ISO 23695:2023

Water quality — Determination of ammonium nitrogen in water — Small-scale sealed tube method

This document specifies a method for the determination of ammonium nitrogen (NH4-N) in drinking water, groundwater, surface water, wastewater, bathing water and mineral water using the small-scale sealed tube method. The result can be expressed as NH4 or NH4-N or NH3 or NH3-N. NOTE 1 In the habitual language use of sewage treatment and on the displays of automated sealed-tube test photometers or spectrophotometers, NH4 without indication of the positive charge has become the common notation for the parameter ammonium. This notation is adopted in this document even though not being quite correct chemical nomenclature. This method is applicable to (NH4-N) concentration ranges from 0,01 mg/l to 1 800 mg/l of NH4-N. The measuring ranges of concentration can vary depending on the type of small-scale sealed tube method of different manufacturers. Concentrations even slightly higher than the upper limit indicated in the manufacturers manual relating to the small-scale sealed tube method used, cannot be reported as accurate results. It is up to the user to choose the small-scale sealed tube test with the appropriate application range or to adapt samples with concentrations exceeding the measuring range of a test by preliminary dilution. NOTE 2 The results of a small-scale sealed tube are most precise in the middle of the application range of the test. All manufacturers' methods are based on the Berthelot reaction and its modifications to develop indophenol blue colour. Reagents mixtures can differ slightly based on manufacturers small-scale sealed tube method, see Clause 9. This method is applicable to non-preserved samples by using small-scale sealed tubes for the determination of drinking water, groundwater, surface water, wastewater and to preserved samples. The method is applicable to samples with suspended materials if these materials are removable by filtration.

Qualité de l'eau — Détermination de l'azote ammoniacal dans l'eau — Méthode à petite échelle en tubes fermés

General Information

• Status: Published
• Publication Date: 01-Feb-2023
• ICS: 13.060.50 - Examination of water for chemical substances
• Technical Committee: ISO/TC 147/SC 2 - Physical, chemical and biochemical methods
• Drafting Committee: ISO/TC 147/SC 2/WG 81 - TN, nitrate, ammonium using cell tests
• Current Stage: 6060 - International Standard published
• Start Date: 02-Feb-2023
• Due Date: 18-Jul-2022
• Completion Date: 02-Feb-2023

Standards Content (Sample)

TC /SC
Date:  2022-07-29

TC /SC /WG ISO/FDIS 23695:2022(E)
ISO/TC 147/SC 2/WG 81
Secretariat: DIN

Document type:
Document subtype:
Document stage:
Document language:

---------------------- Page: 1 ----------------------
COPYRIGHT PROTECTED DOCUMENT
Water quality — Determination of ammonium nitrogen in water — Small-scale
sealed tube method
First edition
Date: 2022-09-21
Document type:
Document subtype:
Document stage:
Document language:

---------------------- Page: 2 ----------------------
ISO/FDIS 23695:2022(E)
© ISO 2022
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of
this publication may be reproduced or utilized otherwise in any form or by any means, electronic or
mechanical, including photocopying, or posting on the internet or an intranet, without prior written
permission. Permission can be requested from either ISO at the address below or ISO’sISO's member body
in the country of the requester.
ISO Copyright Office
Ch. de Blandonnet 8 • CP 401 • CH-1214 Vernier, Geneva , Switzerland
Tel. Phone: + 41 22 749 01 11
Email: [e-mail] + 41 22 749 09 47
[e-mail]

Website: www.iso.org
Published in Switzerland.
© ISO 2022 – All rights reserved
iv

---------------------- Page: 3 ----------------------
ISO/FDIS 23695:2022(E)
Contents Page
Foreword . 6
Introduction . 7
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Principle . 2
5 Interferences . 2
6 Sampling and sample preparation . 3
7 Reagents . 4
8 Apparatus . 4
9 Reaction conditions for the colour reaction . 5
9.1 General . 5
9.2 Salicylate based reaction . 5
9.3 Chlorophenol based reaction . 5
10 Quality control . 6
10.1 Verification of the spectrophotometer calibration and acceptability criteria . 6
10.2 System and interferences checks . 6
11 Calculation. 6
12 Expression of results . 7
13 Test report . 8
Annex A (informative) Principle of alternative distillation . 9
Annex B (informative) Performance data . 13
Bibliography . 14
© ISO 2022 – All rights reserved
v

---------------------- Page: 4 ----------------------
ISO/FDIS 23695:2022(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. 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, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO
collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of any
patent rights identified during the development of the document will be in the Introduction and/or on
the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the World
Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 147, Water quality, Subcommittee SC 2,
Physical, chemical and biochemical methods.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
© ISO 2022 – All rights reserved
vi

---------------------- Page: 5 ----------------------
ISO/FDIS 23695:2022(E)
Introduction
Ammonium nitrogen is one of the possible forms of nitrogen present in water. It can come directly from
industrial or public waste, from fertilizers or can be generated by the microbial breakdown of urea and
proteins under anaerobic conditions. Ammonium nitrogen can also be found naturally in water in
aquifers with low flow velocities, which are confined and contain organic matter.
© ISO 2022 – All rights reserved
vii

---------------------- Page: 6 ----------------------
FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 23695:2022(E)

Water quality — Determination of ammonium nitrogen in
water — Small-scale sealed tube method
WARNING — Persons using this document should be familiar with normal laboratory practice. This
document does not purport to address all of the safety problems, if any, associated with its use. It is the
responsibility of the user to establish appropriate safety and health practices.
IMPORTANT — It is absolutely essential that tests conducted in accordance with this document be
carried out by suitably qualified staff.
1 Scope
This document specifies a method for the determination of ammonium nitrogen (NH -N) in drinking
4
water, groundwater, surface water, wastewater, bathing water and mineral water using the small-scale
sealed tube method. The result can be expressed as NH or NH -N or NH or NH -N.
4 4 3 3
NOTE 1 In the habitual language use of sewage treatment and on the displays of automated sealed-tube test
photometers or spectrophotometers, NH without indication of the positive charge has become the common
4
notation for the parameter ammonium. This notation is adopted in this document even though not being quite
correct chemical nomenclature.
This method is applicable to (NH -N) concentration ranges from 0,01 mg/l to 1 800 mg/l of NH -N. The
4 4
measuring ranges of concentration can vary depending on the type of small-scale sealed tube method of
different manufacturers. Concentrations even slightly higher than the upper limit indicated in the
manufacturers manual relating to the small-scale sealed tube method used, cannot be reported as
accurate results. It is up to the user to choose the small-scale sealed tube test with the appropriate
application range or to adapt samples with concentrations exceeding the measuring range of a test by
preliminary dilution.
NOTE 2 The results of a small-scale sealed tube are most precise in the middle of the application range of the test.
All manufacturers' methods are based on the Berthelot reaction and its modifications to develop
indophenol blue colour. Reagents mixtures can differ slightly based on manufacturers small-scale sealed
tube method, see Clause 9. This method is applicable to non-preserved samples by using small-scale
sealed tubes for the determination of drinking water, groundwater, surface water, wastewater and to
preserved samples. The method is applicable to samples with suspended materials if these materials are
removable by filtration.
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 edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 5664, Water quality — Determination of ammonium — Distillation and titration method
Water quality — Sampling — Part 1: Guidance on the design of sampling programmes and
ISO 5667--1,
sampling techniques
© ISO 2022 – All rights reserved
1

---------------------- Page: 7 ----------------------
ISO/FDIS 23695:2022(E)
ISO 5667--3, Water quality — Sampling — Part 3: Preservation and handling of water samples
ISO 5667--10, Water quality — Sampling — Part 10: Guidance on sampling of waste water
ISO 8466--1, Water quality — Calibration and evaluation of analytical methods and estimation of
performance characteristics — Part 1: Statistical evaluation of the Linear calibration function
ISO/IEC 17025, General requirements for the competence of testing and calibration laboratories
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminologicalterminology databases for use in standardization at the following
addresses:
— ISO Online browsing platform: available at https://www.iso.org/obp
— IEC Electropedia: available at https://www.electropedia.org/
3.1
small-scale sealed tube
glass tube commercially available on the market prefilled by different manufacturers with reagent(s),) to
develop a colour to be read by a photometer or spectrophotometer.
4 Principle
This method is based on the principle of Berthelot reaction and its modification to develop indophenol
blue colour. In strongly alkaline solution, ammonia ions react with dichloroisocyanurate and salicylate
ions or chlorophenol ions, forming blue indophenol. The presence of sodium nitroprusside as catalyst
promotes the development of the blue colour. Small-scale sealed tube is to be read on a photometer or
spectrophotometer.
The method serves to obtain the concentration of ammonium nitrogen present in the sample.
5 Interferences
Typical interferences are due to both cations and anions. Examples for maximum tolerable concentration
values are listed in Table 1. These values refer to both small-scale sealed tube methods applicable at high
concentrations and to those applicable at low concentrations of NH -N.
4
Every manufacturer of small-scale sealed tubes shall provide information about interference levels above
which the ion interferes. The concentration of interfering substances can depend on the ratio of sampled
volume and predosed reagents, in the small-scale sealed tube.
Table 1 — Example of interfering ions
Ion Maximum tolerable concentration
 mg/l
Cl⎺ 1 000
2−
1 000
SO
4
+
K 500
© ISO 2022 – All rights reserved
2

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ISO/FDIS 23695:2022(E)
−
250
NO
3
+
Na 500
2− 50
CO
3
2+
Ca 500
2+
Cu 50
3+
Cr 50
2+
Co 50
2+
Zn 50
Cr(VI) 50
Primary amines can react under analysis conditions and lead to overestimated NH -N values. All reducing
4
substances interfere and lead to underestimated results. The presence of urea is tolerated up to
concentrations which are 10 000 times greater than those of the ammonia present in the sample to be
analysed.
Turbidity, colour and high salinity levels can interfere both in the instrumental measurement and in the
speed of colour development.
As specified in ISO 5667-3, preliminary filtration is necessary using filters with 0,45 μm pore width. The
filtration has to be performed on-site. Filtration shall be carried out under pressure and not under
vacuum, to avoid ammonia leakage. Before filtering, the filter shall be washed with water with the same
pH as the sample. Generally, it can be done with the sample itself by discarding the first millilitres of
sample, already filtered.
When measuring a reagent blank value, follow the normal procedure but use pure water (7.1) instead of
sample.
When measuring a blank value caused by a coloured sample, add the sample to a small-scale sealed tube
but do not add further reagents. Then follow the normal procedure.
In some cases, interferences can be eliminated using appropriate dilutions such that interfering ions fall
below the maximum tolerable concentration and NH -N remains within the measurement range.
4
It is the laboratory's responsibility to identify interferences by, for example, spiking with reference
material containing known amounts of ammonium nitrogen to the sample containing the suspected ion
or to a solution of known concentration of the suspected ion.
In case of higher concentration of interfering substances, highly coloured wastewater or turbid
suspension which cannot be easily filtered or diluted, as described above, proceed with a distillation as
described in ISO 5664. An alternative method for distillation is described in Annex A.
6 Sampling and sample preparation
For methods of sampling and storing samples before analysis see, proceed according to ISO 5667--1,
ISO 5667--3 and ISO 5667--10.
Persons performing the analysis shall be aware of the risks associated with the method.
It shall be noted that, in the case of acidification of unknown samples, toxic gases such as HCN and H S
2
maycan form. Work in a fume cupboard.
Non-preserved samples shall be analysed as soon as possible, following in accordance with ISO 5667-3.
Longer storage periods require stabilization by acidification with sulfuric acid to pH < < 2; if the sample
© ISO 2022 – All rights reserved
3

---------------------- Page: 9 ----------------------
ISO/FDIS 23695:2022(E)
is acidified, before proceeding with the determination, the pH shall be brought within the range indicated
in the procedure for the test being used. When stabilizing samples, make sure to use ammonium-free
reagents. Store samples in the refrigerator as described in ISO 5667--3.
Due to the differences in used small-scale sealed tube between all the manufacturers it is recommended
to follow manufacturers' manuals.
7 Reagents
7.1 Water, the concentration of nitrogen in the used water shall be below 25 % of the lower
measurement range of the used sealed tube.
7.2 Ammonium chloride, NH Cl, of analytical grade, previously dried at 105 °C for 2 h, to be used for
4
preparing suitable solutions to verify the calibration in the NH -N concentration range. Commercially
4
available ammonium chloride solutions, with known concentration, can also be used as reference
material.
7.3 Reagents provided by the manufacturers for the small-scale sealed tube method and used to
determine NH -N with colour reactions (see Clause 9)
4
7.3.1 Sodium dichloroisocyanurate, C Cl N NaO .
3 2 3 3
7.3.2 Sodium salicylate, C H NaO .
7 5 3
7.3.3 Sodium nitroprusside, Na [Fe(CN) NO].
2 5
7.3.4 Chlorophenol, (Cl)C H OH.
6 4
7.3.5 Sodium hydroxide, NaOH
7.3.6 Lithium hydroxide, LiOH
8 Apparatus
Usual laboratory apparatus and, in particular, the following.
8.1 Small-scale sealed tubes, for different measuring ranges of NH -N concentrations: low, medium,
4
high and very high.
8.2 Photometer or spect
...

FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 23695
ISO/TC 147/SC 2
Water quality — Determination of
Secretariat: DIN
ammonium nitrogen in water —
Voting begins on:
2022-10-11 Small-scale sealed tube method
Voting terminates on:
2022-12-06
RECIPIENTS OF THIS DRAFT ARE INVITED TO
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
THEY ARE AWARE AND TO PROVIDE SUPPOR TING
DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
Reference number
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
ISO/FDIS 23695:2022(E)
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN-
DARDS TO WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS. © ISO 2022

---------------------- Page: 1 ----------------------
ISO/FDIS 23695:2022(E)
FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 23695
ISO/TC 147/SC 2
Water quality — Determination of
Secretariat: DIN
ammonium nitrogen in water —
Voting begins on:
Small-scale sealed tube method
Voting terminates on:
COPYRIGHT PROTECTED DOCUMENT
© ISO 2022
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
RECIPIENTS OF THIS DRAFT ARE INVITED TO
ISO copyright office
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
CP 401 • Ch. de Blandonnet 8
THEY ARE AWARE AND TO PROVIDE SUPPOR TING
CH-1214 Vernier, Geneva
DOCUMENTATION.
Phone: [phone]
IN ADDITION TO THEIR EVALUATION AS
Reference number
Email: [e-mail]
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
ISO/FDIS 23695:2022(E)
Website: www.iso.org
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
Published in Switzerland
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN­
DARDS TO WHICH REFERENCE MAY BE MADE IN
ii
  © ISO 2022 – All rights reserved
NATIONAL REGULATIONS. © ISO 2022

---------------------- Page: 2 ----------------------
ISO/FDIS 23695:2022(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Principle . 2
5 Interferences . 2
6 Sampling and sample preparation . 3
7 Reagents . 3
8 Apparatus . 4
9 Reaction conditions for the colour reaction . 4
9.1 General . 4
9.2 Salicylate based reaction . . 4
9.3 Chlorophenol based reaction . 5
10 Quality control . 5
10.1 V erification of the spectrophotometer calibration and acceptability criteria . 5
10.2 System and interferences checks . 6
11 Calculation . 6
12 Expression of results .7
13 Test report . 7
Annex A (informative) Principle of alternative distillation . 8
Annex B (informative) Performance data .11
Bibliography .12
iii
© ISO 2022 – All rights reserved

---------------------- Page: 3 ----------------------
ISO/FDIS 23695:2022(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. 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, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 147, Water quality, Subcommittee SC 2,
Physical, chemical and biochemical methods.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
  © ISO 2022 – All rights reserved

---------------------- Page: 4 ----------------------
ISO/FDIS 23695:2022(E)
Introduction
Ammonium nitrogen is one of the possible forms of nitrogen present in water. It can come directly from
industrial or public waste, from fertilizers or can be generated by the microbial breakdown of urea
and proteins under anaerobic conditions. Ammonium nitrogen can also be found naturally in water in
aquifers with low flow velocities, which are confined and contain organic matter.
v
© ISO 2022 – All rights reserved

---------------------- Page: 5 ----------------------
FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 23695:2022(E)
Water quality — Determination of ammonium nitrogen in
water — Small-scale sealed tube method
WARNING — Persons using this document should be familiar with normal laboratory practice.
This document does not purport to address all of the safety problems, if any, associated with its
use. It is the responsibility of the user to establish appropriate safety and health practices.
IMPORTANT — It is absolutely essential that tests conducted in accordance with this document
be carried out by suitably qualified staff.
1 Scope
This document specifies a method for the determination of ammonium nitrogen (NH -N) in drinking
4
water, groundwater, surface water, wastewater, bathing water and mineral water using the small­scale
sealed tube method. The result can be expressed as NH or NH ­N or NH or NH ­N.
4 4 3 3
NOTE 1 In the habitual language use of sewage treatment and on the displays of automated sealed-tube test
photometers or spectrophotometers, NH without indication of the positive charge has become the common
4
notation for the parameter ammonium. This notation is adopted in this document even though not being quite
correct chemical nomenclature.
This method is applicable to (NH ­N) concentration ranges from 0,01 mg/l to 1 800 mg/l of NH ­N. The
4 4
measuring ranges of concentration can vary depending on the type of small-scale sealed tube method
of different manufacturers. Concentrations even slightly higher than the upper limit indicated in the
manufacturers manual relating to the small­scale sealed tube method used, cannot be reported as
accurate results. It is up to the user to choose the small­scale sealed tube test with the appropriate
application range or to adapt samples with concentrations exceeding the measuring range of a test by
preliminary dilution.
NOTE 2 The results of a small­scale sealed tube are most precise in the middle of the application range of the
test.
All manufacturers' methods are based on the Berthelot reaction and its modifications to develop
indophenol blue colour. Reagents mixtures can differ slightly based on manufacturers small-scale
sealed tube method, see Clause 9. This method is applicable to non-preserved samples by using small-
scale sealed tubes for the determination of drinking water, groundwater, surface water, wastewater and
to preserved samples. The method is applicable to samples with suspended materials if these materials
are removable by filtration.
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 edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 5664, Water quality — Determination of ammonium — Distillation and titration method
ISO 5667­1, Water quality — Sampling — Part 1: Guidance on the design of sampling programmes and
sampling techniques
ISO 5667­3, Water quality — Sampling — Part 3: Preservation and handling of water samples
ISO 5667­10, Water quality — Sampling — Part 10: Guidance on sampling of waste water
ISO 8466­1, Water quality — Calibration and evaluation of analytical methods — Part 1: Linear calibration
function
1
© ISO 2022 – All rights reserved

---------------------- Page: 6 ----------------------
ISO/FDIS 23695:2022(E)
ISO/IEC 17025, General requirements for the competence of testing and calibration laboratories
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
small-scale sealed tube
glass tube commercially available on the market prefilled by different manufacturers with reagent(s) to
develop a colour to be read by a photometer or spectrophotometer
4 Principle
This method is based on the principle of Berthelot reaction and its modification to develop indophenol
blue colour. In strongly alkaline solution, ammonia ions react with dichloroisocyanurate and salicylate
ions or chlorophenol ions, forming blue indophenol. The presence of sodium nitroprusside as catalyst
promotes the development of the blue colour. Small­scale sealed tube is to be read on a photometer or
spectrophotometer.
The method serves to obtain the concentration of ammonium nitrogen present in the sample.
5 Interferences
Typical interferences are due to both cations and anions. Examples for maximum tolerable concentration
values are listed in Table 1. These values refer to both small­scale sealed tube methods applicable at
high concentrations and to those applicable at low concentrations of NH ­N.
4
Every manufacturer of small-scale sealed tubes shall provide information about interference levels
above which the ion interferes. The concentration of interfering substances can depend on the ratio of
sampled volume and predosed reagents, in the small­scale sealed tube.
Table 1 — Example of interfering ions
Ion Maximum tolerable concentration
mg/l
Cl⎺ 1 000
2−
1 000
SO
4
+
K 500
−
250
NO
3
+
Na 500
2− 50
CO
3
2+
Ca 500
2+
Cu 50
3+
Cr 50
2+
Co 50
2+
Zn 50
Cr(VI) 50
2
  © ISO 2022 – All rights reserved

---------------------- Page: 7 ----------------------
ISO/FDIS 23695:2022(E)
Primary amines can react under analysis conditions and lead to overestimated NH ­N values. All
4
reducing substances interfere and lead to underestimated results. The presence of urea is tolerated up
to concentrations which are 10 000 times greater than those of the ammonia present in the sample to
be analysed.
Turbidity, colour and high salinity levels can interfere both in the instrumental measurement and in the
speed of colour development.
As specified in ISO 5667-3, preliminary filtration is necessary using filters with 0,45 μm pore width.
The filtration has to be performed on-site. Filtration shall be carried out under pressure and not under
vacuum, to avoid ammonia leakage. Before filtering, the filter shall be washed with water with the same
pH as the sample. Generally, it can be done with the sample itself by discarding the first millilitres of
sample, already filtered.
When measuring a reagent blank value, follow the normal procedure but use pure water (7.1) instead
of sample.
When measuring a blank value caused by a coloured sample, add the sample to a small-scale sealed
tube but do not add further reagents. Then follow the normal procedure.
In some cases, interferences can be eliminated using appropriate dilutions such that interfering ions
fall below the maximum tolerable concentration and NH ­N remains within the measurement range.
4
It is the laboratory's responsibility to identify interferences by, for example, spiking with reference
material containing known amounts of ammonium nitrogen to the sample containing the suspected ion
or to a solution of known concentration of the suspected ion.
In case of higher concentration of interfering substances, highly coloured wastewater or turbid
suspension which cannot be easily filtered or diluted as described above, proceed with a distillation as
described in ISO 5664. An alternative method for distillation is described in Annex A.
6 Sampling and sample preparation
For methods of sampling and storing samples before analysis, proceed according to ISO 5667-1,
ISO 5667­3 and ISO 5667­10.
Persons performing the analysis shall be aware of the risks associated with the method.
It shall be noted that, in the case of acidification of unknown samples, toxic gases such as HCN and H S
2
can form. Work in a fume cupboard.
Non-preserved samples shall be analysed as soon as possible, in accordance with ISO 5667-3. Longer
storage periods require stabilization by acidification with sulfuric acid to pH < 2; if the sample is
acidified, before proceeding with the determination, the pH shall be brought within the range indicated
in the procedure for the test being used. When stabilizing samples, make sure to use ammonium-free
reagents. Store samples in the refrigerator as described in ISO 5667­3.
...