mean absorbance of the test solution determined in 7.5.3 before referring to the calibration graph 
(7.5.2) to obtain the cadmium content of the solution. ISO 6561-1:2005(E) 
© ISO 2005 – All rights reserved  5
 8 Expression of the results 
8.1 Method of calculation and equations 
8.1.1 Liquid products 
The cadmium content of the sample, expressed in milligrams per litre of product, is equal to 
1100m×  (1) 
where m1 is the mass, in micrograms, of cadmium contained in the injected volume of the test portion, read 
from the calibration graph. 
8.1.2 Semi-solid and solid products 
The cadmium content of the sample, expressed in milligrams per kilogram of product, is equal to 
1
01000m
m× (2) 
where 
m0 is the  mass, in grams, of the test portion (7.2.2); 
m1 is the mass, in micrograms, of cadmium contained in the injected volume of the test portion, read 
from the calibration graph. 
8.2 Other method of expression of results 
To express the cadmium content on the dry basis, modify the equations accordingly. 
9 Repeatability 
The absolute difference between two independent single test results, obtained using the same method on identical test material in the same laboratory by the same operator using the same equipment within a short 
interval of time, will in not more than 5 % of cases be greater than 10 % of the arithmetic mean of the two 
results. 
10 Test report 
The test report shall specify: 
a) all information necessary for the complete identification of the sample; b) the sampling method used, if known; c) the test method used, with reference to this part of ISO 6561; 
d) all operating details not specified in this part of ISO 6561, or regarded as optional, together with details of 
any incidents which may have influenced the test result(s); 
e) the test result(s) obtained, or, if the repeatability has been checked, the final quoted result obtained. ISO 6561-1:2005(E) 
ICS  67.080.01 
Price based on 5 pages 
© ISO 2005 – All rights reserved