EN ISO 7393-3:2000

SLOVENSKI STANDARD
01-december-2000
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SIST ISO 7393-3:1996
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Water quality - Determination of free chlorine and total chlorine - Part 3: Iodometric
titration method for the determination of total chlorine (ISO 7393-3:1990)
Wasserbeschaffenheit - Bestimmung von freiem Chlor und Gesamtchlor - Teil 3:
Iodometrisches Verfahren zur Bestimmung von Gesamtchlor (ISO 7393-3:1990)
Qualité de l'eau - Dosage du chlore libre et du chlore total - Partie 3: Méthode par titrage
iodométrique pour le dosage du chlore total (ISO 7393-3:1990)
Ta slovenski standard je istoveten z: EN ISO 7393-3:2000
ICS:
13.060.50 3UHLVNDYDYRGHQDNHPLþQH Examination of water for
VQRYL chemical substances
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

IS0
INTERNATIONAL
7393-3
STANDARD
Second edition
1990-06-01
Determination of free chlorine
Water quality -
and total chlorine -
Part 3:
lodometric titration method for the determination of
total chlorine
- Dosage du &lore libre et du &lore total -
Quake’ de l’eau
Patiie 3: M&hode par titrage iodom&trigue pour le dosage du &lore total
Reference number
IS0 7393-3 : 1990 (El
IS0 7393-3 : 1990 0
Foreword
IS0 (the International Organization for Standardization) is a worldwide federation of
national standards bodies (IS0 member bodies). The work of preparing International
Standards is normally carried out through IS0 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, govern-
mental 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 IS0 Council. They are approved in accordance with IS0 procedures requiring at
least 75 % approval by the member bodies voting.
International Standard IS0 7393-3 was prepared by Technical Committee ISO/TC 147,
Water quality.
This second edition cancels and replaces the first edition (IS0 7393-3 : 19861, of which
it constitutes a minor revision.
IS0 7393 consists of the following parts, under the general title Water quality - Deter-
mina tion of free chlorine and total chlorine :
-
Part I : Titrime tric method using N , N-die th yl- 7,4-phen ylenediamine
-
Part 2: Calorimetric method using NJ-diethyl- 1,4-phenylenediamine for
routine control purposes
-
Part 3: lodometric titration method for the determination of total chlorine
Annex A forms an integral part of this part of IS0 7393. Annexes B and C are for infor-
mation only.
0 IS0 1990
All rights reserved. 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 permission in
writing from the publisher.
International Organization for Standardization
Case postale 56 l CH-1211 Geneve 20 l Switzerland
Printed in Switzerland
INTERNATIONAL STANDARD IS0 7393-3 : 1990 (E)
Determination of free chlorine and total
Water quality -
chlorine -
Part 3:
lodometric titration method for the determination of total
chlorine
32 combined chlorine: The fraction of total chlorine
1 Scope
piesent in the form of chloramines and organic chloramines.
This part of IS0 7393 specifies an iodometric titration method
for the determination of total chlorine in water.
3.3 total chlorine: Chlorine present in the form of “free
chlorine” or “combined chlorine” or both.
The method is applicable for the measurement of concen-
trations in terms of chlorine (Cl& from 0,Ol mmol/l to
0,21 mmol/l (0,71 mg/I to 15 mg/l).
3.4 chloramines: Derivatives of ammonia by substitution of
one, two or three hydrogen atoms with chlorine atoms
Several substances interfere in the determination (see
(monochloramine NH&I, dichloramine NHCI,, and nitrogen
clause IO).
trichloride NC&) and all chlorinated derivatives of organic
.
nitrogen compounds.
In annex B a method for direct titration is specified. This is
usually applied to the determination of chlorine concentrations
above 7 ~mol/l (0,5 mg/I) in treated drinking water. Table 1 - Terms and synonyms in relation to actual
compounds in the solution
Term Synonym Compounds 1
2 Normative references
I I
Active free Elemental chlorine,
The following standards contain provisions which, through
chlorine hypochlorous acid
Free chlorine Free chlorine
reference in this text, constitute provisions of this part of
Potential free Hypochlorite
IS0 7393. At the time of publication, the editions indicated
chlorine
--
were valid. All standards are subject to revision, and parties to
‘--
Elemental chlorine,
agreements based on this part of IS0 7393 are encouraged to
hypochlorous acid,
Total chlorine Total residua II chlorine
investigate the possibility of applying the most recent editions
hypochlorite,
of the standards indicated below. Members of IEC and IS0
chloramines
maintain registers of currently valid International Standards.
IS0 5667-l : 1980, Water quality - Sampling - Part i:
Guidance on the design of sampling programmes.
4 Principle
IS0 5667-2 : 1982, Water quality - Sampling - Part2:
Reaction in acid solution of total chlorine and potassium iodide
Guidance on sampling techniques.
with liberation of free iodine. Instantaneous reduction of the
iodine by a known excess of thiosulfate standard solution
previously added to the solution. Titration of the unreacted
3 Definitions (see table 1)
thiosulfate with potassium iodate standard reference solution.
For the purposes of this part of IS0 7393, the following defi-
nitions apply.
5 Reagents
3.1 free chlorine: Chlorine present in the form of .
hypochlorous acid, hypochlorite ion or dissolved elemental During the analysis, use only reagents of recognized analytical
grade, and water as specified in 5.1.
chlorine.
ISO7393-3:1990 E)
51 . Water, free from chlorine and reducing substances. dardization, 2 ml of phosphoric acid (5.3) and ‘I ml of starch
solution (5.6). Titrate immediately with the potassium iodate
standard reference solution (5.4) until the appearance of a blue
* Demineralized or distilled water of which the quality is checked
coloration persisting for at least 30 s occurs. Note the volume
as follows.
of iodate consumed.
Into two 250 ml chlorine-demand free conical flasks (see
millimoles per litre,
The actual concentration, c,, expressed in
clause 6) place, in order,
of the sodium thiosulfate solution is given by the equation
a) in the first: 100 ml of the water to be checked, and
about 1 g of potassium iodide (5.2),2 ml of phosphoric acid V2 c2
c, =
(5.3) and 1 ml of starch solution (5.6);
VI
b) in the second: 100 ml of the water to be checked,
about 1 g of potassium iodide (5.2),2 ml of phosphoric acid
c2 is the concentration, expressed in millimoles per litre,
(5.3) and 1 ml of starch solution (5.6). Add 10 drops of
of the potassium iodate standard reference solution
0,l g/l sodium hypochlorite solution (obtained by dilution
Ml /6 KIO,) = 10 mmol/l];
of commercial concentrated sodium hypochlorite solution,
of which the concentration is determined iodometrically).
V, is the volume, in millilitres, of sodium thiosulfate sol-
ution (5.5.1) used for the standardization (V, = 10 ml) ;
No coloration shall appear in the first flask when the water is
free from chlorine. In the second flask a light blue colour shall
is the volume, in millilitres potassiu m
stan-
I of
V2
appear.
dard reference solution used in the titration.
In the case of demineralized or distilled water not having the
desired quality, it must be chlorinated. After a period of contact 56 .
Starch, 5 g/l solution, or similar commercial indicator.
followed by dechlorination, the final quality has to be re-
checked.
6 Apparatus
dechlorination is given
A procedure for chlorination followed
bY
in annex A.
Usual laboratory equipment and
Burette, with fine tip, permitting the delivery of about
5.2 Potassium iodide (Kl) crystals.
30 drops/ml, measuring up to 25 ml, graduated in divisions of
0,05 ml.
5.3 Phosphoric acid, solution, c(H,PO,) = 0,87 mol/l.
NOTE ON PREPARATION OF GLASSWARE
Dissolve 64 ml of phosphoric acid (Q = I,69 g/ml) in water,
cool and dilute to 1 000 ml.
Chlorine-demand free glassware is obtained by filling with 0,l g/l
sodium hypochlorite then, after 1 h, rinsing thoroughly with distilled
water and with water free from chlorine-demand.
5.4 Potassium iodate, standard reference solution,
= 10 mmol/l.
d/6 KIO,)
7 Sampling and samples
Weigh, to the nearest milligram, 0,360 g of dry potassium
iodate. Dissolve in water in a 1 000 ml one-mark volumetric
See IS0 5667-l and IS0 5667-2.
flask, make up to the mark with water and mix.
5.5 Sodium thiosulfate, standard volumetric solution,
8 Procedure
c(Na2S20~~ 5H2G) = 10 mmol/l.
8.1 Test portion
55.1 Preparation
Start determinations immediately after taking samples. At all
Dissolve about 248 g of sodium thiosulfate in about 250 ml of
times avoid bright light, agitation and heat.
water in a 1 000 ml one-mark volumetric flask. Make up to the
mark with water and mix.
Take a test portion of volume not greater than 200 ml and con-
taining not mo
...