SIST EN ISO 15923-1:2025

SLOVENSKI STANDARD
01-marec-2025
Kakovost vode - Določanje izbranih parametrov s sistemi diskretne analize - 1. del:
amoniak, nitrat, nitrit, klorid, ortofosfat, sulfat in silikat s fotometrijsko detekcijo
(ISO 15923-1:2013)
Water quality - Determination of selected parameters by discrete analysis systems - Part
1: Ammonium, nitrate, nitrite, chloride, orthophosphate, sulfate and silicate with
photometric detection (ISO 15923-1:2013)
Wasserbeschaffenheit - Bestimmung von ausgewählten Parametern mittels
Einzelanalysensystemen - Teil1: Ammonium, Nitrat, Nitrit, Chlorid, Orthophosphat, Sulfat
und Silikat durch photometrische Detektion (ISO 15923-1:2013)
Qualité de l'eau - Détermination de paramètres sélectionnés par des systèmes d'analyse
discrète - Partie 1: Ammonium, nitrate, nitrite, chlorure, orthophosphate, sulfate et
silicate par détection photométrique (ISO 15923-1:2013)
Ta slovenski standard je istoveten z: EN ISO 15923-1:2024
ICS:
13.060.50 Preiskava vode na kemične Examination of water for
snovi chemical substances
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 15923-1
EUROPEAN STANDARD
NORME EUROPÉENNE
August 2024
EUROPÄISCHE NORM
ICS 13.060.50
English Version
Water quality - Determination of selected parameters by
discrete analysis systems - Part 1: Ammonium, nitrate,
nitrite, chloride, orthophosphate, sulfate and silicate with
photometric detection (ISO 15923-1:2013)
Qualité de l'eau - Détermination de paramètres Wasserbeschaffenheit - Bestimmung von ausgewählten
sélectionnés par des systèmes d'analyse discrète - Parametern mittels Einzelanalysensystemen - Teil1:
Partie 1: Ammonium, nitrate, nitrite, chlorure, Ammonium, Nitrat, Nitrit, Chlorid, Orthophosphat,
orthophosphate, sulfate et silicate par détection Sulfat und Silikat durch photometrische Detektion (ISO
photométrique (ISO 15923-1:2013) 15923-1:2013)
This European Standard was approved by CEN on 5 August 2024.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2024 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 15923-1:2024 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
The text of ISO 15923-1:2013 has been prepared by Technical Committee ISO/TC 147 "Water quality”
of the International Organization for Standardization (ISO) and has been taken over as EN ISO 15923-
1:2024 by Technical Committee CEN/TC 230 “Water analysis” the secretariat of which is held by DIN.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by February 2025, and conflicting national standards
shall be withdrawn at the latest by February 2025.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
Any feedback and questions on this document should be directed to the users’ national standards body.
A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and the
United Kingdom.
Endorsement notice
The text of ISO 15923-1:2013 has been approved by CEN as EN ISO 15923-1:2024 without any
modification.
INTERNATIONAL ISO
STANDARD 15923-1
First edition
2013-12-15
Water quality — Determination of
selected parameters by discrete
analysis systems —
Part 1:
Ammonium, nitrate, nitrite, chloride,
orthophosphate, sulfate and silicate
with photometric detection
Qualité de l’eau — Détermination de paramètres sélectionnés par des
systèmes d’analyse discrète —
Partie 1: Ammonium, nitrate, nitrite, chlorure, orthophosphate,
sulfate et silicate par détection photométrique
Reference number
ISO 15923-1:2013(E)
©
ISO 2013
ISO 15923-1:2013(E)
© ISO 2013
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
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Published in Switzerland
ii © ISO 2013 – All rights reserved

ISO 15923-1:2013(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Principle . 1
4 Interferences . 2
5 Reagents . 2
6 Apparatus . 2
7 Sampling and sample preparation . 2
8 Calibration . 3
8.1 Calibration function . 3
8.2 Calibration validity check . 3
9 Procedure. 3
10 Calculation . 4
11 Expression of results . 4
12 Test report . 4
Annex A (normative) Correction for inherent colour . 6
Annex B (normative) Determination of ammonium . 7
Annex C (normative) Determination of the sum of nitrate and nitrite by the hydrazine method .9
Annex D (normative) Determination of nitrite .12
Annex E (normative) Determination of chloride by the thiocyanate method .14
Annex F (normative) Determination of orthophosphate .16
Annex G (normative) Determination of sulfate by the turbidimetric method .19
Annex H (normative) Determination of silicate .21
Annex I (informative) Performance data .23
Bibliography .25
ISO 15923-1:2013(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. 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. 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.
The committee responsible for this document is ISO/TC 147, Water quality, Subcommittee SC 2, Physical,
chemical and biochemical methods.
ISO 15923 consists of the following parts, under the general title Water quality — Determination of
selected parameters by discrete analysis systems:
— Part 1: Ammonium, nitrate, nitrite, chloride, orthophosphate, sulfate and silicate with photometric detection
iv © ISO 2013 – All rights reserved

ISO 15923-1:2013(E)
Introduction
Many photometric determinations can be automated with a discrete analysis system. With one single
apparatus, a large number of different parameters can be determined, and the parameters to be determined
can be specified for each sample. Working with small volumes requires less sample material and reagent.
Samples that fall beyond the normal measuring range can either be automatically diluted or measured
again with a different measuring range.
This part of ISO 15923 specifies methods for the automatic determination of ammonium, nitrate, nitrite,
chloride, orthophosphate, and silicate with photometric detection and a turbidimetric determination
of sulfate using a discrete analysis system. The field of application is water (ground, potable, surface,
waste, eluates, and boiler water).
INTERNATIONAL STANDARD ISO 15923-1:2013(E)
Water quality — Determination of selected parameters by
discrete analysis systems —
Part 1:
Ammonium, nitrate, nitrite, chloride, orthophosphate,
sulfate and silicate with photometric detection
WARNING — Persons using this part of ISO 15923 should be familiar with normal laboratory
practice. This part of ISO 15923 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 and to ensure compliance with any national regulatory conditions.
IMPORTANT — It is absolutely essential that tests conducted in accordance with this part of
ISO 15923 be carried out by suitably qualified staff.
1 Scope
This part of ISO 15923 specifies methods for the automatic performance of spectrophotometric and
turbidimetric analyses with a discrete analysis system for determining ammonium, nitrate, nitrite,
chloride, orthophosphate, sulfate, and silicate. The field of application is ground, potable, surface, waste,
eluates, and boiler water.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. 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 — Specification and test methods
ISO 5667-3, Water quality — Sampling — Part 3: Preservation and handling of water samples
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 8466-2, Water quality — Calibration and evaluation of analytical methods and estimation of performance
characteristics — Part 2: Calibration strategy for non-linear second-order calibration functions
3 Principle
A discrete analysis system is an automated system for spectrophotometric and turbidimetric
determinations.
The colour reactions take place in reaction cells, which may be cuvettes, in an incubator. For each
determination, a separate reaction cell is used. Preset volumes of the sample and the reagents are
pipetted into the cells and mixed.
After expiry of the incubation period, the absorbance of the solution is measured at the wavelength
applicable to the determination. This is done by passing the cuvettes through the photometer or by
transferring the measuring solution from the reaction cells to a photometer with a flow-through cell.
ISO 15923-1:2013(E)
4 Interferences
Particles present in the sample can lead to blockages and will interfere with the photometric
measurement. Filtration of all samples through a 0,45 μm membrane filter is recommended, except for
the determination of total phosphate and Kjeldahl nitrogen digests (see Annexes B and F). Particles can
also be removed by settlement, centrifugation, or dialysis.
This method is applicable to samples in a pH range from 5 to 9, which covers most natural waters.
Samples outside this range may require pH correction.
Inherent colour or turbidity of the sample interferes with the analysis. On the prevention of such
interference, see Annex A. Interferences specific to each parameter are discussed in Annexes B to H.
NOTE Interference by inherent colour shall be compensated by measuring the absorbance of the sample
before the addition of the chromogenic reagent (sample blanking) or by making use of a compensating solution
(measuring solution without a chromogenic compound). For further details, see Annex A. A safe procedure for
the correction of turbidity cannot really be given. The Lambert-Beer law does not apply to turbid solutions.
Furthermore, many chromogenic reagents and coloured complexes are adsorbed on particles.
5 Reagents
Reagents for each parameter are specified in Annexes B to H. Use only reagents of recognized analytical
grade, unless otherwise specified in the relevant annex. Dry all solid reagents for at least 1 h at (105 ± 5) °C,
provided that they are thermally stable. Store the dried solid in a desiccator before weighing. Reagent
volumes specified in Annexes B to H may be adjusted to suit local requirements or different instrument
specifications.
5.1 Water, complying with grade 1 as defined in ISO 3696.
6 Apparatus
6.1 Discrete analysis system, generally consisting of the following components:
6.1.1 Sample injection device, for automated or manual operation.
6.1.2 Sample container.
6.1.3 Reagent container, refrigerated or not.
6.1.4 Incubator with temperature control, capable of maintaining a constant temperature of e.g. 37 °C.
6.1.5 UV/VIS detector, e.g. spectrophotometer, suitable for a wavelength range usually between
340 nm and 880 nm.
6.1.6 Control and data processing unit.
6.1.7 Recording device, e.g. PC with software for data acquisition and evaluation.
7 Sampling and sample preparation
Use clean vessels for sampling.
Turbidity or particulates interfere with spectrophotometric detection. Clarify samples by filtration
through a 0,45 μm membrane (settlement, centrifugation, or dialysis may also be used). To avoid
2 © ISO 2013 – All rights reserved

ISO 15923-1:2013(E)
contamination by the filter membrane, discard the first 20 ml to 30 ml of filtrate. Samples for the
determination of total phosphate should not be filtered. Refer to Annex F.
Prepare and store the sample in accordance with Annexes B to H or with ISO 5667-3 if no specific
guidance is given in the relevant annex.
Prepare a sample of water (5.1) in the same way as the sample, to be used as a blank.
Prepare a control standard solution from the primary control standard containing a level of analyte
similar to the samples. Run as a sample at appropriate intervals in the batch, according to local
requirements. A minimum interval of once every 20 samples is recommended.
8 Calibration
8.1 Calibration function
When the analytical system is first evaluated and at intervals afterwards, establish a calibration function
for each parameter (see ISO 8466-1 or ISO 8466-2) as follows:
Using the primary calibration standard, prepare an appropriate series of calibration solutions for the
respective parameter as described in Annexes B to H, including a zero-concentration solution.
Analyse the calibration solutions according to Clause 9 and the instrument manufacturer’s instructions.
Confirm the validity of the data obtained and use to calculate the regression line as specified in
ISO 8466-1 or ISO 8466-2.
Verify the continuing validity of the established calibration function by analysing an appropriate
calibration standard solution, at regular intervals according to the accuracy requirements or at least at
the end of the batch.
Recalibrate if necessary.
8.2 Calibration validity check
If the full calibration function is not established daily, carry out an initial calibration validity check by
analysing two calibration standard solutions in the lower and upper third of the calibrated working
range after the setup procedure (see Clause 9).
Verify the continuing validity of the established calibration function by analysing an appropriate
calibration standard solution at regular intervals according to the accuracy requirements or at least at
the end of the batch.
Recalibrate if necessary.
9 Procedure
Set up the discrete analysis system according to the instrument manufacturer’s instructions.
Calibrate the system according to Clause 8 and the instrument manufacturer’s instructions.
Prepare the samples according to Clause 7 and Annexes B to H. A consistent incubation temperature
and time are essential for the stability of the absorbance measurements. For guidance on recommended
incubation temperatures and times, refer to Annexes B to H. Note that the incubation times given in
Annexes B to H are recommendations, which may be varied according to experience.
Measure the absorbance of the samples using the conditions in Annexes B to H and the instrument
manufacturer’s instructions. Measure the blank according to Annex A and the instrument manufacturer’s
instructions.
ISO 15923-1:2013(E)
If the absorbance of the sample exceeds that of the top calibration solution, dilute the sample, or reduce
the sample intake by an appropriate factor to bring it into the upper half of the calibration range, and
reanalyse. If necessary, blank correct the sample absorbances (see Annex A).
The procedures in Annexes B to H may be modified for different instruments or to change the range or
sensitivity of the method for different parameter concentrations or sample types.
10 Calculation
Calculate the mass concentration, ρ, of the parameter in question in micrograms per litre (µg/l) or
milligrams per litre (mg/l) from the calibration line (see Clause 8), using the corrected absorbance
values obtained (see Clause 9), as specified in ISO 8466-1 or ISO 8466-2. Take account of any dilution
factors. This calculation can usually be carried out automatically using the instrument software.
11 Expression of results
Results shall be expressed to a maximum of three significant figures.
EXAMPLES Phosphate = 1,11 mg/l P (3 sig fig), 1,1 mg/l P (2 sig fig), 1 mg/l (1 sig fig).
Before reporting results, it is important to determine the required units of expression. For example,
ammonium, nitrate, and nitrite can be expressed as N or as the relevant ion. Results for orthophosphate
can be expressed as P or PO , and silicate may be expressed as SiO SiO , or Si.
4 4, 2
Appropriate conversion factors are given in Table 1.
Table 1 — Conversion factors
Parameter Units Conversion factor Converted units
Ammonia mg/l N 1,286 mg/l NH
Ammonia mg/l NH 0,777 8 mg/l N
Nitrate mg/l N 4,427 mg/l NO
Nitrate mg/l NO 0,225 9 mg/l N
Nitrite mg/l N 3,285 mg/l NO
Nitrite mg/l NO 0,304 4 mg/l N
Orthophosphate mg/l P 3,066 mg/l PO
Orthophosphate mg/l PO 0,326 1 mg/l P
Silicate mg/l Si 3,279 mg/l SiO
Silicate mg/l SiO 0,305 0 mg/l Si
Silicate mg/l Si 2,139 mg/l SiO
Silicate mg/l SiO 0,467 4 mg/l Si
Silicate mg/l SiO 1,533 mg/l SiO
2 4
Silicate mg/l SiO O,652 5 mg/l SiO
4 2
12 Test report
The test report shall contain at least the following information:
a) the test method used, together with a reference to this part of ISO 15923 (i.e. ISO 15923-1:2013);
b) the details required for identification of the sample;
c) the date of the analysis;
4 © ISO 2013 – All rights reserved

ISO 15923-1:2013(E)
d) the analytical results (see Clause 11);
e) any deviation from this method and a report of circumstances that may have affected the results.
ISO 15923-1:2013(E)
Annex A
(normative)
Correction for inherent colour
A.1 General
The two possibilities for the correction of inherent colour are described in A.2 and A.3. As a rule, it is
not possible to correct for turbidity. In many cases, interference due to particles can be prevented by
carefully filtering, settling, centrifuging, or dialysing samples.
A.2 Sample blanking
Sample blanking is possible only if reaction cells are used which also serve as cuvettes. The blank
measurement is done after dispensing the sample and, if applicable, one or more reagents that could
produce a colour change in the sample (for example, because of the influence of the pH on the colour of
the sample), but before dispensing the chromogenic reagent. This blank value is subtracted from the
final absorption of the measuring solution, taking into account the ratio between the volumes of the
measuring solutions. The standards are measured in the same way.
A.3 Use of a compensating solution
When using a compensating solution, a second measuring solution is prepared that consists of the
same volumes of sample and reagent, in which the compound responsible for forming the colour is
omitted. This can be done by adding, instead of the chromogenic reagent, an equal volume of water or by
preparing a separate reagent from which the chromogenic compound is omitted. The absorption of the
compensating solution is deducted from the absorption of the sample solution.
6 © ISO 2013 – All rights reserved

ISO 15923-1:2013(E)
Annex B
(normative)
Determination of ammonium
B.1 Principle
Ammonium reacts with hypochlorite, formed by alkaline hydrolysis of sodium dichloroisocyanurate,
and with salicylate at a pH of approximately 12,6, in the presence of sodium nitroprusside as a catalyst,
to produce a compound with a blue colour. The reagent contains citrate to mask interference by cations,
such as calcium and magnesium ions. The absorbance at 660 nm is a measure of the ammonium content.
[5]
NOTE This method is based on the same chemistry given in ISO 7150-1.
B.2 Interferences
Interference by cations, especially calcium and magnesium ions, is masked by citrate. In saline samples,
this interference can nevertheless occur if the complexing capacity of the citrate is exceeded. This can
[5]
be prevented by carrying out a distillation in accordance with ISO 7150-1. Distillation is also advised
for strongly coloured samples.
Extremely high or low pH values of the samples can interfere. Primary amines and components that can
reduce hypochlorite can interfere with the determination, but these are rarely present in interfering
concentrations in water samples. If the presence of any of these interferents is suspected in samples, the
magnitude of the interference should be assessed prior to analysis.
B.3 Reagents
B.3.1 Nitric acid solution, ρ (HNO ), approximately 4 g/l.
Carefully add (4 ± 0,4) ml of concentrated nitric acid [HNO ] to 800 ml of water in a graduated 1 l
measuring flask and mix. Fill to the mark with water.
This solution is stable for 1 y if stored at room temperature.
B.3.2 Sodium nitroprusside reagent
In a 250 ml measuring flask, dissolve (32,5 ± 0,3) g of sodium salicylate [C H O Na] and (32,5 ± 0,3) g of
7 5 3
sodium citrate [C H Na O ∙2H O] in approximately 200 ml of water. Ensure that the pH is < 8,0. If necessary,
6 5 3 7 2
acidify with nitric acid (B.3.1). Add (0,243 ± 0,002) g of sodium nitroprusside [Na (Fe(CN) NO)∙2H O]
2 5 2
and dissolve. Fill to the mark with water.
This solution is stable for 1 w in a dark bottle at 2 °C to 8 °C.
NOTE If necessary, add a suitable detergent, e.g polyoxyethylene lauryl ether, to prevent air bubbles from
adhering to the wall of the cuvette while mixing the sample and reagents.
B.3.3 DIC reagent
In a 250 ml measuring flask, dissolve (8,0 ± 0,1) g of sodium hydroxide [NaOH] in approximately
200 ml of water and mix, leave to cool down and add (0,500 ± 0,005) g of sodium dichloroisocyanurate
[Cl Na(NCO) ∙2H O] and dissolve. Fill to the mark with water.
2 3 2
ISO 15923-1:2013(E)
This solution is stable for 1 w in a dark bottle at 2 °C to 8 °C.
B.3.4 Primary calibration standard ammonium, ρ = 300 mg/l.
N
In a 1 l calibrated flask, dissolve (1,415 ± 0,001) g of ammonium sulfate [(NH ) SO ] in approximately
4 2 4
750 ml of water and fill to the mark with water.
This solution is stable for 3 mo at 2 °C to 8 °C.
B.3.5 Primary control standard ammonium,
...