Reference number  
DRS 127 -2: 2017  
© RSB 2017  
 
 
 RWANDA 
STANDARD  DRS 
127-2 
 
First edition  
2017 -mm-dd 
 
Bleaching agents — Specification  
Part 2: 
Sodium hypochlorite solutions  for 
industrial and domestic use  
  DRS 127 -2: 2017  
©RSB 2017 - All rights reserved                  ii 
 In order to match with technological development and to keep continuous progress in industries, 
standards are subject to periodic review. Users shall ascertain that they are in possession of the latest 
edition  
 
 
 
 
 
 
 
 
© RSB 2017  
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized 
in any form or by any means, electronic or mechanical, including photocopying and microfilm, without 
prior written permission from R SB. 
Requests for permission to reprodu ce this document should be addressed to : 
Rwanda Standards  Board  
P.O Box 7099 Kigali -Rwanda  
KK 15 Rd, 49  
Tel. +250 252 586103/ 582945  
Toll Free: 3250  
E-mail: info@rsb.gov.rw  
Website: www.rsb.gov.rw  DRS 127 -2: 2017  
iii                ©RSB 2017 - All rights reserved  
 Contents  Page 
Foreword  ................................ ................................ ................................ ................................ ............................  iv 
1 Scope  ................................ ................................ ................................ ................................ ......................  1 
2 Normative references  ................................ ................................ ................................ ............................  1 
3 Terms and definitions  ................................ ................................ ................................ ...........................  1 
4 Requirements  ................................ ................................ ................................ ................................ .........  2 
4.1 General  ................................ ................................ ................................ ................................ ...................  2 
4.2 Sodium hypochlorite solution for industrial use  ................................ ................................ ...............  2 
4.2.1  General  ................................ ................................ ................................ ................................ ...................  2 
4.2.2  Physical and chemical requirements  ................................ ................................ ................................ .. 2 
4.2.3  Stability  ................................ ................................ ................................ ................................ ...................  3 
4.3 Sodium hyp ochlorite solutions for domestic use  ................................ ................................ ..............  3 
4.3.1  General  ................................ ................................ ................................ ................................ ...................  3 
4.3.2  Physical and chemical requirements  ................................ ................................ ................................ .. 3 
4.3.3  Stability  ................................ ................................ ................................ ................................ ...................  3 
5 Labelling and packaging ................................ ................................ ................................ .......................  4 
5.1 Labelling  ................................ ................................ ................................ ................................ .................  4 
5.2 Packaging  ................................ ................................ ................................ ................................ ...............  5 
Annex  A (normative)  User information  ................................ ................................ ................................ ...........  6 
Annex  B (normative)  Determination of available chlorine  ................................ ................................ ............  7 
B.1 Principle of test methods  ................................ ................................ ................................ ............................  7 
B.2 Reagents  ................................ ................................ ................................ ................................ .......................  7 
B.2.1 Glacial acetic acid  ................................ ................................ ................................ ................................ ..... 7 
B.2.2 Standard potassium iodate solution – 0.1N  ................................ ................................ ...........................  7 
B.2.3 Starch indicator solution – 0.5 per cent . ................................ ................................ ................................  7 
B.2.4 Potassium iodate crystals – Iodate free.  ................................ ................................ ................................ . 7 
B.2.5 Standard Sodium thiosulphate solution – 0.1N.  ................................ ................................ ....................  7 
B.3 Procedure  ................................ ................................ ................................ ................................ .....................  7 
B.4 Calculation  ................................ ................................ ................................ ................................ ....................  8 
Annex  C (norma tive)  Sediment content  ................................ ................................ ................................ ..........  9 
Annex  D (normative)  Sodium hypochlorite content  ................................ ................................ ....................  10 
Annex E (Normative)  Sodium hydroxide content  ................................ ................................ ........................  13 
Annex F (normative)  Gassing rate of sodium hypochlorite  ................................ ................................ ........  15 
Annex G  (normative)  Iron content, cobalt content, copper content and nickel content  ........................  18 
 DRS 127 -2: 2017  
©RSB 2017 - All rights reserved                  iv 
 Foreword  
Rwanda Standard s are prepared  by Technical Committees and approved by R wanda Standards Board (RSB) 
Board  of Directors in  accordance with the procedures of RSB, in compliance with Annex 3 of the WTO/TBT 
agreement on the preparation, adoption and application of standards.  
The main task o f technical committees is to prepare national standards.  Final Draft Rwanda S tandards 
adopted by Technical committ ees are ratified  by me mbers of RSB Board of Director s for publication and 
gazettment as Rwanda Standards.  
DRS 127 -2 was prepared by Technical Committee RSB/TC 011, Cosmetics, Toiletries and Surface Active 
Agents . 
In the preparation of this standard, reference was made to the following standard s: 
1) KS 03 -1290 -1, Specification for bleaching agents, Part 1. Sodium hypochlorite solutions  
2) AWWA B 300 – 80 American Water Works Association standards  for hypochlorites . 
The assistance de rived from the above source is hereby acknowledged with thanks.  
RS 127 consists of the following parts, under the general title , Bleaching agents Specification  
- Part 1: Sodium hypochlorite solutions for water treatment  
- Part 2: Sodium hypochlorite solutions for industrial and domestic use  
Committee membership  
The following organizations were represented on the Technical Committee on Cosmetics, Toiletries and 
Surfac e Active Agents (RSB/TC 011) in the preparation of this standard.  
ALYVO Rwanda Ltd  
Better Home Ltd  
Eden Business Center Ltd  
National Industrial Research and Development Agency (NIRDA)  
Private Sector Federation/Beauty Makers Association (PSF/BMA)  
Rwanda Bio medical Centre (RBC)  DRS 127 -2: 2017  
v                ©RSB 2017 - All rights reserved  
 Rwanda National Police (RNP)  
Sulfo Rwanda Industries Ltd  
Trust Industries Ltd  
University of Rwanda/College of Sciences and Technology (UR/CST)  
Rwanda  Standards Board  (RSB) – Secretariat  
 DRS 127 -2: 2017  
1                ©RSB 2017 - All rights reserved  
 Bleaching agents — Specification  — Part 2: Sodium 
hypochlorite solutions for industrial and domestic use  
1 Scope  
This Draft Rwanda Standard prescribes the requirements and methods of test for sodium hypochlorite for use 
as bleaching and disinfecting agents.  
This document  applies to three aqueous concentrations of sodium hypochlorite solution suitable for industrial 
and domestic use . 
This standard does not apply to sterilizers.  
2 Normative references  
The following documents are referred to in the text in such a way that some or all of  their content constitutes 
requirements of this document.  For dated references, only the ed ition cited applies. For undated references, 
the latest edition of the referenced document (including any amendments) applies.  
EAS 295 , Sodium Hypochlorite solutions for domestic use – Specification  
RS 127 -1, Bleaching agents – specification – Part 1: Sodium hypochlorite solutions for water treatment  
ASTM D2022 -89, Standard Test Methods of Sampling and Chemical Analysis of Chlorine -Containing 
Bleaches  
3 Terms and definitions  
For the purposes of this  standard , the follow ing terms and definitions  apply . 
3.1 
available chlorine  
quantity of chlorine chemically equivalent to the oxygen that would be released during the complete 
decomposition of the sodium hypochlorit e to sodium chloride and oxygen  
Note  - This is a conventional way of expressing the concentration of sodium hypochlorite solution. The available chlorine is 
0.95 times the sodium hypochlorite content and is a measure of the oxidising power of sodium hypochlorite solutions.  
3.2 
nominal concentration  
minimum available chlorine content of the sodium hypochlorite solution under test, at the time of manufacture   
©RSB 2017 - All rights reserved                  2 
 4 Requirements  
4.1 General  
Sodium hypochlorite solutions shall be of one of the following nominal concentrations, as required (see Annex 
A): 
a) 150 g/L for industrial use;  
b) 50 g/L for domestic use; or  
c) 35 g/L for domestic use.  
4.2 Sodium hypochlorite solution for industrial use  
4.2.1  General  
The solution shall be a clear liquid free from suspended or particulate matter and shall be miscible in all  
proportions with distilled water.  
4.2.2  Physical and chemical requirements  
The solution shall comply with th e requirements given in Table 1:  
Table 1 — Physical and chemical requirements for a sodium hypochlorite solution for industrial use  
S/N Property  Requirem ent Test method  
1.  pH, min 11 - 
2.  Freezing point, oC -25 - 
3.  Available chlorine  ( %, m/v), min  3.5 Annex B 
4.  Sediment content, % (mass fraction expressed as a 
percentage), max.  0.1 Annex C  
5.  Sodium hypochlorite content determined on the date of 
manufacture, g/L, min.  150 Annex D  
6.  Sodium hypochlorite content determined on the 14th day ± 2 
d after date of manufacture, g/L, min.  130 Annex D  
7.  Sodium hydroxide content, g/L, min. max.  10 - 60 Annex E  
8.  Gassing at 37 °C, cm3 over a 20 h period, max.  35 Annex F  
9.  Iron content, mg/L, max.  10 Annex G 
10.  Cobalt content, mg/L, max.  5 Annex G 
11.  Copper content, mg/L, max.  5 Annex G 
12.  Nickel content, mg/L, max.  5 Annex G DRS 127 -2: 2017  
3                ©RSB 2017 - All rights reserved  
 4.2.3  Stability  
When (after receipt) the solution has been stored in the dark at a temperature of 20 °C to 25 °C, the sodium 
hypochlorite content, determined in accordance with 5.5 on the 14th day ± 2 d after date of manufacture, shall 
be at least 130 g/L.  
NOTE  See annex A for notes to users on the two main ways sodium hypochlorite solution decomposes.  
4.3 Sodium hypochlorite solutions for domestic use  
4.3.1  General  
4.3.1.1  When so required, the solution shall contain laundry blue. The laundry blue might settle on 
standing but shall disperse co mpletely in the solution when the solution, in the original container, is shaken for 
30 s.  
4.3.1.2  The solution shall be a clear liquid, and shall be free from sediment and suspended matter other 
than the required laundry blue. A solution shall be consider ed to be clear if all salts that have crystallized from 
the solution dissolve completely when the solution is mixed with twice its volume of distilled water.  
4.3.2  Physical and chemical requirements  
The solution shall comply with the requirements given in Table 2. 
4.3.3  Stability  
When (after receipt) the solution has been stored in the dark at a temperature of 20 °C to 25 °C, the sodium 
hypochlorite content, determined in accordance with 5.5 on the 60th day ± 2 d after date of manufacture, shall 
be as follows:  
a) solutions of 5 % nominal concentration : not less than 45 g/L; and  
b) solutions of 3.5 % nominal concentration : not less than 32 g/L.  
   
©RSB 2017 - All rights reserved                  4 
  
Table 2 — Physical and chemical requirements for a sodium hypochlorite solution for domestic use  
S/N Property  Requirement  Test method  
1.  pH, min  11 - 
2.  Freezing point, oC -25 - 
3.  Available chlorine ( %, m/v), min  3.5 Annex B 
4.  Sediment content, % (mass fraction expressed 
as a percentage), max.  0.1 Annex C  
5.  Sodium hypochlorite content determined on the 
14th day ± 2 d after date of manufacture, g/L, 
min.  
5 % nominal concentration  
3.5 % nominal c oncentration  50 
35 Annex D  
6.  Sodium hypochlorite content determined on the 
60th day ± 2 d after date of manufacture, g/L, 
min.  
5 % nominal concentration  
3.5 % nominal concentration  45 
32 Annex D  
7.  Sodium hydroxide content, g/L, max.  15 Annex E  
5 Labelling and packaging  
5.1 Labelling  
5.1.1  Containers shall be marked with the following conspicuous, legible and indelible information:  
a) name of the product;  
b) name of address of the manufacturer, an d registered trade mark, if any;  
c) instructions for use and dilution factor;  
d) batch or code number;  
e) date of manufacture and expiry date;  
f) net volume of the solution;  
g) available chlorine ; 
h) color ; and  
i) country of origin . DRS 127 -2: 2017  
5                ©RSB 2017 - All rights reserved  
 5.1.2 The container shall also be marked with the following information:  
a) the warning “Corrosive”;  
b) the instructio n “Use in well ventilated room”;  
c) the instr uction “First aid instructions”;  
d) the words “K eep away from heat or sunlight”; and  
e) the words "Keep out of the reach of children" or words having similar meaning ”. 
5.2 Packaging  
5.2.1  The containers used for packaging sodium hypochlorite solutions shall be of material inert tothe 
contents and shall protect the solution from sunlight.  
5.2.2  The containers shall not be metallic.  The only metals that should be used with bleach are titanium or 
tantalum.  
5.2.3  The containers shall be strong eno ugh to withstand normal usage and transpor tation.  
©RSB 2017 - All rights reserved                  6 
 Annex  A 
(normative)  
 
User information  
A.1 The decomposition of sodium hypochlorite takes place in two main ways:  
a) 3NaOCl→2NaCl + NaClO 3; and  
b) 2NaOCl→2NaCl + O 2. 
Normally, in the dark, over 90% of the decomposition follows the chlorate -forming mechanism  (a) and the 
remainder follows the oxygen -forming reaction (b).  
A.2 The following are some of the factors that increase the rate at which decomposition of the solution occurs:  
a) concentration : the rate of decompositio n falls off rapidly as the solution loses strength;  
b) temperature : elevated temperatures greatly increase the rate of decomposition;  
c) metallic impurities : certain trace metallic impurities such as copper, nickel, cobalt and iron catalyse the 
oxygen -forming reaction;  
d) exposure to light : the rate of both the chlorate -forming reaction and the oxygen -forming reaction is 
increased by exposure to blue or ultraviolet light; and  
e) pH value of solution : sodium hypochlorite is stabilized by sodium hyd roxide, and the pH value of the 
solution should exceed 11 . DRS 127 -2: 2017  
7                ©RSB 2017 - All rights reserved  
 Annex  B 
(normative)  
 
Determination of available chlorine  
B.1 Principle of test methods  
The sample is added to an acidified solution of potassium iodine and the released iodine titrated with standard 
sodiu m thiosulphate solution to the starch end point.  
B.2 Reagents  
B.2.1 Glacial acetic acid  
B.2.2 Standard potassium iodate solution – 0.1N  
B.2.3 Starch indicator solution – 0.5 per cent . 
Mix 0.5 per cent of solution starch with 5 mL of cold water and 95 mL of  boiling water. Mix, cool and store in 
glass bottle. Replace frequently or add 0.1 per cent m/v salicylic acid to the starch solution to minimize 
deterioration.  
B.2.4 Potassium iodate crystals – Iodate free . 
B.2.5 Standard Sodium thiosulphate solution – 0.1N. 
Dissolve 25 g of sodium thiosulphate (Na 2S2O3.5H 2O) crystals in freshly boiled and cooled water, and dilute to 
1 000 mL.  
NOTE: the solution is more stable if the glassware is cleaned with sulphulic or chromic acids and thoroughly rinsed with 
water befor e use.  
B.3 Procedure  
Dissolve 2 g to 3 g of potassium iodide crystals in 50 mL of water in 250 mL conical flask.  
Add10 mL of glacial acetic acid, then pipette out a 3 mL aliquot of sample into the solution, keeping the tip of 
the pipette beneath the surfac e of the solution until drained.  
Titrate at once with 0.1N standard sodium thiosulphate solution until the iodine colour is nearly gone then add 
1 mL of starch indicator solution and complete the titration to the disappearance of the blue colour.   
©RSB 2017 - All rights reserved                  8 
 B.4 Calcu lation  
Available chlorine (as Cl) per cent mass by volume  
=(𝐴𝑁𝑥  0.03546  𝑥 100 )
𝑉 
Where,  
A = volume in mL of standard sodium thiosulphate solution required for titration of the sample,  
N = Normality of the standard sodium thiosulphate solution, and  
V = volume in mL of original sample in aliquot used.  
  DRS 127 -2: 2017  
9                ©RSB 2017 - All rights reserved  
 Annex  C 
(normative)  
 
Sediment content  
C.1 Procedure  
C.1.1 Mix the test specimen of sodium hypochlorite solution (see 5.3.1) thoroughly and then accurately 
weigh out approximately 300 g into a 500 mL beaker.  
C.1.2 Filter the solution through a Whatman GF/A glass -fibre filter paper that has been dried at 100 °C ± 2 
°C and tared, or equivalent.  
C.1.3 Wash the beaker and the sediment five times with 20 mL portions of cold water and then dry the 
glass fibre filter pap er with the sediment at 100 °C ± 2 °C until a constant mass is attained.  
C.2 Calculation  
Calculate the sediment content, S, as a percentage, as follows:  
100
12mmS
 
where  
m2 is the mass of the sediment after it has been dried, in grams;  
m1 is the mass of test specimen taken, in grams.  
 
 
  
©RSB 2017 - All rights reserved                  10 
 Annex  D 
(normative)  
 
Sodium hypochlorite content  
D.1 Reagents  
D.1.1 Potassium iodide (KI).  
D.1.2 Glacial acetic acid (CH 3COOH).  
D.1.3 Sodium carbonate (Na 2CO 3). 
D.1.4 Mercuric iodide (HgI 2). 
D.1.5 Starch indicator solution  
Prepare the starch solution immediately before use, as follows:  
Make a paste of 1 g of soluble starch and a small amount of water. Pour the paste into 100 mL of boiling 
water, stirring it constantly. Boil for approximately 1 min and cool.  
D.1.6 Standard potassium dichromate solution , c(K2Cr2O7) = 0,01667 mol/L  
Dissolve exactly 4.904 g of potassium dichromate, previously dried at 105 °C ± 2 °C for 2 h and cooled in a 
desiccator, in water and dilute to 1 000 mL in a volumetric flask.  
D.1.7 Sodium thiosulfate solution (± 0.1 mol/L).  
D.1.7.1 Preparation  
Prepare a stock volumetric solution as follows:  
a) Dissolve 25 g ± 1 g of sodium thiosulfate pentahydrate (NaS 2O3·5H 2O) in freshly boiled and cooled 
water.  
b) Add 0.1 g of sodium carbonate (see  5.5.1.3) and 0.01 g of mercuric iodide (see 5.5.1.4) and dissolve.  
c) Dilute to 1 000 mL with freshly boiled and cooled water in a volumetric flask.  
d) Transfer to an amber -coloured glass -stoppered bottle and store in the dark.  
e) Standardize the solution  before use (see 5.5.1.7.2).  DRS 127 -2: 2017  
11                ©RSB 2017 - All rights reserved  
 f) Discard the solution when it becomes turbid.  
D.1.7.2 Standardization  
Standardize the sodium thiosulfate solution as follows:  
a) Pipette 20.0 mL of the potassium dichromate solution (see 5.5.1.6) into a glass -stoppered iodine  flask.  
b) Remove the stopper and quickly add 3 g of potassium iodide, 2 g of sodium bicarbonate and 5 mL of 
concentrated hydrochloric acid.  
c) Insert the stopper gently in the flask, swirl to mix, and allow to stand in the dark for 10 min.  
d) Rinse the stopper and the inner walls of the flask with water and titrate with the sodium thiosulfate 
volumetric solution (see 5.5.1.7) until a pale straw colour is obtained.  
e) Add 2 mL of the starch solution (see 5.5.1.5) and continue the titration until a blue co lour is discharged.  
f) Carry out a blank determination by repeating the procedure but omitting the potassium dichromate.  
g) Calculate the concentration, M, of the sodium thiosulfate solution, in moles per litre, as follows:  
V..M6 016670020  
 
     = 
V.02  
where  
V is the volume of sodium thiosulfate solution used in the titration after the correction for the 
blank, in millilitres.  
NOTE  Alternative methods of standardization may be used provided that they give equivalent results.  
D.2 Proc edure  
D.2.1 Pipette 25.0 mL of the sample into a 1 000 mL volumetric flask and dilute with water up to the mark.  
D.2.2 Pipette 25.0 mL of the diluted sample into a 250 mL glass -stoppered iodine flask and add 50 mL of 
water.  
D.2.3 Add 2 g of potassium iodid e and 10 mL of glacial acetic acid. Insert the stopper and allow to stand in 
the dark for 10 mins.   
©RSB 2017 - All rights reserved                  12 
 D.2.4 Rinse the stopper and the inner walls of the flask with water.  
D.2.5 Titrate the liberated iodine with the standardized sodium thiosulfate solution (see 5.5.1.7) to a pale 
straw yellow colour.  
D.2.6 Add 1 mL of starch indicator solution (see 5.5.1.5) and titrate drop by drop until the faint blue colour 
changes to colourless, for at least 30 s.  
D.2.7 Carry out a blank determination by repeating the pro cedure but omitting the sample.  
D.3 Calculation  
Calculate the sodium hypochlorite (NaOCl) content, C, in grams per litre, as follows:  
C = V × 59.56 × M 
where  
V is the volume of sodium thiosulfate solution used in the titration after correction for the blank, 
in millilitres;  
M is the molarity of sodium thiosulfate solution, in moles per litre.  
 
  DRS 127 -2: 2017  
13                ©RSB 2017 - All rights reserved  
 Annex E  
(Normative ) 
 
Sodium hydroxide content  
E.1 Reagents  
E.1.1 Barium chloride solution , 10 g/100 mL  
Dissolve 100 g of barium chloride (BaCl 2.2H 2O) in water and dilute to 1 L with water. Filter the solution if 
turbid.  
E.1.2 Hydrogen peroxide solution  
Approximately 3 % (10 volumes).  
E.1.3 Sodium hydroxide solution , 0.4 g/100 mL  
Dissolve 0.4 g of sodium hydroxide in water, cool and dilute to 100.0 mL in a volume tric flask. Store in a 
plastics container.  
E.1.4 Phenolphthalein indicator solution  
Dissolve 1 g of phenolphthalein in 100 mL of ethanol (95 %).  
E.1.5 Screened methyl orange indicator solution  
Dissolve 0.2 g of methyl orange and 0.28 g of xylene cyanol FF in 100 mL of ethanol (50 %).  
E.1.6 Standard hydrochloric acid solution ( c (HCl) = 0.10 mol/L)  
Dilute 8.9 mL of concentrated hydrochloric acid ( d at 25 °C ≥ 1.160) with water. Standardize against sodium 
carbonate, using the screened methyl orange as indicat or. 
E.2 Procedure  
E.2.1 Place 50 mL of the barium chloride solution and 40 mL of the hydrogen peroxide solution in a 250 mL 
conical flask.  
E.2.2 Add 10 drops of the phenolphthalein indicator and then add the sodium hydroxide solution drop by 
drop until a permanent faint pink colour is obtained.  
E.2.3 Immediately pipette 10 mL of the test specimen of sodium hypochlorite solution drop by drop into the 
flask, taking care that the effervescence does not become excessive.   
©RSB 2017 - All rights reserved                  14 
 E.2.4 When the effervescence subsides, swirl the flask vigorously for 1 min.  
E.2.5 Add another drop of phenolphthalein indicator and rapidly titrate the solution with the standard 
hydrochloric acid solution (see 5.6.1.6) until the pink colour first disappears.  
E.2.6 Do not continue the titratio n if the pink colour re -appears on standing.  
E.3 Calculation  
Calculate the sodium hydroxide content, X, in grams per litre, as follows:  
X = V × M × 4.0  
where  
V is the volume of hydrochloric acid solution used in the titration, in millilitres;  
M is the conc entration of the standard hydrochloric acid solution, in moles per litre.  
  DRS 127 -2: 2017  
15                ©RSB 2017 - All rights reserved  
 Annex F  
(normative)  
 
Gassing rate of sodium hypochlorite  
F.1 Outline of method  
The gas evolved from a weighed sample maintained at a controlled temperature is collected and measured 
volumetrically.  
F.2 Apparatus  
F.2.1 Water -bath and thermostatic water circulator , capable of maintaining a temperature of 37 °C.  
F.2.2 Dreschel bottle , of 250 mL and that is externally covered to exclude light.  
F.2.3 Graduated burette , of 50 mL ca pacity.  
F.2.4 Top-pan balance , capable of weighing to an accuracy of 0.1 g.  
F.2.5 Tallform beaker , of 500 mL capacity.  
F.2.6 Delivery tube , of glass connected to the Dreschel bottle.  
F.3 Procedure  
F.3.1 Weigh out 300 g ± 0.5 g of the sample into the Dreschel bottle.  
F.3.2 Place the Dreschel bottle in the water -bath at 37 °C ± 1° C.  
F.3.3 Fill the beaker with approximately 400 mL of water and immerse the end of the delivery tube in the 
beaker. Check that the water does not suck back beyond the second b end in the delivery tube  
F.3.4 Completely fill the burette with water and invert in the beaker, ensuring that no air is trapped in the 
burette and that the end of the burette is well submerged in the water.  
F.3.5 Secure the open end of the burette over the  end of the delivery tube so that the gas evolved is 
trapped in the burette.  
F.3.6 Use the burette tap to adjust the volume of water in the burette to the 50 mL mark.  
F.3.7 Leave the sample in the water -bath for 1 h to equilibriate to the correct temperatu re.  
©RSB 2017 - All rights reserved                  16 
 F.3.8 Record the volume ( V1) of gas (mL) collected in the inverted burette.  
F.3.9 Leave the sample in the water -bath for a further 20 h and then record the total volume ( V2) of gas 
(mL) collected in the inverted burette.  
NOTE  Take the reading in millilitres as equivalent to the volume of gas in cubic centimetres.  
F.3.10 Calculate the gassing rate per 20 h (see 5.7.4).  
F.3.11 Repeat 5.7.3.1 to 5.7.3.10 (inclusive) at least once more.  
F.4 Calculation  
Calculate the gassing rate, GR, of the gas collec ted, in cubic centimetres per 20 h, as follows:  
GR = V2 − V1 
where  
V2 is the total volume of gas collected after 20 h, in cubic centimeters;  
V1 is the volume of gas collected after 1 h, in cubic centimeters.  
Express the final results as an average of the c alculated results for each determination.  
 DRS 127 -2: 2017  
17                ©RSB 2017 - All rights reserved  
  
Figure 1 — Apparatus for measuring the gassing rate of sodium hypochlorite  
 
 
  
 
©RSB 2017 - All rights reserved                  18 
 Annex G  
(normative)  
 
Iron content, cobalt content, copper content and nickel content  
G.1 Apparatus  
Atomic absorption spectrometer , capable of operating under the conditions given in Table 3.  
G.2 Reagents  
G.2.1 Nitric acid solution (1:1)  
Carefully add 100 mL of concentrated nitric acid ( d at 25 °C ≥ 1.339) to 100 mL of water while mixing.  
G.2.2 Hydrochloric acid  
Concentrated hydrochloric acid (a mass fraction of 32 %: d at 25 °C ≥ 1.160).  
G.2.3 Hydrochloric acid solution (1:1)  
Carefully add 100 mL of concentrated hydrochloric acid (see 5.8.2.2) to 100 mL of water while mixing.  
G.2.4 Sodium chloride solution (30 g/ L) 
Dissolve 30.00 g of sodium chloride in 100 mL water in a 1 L volumetric flask, and make up to the mark with 
water.  
G.3 Standard solutions  
G.3.1 General  
Prepare four standard solutions, as detailed in 5.8.3.2 to 5.8.3.5 (inclusive), that contain iron, co balt, copper 
and nickel respectively, in a concentration of 1 000 mg/L.  
5.8.3.2  Iron solution  
Dissolve exactly 1.000 g of a mass fraction of 99.99 % metallic iron in 25 mL of 1:1 hydrochloric acid in a 150 
mL tallform beaker. Leave the beaker covered with a watch glass in a water -bath until the metallic iron is 
completely dissolved. Transfer quantitatively to a 1 L volumetric flask, and make up to the mark with water.  
G.3.3 Cobalt solution  DRS 127 -2: 2017  
19                ©RSB 2017 - All rights reserved  
 Dissolve exactly 1.000 g of a mass fraction of 99.99 % metallic coba lt in a minimum volume of 1:1 nitric acid, 
transfer quantitatively to a 1 L volumetric flask, and make up to the mark with water.  
G.3.4 Copper solution  
Dissolve exactly 1.000 g of a mass fraction of 99.99 % metallic copper in a minimum volume of 1:1 nitric  acid, 
transfer quantitatively to a 1 L volumetric flask, and make up to the mark with water.  
G.3.5 Nickel solution  
Dissolve exactly 1,000 g of a mass fraction of 99.99 % metallic nickel in 20 mL of 1:1 nitric acid, transfer 
quantitatively to a 1 L volumet ric flask, and make up to the mark with water.  
NOTE  Commercially available standard solutions may also be used.  
G.4 Procedure  
G.4.1 Instrument operating conditions  
Adjust the instrument controls to the settings given in table 3, appropriate to the element being determined, 
using acetylene as the fuel for the burner, and air as the support.  
Table G1— Instrument settings  
1  2 3 4 5 
Instrument setting  Setting a for the determination of  
Iron Cobalt  Copper  Nickel  
Wavelength, nm  248.3  240.7  324.7  232.0  
Slit width, nm  0.2 0.2 0.2 0.2 
Lamp current, mA  5,0 7.0 3.5 3.5 
Scale expansion  Up to × 10  Up to × 10  Up to × 10  Up to × 10  
a  Small variations in the above settings might be necessary for different instruments.  
G.4.2 Calibration of instrument  
From  the standard solutions (see 5.8.3), prepare calibration solutions as follows:  
a) pipette 10 mL of 1 000 mg/L of iron, cobalt, copper and nickel into separate 100 mL volumetric flasks, 
make up to the mark with water and mark it 100 mg/L;  
b) prepare 1 mg/L,  5 mg/L and 10 mg/L standards by pipetting 1 mL, 5 mL and 10 mL of each of the 100 
mg/L standards into separate 100 mL flasks;  
c) make up to the mark, using the 30 g/L sodium chloride solution to ensure a similar matrix to the test 
specimen of sodium hypoc hlorite solution;   
©RSB 2017 - All rights reserved                  20 
 d) as a blank, use the same 30 g/L sodium chloride solution;  
e) aspirate each solution through the instrument and read its absorbance value at the specified settings 
(see Table 3); and  
f) for each element, prepare a calibration curve by p lotting the concentrations of the three standard 
solutions, in milligrams per litre, against their absorbance values minus the absorbance value of the 
blank.  
G.4.3 Determination of iron content, cobalt content, copper content and nickel content  
G.4.3.1 Pipette 10 mL of the test specimen of sodium hypochlorite solution into a 150 mL tallform beaker and 
slowly add 1 mL of concentrated hydrochloric acid while stirring. (The test specimen is treated with 
hydrochloric acid to remove the formed chlorine and to fo rm sodium chloride in solution.)  
G.4.3.2 Cover the beaker with a watch glass and allow the ensuing heat to complete the following exothermic 
reaction:  
NaOCl+2HCl → NaCl+H2O+Cl 2 
G.4.3.3 If the solution is not clear, add another 1 mL of concentrated hydrochl oric acid and allow the reaction 
to continue; repeat the procedure until the solution is clear.  
G.4.3.4 Allow the solution to cool and as soon it has lost all of its yellow colour and a crystalline precipitate 
has formed, transfer the contents quantitatively into a 100 mL volumetric flask and make up to the mark with 
water.  
G.4.3.5 Aspirate the solution through the instrument and read its absorbance value for each element, at the 
specified settings (see Table 3).  
NOTE  It is recommended that procedures be conducted in the following sequence:  
– optimize instrument;  
– read blank;  
– read standards; and  
– read test specimen.  
G.5 Calculation  
Calculate the concentration, Y, in milligrams per litre, of each of the four elements in the test specimen, using 
the following formula:  
VCY100
 
where  DRS 127 -2: 2017  
21                ©RSB 2017 - All rights reserved  
 C is the concentration of the element in the dilute test specimen of sodium hypochlorite solution 
(as read off from the appropriate calibration curve), in milligrams per litre;  
V is the volume of test speci men used (see G.4.3.1).  
 DRS 127-2: 2017  
ICS 71.060  
 
 
©RSB 2017 - All right s reserved