DRAFT UGANDA STANDARD  
  DUS 
925:2021  
Second  Edition  
2021 -mm-dd 
 
 
 Reference number  
DUS 925: 2021  
© UNBS 2021   
  
Chemicals used for treatment of water intended for human use 
— Sodium hypochlorite — Specification  
 DUS 925: 2021  
ii © UNBS 2021  – 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 provi sions of a contract. Users are 
responsible for its correct application  
© UNBS 2021   
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, including photocopying and microfilm, without prior written 
permission from UNBS.  
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The Executive Director  
Uganda National Bureau of Standards  
P.O. Box 6329  
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Uganda  
Tel: +256 41 4 333 2 50/1/2/3  
Fax: +256 41 4 286 123  
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Web: www.unbs.go.ug   
  iii 
 Contents  Page 
Foreword  ................................ ................................ ................................ ................................ ..........................  vvi 
1 Scope  ................................ ................................ ................................ ................................ ......................  1 
2 Normative references  ................................ ................................ ................................ ............................  1 
3 Terms and definitions  ................................ ................................ ................................ ...........................  1 
4 Requirements  ................................ ................................ ................................ ................................ .........  2 
4.1 General requirements  ................................ ................................ ................................ ...........................  2 
4.2 Specific requirements  ................................ ................................ ................................ ...........................  2 
4.3 Heavy metal requirements for Sodium hypochlorite  ................................ ................................ .........  3 
5  Sampling  ................................ ................................ ................................ ................................ ................  3 
5.1  General  ................................ ................................ ................................ ................................ ...................  3 
5.2  Sampling from tankers ................................ ................................ ................................ ..........................  3 
5.3  Sampling from other containers  ................................ ................................ ................................ ..........  3 
5.3.1  Containers with the capacity more than one litre  ................................ ................................ ..............  3 
5.3.2   Containers with the capacity of or less one litre  ................................ ................................ ..............  4 
6  Packaging,  ................................ ................................ ................................ ................................ ..............  4 
7.  labelling  ................................ ................................ ................................ ................................ .................  4 
8  Bulk storage  ................................ ................................ ................................ ................................ ...........  5 
Annex A  (normative)   Determination of avai lable chlorine  ................................ ................................ ..........  6 
A.1  Principle  ................................ ................................ ................................ ................................ .................  6 
A.2  Reagents  ................................ ................................ ................................ ................................ ...............  6 
A.2.1   Acetic acid, glacial  ................................ ................................ ................................ ...............................  6 
A.2.2   Potassium iodide (KI), crystals, iodate free  ................................ ................................ .......................  6 
A.2.3  Hydrochloric acid, 0.1 M  ................................ ................................ ................................ .......................  6 
A.2.4  Sodium thiosulphate (Na2S2O3.5H2O), standard solution, 0.1 M.  ................................ ...................  6 
A.2.5   Starch indicator solution,  ................................ ................................ ................................ ....................  6 
A.3  Procedure  ................................ ................................ ................................ ................................ ..............  6 
A.4  Calculations  ................................ ................................ ................................ ................................ ..........  7 
A.4.1   Calculate the available chlorine as follows:  ................................ ................................ ......................  7 
A.4.2   Calculate the sodium hypochlorite content as follows;  ................................ ................................ ... 7 
Annex B (normative)   Determination of sodium hydroxide content  ................................ ............................  8 
B.1  Principle  ................................ ................................ ................................ ................................ ................  8 
B.2  Reagents  ................................ ................................ ................................ ................................ ...............  8 
B.2.1   Barium chloride solution (100g/L),  ................................ ................................ ................................ ..... 8 
B.2.2   Hydrochloric acid, standard (0.1 N),  ................................ ................................ ................................ ... 8 
B.2.3   Hydrogen peroxide, approximately 3%.  ................................ ................................ .............................  8 
B.2.4   Phenol phthalein indicator solution (0.5 g/100 me),  ................................ ................................ ..........  8 
B.3  Procedure  ................................ ................................ ................................ ................................ ..............  8 
B.4  Calculation  ................................ ................................ ................................ ................................ ............  8 
Annex C (normative)   Method of determination of insoluble matter  ................................ ..........................  10 
C.1  Apparatus  ................................ ................................ ................................ ................................ .............  10 
C.1.1   Gooch crucible  ................................ ................................ ................................ ................................ ... 10 
C.1.2   Balance  ................................ ................................ ................................ ................................ ................  10 
C.1.3   Oven  ................................ ................................ ................................ ................................ .....................  10 
C.2  Procedure  ................................ ................................ ................................ ................................ .............  10 
C.3  Calculation  ................................ ................................ ................................ ................................ ..........  10 
Annex D  (normative)  Measurement of pH value.  ................................ ................................ ........................  11 DUS 925: 2021  
iv © UNBS 2021  – All rights reserved  
 D.1  Measure the pH, at ro om temperature, using a pH meter equipped with a glass electrode 
capable of measuring pH values to an accuracy of 0.1 or better.  ................................ .................  11 
Annex E  (normative)   Method for determination of Sodium chlo rate ................................ ......................  12 
E.1 General  ................................ ................................ ................................ ................................ .................  12 
E.2  Apparatus  ................................ ................................ ................................ ................................ ...........  12 
E.3 Reagents  ................................ ................................ ................................ ................................ ..............  13 
E.3.1  Concentrated Hydrochloric Acid.  ................................ ................................ ................................ ...... 13 
E.3.2  Sodium Bromide Solution, 10 percent (mlv).  ................................ ................................ ...................  13 
E.3.3   Potassium Iodide Sclution, 10 percent (m/v)  ................................ ................................ ..................  13 
E.3.4  Standard Sodium Thiosulphate Solution, 0.05 N.  ................................ ................................ ...........  13 
E.3.5  Starch Indicator Solution, 0.5 percent (mlv).  ................................ ................................ ...................  13 
E.3.6  Sodium Bicarbonate - pure grade.  ................................ ................................ ................................ .... 13 
E.4 Procedure.  ................................ ................................ ................................ ................................ ...........  13 
E.5  Calculation  ................................ ................................ ................................ ................................ ..........  13 
Annex F  (normative)   Method of determination of iron  ................................ ................................ ..............  14 
F.1  Apparatus  ................................ ................................ ................................ ................................ ...........  14 
F.2  Reagents  ................................ ................................ ................................ ................................ .............  14 
F.2.1   Ammonium Persulphate  ................................ ................................ ................................ ...................  14 
F.2.2  Butanolic Potass ium Thiocyanate Solution Dissolve 10 g of potassium thiocyanate in 10 
ml of water. Add sufficient n -butanol to make up to 100 ml and shake vigorously till the 
solution is clear. ................................ ................................ ................................ ................................ .. 14 
F.2.3   Standa rd Iron Solution A  ................................ ................................ ................................ ..................  14 
F.2.4   Standard Iron Solution B  ................................ ................................ ................................ ..................  14 
F.3  Procedure  ................................ ................................ ................................ ................................ ...........  14 
Bibliography  ................................ ................................ ................................ ................................ .....................  15 
 
  
  
  v 
 Foreword  
Uganda National Bureau of Standards (UNBS) is a parastatal under the Ministry of Trade , Industry and 
Cooperatives established under Cap 327 , of the Laws of Uganda , as amended .  UNBS is mandat ed 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 Alimentarius Commission on Food Standards, and  
(c) the National Enquiry Point on TBT  Agreement  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 given field or area and consists of key stakeholders 
including go vernment, academia, consumer groups, private sector and other interested parties.  
Draft Uganda Standards adopted by the Technical Committee are widely circulated to stakeholders and the 
general public for comments. The committee reviews the comments befor e recommending the draft standards 
for approval and declaration as Uganda Standards by the National Standards Council.  
The committee responsible for this document is Technical Committee UNBS /TC 5, Chemicals and 
environment . 
This second edition cancels and replaces the first edition ( US 925:2012 ), which has been technically revised .  
 DUS 925: 2021  
vi © UNBS 2021  – All rights reserved  
  DRAFT UGANDA STANDARD  DUS 925: 2021  
 
© UNBS 2021  – All rights reserved  1 
 Chemicals used for treatment of water intended for human use 
— Sodium hypochlorite — Specification  
1 Scope   
This Committee draft Uganda Standard specifies the requirements a nd methods of sampling and test for 
sodium hypochlorite solution used for disinfection of water intended for human use. 
2 Normative references   
The following referenced documents referred to in the text in such a way that some or all of their content 
const itutes requirements 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 3696, Water for analytical laboratory use — Specificat ions and test methods  
ISO 3165, Sampling of chemical products for industrial use — Safety in sampling  
ISO 6206, Chemical products for industrial use — Sampling — Vocabulary  
US ISO 17378 -2 water quality — determination of arsenic and antimony — part 2: met hod using hydride 
generation atomic absorption spectrometry (HG -AAS)  
US ISO 8288  water quality — determination of cobalt, nickel, copper, zinc, cadmium and lead — flame atomic 
absorption spectrometric methods  
US ISO 9174  water quality — determination of ch romium — atomic absorption spectrometric methods  
US ISO/TS 17379 -2 water quality — determination of selenium — part 2: method using hydride generation 
atomic absorption spectrometry (HG -AAS)  
US ISO 12846  water quality — determination of mercury — method us ing atomic absorption spectrometry 
(AAS) with and without enrichment  
US 1847:2017, Standard Test Methods for Speciﬁc Gravity, Apparent, of Liquid Industrial Chemicals  
 
3 Terms and definitions   
For the purposes of this document, the following terms and definitions apply.  
ISO and IEC maintain terminological databases for use  in standardization at the following addresses:  
— ISO Online browsing platform: available at http://www.iso.org/obp   
2 © UNBS 2021  – All rights reserved  
 3.1  
available c hlorine  
this is the measure of the oxidizing power of the chlorin e present as hypoch lorite.  
3.2  
lot 
a number of containers consisting of product of the same type and style, which have been manufactured and 
packed under essentially the same conditions . 
3.3 
 nominal concentration  
the minimum available chlorine content of the sodium hypoch lorite solution under test, at the time of 
manufacture  
 4 Requirements  
4.1 General requirements   
4.1.1 The sodium hypochlorite solution shall be a clear , or slightly cloudy liquid , with a  faint chlorinous 
odour  and shall be miscible in all proportions with  water  
4.1.2  The sodium hypochlorite solution supplied shall contain no soluble mineral or organic substances in a 
quantity that would be deleterious or injurious to anyone consuming water treated  with acceptable quantities 
of the hypochlorite  
4.2 Specific  requirement s 
sodium hypochlorite solution  shall comply with the specific requirement given in  table  1 when tested in 
accord ance  to the methods described therein . 
Table 1— Specific requirements for  sodium hypochlorite solution   
Parameter  Requirement  Test method  
Specific gravity at  20 °C  1.14 - 1.24.   US 1847:2017  
Available chlorine content , g/l 10.0 - 15.0  Annex A 
Total free alkali (as NaOH) , % 
m/v, max  1.2 Annex  B 
Insoluble matter , % m/v, max   0.15 Annex C 
pH 9 - 12 Annex D 
Sodium chlorate  Traces  Annex E  
 
 
 
 DUS 925: 2021  
© UNBS 2021  – All rights reserved  3 
 4.3 Heavy metal requirements for Sodium hypochlorite  
Heavy metal requirements  
Parameter, in mg/l (max)  Requirement  Test method  
Arsenic (As)   0.01  US ISO 17378 -2  
Cadmium (Cd)  0.003  US ISO 8288, Method 1  
Chromium (Cr ) 0.05 US ISO 9174  
Mercury (Hg)  0.001  US ISO 12846  
Nickel (Ni)  0.02 US ISO 8288, Method 1  
 Lead (Pb)  0.01 
Antimony (Sb ) 0.005  US ISO 17378 -2 
Selenium (Se)  0.01 US ISO/TS 17379 -2 
Iron  0.3 Annex F  
 
5  Sampling  
5.1  General  
The sampling procedure in Table 2  shall be app lied in determining whether a lot, submitted for inspection and 
test, complies with the relevant requirements of this specification  
Table 2  — Number of containers to be taken for sampling various lot sizes  
Lot size number of containers  Sample size number o f containers  
1 to 4.  All  
5 to 50.  4  
51 to 100.  5  
101 to 500.  8  
501 to 1500.  10  
1501 and above.  12 
 
5.2  Sampling from tankers  
Take from four levels in the tanker or at four stages during filling of the tanker, a composite sample of 500 m l. 
Divide this sample into two equal portions and place each portion in a sample bottle. Use one portion for the 
determination of the insoluble matter, the available chlorine and the free sodium hydroxide contents.  
5.3  Sampling from other containers  
5.3.1  Conta iners with the capacity more than one litre  
From the lot, take at random the number of containers relative to the lot size as given in Table 2. From each 
container so drawn take a 500 mL sample. Divide each sample into two equal portions and place each por tion  
4 © UNBS 2021  – All rights reserved  
 in a sample bottle. Use one portion of each sample for the determination of the available chlorine and the free 
sodium hydroxide contents and reserve the other portion for the determination of the sodium chlorate content.  
The containers and the sample s so taken shall be deemed to represent the lot.  
5.3.2   Containers with the capacity of or less one litre  
From the lot, take at random the number of containers relative to the lot size as given in Table 2. If the 
containers are packed in cartons, take at random the number of cartons relative to the lot size and from each 
carton so drawn take at random one container. Use half of the samples for the determination of the insoluble 
matter, available chlorine and the free sodium hydroxide contents.  
The contain ers and the samples so taken shall be deemed to represent the lot.  
6  Packaging,  
Sodium hypochlorite shall be pack aged: 
a)  in containers of polyethylene or polyvinyl chloride (PVC) with external glass fibre reinforcement (GFR) ;  
b)  in steel tank wagons lined with rubber or coated with a suitable plastic.  
The containers shall be closed in such a manner that no pressure can build up inside, and no liquid  or vapour  
can escape. The closure shall be protected from unintentional opening.  
  
7.  labelling  
The fo llowing information shall be legibly and indelibly marked on the container:  
a)  name of product, 'SODIUM HYPOCHLORITE';  
b)  chemical formular (NaCIO or NaOCI);  
c)  name and address of manufacturer or supplier or both;   
d)  net volume of the contents;  
e)  batch number or mark/code in lieu of the number;   
f)  nominal available chlorine content;  
g)  shelf life;  
h)  instructions for use;   
i) storage instructions with the words, 'STORE IN A COOL PLACE' and “KEEP AWAY FROM DIRECT 
SUNLIGHT”;   
j)  safety instructions with the words:  
(i)  “KEEP AWAY FROM CHILDREN”;  
(ii)  “HARMFUL IF SWALLOWED OR INHALED”;  
(iii)  “AVOID CONTACT WITH EYES, SKIN AND CLOTHING”;  DUS 925: 2021  
© UNBS 2021  – All rights reserved  5 
 (iv)  “AVOID BREATHING MIST AND ALWAYS KEEP CONTAINER CLOSED AFTER USE”; and  
(v)  “WASH HANDS AFT ER USE”; and  
k) first aid instructions, “IF SWALLOWED DO NOT INDUCE VOMITING. GIVE LARGE QUANTITIES OF 
WATER AND SEEK FOR MEDICAL ADVISE”.  
8  Bulk storage  
Sodium hypochlorite shall be protected against light, and particularly direct sunlight. It shall be stored in cool 
rooms in containers made from metal with internal coating or suitable plastics materials. In order to protect 
metal containers from corrosion, they shall be either rubber -lined or plastics -coated.  
NOTE  Pressure build -up in the containers sh ould be prevented by suitable venting.  
  
  
  
 .  
6 © UNBS 2021  – All rights reserved  
 Annex A  
(normative)  
 
 Determination of available chlorine  
A.1  Principle  
The sample is added to an acidified solution of potassium iodide and the released iodine is titrated with 
standard sodium thiosulpha te solution to the usual starch end point.  
A.2  Reagents  
A.2.1  Acetic acid, glacial  
A.2.2  Potassium iodide (KI), crystals, iodate free  
A.2.3  Hydrochloric acid, 0.1 M  
A.2.4  Sodium thiosulphate (Na2S2O3.5H2O), standard solution , 0.1 M . 
Dissolve 25 g of  Na2SO 3 crystals in freshly boiled and cooled water and dilute to 1 L. The solution is more 
stable if the glassware is cleaned with sulphuric -chromic acid and thoroughly rinsed with water. Standardize 
against potassium iodate (KIO 3) as follows: Weigh out a ccurately 3.567 g of dry KIO 3 and transfer to a 1 L 
volumetric flask. Dissolve with water, make up to the mark and mix thoroughly. This solution will be exactly 
0.1000 N.  
To standardize the Na 2S2O3. solution, carefully pipette a 25 mL aliquot of the KIO 3 solution into a 250 mL 
Erlenmeyer flask and dilute to 100 mL with water. Add 1 g of KI crystals. When it is dissolved, add 15 mL of 
1.0 N hydrochloric acid and titrate immediately with the Na 2S2O3. solution. When the solution becomes light 
yellow, add 1 mL  of starch indicator solution and complete the titration to the disappearance of the blue colour. 
Standardize at least monthly.  
Calculate the normality of the Na 2S2O3 solution as follows:  
Normality, N1 = ( 25 x 0.1)/ V  
where,  
V  is the v olume  of Na2S2O3.  solution required for titration of KIO3 solution.  
A.2.5  Starch indicator solution,  
 mix 0.5 g of soluble starch with 5 mL of cold water and add to 95 mL of boiling water. Mix, cool and store in a 
sterilized bottle. Replace frequently or add 0.1 % salicy lic acid to minimize deterioration.  
A.3  Procedure  
Dissolve 2 g to 3 g of KI crystals to 50 mL of water in a 250 mL Erlenmeyer flask. Add 10 mL of acetic acid. 
Then pipette the aliquot of sample into the solution keeping the tip of the pipette beneath th e surface of the 
solution until drained. Titrate at once with 0.1 N Na 2S2O3 solution until the iodine colour is nearly gone then DUS 925: 2021  
© UNBS 2021  – All rights reserved  7 
 add 1 mL of starch indicator solution and complete the titration to the disappearance of the iodine colour. 
Record the titratio n as A  
A.4  Calculations  
A.4.1  Calculate the available chlorine as follows:   
Available chlorine as CI, g/L = (AN 1×35.46)  ÷V 
 A.4.2  Calculate the sodium h ypochlorite content as follows;  
Sodium hypochlorite (NaOCI), g/L = (AN 1×37.22)  ÷V 
where  
A  is the volume, in millilitres, of Na 2S2O3 solution required for titration of the sample;  
N1  is the normality of the Na 2S2O3 solution; and  
V  is the volume, in millilitres, of o riginal sample in aliquot used.  
  
8 © UNBS 2021  – All rights reserved  
 Annex B 
(normative)   
 
Determination of sodium hydro xide content  
B.1  Principle  
A sample is added to a neutralised, mixed solution of barium chloride and hydrogen peroxide, which 
precipitates any carbonate and reduces the hypochlorite to chloride. The free alkali is then titrated with 
standard hydrochlori c acid using phenolphthalein indicator.  
B.2  Reagents  
B.2.1  Barium chloride solution (100g/L),  
Dissolve 100 g of chemically pure barium chloride (BaCI2.2H2O) in distilled water and dilute to one litre with 
distilled water. Filter the solution if turbid .  
B.2.2  Hydrochloric acid, standard (0.1 N),  
Prepare a 0.1 N solution of hydrochloric acid (HCI) and standardize against primary standard solution 
carbonate and methyl red mixed indicator.  
B.2.3  Hydrogen peroxide, approximately 3%.  
B.2.4  Phenolphtha lein indicator solution (0.5 g/100 me),  
Dissolve 0.5 g of phenolphthalein in 60 mL of 95 % ethyl alcohol and dilute to 100 L with sodium hydroxide 
solution.  
Dissolve 4.0 g of chemically pure sodium hydroxide in distilled water and dilute to 1 L with dist illed water.  
B.3  Procedure  
Place 50 mL of barium chloride solution and 30 mL of hydrogen peroxide in a 250 mL Erlenmayer flask (or 
6.in porcelain dish). Add 10 drops of phenolphthalein indicator solution and neutralize with sodium hydroxide 
solution. In troduce into this neutral mixture 10 mL of the liquid bleach, shake or stir vigorously for 1 min and 
titrate the sodium hydroxide solution with 0.1 N hydrochloride acid until the pink colour disappears.  
Record volume of the standard acid used as V 1. 
Carry out a reagent blank titration as above without the 10 mL of the bleach solution. Record volume of 
standard acid used as V 0 
B.4  Calculation  
The free alkali, as NaOH, expressed as % m/v is calculated as;  
Free alkali = (V 1-V0) ×N×0.4  DUS 925: 2021  
© UNBS 2021  – All rights reserved  9 
 where  
V1  is the volu me, in millilitres, of hydrochloric acid solution used in the titration of sample.  
V0  is the volume, in millilitres, of hydrochloric acid solution used in the titration of reagent blank.  
N  is the normality of the hydrochloric acid solution  
 
  
10 © UNBS 2021  – All rights reserved  
 Annex C 
(normative)  
 
 Method of determination of insoluble matter  
C.1  Apparatus   
C.1.1  Gooch crucible   
C.1.2  Balance   
C.1.3  Oven   
C.2  Procedure  
Pour approximately 100 mL of the sodium hypochlorite solution into a tared 400 mL beaker placed on a 
laboratory pl atform balance and weigh to the nearest 0.1 g. Add 100 mL of distilled water and mix thoroughly. 
Filter through a tared Gooch crucible. Wash the beaker and crucible with distilled water. Dry the crucible to a 
constant weight at 100 °C - 105 °C .  
C.3  Calcu lation  
Percent insoluble matter = (Grams  of residue  / Grams  of sample) × 100 DUS 925: 2021  
© UNBS 2021  – All rights reserved  11 
 Annex D  
(normative)   
Measurement of pH value.  
D.1  Measure the pH, at room temperature, using a pH meter equipped with a glass 
electrode capable of measuring pH values to an acc uracy of 0.1 or better.  
 
  
12 © UNBS 2021  – All rights reserved  
 Annex E  
 (normative)  
 
 Method for determination of Sodium chlorate  
E.1 General  
Sodium chlorate is reduced with sodium bromide in 8 N hydrochloric acid. After dilution and addition of 
potassiu m iodide, the released iodine ( equivale nt to the hypochlorate plus chlorate) is titrated with standard 
sodium thiosulphate solution and star ch indicator.  
E.2  Apparatus  
The apparatus ( Fig1) consists of 1 OOOml wide -mouthed reaction bottle (A), fitted with a double hole ru bber 
stopper  E carrying a separa ting funnel B,  conveniently graduated or marked at the 10 , 20 and 100 ml levels, 
and a deli very tube leading to a 50 -ml test tube gas trap C, which is fitted with rubber tubing and a glass 
mouthpiece, D  
 DUS 925: 2021  
© UNBS 2021  – All rights reserved  13 
 E.3 Reagents  
E.3.1 Concentrated Hydro chlori c Acid . 
E.3.2  Sodium Bromide Solution, 10 percent (  mlv ). 
E.3.3  Potassium Iodid e Sclution , 10 percent (  m/v ) 
E.3.4  Standard Sodium Thiosulphate Solution , 0.05 N.  
E.3.5  Starch Indicator Solution , 0.5 percent ( mlv).  
E.3.6 Sodium Bicarbonate - pure grad e. 
E.4 Procedure . 
Pipette out an aliquot of the sample (same amount as used for available chlorine determination ) into the 
reaction bottle ( A), add  1 ml of concentrated hydrochlol ic acid and 0.3 g of pure sodium bicarbonate to expel 
all the air from the ve ssel through the long test tube (C), containing saturated solution of sodium bicarbonate. 
Then add 20 ml of sodium bromide solution followed by 80 ml of concentrated hydrochloric acid. Stopper the 
bottle and shake well. Allow to stand for 10 minutes. Add 2 0 ml of 10 percent potassium iodide solution 
through the separating funnel carefully and titrate the liberated iodine  against 0.05 N sodium thiosul phate 
solution using a few drops of starch indic ator solution.  
Run a blank with all the reagent except the sa mple by proceeding in the same manner as  that of th e test.  
E.5  Calculation  
Sodium chlorate, g/l  = [(V2 - V1) × N × 17.75] ÷V 
Where,  
V2 = volume in ml of sodium thiosulphate, solution used for the test;  
V1 = volume in ml of sodium thiosulphate solution u sed for the blank;  
N = normality of sodium thiosulphate solution; and  
V = volume in ml of original sample solution in aliquot used.  
  
14 © UNBS 2021  – All rights reserved  
 Annex F  
(normative)  
 
 Method of determination of iron  
F.1  Apparatus  
Nessler Cylinders - 50-ml capacity.  
F.2  Reagents  
F.2.1  Ammonium Persulphate  
F.2.2  Butanolic Potassium Thiocyanate Solution Dissolve 10 g of potassium thiocyanate in 
10 ml of water. Add sufficient n -butanol to make up to 100 ml and shake vigorously till the 
solution is clear.  
F.2.3  Standard Iron Soluti on A  
Dissolve 0.7022 g of ferrous ammonium  sulphate [ FeSO 4 (NH 4)2 SO 4 6H2O] in 100  ml of water, add 5 ml of 1:5 
(v/v) sulphuric acid and run in cautiously a dilute solution of potassium permanganate (0.2 percent, m/v) until a 
slight pink coloration rema ins after stirring well. Dilute with water to 1000 ml and mix thoroughly. One millilitre 
of this solution contains 0.1 mg of iron as Fe.  
F.2.4  Standard Iron Solution B  
Take 100 ml of the standard iron Solution A and dilute to 1000 ml with water in a 1000 ml volumetric flask. 
This dilute solution should be prepared fresh. One millilitre of this solution contains 0.01 mg of iron  (as Fe).  
F.3  Procedure  
Weigh 50.0 g of the material and evaporate it almost to dryness. Dilute it to 30 ml, add about 30 mg of 
ammoni um persulphate and 15 ml of butanolic potassium thiocyanate solution. Make up to 50 ml, shake 
vigorously for about 30 seconds and allow the layers to separate. Carry out a control test in another Nessler 
cylinder using 2 ml of standard iron Solution B . 
Com pare the intensity of the colour produced in the butanol layers in the two cylinders.  
The limit prescribed in Table 1 shall be taken as not having been exceeded if the intensity of colour produced 
with the material is not greater than that produced in the control test.  DUS 925: 2021  
© UNBS 2021  – All rights reserved  15 
 Bibliography  
[1] SANS 50901:1999,  Chemicals used for treatment of water intended for human consumption — 
Sodium hypochlorite  
[2] US 925:2012,  Chemicals used for treatment of water intended for human consumption — Sodium 
hypochlorite — Specif ication  
 [3] IS11673:1 992, Sodium  hypochlorite  solution - specification  
 
  
 DUS 9 25: 2021  
© UNBS 2021  – All rights reserved  17 
 Certification marking  
Products that conform to Uganda standards may be marked with Uganda National Bureau of Standards 
(UNBS) Certification Mark shown in the figure below.  
The us e of the UNBS Certification Mark is governed by the Standards Act, and the Regulations made 
thereunder. This mark can be used only by those licensed under the certification mark scheme operated by 
the Uganda National Bureau of Standards and in conjunction with the relevant Uganda Standard. The 
presence of this mark on a product or in relation to a product is an assurance that the goods comply with the 
requirements of that standard under a system of supervision, control and testing in accordance with the 
certification mark scheme of the Uganda National Bureau of Standards. UNBS marked products are 
continually checked by UNBS for conformity to that standard.  
Further particulars of the terms and conditions of licensing may be obtained from the Director, Uganda  
National Bureau of Standards.  
 
 DUS 925: 2021    
 
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