UGANDA STANDARD 
        US ISO 6634
First Edition
2009-mm-dd
 
Reference numbe r 
     US ISO 6634:1982
 © UNBS 2009
  
Fruits, vegetables and derived products — Determination of 
arsenic content — Silver diethyldithiocarbamate 
spectrophotometric method 
 US ISO 6634: 1982
 
© 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 6634:1982  
© 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 6634, Fruits, vegetables and derived products — Determination of arsenic
content — Silver diethyldithiocarbamate spectrophotometric method,  is identical with and has been 
reproduced from an Internati onal Standard, ISO 6634:1982, Fruits, vegetables and derived products — 
Determination of arsenic content — Silver diethyldithiocarbamate spectrophotometric 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 
INTERNATIONAL ORGANIZATION FOR STANDARDIZATIONWME~YHAPO~HAR OPl-AHM3AUWR fl0 CTAH~PTM3AL(MM.ORGANISATION INTERNATIONALE DE NORMALISATION 
Fruits, vegetables and derived products - Determination 
of arsenic content - Silver diethyldithiocarbamate 
spectrophotometric method 
Fruits, Egumes et produits d&iv& - DtStermina tion de Ia teneur en arsenic - Methode spectrophotometrique au 
di&th yldithiocarbama te d’iprgen t 
First edition - 1982-12-01 
UDC 634.V635.6 : 543.42 : 546.19 Ref. No. ISO 6634-1982 (E) 
Descriptors : agricultural products, fruits, vegetables, Chemical analysis, determination of content, arsenic. 
Price based on 5 pages Foreword 
ISO (the International Organization for Standardization) is a worldwide federation of 
national Standards institutes (lS0 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 6634 was developed by Technical Committee ISO/TC 34, 
Agricultural food products, and was circulated to the member bodies in June 1981. 
lt has been approved by the member bodies of the following countries : 
Austria Iran 
Brazil Israel 
Canada Kenya 
Czechoslovakia Korea, Dem. P. Rep. of 
Egypt, Arab Rep. of Korea, Rep. of 
Ethiopia Malaysia 
France Netherlands 
Germany, F. R. New Zealand 
Hungary Philippines 
India Poland Portugal 
Romania 
South Africa, Rep. of 
Spain 
Sri Lanka 
Tanzania 
Thailand 
Turkey 
Y ugoslavia 
The member body 
tech nical grounds of the following country expressed disapproval of the document on 
0 International Organkation for Standardkation, 1982 
_ 
Printed in Switzerland INTERNATIONAL STANDARD ISO 6634-1982 (E) 
Fruits, vegetables and derived products - Determination 
of arsenic content - Silver diethyldithiocarbamate 
spectrophotometric method 
1 Scope and field of application 
This International Standard specifies a method for the determi- 
nation of the arsenic content of fruits, vegetables and derived 
products. of blotting-Paper folded into several layers, and allow to dry. 
Store in a dry bottle. 
The platinized zinc thus prepared shall be submitted to the 
preliminary test (see 6.1.1). 
NOTE - Non-platinized zinc granules may be used if the product is 
shown to be suitable by the preliminary test. 
2 Reference 
ISO 5515, Fruits, vegetables and derived products - Decom- 
Position of organic matter Prior to analysis - Wet method. 
3 Principle 
Decomposition of a test Portion, reduction of arsenic(V) to 
arsenic(lll) with tinUl) chloride and transformation of the 
arsenic into arsine by the action of nascent hydrogen. Forma- 
tion of a red coloured complex by the action of the arsine on 
silver diethyldithiocarbamate and spectrophotometric measure- 
ment at a wavelength of 520 nm. 
4 Reagents 
All reagents shall be of recognized analytical purity and shall, in 
particular, be free from arsenic [with the exception of the stan- 
dard arsenic Solution (4.911. The water used shall be distilled 
water or water of at least equivalent quality. 
4.1 Sulphuric acid, e20 = 1,84 g/ml. 
4.2 Nitrit acid, e20 = 1,38 g/mI. 4.5 Potassium hydroxide, in pellets. 
4.6 TinW) chloride solution, prepared as follows. 
Carry out a cold attack on 20 g of pure granulated tin with 
100 ml of concentrated hydrochloric acid (en, = 1,19 g/ml). 
Store in the presence of metallic tin, protected from air, in a 
bottle provided with a security device (to avoid overpressures 
caused by the Iiberation of hydrogen). 
4.7 Potassium iodide, 100 g/l Solution. 
4.8 Sodium hydroxide, Standard volumetric Solution, 
c(NaOH) = 1 mol/l. 
4.9 Arsenic, Standard Solution corresponding to 10 mg of 
arsenic(V) per litre, prepared as follows. 
4.9.1 Dissolve, in a 500 ml flask, 264 mg of pure, dry arsenic 
trioxide in IO ml of the sodium hydroxide Solution (4.81, make 
up the volume to about 100 ml with water, add 15 ml of 1 mol/1 
hydrochloric acid Solution and two drops of bromine; heat to 
boiling in Order to expel the excess bromine, cool, transfer 
quantitatively to a 200 ml volumetric flask and make up to the 
mark with water. 
4.3 Perchlorit acid, e20 = 1,67 g/ml. 
1 ml of this Solution contains 1 mg of arsenic. 
4.4 Platinized zinc, prepared as follows. 
Place a Portion of granulated zinc in a capsule, and pour in a 
volume of 0,05 g/l platinum chloride solution sufficient to 
cover the zinc. Leave in contact for 30 min, pour off the liquid, 
wash with water, leave the platinized zinc to drain on a Square 4.9.2 By means of a pipette, transfer 10 ml of the Solution 
(4.9.1) to a 1 000 ml volumetric flask. Make up to the mark with 
water. 
1 ml of this Standard Solution contains IO pg of arsenic(VL ISO 66344982 (E) 
4. IO Silver diethyldithiocarbamate, Standard solution, 
prepared as follows.1) 5.6 Apparatus fo r the determination 
example as shown in the fig ure, comprising Of arsenic, for 
4.10.1 Dissolve 3,4 g of silver nitrate in 200 ml of water; cool 
the Solution to a temperature close to 10 OC. 56.1 Conical flask, sf capacity 100 ml, fitted with a screw 
thread joint System for connection to the column 5.6.2. 
4.10.2 Dissolve 4,5 g of sodium diethyldithiocarbamate in 
200 ml of water; cool this Solution to the same temperature as 
the silver nitrate Solution (4.10.12. 5.6.2 Column, of height 200 mm and diameter 15 mm, to fit 
the flask (5.6.1) at its base and fitted with a screw thread joint 
at the top. 
4.10.3 Add slowly, and with constant shaking, the sodium 
diethyldithiocarbamate solution to the silver nitrate Solution; 
collect the precipitate on a fritted glass crucible of porosity 
grade P 40, wash with water previously cooled to a tem- 
perature close to 10 OC, then dry under reduced pressure at 
ambient temperature, in the dark. 56.3 Delivery tube, of internal diameter 4 mm, bent twice, 
at right angles 80 mm apart, to fit the column (5.6.2) at one end 
and tapered at the opposite end. 
5.6.4 Bubbler, which may consist of a measuring cylinder sf 
capacity IO ml graduated in 0,l ml divisions. 
Dissolve the dried silver diethyldithiocarbamate in cold 
pyridine. Add cold water to precipitate the product. Filter the 
precipitate and wash with cold water until all traces of pyridine 
have been eliminated (this tan be verified using a pH indicator 
Paper : the pH of the washings shall not be greater than 6,5). 
Dry the light yellow crystals of silver diethyldithiocarbamate in a 
desiccator under reduced pressure. 5.7 Spectrophotometer, suitable for use in the visible 
region of the spectrum, for measurements of absorbance at 
520 nm, fitted with suitable cells of optical.path length 10 mm. 
5.8 Analytical balance. 
The crystals shall be 
fitted with a ground kept in a cold, dark place in a glass bottle 
glass stopper. 6 Procedure 
4.10.4 Dissolve 0,4 g of L-ephedrine in about 200 ml sf 
chloroform, add 0,6 g of the silver diethyldithiocarbamate 
crystals (4.10.31, Shake for 15 to 20 min, filter, and make up the 
volume to 250 ml with chloroform. 6.1 Preliminary tests on reagentsz) 
6.1.1 Verification of the reactivity 
diethyldithiocarbamate solution sf the zinc and 
This reagen t may be stored in a refrigerator in the 
tW0 ?weeks in a well stoppered bottle. dark for up to 
6.1.1.1 Place, at the bottom of the column (5.6.2) of the ap- 
paratus (5.6), a plug of giass wo01 and add potassium hydrox- 
ide pellets (4.5) to a height of 6 to 8 cm. Fit the delivery tube 
(5.6.3) to the column (5.6.2). 4.11 Phenolphthalein, 30 g/l ethanolic solution. 
Place the end of the delivery tube (5.6.3) in the bubbjer (5.6.4) 
into which 4 ml of the silver diethyldithiocarbamate solution 
(4.10) have been placed. Cool the reagent by placing the bub- 
bler in an ice-water bath. 5 Apparatus 
Ordinary laboratory equipment, and in particular 
51 . Round-bottomed flasks, sf capacity 1 000 ml. 
6.1 .1.2 Place in the conical flask (5.6.1) 0,5 ml of the Standard 
arsenic solution (4.9) and sufficient water to make the volume 
up to about 35 ml; add 5 ml of the sulphuric acid (4.1), cool, 
add 2 drops of the tin(ll) chloride solution (4.61, and then 5 ml 
of the potassium iodide Solution (4.7). Leave in contact for 
15 min, add 5 g of the platinized zinc (4.4), and plug rapidly by 
fitting the column (5.6.2) and the delivery tube (5.6.3). 5.2 Volumetric flasks, of capacity 50 and 250 ml. 
5.3 Beakers, of capacity 50 ml. 
5.4 Pipettes, of capacity 1, 2, 5, 10, 20 and 50 ml. 
Place the conical flask in a 
apparatus in a da rk place. cold water and put the 
5.5 Burette. 
1) This Jeagent is also available commercially. 
2) These tests shall only be carried out when using a new SUPPlY of reagents. 
2 ISO 66344982 0 
6.“1.1.3 Allow the reaction to proceed for at least 1 h. Remove 
the delivery tube (5.6.3). If necessary, adjust the volume in the 
bubbler to 4 ml with the silver diethyldithiocarbamate Solution 
(4.10). Mix. 6.4 Blank test 
Carry out a blank test follow 
determination, but replacing ng the Same procedur ‘es as for the 
the test portion by 50 ml of water. 
By means of the spectrophotometer (5.7), measure the 
absorbance at 520 nm of the solution in the bubbler, using as 
the reference Solution the silver diethyldithiocarbamate Solution 
(4.10). The absorbance shall be at least 0,12. NOTE - The blank test is not necessary if the absence 
reagents used for decomposition has been verified. of 
6.5 Decomposition 
6.12 Verification of the 
reagents absence of arsenic in the 
Add to the contents of the flask 10 ml of the sulphuric acid 
(4.1) and 20 to 30 ml of the nitric acid (4.2) and, if necessary, a 
few drops of the perchloric acid (4.3). Proceed as described in 
ISO 5515. 6.1.2.1 Prepare the column (5.6.2), the delivery tube (5.6.3) 
and the bubbler (5.6.4) of the apparatus (5.6) in the same way 
as for the test specified in 6.1 .l. 1. When decomposition is complete, transfer the Solution to a 
50 ml volumetric flask (5.2), rinse the original flask with water, 
and use the rinsings to make up the volume in the volumetric 
flask to the mark. Mix by shaking. 6.1.2.2 Place in the conical flask (5.6.1) 35 ml of water and 
5 ml of the sulphuric acid (4.1) and cool; then add 2 drops of 
the tin(ll) chloride Solution (4.6), and 5 ml of the potassium 
iodide Solution (4.7). Leave in contact for 15 min, add 5 g of 
the platinized zinc (4.4), plug rapidly by fitting the column 
(5.6.2) and the delivery tube (5.6.3) and place the apparatus in a 
dark place. 6.6 Titration of the acidity of the solution 
Transfer, by means of a pipette, 2 ml of the Solution obtained in 
6.5 to a beaker (5.3), dilute with a few millilitres of water, and 
titrate against the sodium hydroxide Solution (4.8) in the 
presence of two drops of phenolphthalein (4.11). Proceed as described in 6.1 J.3. 
The absorbance, compared with that of the silver 
diethyldithiocarbamate Solution as reference Solution (4. IO), 
shall be less than 0,015. The concentration, C, of sulphuric acid 
in 6.5, expressed in grams per 100 ml, the Solution 
equal to obtained 
IS 
NOTE - The a bsen ce of arsenic 
verified by the blank test ( 6.4). in the nitric and perch loric acids is 0,049 x n x 50 
where n is the volume, in millilitres, of sodium hydroxide solu- 
tion (4.8) used, 6.2 Preparation of the test Sample 
or, expressed in millilitres of sulphuric acid 
k?20 = 184 g/ml) per 100 ml of solution Mix the laboratory Sample thoroughly. If necessary, first 
remove seeds and hard seed-cavity Walls and pass the re- 
mainder through a mechanical grinder. 
c C’ =- 
1184 Allow frozen or deep-frozen products to thaw beforehand in a 
closed vessel and add the liquid formed during this process to 
the product before homogenization. 
6.7 Colorimetric determination 6.3 T’est Portion 
6.7.1 Prepare the column (5.6.2), the delivery tube (5.6.3) and 
the bubbler (5.6.4) of the apparatus (5.6) as indicated in 
6.1.1.1. 6.3.1 Liquid products 
By means of a pipette, transfer 50 ml of the test Sample (6.2) to 
a 1 000 ml flask (5.1). 
lf the 
cool. liquid contains ethanol, expel it by boiling, and allow to 
5 x 100 v=- 
C’ 6.3.2 Pastyp solid or dehydrated products 
Weigh, to the nearest 0,Ol g, a mass of the test Sample (6.2) 
corresponding to 50 to 100 g of fresh product, according to the 
nature of the Sample, and place it in a 1 000 ml flask (5.1). If necessary, 
Allow to cool add to obtain a volume of about 40 ml. 
NOTE - If the Sample is rich in organic matter, decomposition will re- 
quire more time and the mass of the test Portion should, therefore, be 
minimal. 
3 ISO 66344982 (El 
conical flask (5.6.1). Rapidly stopper the flask by fitting the 
column (5.6.2) and the delivery tube (5.6.3) and place the 
apparatus in the dark, with the conical flask placed in a cold 
water bath. 
6.7.3 Allow the reaction to proceed for at least 1 h. Remove 
the delivery tube. Adjust the volume in the bubber to 4 ml with 
diethyldithiocarbamate Solution (4.10). 
By means of the spectrophotometer (5.71, measure the ab- 
sorbance at 520 nm of the Solution obtained, using the blank . 
test Solution (6.41, or the silver diethyldithiocarbamate Solution 
(4.101, as the reference Solution, according to the case. 
6.8 Calibration curve 
Proceed as described in 6.1.1 using 0,5 - 1 - 1,5 and 2 ml 
of the Standard arsenic Solution (4.9.2) corresponding to 
5 - 10 - 15 and 20 pg of arsenic, and plot a graph having, 
for example, the mass in micrograms of arsenic as abscissae 
and the corresponding values of absorbance as 
ordinates. 
7 Expression of results 7.1.2 Pasty, solid or dehydrated products 
The arsenic content, expressed 
product as received, is equal to In milligrams Per kilogram of 
rnl x 50 
V x m. 
m. is the mass, in grams, of the test Portion (6.3.2); 
ml is the mass of arsenic, expressed in micrograms, ob- 
tained from the calibration graph and corresponding to the 
absorbance measured in 6.7.3; 
V is the volume, in millilitres, of Solution taken for the 
determination in 6.7.2. 
If it is desired to express the arsenic content in relation to 
dry product, take this fact into account in the calculation. 
7.2 Repeatability the 
7.1 Method of calculation and formulae + The differente between the results of two determinations, car- 
ried out simultaneously or in rapid succession by the same 
7.1.1 Liquid products 
The arsenic content, expressed 
as received, is equal to in milligrams per litre of prod uct 
where analyst, on the same Sample, shall not exceed 10 % as a 
relative value. 
8 Test report 
The test report shall show the method used and the result ob- 
tained. It shall also mention the method of expression used and 
ml is the mass of arsenic, expressed in micrograms, 
obtained from the calibration graph and corresponding to 
the absorbance measured in 6.7.3; any operating conditions not specified in this International 
Standard, or regarded as optional, as well as any circum- 
stances that may have influenced the result. 
V is the volume, in millilitres, of Solution taken for the 
determination in 6.7.2. The test report shall include all the information necessary for 
the complete identification of the Sample. Dimensions in millimetres 
015 ---l 
@int15, 
Column .--- 80 
0 
Ei 
Capacity 
IOOmL 
i -@int.4 
- Delivery tube 
,@ext. 6 
- Bubbler 
,@int.11 
Figure - Example of apparatus for the determination of arsenic (5.6) This page intentionally left blank