SIST EN 25814:1996
(Main)Water quality - Determination of dissolved oxygen - Electrotechnical probe method (ISO 5814:1990)
Water quality - Determination of dissolved oxygen - Electrotechnical probe method (ISO 5814:1990)
Includes a procedure by means of an electrochemical cell which is isolated from the sample by a gas permeable membrane. Depending on the type of probe employed measurement can be made either as concentration of oxygen, percentage saturation or both. The procedure is suitable for measurements made in the field and for continuous monitoring and in the laboratory. It is the preferred procedure for highly coloured and turbid waters. It is suitable for natural, waste and saline waters.
Wasserbeschaffenheit - Bestimmung des gelösten Sauerstoffs - Elektrochemisches Verfahren (ISO 5814:1990)
Qualité de l'eau - Dosage de l'oxygene dissous - Méthode électrochimique a la sonde (ISO 5814:1990)
La présente Norme internationale prescrit une méthode électrochimique de dosage de l'oxygène dissous dans les eaux à l'aide d'une cellule électrochimique qui est isolée de l'échantillon par une membrane perméable aux gaz. Selon le type de sonde employé, le mesurage peut être fait soit en tant que concentration d'oxygène, en milligrammes par litre, soit en tant que taux de saturation (% d'oxygène dissous) ou les deux. La méthode mesure l'oxygène dans l'eau correspondant à un taux de saturation de 0 % à 100 %. Cependant, la plupart des appareils permettent des mesurages de valeurs supérieures à 100 %, c'est-à-dire une supersaturation. La méthode est utilisable pour les mesurages effectués sur le terrain et pour le contrôle permanent de l'oxygène dissous, ainsi que pour les dosages en laboratoire. C'est la méthode à préférer pour les eaux fortement colorées et troubles, ainsi que pour celles qui renferment des substances fixant le fer et l'iode, et susceptibles d'interférer avec la méthode iodométrique spécifiée dans l'ISO 5813. Les gaz et vapeurs, tels que le chlore, l'anhydride sulfureux, l'hydrogène sulfuré, les amines, l'ammoniac, l'anhydride carbonique, le brome et l'iode, éventuellement présents et diffusant à travers la membrane, peuvent fausser le résultat en influençant l'intensité de courant mesurée. D'autres substances présentes dans l'échantillon peuvent influencer l'intensité de courant mesurée en donnant lieu à un colmatage o 429u à une détérioration de la membrane, ou encore à une corrosion des électrodes ; les solvants, les huiles, les sulfures, les carbonates et les algues figurent parmi ces substances. La méthode est utilisable pour les eaux naturelles, résiduaires et salines. Si elle est utilisée pour des eaux salines telles que les eaux de mers, ou les eaux d'estuaires, une correction due à la salinité est essentielle.
Kakovost vode - Ugotavljanje raztopljenega kisika - Elektrokemijska metoda (ISO 5814:1990)
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
SIST EN 25814:1996
01-oktober-1996
Kakovost vode - Ugotavljanje raztopljenega kisika - Elektrokemijska metoda (ISO
5814:1990)
Water quality - Determination of dissolved oxygen - Electrotechnical probe method (ISO
5814:1990)
Wasserbeschaffenheit - Bestimmung des gelösten Sauerstoffs - Elektrochemisches
Verfahren (ISO 5814:1990)
Qualité de l'eau - Dosage de l'oxygene dissous - Méthode électrochimique a la sonde
(ISO 5814:1990)
Ta slovenski standard je istoveten z: EN 25814:1992
ICS:
13.060.50 3UHLVNDYDYRGHQDNHPLþQH Examination of water for
VQRYL chemical substances
SIST EN 25814:1996 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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ISO 5814:1990(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide
federation of national Standards bodies (ISO member bodies). The work
of preparing International Standards is normally carried out through ISO
technical committees. Esch 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 patt in the
work. ISO collaborates closely with the International Electrotechnical
Commission (IEC) on all matters of electrotechnical standardization.
Draft International Standards adopted by the technical committees are
circulated to the member bodies for voting. Publication as an Interna-
tional Standard requires approval by at least 75 % of the member bodies
casting a vote.
International Standard ISO 5814 was prepared by Technical Committee
ISO/TC 147, Water quality.
This second edition cancels and replaces the first edition (ISO
5814:1984), of which it constitutes a minor revision.
Annexes A and B of this International Standard are for information only.
8 ISO 1990
All rights reserved. No part of this publication may be reproduced or utilized in any form
or by any means, electronie or mechanical, including photocopylng and microfilm, without
Permission in writing from the publisher.
International Organization for Standardization
Case Postale 56 l CH-1211 Geneve 20 l Switzeriand
Printed in Switzerland
ii
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ISO 5814:1990(E)
INTERNATIONAL STANDARD
Determination of dissolved Oxygen -
Water quality -
Electrochemical probe method
cation, the edition indicated was valid. All Standards
1 Scope
are subject to revision, and Parties to agreements
based an this International Standard are encour-
This International Standard specifies an
aged to investigate the possibility of applying the
electrochemical method for the determination of
most recent edition of the Standard indicated below.
dissolved Oxygen in water by means of an
Members of IEC and ISO maintain registers of cur-
electrochemical cell which is isolated from the
rently valid International Standards.
Sample by a gas permeable membrane.
ISO 5813:1983, Water quality - Determination of dis-
Depending on the type of probe employed, meas-
solved Oxygen - lodometric method.
urement tan be made either as concentration of
Oxygen in milligrams per litre, percentage Saturation
(% dissolved Oxygen) or both. The method meas-
ures Oxygen in water corresponding to 0 % to
3 Princlple
100 % Saturation. However, most instruments per-
mit measurement of values higher than 100 % i.e. Immersion of a probe, consisting of a cell enclosed
Supersaturation.
by a selective membrane and containing the
electrolyte and two metallic electrodes, in the water
The method is suitable for measurements made in
to be analysed. (The membrane is practically
the field and for continuous monitoring of dissolved
impermeable to water and ionic dissolved matter,
Oxygen as well as measurements made in the labo-
but is permeable to Oxygen and a certain number
ratory. lt is the preferred method for highly coloured
of the other gases and lyophylic substances.)
and turbid waters, and also for waters containing
iron and iodine fixing substances, all of which may
Because of the potential differente between the
interfere in the iodometric method specified in electrodes, caused by galvanic action or an external
ISO 5813. Gases and vapours such as chlorine, sul- voltage, Oxygen passing through the membrane is
fur dioxide, hydrogen sulfide, amines, ammonia, reduced at the cathode, while metal ions pass into
carbon dioxide, bromine and iodine which diffuse Solution at the anode.
through the membrane, may interfere, if present, by
The current so produced is directly proportional to
affecting the measured current. Other substances
the rate of transport of Oxygen through the mem-
present in the Sample may interfere with the meas-
brane and the layer of electrolyte and hence to the
ured current by causing obstruction, or deterioration
partial pressure of the Oxygen in the Sample at a
of the membrane or corrosion of the electrodes.
given temperature.
These include solvents, oils, sulfides, carbonates
and algae.
The permeability of the membrane to gases varies
greatly with temperature, and compensation is re-
The method is suitable for natural, waste and Saline
quired for readings taken at different temperatures
waters. If used for Saline waters such as sea waters,
of the Sample. This tan be done mathematically, for
or estuarine waters, a correction for salinity is es-
example, by the use of a suitable nomograph or
sential.
Computer program. The majority of modern instru-
ments automatically compensate for temperature
Variation by inclusion of temperature-sensitive ele-
2 Normative reference
ments in the electronie circuitry. However, instru-
ments reading directly in percentage solubility,
The following Standard contains provisions which,
unless provided with a pressure transducer in the
through reference in this text, constitute provisions
circuitry to compensate for pressure differentes, will
of this International Standard. At the time of publi-
1
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ISO 5814:1990(E)
6.1.4 lt is essential that the Sample should flow
display an observed percentage reading. This is a
past the membrane of the probe to prevent the oc-
reading with respect to atmospheric pressure and
currence of false readings due to depletion of the
not the true reading if the pressure differs from at-
Oxygen in the patt of the Sample in immediate ton- 1
mospheric pressure.
tact with the membrane. Ensure that the flow rate is
such that variations in readings are not produced,
4 Reagents
and consult the instrument manufacturer’s in-
structions on this matter.
During the analysis, use only reagents of recognized
analytical grade and only distilled water or water of
6.1.5 In the case of a discrete Sample, carry out the
equivalent purity.
determination in a vessel filled to overflowing,
sealed to exclude air and containing a stirrer, for
4.1 Sodium sulfite, anhydrous (Na,SO,) or
example a magnetic bar. Adjust the stirring rate
heptahydrate, (Na,S0,.7H,O).
such that the reading remains stable after reaching
equilibrium, and there is no entrapment of air.
4.2 Cobalt(H) salt, for example cobalt(ll) chloride
hexahydrate (CoCI,.GH,O). 6.1.6 In the case of a flowing Sample, such as a
water course, check the flow rate to ensure that it is
sufficient. If not, either move the probe about in the
5 Apparatus
Sample or take a discrete Sample and treat it as
described in 6.1.5.
5.1 Measuring instrument, comprising the following
components.
6.2 Calibration
51.1 Measuring probe, either of the galvanic type
The procedure is described in 6.2.1 to 6.2.3, but it is
(for example lead/silver) or the polarographic type
necessary to consult the instrument manufacturer’s
(for example silver/gold) with, if required, a
instructions.
temperature-sensitive compensating device.
6.2.1 Regulation
51.2 Meter, graduated to show the concentration
of dissolved Oxygen directly, and/or the percentage
Adjust the electrical Zero of the instrument, where
Saturation with Oxygen, or the current in microam-
applicable.
peres.
NOTE 1 Some instr euments are zero compensated and
need no adjustment.
5.2 Thermometer, graduated in divisions of 0,s OC.
6.2.2 Checking the rero
5.3 Barometer, graduated in divisions of 10 Pa.
Check and, if possible, adjust the Zero setting of the
instrument by immersing the probe in 1 litre of water
6 Procedure
to which about 1 g of sodium sulfite (4.1) and about
1 mg of the cobalt(ll) salt (4.2) have been added to
When using the measuring instrument, the man-
render the water free from Oxygen.
ufacturer’s instructions should be followed.
Modern probes typically achieve a stable re-
NOTE 2
6.1 Measurlng technlque and precautions to
sponse in 2 min to 3 min. However, different probes tan
be taken have different response rates and the manufacturer’s in-
structions should be consulted.
6.1.1 Never tauch the active surface of the mem-
6.2.3 Calibratlon at a value near Saturation
brane with the fingers.
Bubble air through water at a constant temperature
6.1.2 After changing the electrolyte and the mem-
so that its Oxygen content is brought to Saturation
brane, or if the membrane has been allowed to dry
or near Saturation. Leave for about 15 min at this
out, wet the membrane and allow the reading to
temperature and determine the dissolved Oxygen
become stable before carrying out the calibration
concentration, for example by the iodometric
(see 6.2 ). The time required depends on that nec-
method specified in ISO 5813.
essary for consumption of the Oxygen dissolved in
the electrolyte.
Regulate the instrument.
Immerse the probe in a bottle completely filled with
6.1.3 Ensure that air bubbles are not trapped in the
the Sample, prepared and standardized as de-
probe when immersing it in the Sample.
2
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ISO ?5814:1990(E)
scribed. After allowing the probe to stabiiize in the
7 Calculation and expression of results
stirred Solution for 10 min (see the note to 6.2.2 ),
adjust the instrument reading to the known Oxygen
concentration of the Sample, if necessary. 7.1 Dissolved Oxygen concentration
Replace the electrolyte and the membrane when the
Express the dissolved Oxygen concentration, in
instrument tan no longer be calibrated or when the
milligrams of Oxygen per litre, and report the result
response becomes unstable or slow (see the man-
to the first decimal place.
ufacturer’s instructions).
If the reading
...
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