EN ISO 15681-2:2018

SLOVENSKI STANDARD
01-maj-2019
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SIST EN ISO 15681-2:2005
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Water quality - Determination of orthophosphate and total phosphorus contents by flow
analysis (FIA and CFA) - Part 2: Method by continuous flow analysis (CFA) (ISO 15681-
2:2018)
Wasserbeschaffenheit - Bestimmung von Orthophosphat und Gesamtphosphor mittels
Fließanalytik (FIA und CFA) - Teil 2: Verfahren mittels kontinuierlicher Durchflussanalyse
(CFA) (ISO 15681-2:2018)
Qualité de l'eau - Dosage des orthophosphates et du phosphore total par analyse en flux
(FIA et CFA) - Partie 2: Méthode par analyse en flux continu (CFA) (ISO 15681-2:2018)
Ta slovenski standard je istoveten z: EN ISO 15681-2:2018
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.

EN ISO 15681-2
EUROPEAN STANDARD
NORME EUROPÉENNE
December 2018
EUROPÄISCHE NORM
ICS 13.060.50 Supersedes EN ISO 15681-2:2004
English Version
Water quality - Determination of orthophosphate and total
phosphorus contents by flow analysis (FIA and CFA) - Part
2: Method by continuous flow analysis (CFA) (ISO 15681-
2:2018)
Qualité de l'eau - Dosage des orthophosphates et du Wasserbeschaffenheit - Bestimmung von
phosphore total par analyse en flux (FIA et CFA) - Orthophosphat und Gesamtphosphor mittels
Partie 2: Méthode par analyse en flux continu (CFA) Fließanalytik (FIA und CFA) - Teil 2: Verfahren mittels
(ISO 15681-2:2018) kontinuierlicher Durchflussanalyse (CFA) (ISO 15681-
2:2018)
This European Standard was approved by CEN on 10 August 2018.

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, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey 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
© 2018 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 15681-2:2018 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 15681-2:2018) has been prepared by Technical Committee ISO/TC 147 "Water
quality" in collaboration with 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 June 2019, and conflicting national standards shall be
withdrawn at the latest by June 2019.
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.
This document supersedes EN ISO 15681-2:2004.
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, Former Yugoslav Republic of Macedonia,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.
Endorsement notice
The text of ISO 15681-2:2018 has been approved by CEN as EN ISO 15681-2:2018 without any
modification.
INTERNATIONAL ISO
STANDARD 15681-2
Second edition
2018-10
Water quality — Determination
of orthophosphate and total
phosphorus contents by flow analysis
(FIA and CFA) —
Part 2:
Method by continuous flow analysis
(CFA)
Qualité de l'eau — Dosage des orthophosphates et du phosphore total
par analyse en flux (FIA et CFA) —
Partie 2: Méthode par analyse en flux continu (CFA)
Reference number
ISO 15681-2:2018(E)
©
ISO 2018
ISO 15681-2:2018(E)
© ISO 2018
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
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Published in Switzerland
ii © ISO 2018 – All rights reserved

ISO 15681-2:2018(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Interferences . 2
4.1 General interferences . 2
4.2 Interferences in the determination of total-P . 2
5 Principle . 3
5.1 Determination of orthophosphate . 3
5.2 Total phosphorus with manual digestion . 3
5.3 Total phosphorus with integral UV digestion and hydrolysis . 3
6 Reagents . 3
7 Apparatus . 7
8 Sampling and sample preparation . 9
9 Procedure. 9
9.1 Preparation for analysis . 9
9.2 Instrument performance check . 9
9.3 Reagent blank check . 9
9.4 Calibration .10
9.5 Check of UV digestion and hydrolysis for total P determination (Figures A.2 and A.3) .10
9.6 Measurement .10
9.7 Closing down the system .10
10 Calculation of results .11
11 Expression of results .11
12 Test report .11
Annex A (informative) Examples of a CFA system .12
Annex B (informative) Performance data .15
Annex C (informative) Determination of orthophosphate-P and total-P by CFA and tin(II)
chloride reduction .17
Bibliography .18
ISO 15681-2:2018(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.
This second edition cancels and replaces the first edition (ISO 15681-2:2003), which has been technically
revised. The main changes compared to the previous edition are as follows:
a) the reagents have been adjusted to decrease the pH to enhance the colour reaction;
b) the figures in Annex A have been revised.
A list of all parts in the ISO 15681 series can be found on the ISO website.
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 2018 – All rights reserved

ISO 15681-2:2018(E)
Introduction
Methods of determining water quality using flow analysis automated wet chemical procedures are
particularly suitable for the processing of many analytes in water in large sample series at a high
analysis frequency.
[6][8] [9]
Analysis can be performed by flow injection analysis (FIA) or continuous flow analysis (CFA) .
Both methods share the feature of an automatic dosage of the sample into a flow system (manifold)
where the analyte in the sample reacts with the reagent solutions on its way through the manifold. The
sample preparation may be integrated in the manifold. The amount of reaction product is measured in a
flow detector (e.g. flow photometer). This document describes the CFA method.
The user should be aware that particular problems could require the specification of additional
marginal conditions.
INTERNATIONAL STANDARD ISO 15681-2:2018(E)
Water quality — Determination of orthophosphate and
total phosphorus contents by flow analysis (FIA and CFA) —
Part 2:
Method by continuous flow analysis (CFA)
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 continuous flow analysis (CFA) methods for the determination of
orthophosphate in the mass concentration range from 0,01 mg/l to 1,00 mg/l P, and total phosphorus
in the mass concentration range from 0,10 mg/l to 10,0 mg/l P. The method includes the digestion of
organic phosphorus compounds and the hydrolysis of inorganic polyphosphate compounds, performed
either manually, as described in ISO 6878 and in References [4], [5] and [7], or with an integrated
ultraviolet (UV) digestion and hydrolysis unit.
This document is applicable to various types of water, such as ground, drinking, surface, leachate and
waste water. The range of application can be changed by varying the operating conditions.
This method is also applicable to the analysis of seawater, but with changes in sensitivity by adapting
the carrier and calibration solutions to the salinity of the samples.
It is also applicable to analysis using 10 mm to 50 mm cuvettes depending on the desired range. For
extreme sensitivity, 250 mm and 500 mm long way capillary flow cells (LCFCs) can be used. However,
the method is not validated for these two uses. Changes in sensitivity and calibration solutions could be
required.
Annex A provides examples of a CFA system. Annex B gives performance data from interlaboratory
trials. Annex C gives information of determining orthophosphate-P and total-P by CFA and tin(II)
chloride reduction.
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 3696, Water for analytical laboratory use — Specification and test methods
ISO 5667-1, Water quality — Sampling — Part 1: Guidance on the design of sampling programmes and
sampling techniques
ISO 5667-3:2018, Water quality — Sampling — Part 3: Preservation and handling of water samples
ISO 6878:2004, Water quality — Determination of phosphorus — Ammonium molybdate spectrometric
method
ISO 15681-2:2018(E)
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 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
4 Interferences
4.1 General interferences
Refer to ISO 6878:2004, Annex A for a list of general interferences. In addition, or contrary to the cited
standard, the following applies:
a) arsenate causes serious interference: 100 µg/l As, present as arsenate, results in a response
comparable to approximately 30 µg/l P;
b) if the silicate concentration in samples is not greater than 60 times the phosphorus concentration,
interferences by silicate can be neglected;
c) fluoride interference is significant above 50 mg/l;
d) nitrite interference is significant above 5 mg/l; the interference can be eliminated by acidifying
samples after collection;
e) for samples containing high concentrations of oxidizing agents, the amount of added reduction
reagent can be insufficient; in this case, remove the oxidizing material prior to digestion;
f) the self-absorption of the sample can be compensated for by measuring, in addition to the sample
signal (9.6), the signal of the sample without the admixture of the reagents; in this case, the
difference of the two responses is used for the evaluation (Clause 10).
4.2 Interferences in the determination of total-P
Samples containing solids or suspended particles can show low values when analysed by the UV
method, if the particles are not completely transported into the UV unit. The error can be minimized
by stirring the sample immediately before or during sampling, in order to ensure that a representative
sample is delivered into the analyser, and by reducing the particle size.
The interferences from silicate, nitrite, fluoride and iron described for the orthophosphate
determination are generally not observed in the UV method, due to the pre-digestion and the higher
analytical range.
The efficiency of the UV digestion can be affected for water samples with chemical oxygen demand
(COD) values of more than 10 times the highest concentrations of the calibration solutions (6.22). In this
case, the sample should be diluted.
2 © ISO 2018 – All rights reserved

ISO 15681-2:2018(E)
5 Principle
5.1 Determination of orthophosphate
The sample is mixed with a surfactant solution, followed by an acidic solution containing molybdate
and antimony ions. The resulting phospho-antimony-molybdate complex is reduced by ascorbic acid to
[4][7] [3]
molybdenum blue . The pH of the reaction mixture shall be between pH 0,6 and pH 0,9 .
5.2 Total phosphorus with manual digestion
Phosphorus compounds in the sample are oxidized manually with a potassium peroxodisulfate
solution, in accordance with ISO 6878 or with an equivalent procedure. The resulting orthophosphate
is determined by the molybdenum blue reaction using the colour reaction described in 5.1. The samples
can be neutralized manually in accordance with ISO 6878 or by taking into account the amount of acid
used in this procedure when calculating the acid to be used in the molybdenum reagent.
5.3 Total phosphorus with integral UV digestion and hydrolysis
The sample is mixed with potassium peroxodisulfate and passed through a UV digester, followed by
acid digestion to hydrolyse polyphosphates. The resulting orthophosphate is measured using the colour
[3]
reaction described in 5.1. The pH of the reaction mixture shall be between pH 0,6 and pH 0,9 . The pH
of the reaction mixture is critical to avoid interferences from silicate.
6 Reagents
Use analytical grade chemicals unless otherwise specified. Molybdate and antimony waste solutions
should be disposed properly.
6.1 Water, conforming to grade 1 of ISO 3696.
The phosphate blank value shall be checked (see 9.3).
6.2 Sulfuric acid, H SO .
2 4
6.2.1 Sulfuric acid I, ρ = 1,84 g/ml; 95 % to 98 %.
6.2.2 Sulfuric acid II, c(H SO ) = 2,45 mol/l.
2 4
To approximately 800 ml of water (6.1), carefully add 136 ml of sulfuric acid I (6.2.1) while stirring. Cool
and dilute to 1 000 ml with water (6.1).
6.2.3 Sulfuric acid III, c(H SO ) = 2,45 mol/l.
2 4
To 1 000 ml of sulfuric acid II (6.2.2), add 1 g of sodium dodecyl sulfate (6.7) and mix.
6.3 Sodium hydroxide, NaOH.
6.4 Ammonium heptamolybdate tetrahydrate, (NH ) Mo O ⋅4H O.
4 6 7 24 2
6.5 Antimony potassium tartrate trihydrate, K (SbO) C H O ⋅3H O.
2 2 8 4 10 2
6.6 Ascorbic acid, C H O .
6 8 6
6.7 Sodium dodecyl sulfate, NaC H SO .
12 25 4
ISO 15681-2:2018(E)
6.8 Potassium peroxodisulfate, K S O .
2 2 8
6.9 Potassium dihydrogen phosphate, KH PO , dried at 105 °C ± 5 °C to constant mass.
2 4
6.10 Potassium pyrophosphate, K P O .
4 2 7
6.11 Organophosphorus compounds, to check the UV digestion.
6.11.1 Pyridoxal-5-phosphate monohydrate, C H NO P⋅H O.
8 10 6 2
6.11.2 Disodium phenylphosphate, C H Na PO .
6 5 2 4
6.12 Surfactant solutions.
6.12.1 Surfactant solution I, see (A) or (B) in Figure A.1.
Dissolve 1 g of sodium dodecyl sulfate (6.7) in about 800 ml of water (6.1) and dilute to 1 000 ml with
water (6.1).
The solution is stable for six months if stored at room temperature.
6.12.2 Surfactant solution II, see (A) or (B) in Figure A.1.
Dissolve 10 g of sodium dodecyl sulfate (6.7) in about 800 ml of water (6.1) and dilute to 1 000 ml with
water (6.1).
The solution is stable for six months if stored at room temperature.
6.13 Molybdate solution.
Dissolve 40 g of ammonium heptamolybdate tetrahydrate (6.4) in about 800 ml of water (6.1) and dilute
to 1 000 ml with water (6.1).
Do not use a metal spatula when weighing the ammonium heptamolybdate tetrahydrate (6.4). The
solution is stable for three months if stored at room temperature. Avoid any contact between metal and
the ammonium heptamolybdate.
6.14 Antimony potassium tartrate solution.
Dissolve 2,5 g of antimony potassium tartrate trihydrate (6.5) in about 800 ml of water (6.1) and dilute
to 1 000 ml with water (6.1).
The solution is stable for three months if stored at room temperature.
6.15 An
...