EN ISO 15681-1:2004

Water quality - Determination of orthophosphate and total phosphorus contents by flow analysis (FIA and CFA) - Part 1: Method by flow injection analysis (FIA) (ISO 15681-1:2003)

ISO 15681-1:2003 specifies flow injection analysis (FIA) methods for the determination of orthophosphate in the mass concentration range from 0,01 mg/l to 1,0 mg/l (P), and total phosphorus by manual digestion in accordance with ISO 6878 for the mass concentration range from 0,1 mg/l to 10 mg/l (P). The range of application can be changed by varying the operating conditions.
ISO 15681-1:2003 is applicable to various types of water (such as ground, drinking, surface, leachate and waste waters).
This method is also applicable to the analysis of seawater, but with changes in sensitivity, by adaptation of the carrier and calibration solutions to the salinity of the samples.

Wasserbeschaffenheit - Bestimmung von Orthophosphat und Gesamtphosphor mittels Fließanalytik (FIA und CFA) - Teil 1: Verfahren mittels Fließinjektionsanalyse (FIA) (ISO 15681-1:2003)

Dieser Teil von ISO 15681 legt ein Fließinjektionsanalyseverfahren (FIA) für die Bestimmung von Orthophosphat in Massenkonzentrationen von 0,01 mg/l bis 1,0 mg/l P und Gesamtphosphor nach manuellem Aufschluss nach ISO 6878, [5], [6] für Massenkonzentrationen von 0,1 mg/l bis 10 mg/l P fest. Der Anwendungsbereich kann durch Veränderung der Betriebsbedingungen variiert werden.
Dieser Teil von ISO 15681 ist auf unterschiedliche Wässer anwendbar (wie Grund-, Trink-, Oberflächen-wasser, Eluate und Abwasser).
Das Verfahren kann auch auf Meerwasser angewandt werden, jedoch unter Änderung der Empfindlichkeit; die Träger- und Bezugslösungen müssen an die Salinität der Probe angepasst werden.

Qualité de l'eau - Dosage des orthophosphates et du phosphore total par analyse en flux (FIA et CFA) - Partie 1: Méthode par analyse avec injection en flux (FIA) (ISO 15681-1:2003)

L'ISO 15681-1:2003 spécifie des méthodes par analyse avec injection en flux (FIA) pour le dosage des orthophosphates dans le domaine de concentrations en masse allant de 0,01 mg/l à 1,0 mg/l (P), et pour le dosage du phosphore total par digestion manuelle conformément à l'ISO 6878 pour le domaine de concentrations en masse allant de 0,1 mg/l à 10 mg/l (P). Il est possible de modifier le domaine d'application en faisant varier les conditions opératoires.
L'ISO 15681-1:2003 est applicable à différents types d'eau (tels que eau souterraine, eau potable, eau de surface, lixiviats et eaux usées).
Cette méthode est également applicable à l'analyse de l'eau de mer moyennant une modification de la sensibilité et une adaptation des solutions vecteurs et des solutions d'étalonnage à la salinité des échantillons.

Kakovost vode - Določanje ortofosfata in celotnega fosforja s pretočno analizo (FIA in CFA) - 1. del: Metoda z injicirno pretočno analizo (FIA) (ISO 15681-1:2003)

General Information

• Status: Published
• Publication Date: 21-Dec-2004
• ICS: 13.060.50 - Examination of water for chemical substances
• Technical Committee: CEN/TC 230 - Water analysis
• Drafting Committee: CEN/TC 230/WG 1 - Physical and biochemical methods
• Current Stage: 9093 - Decision to confirm - Review Enquiry
• Start Date: 14-May-2009
• Completion Date: 14-May-2009
• Directive: 2000/60/EC - Directive 2000/60/EC of the European Parliament and of the Council of 23 October 2000 establishing a framework for Community action in the field of water policy (substitutes Directive Reference 01/991 - Common Position on WFD)
• Ref Project: SIST EN ISO 15681-1:2005 - Water quality - Determination of orthophosphate and total phosphorus contents by flow analysis (FIA and CFA) - Part 1: Method by flow injection analysis (FIA) (ISO 15681-1:2003)

Overview

EN ISO 15681-1:2004 (identical to ISO 15681-1:2003) specifies a standardized laboratory procedure for measuring orthophosphate and total phosphorus in water using flow injection analysis (FIA). The method covers orthophosphate in the mass concentration range 0.01 mg/L to 1.0 mg/L (P) and total phosphorus after manual digestion (per ISO 6878) in the range 0.1 mg/L to 10 mg/L (P). Applicable to a wide variety of waters - ground, drinking, surface, leachate, wastewaters and, with salinity-adjusted reagents, seawater - this standard is adopted by CEN for consistent water quality monitoring.

Key Topics

• Analytical principle: sample injection into a carrier stream merged with an acidic ammonium molybdate reagent to form molybdophosphoric acid, then reduction (molybdenum blue) and detection by a flow detector (e.g., flow photometer).
• Total phosphorus: requires manual oxidation (potassium peroxodisulfate digestion) in accordance with ISO 6878 to convert bound phosphorus to orthophosphate prior to FIA measurement.
• Concentration ranges & flexibility: routine ranges stated above; working range can be altered by varying FIA operating conditions (carrier, reagent flows, sensitivity).
• Interferences and mitigation:
  • Arsenate causes significant positive bias (100 µg/L As ≈ 30 µg/L P).
  • Silicate interference negligible if <60× phosphorus concentration.
  • Fluoride (>50 mg/L) and nitrite (>5 mg/L) can interfere; acidification or sample pretreatment may be required.
  • Strong oxidizers and high COD may affect digestion - dilution or removal recommended.
  • Self-absorption can be corrected by measuring sample signal without reagents and subtracting.
• Reagents & quality: use analytical grade chemicals, degassed carrier/reagent solutions and phosphate-checked blanks; reagents named include ammonium molybdate, tin(II) chloride (reducer) and digestion reagents per ISO 6878.
• Annexes include example FIA system diagrams, precision/accuracy data and alternative chemistries (e.g., ascorbic acid reduction, DEHA substitution).

Applications

• Routine monitoring of water quality in environmental laboratories and utilities.
• Regulatory compliance testing for drinking water, surface water, groundwater and wastewater effluents.
• Process control at wastewater treatment plants to monitor phosphorus removal.
• Research studies on nutrient cycling, eutrophication risk assessment and marine/coastal monitoring (with salinity-adapted calibrations).

Who uses it: environmental labs, municipal and industrial water laboratories, regulatory bodies, consultants and academic researchers seeking reproducible, high-throughput phosphorus determinations.

Related Standards

• ISO 6878 - Determination of phosphorus (ammonium molybdate spectrometric method) / digestion guidance
• ISO 3696 - Water for analytical laboratory use
• ISO 5667‑1 / -2 / -3 - Water sampling guidance
• ISO 8466‑1 - Calibration and evaluation of analytical methods

Keywords: EN ISO 15681-1:2004, ISO 15681-1:2003, flow injection analysis, FIA, orthophosphate, total phosphorus, water quality, phosphorus determination, ISO 6878.

Standards Content (Sample)

SLOVENSKI STANDARD
01-februar-2005
Nadomešča:
OSIST prEN ISO 15681-1:2004
Kakovost vode - Določanje ortofosfata in celotnega fosforja s pretočno analizo
(FIA in CFA) - 1. del: Metoda z injicirno pretočno analizo (FIA) (ISO 15681-1:2003)
Water quality - Determination of orthophosphate and total phosphorus contents by flow
analysis (FIA and CFA) - Part 1: Method by flow injection analysis (FIA) (ISO 15681-
1:2003)
Wasserbeschaffenheit - Bestimmung von Orthophosphat und Gesamtphosphor mittels
Fließanalytik (FIA und CFA) - Teil 1: Verfahren mittels Fließinjektionsanalyse (FIA) (ISO
15681-1:2003)
Qualité de l'eau - Dosage des orthophosphates et du phosphore total par analyse en flux
(FIA et CFA) - Partie 1: Méthode par analyse avec injection en flux (FIA) (ISO 15681-
1:2003)
Ta slovenski standard je istoveten z: EN ISO 15681-1:2004
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.

EUROPEAN STANDARD
EN ISO 15681-1
NORME EUROPÉENNE
EUROPÄISCHE NORM
December 2004
ICS 13.060.50
English version
Water quality - Determination of orthophosphate and total
phosphorus contents by flow analysis (FIA and CFA) - Part 1:
Method by flow injection analysis (FIA) (ISO 15681-1:2003)
Qualité de l'eau - Dosage des orthophosphates et du Wasserbeschaffenheit - Bestimmung von Othophosphat
phosphore total par analyse en flux (FIA et CFA) - Partie 1: und Gesamtphosphor mittels Fließanalytik (FIA und CFA) -
Méthode par analyse avec injection en flux (FIA) (ISO Teil 1: Verfahren mittels Fließinjektionsanalyse (FIA) (ISO
15681-1:2003) 15681-1:2003)
This European Standard was approved by CEN on 21 December 2004.
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 Central Secretariat 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 Central Secretariat has the same status as the official
versions.
CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,
Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia,
Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36  B-1050 Brussels
© 2004 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 15681-1:2004: E
worldwide for CEN national Members.

Foreword
The text of ISO 15681-1:2003 has been prepared by Technical Committee ISO/TC 147 "Water
quality” of the International Organization for Standardization (ISO) and has been taken over as
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 2005, and conflicting national
standards shall be withdrawn at the latest by June 2005.

According to the CEN/CENELEC Internal Regulations, the national standards organizations of
the following countries are bound to implement this European Standard: Austria, Belgium,
Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary,
Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland,
Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.

Endorsement notice
The text of ISO 15681-1:2003 has been approved by CEN as EN ISO 15681-1:2004 without any
modifications.
INTERNATIONAL ISO
STANDARD 15681-1
First edition
2003-12-15
Water quality — Determination of
orthophosphate and total phosphorus
contents by flow analysis (FIA and
CFA) —
Part 1:
Method by flow injection analysis (FIA)
Qualité de l'eau — Dosage des orthophosphates et du phosphore total
par analyse en flux (FIA et CFA) —
Partie 1: Méthode par analyse avec injection en flux (FIA)

Reference number
ISO 15681-1:2003(E)
©
ISO 2003
ISO 15681-1:2003(E)
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ii © ISO 2003 — All rights reserved

ISO 15681-1:2003(E)
Contents Page
Foreword. iv
Introduction . v
1 Scope. 1
2 Normative references. 1
3 Interferences. 2
3.1 General interferences. 2
3.2 Interferences in the determination of total-P . 2
4 Principle. 2
4.1 Determination of orthophosphate . 2
4.2 Total phosphorus with manual digestion. 2
5 Reagents. 2
6 Apparatus. 6
6.1 Flow injection analysis (FIA). 6
6.2 Additional apparatus. 6
6.3 Additional apparatus for the determination of total phosphorus . 6
7 Sampling and sample preparation . 7
8 Procedure. 7
8.1 Analysis preparation. 7
8.2 Instrument performance check. 7
8.3 Reagent blank check . 7
8.4 Calibration. 8
8.5 Check of digestion efficiency for determination of total-P. 8
8.6 Measurement. 8
8.7 Closing down the system. 8
9 Calculation of results. 9
10 Expression of results. 9
11 Test report. 9
Annex A (informative) Example of an FIA system. 10
Annex B (informative) Precision and accuracy . 11
Annex C (informative) Determination of orthophosphate-P and total-P by FIA using ascorbic acid
reduction. 13
Annex D (informative) Replacement of hydrazine sulfate by DEHA (N,N-diethylhydroxylamine) . 18
Bibliography . 19

ISO 15681-1:2003(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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
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.
ISO 15681-1 was prepared by Technical Committee ISO/TC 147, Water quality, Subcommittee SC 2, Physical,
chemical and biochemical methods.
ISO 15681 consists of the following parts, under the general title Water quality — Determination of
orthophosphate and total phosphorus contents by flow analysis (FIA and CFA):
 Part 1: Method by flow injection analysis (FIA)
 Part 2: Method by continuous flow analysis (CFA)
iv © ISO 2003 — All rights reserved

ISO 15681-1:2003(E)
Introduction
Methods of determining water quality using flow analysis automated wet chemical procedures, and are
particularly suitable for the processing of many analytes in water in large sample series at a high analysis
frequency.
[1], [2] [3]
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 part of ISO 15681 describes the FIA method.
The user should be aware that particular problems could require the specification of additional marginal
conditions.
INTERNATIONAL STANDARD ISO 15681-1:2003(E)

Water quality — Determination of orthophosphate and total
phosphorus contents by flow analysis (FIA and CFA) —
Part 1:
Method by flow injection analysis (FIA)
WARNING — Persons using this part of ISO 15681 should be familiar with normal laboratory practice.
This part of ISO 15681 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. Molybdate and antimony waste solutions
should be disposed of properly. It is absolutely essential that tests conducted according to this part of
ISO 15681 be carried out by suitably qualified staff.
1 Scope
This part of ISO 15681 specifies flow injection analysis (FIA) methods for the determination of orthophosphate
in the mass concentration range from 0,01 mg/l to 1,0 mg/l (P), and total phosphorus by manual digestion in
[5], [6]
accordance with ISO 6878 for the mass concentration range from 0,1 mg/l to 10 mg/l (P). The range of
application can be changed by varying the operating conditions.
This part of ISO 15681 is applicable to various types of water (such as ground, drinking, surface, leachate and
waste waters).
This method is also applicable to the analysis of seawater, but with changes in sensitivity, by adaptation of the
carrier and calibration solutions to the salinity of the samples.
2 Normative references
The following reference documents are indispensable for the application 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 on sampling programmes
ISO 5667-2, Water quality — Sampling — Part 2: Guidance on sampling techniques
ISO 5667-3, Water quality — Sampling — Part 3: Guidance on the preservation and handling of water
samples
1)
ISO 6878:— , Water quality — Determination of phosphorus — Ammonium molybdate spectrometric method
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

1) To be published.
ISO 15681-1:2003(E)
3 Interferences
3.1 General interferences
ISO 6878:—, Annex B gives a list of general interferences. In addition, or contrary to the cited standard, the
following guidelines apply.
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 reducing reagent
can be insufficient. In this case it is advisable to remove the oxidizing material prior to digestion.
f) The self-absorption of the sample can be compensated by measuring, in addition to the sample signal
(8.6), 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 (see Clause 9).
3.2 Interferences in the determination of total-P
The interferences from silicate, nitrite, fluoride and iron described for the determination of orthophosphate are
generally not observed, due to the pre-digestion and the higher analytical range.
The efficiency of the digestion can be affected for water samples with a chemical oxygen demand (COD)
value of more than 10 times the highest concentrations of the calibration solutions (5.16). In this case the
sample should be diluted.
4 Principle
4.1 Determination of orthophosphate
The sample is injected into a carrier stream, which is merged with an acidic ammonium molybdate solution.
[4], [5]
The resulting molybdophosphoric acid is reduced by tin(II) chloride to molybdenum blue .
4.2 Total phosphorus with manual digestion
Phosphorus compounds in the sample are oxidized manually with a potassium peroxodisulfate solution, in
accordance with ISO 6878. The resulting orthophosphate is determined by the molybdenum blue reaction as
[5], [6]
in 4.1 .
5 Reagents
Use analytical grade chemicals unless otherwise specified. The phosphate blank value shall be checked (8.3).
Degas carefully all carrier and reagent solutions for the FIA determinations before use, e.g. by vacuum
filtration or purging with helium (for at least 10 min).
2 © ISO 2003 — All rights reserved

ISO 15681-1:2003(E)
5.1 Water, complying to grade 1 of ISO 3696.
5.2 Sulfuric acid, H SO .
2 4
5.2.1 Sulfuric acid (I), ρ = 1,84 g/ml; 98 % (mass fraction).
5.2.2 Sulfuric acid (II), c(H SO ) = 2,45 mol/l.
2 4
To approximately 800 ml of water (5.1) carefully add 136 ml of sulfuric acid (I) (5.2.1) while stirring. Cool and
dilute to 1 000 ml with water (5.1).
5.3 Ammonium heptamolybdate tetrahydrate, (NH ) Mo O ⋅ 4H O.
4 6 7 24 2
5.4 Hydrazine sulfate, N H SO .
2 6 4
5.5 Tin(II) chloride dihydrate, SnCl · 2 H O.
2 2
5.6 Potassium peroxodisulfate, K S O .
2 2 8
5.7 Potassium dihydrogen phosphate, KH PO , dried to constant mass at 105 °C ± 5 °C.
2 4
5.8 Potassium pyrophosphate, K P O .
4 2 7
5.9 Organophosphorus compounds to check the digestion.
5.9.1 Pyridoxal-5-phosphate monohydrate, C H NO P ⋅ H O or alternatively:
8 10 6 2
5.9.2 Disodium phenylphosphate, C H Na PO .
6 5 2 4
5.10 Molybdate solution (R1 in Figure A.1).
Dissolve 35 ml of sulfuric acid (I) (5.2.1) and 10 g of ammonium heptamolybdate tetrahydrate (5.3) in about
800 ml water (5.1), cool and dilute to 1 000 ml.
The solution is stable for 3 months if stored at room temperature.
5.11 Tin (II) chloride reagent (R2 in Figure A.1).
Dissolve 28 ml of sulfuric acid (I) (5.2.1), 200 mg of tin(II) chloride (5.5) and 2 g of hydrazine sulfate (5.4) in
about 800 ml water (5.1), cool and dilute to 1 000 ml. Store at 4 °C ± 2 °C.
The solution is stable for 1 week if stored at 4 °C ± 2 °C.
NOTE Instead of hydrazine sulfate (5.4), N,N-diethylhydroxylamine, DEHA (Annex D) may be used. This change was
not part of the validation in the interlaboratory trial cited in Annex B.
5.12 Carrier solutions
5.12.1 Carrier solution I, for orthophosphate determination (C1 in Figure A.1).
The carrier solution I is water (5.1).
5.12.2 Carrier solution II, for total phosphorus (P) determination after manual digestion (C1 in Figure A.1).
Add 5 ml of sulfuric acid (I) (5.2.1) to 1 000 ml of water (5.1) and mix.
ISO 15681-1:2003(E)
5.13 Orthophosphate stock solution I, ρ = 50,0 mg/l P.
Dissolve 220 mg ± 1 mg of potassium dihydrogenphosphate (5.7) in water (5.1) and dilute to 1 000 ml. Store
in a tightly closed glass bottle.
The solution is stable for 2 months if stored at 4 °C ± 2 °C.
5.14 Orthophosphate stock solution II, ρ = 10,0 mg/l P.
Dilute 20 ml of orthophosphate stock solution I (5.13) to 100 ml with water (5.1).
Prepare freshly each day of use.
5.15 Orthophosphate stock solution III, ρ = 1,00 mg/l P.
Dilute 2 ml of orthophosphate stock solution I (5.13) to 100 ml with water (5.1).
Prepare freshly each day of use.
5.16 Calibration solutions
Prepare at least 5 calibration solutions, evenly distributed over the working range, by diluting solutions 5.13 to
5.15 according to the range required.
Ranges:
For orthophosphate: Range II: 0,01 mg/l to 0,10 mg/l P
Range I: 0,10 mg/l to 1,00 mg/l P

For total phosphorus: Range II: 0,10 mg/l to 1,00 mg/l P
Range I: 1,00 mg/l to 10,0 mg/l P
Tables 1 to 3 give examples for the preparation of 10 calibration solutions for the above-mentioned ranges.
Table 1 — Example for the preparation of 10 calibration solutions for the orthophosphate range II
(0,01 mg/l to 0,10 mg/l P)
Millilitres of orthophosphate stock 1 2 3 4 5 6 7 8 9 10
solution III (5.15) diluted to 100 ml
Concentration of calibration 0,01 0,02 0,03 0,04 0,05 0,06 0,07 0,08 0,09 0,10
solutions, mg/l P
Table 2 — Example for the preparation of 10 calibration solutions for the orthophosphate range I and
total phosphorus range II (0,1 mg/l to 1,0 mg/l P)
Millilitres of orthophosphate stock 1 2 3 4 5 6 7 8 9 10
solution II (5.14) diluted to 100 ml
Concentration of calibration 0,10 0,20 0,30 0,40 0,50 0,60 0,70 0,80 0,90 1,00
solutions, mg/l P
4 © ISO 2003 — All rights reserved

ISO 15681-1:2003(E)
Table 3 — Example for the preparation of 10 calibration solutions for the total phosphorus range I
(1 mg/l to 10 mg/l P)
Millilitres of orthophosphate stock solution I 2 4 6 8 10 12 14 16 18 20
(5.13) diluted to 100 ml
Concentration of calibration solutions, 1,00 2,00 3,00 4,00 5,00 6,00 7,00 8,00 9,00 10,0
mg/l P
Prepare the calibration solutions immediately before use.
5.17 Standards for verifying hydrolysis and digestion efficiency.
5.17.1 Potassium pyrophosphate stock solution, ρ = 100 mg/l P.
Dissolve 533 mg ± 3 mg of potassium pyrophosphate (5.8) in about 800 ml of water (5.1) and dilute to
1 000 ml. Store in a sealed glass container at 4 °C ± 2 °C.
The solution is stable for 6 months.
5.17.2 Potassium pyrophosphate solution I, to check hydrolysis efficiency, ρ = 0,50 mg/l P, for the total-P
working range II (0,10 mg/l to 1,00 mg/l P).
Dilute 0,5 ml of potassium pyrophosphate stock solution (5.17.1) and 100 µl of sulfuric acid (II) (5.2.2) to
100 ml with water (5.1).
The solution is stable for 1 month if stored at 4 °C ± 2 °C.
5.17.3 Potassium pyrophosphate solution II, to check hydrolysis efficiency, ρ = 5,00 mg/l P, for the total-P
working range I (1,00 mg/l to 10,0 mg/l P).
Dilute 5 ml of potassium pyrophosphate stock solution (5.17.1) and 100 µl of sulfuric acid (II) (5.2.2) to 100 ml
with water (5.1).
The solution is sta
...

SLOVENSKI STANDARD
01-februar-2005
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OSIST prEN ISO 15681-1:2004
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Water quality - Determination of orthophosphate and total phosphorus contents by flow
analysis (FIA and CFA) - Part 1: Method by flow injection analysis (FIA) (ISO 15681-
1:2003)
Wasserbeschaffenheit - Bestimmung von Orthophosphat und Gesamtphosphor mittels
Fließanalytik (FIA und CFA) - Teil 1: Verfahren mittels Fließinjektionsanalyse (FIA) (ISO
15681-1:2003)
Qualité de l'eau - Dosage des orthophosphates et du phosphore total par analyse en flux
(FIA et CFA) - Partie 1: Méthode par analyse avec injection en flux (FIA) (ISO 15681-
1:2003)
Ta slovenski standard je istoveten z: EN ISO 15681-1:2004
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.

EUROPEAN STANDARD
EN ISO 15681-1
NORME EUROPÉENNE
EUROPÄISCHE NORM
December 2004
ICS 13.060.50
English version
Water quality - Determination of orthophosphate and total
phosphorus contents by flow analysis (FIA and CFA) - Part 1:
Method by flow injection analysis (FIA) (ISO 15681-1:2003)
Qualité de l'eau - Dosage des orthophosphates et du Wasserbeschaffenheit - Bestimmung von Othophosphat
phosphore total par analyse en flux (FIA et CFA) - Partie 1: und Gesamtphosphor mittels Fließanalytik (FIA und CFA) -
Méthode par analyse avec injection en flux (FIA) (ISO Teil 1: Verfahren mittels Fließinjektionsanalyse (FIA) (ISO
15681-1:2003) 15681-1:2003)
This European Standard was approved by CEN on 21 December 2004.
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 Central Secretariat 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
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© 2004 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 15681-1:2004: E
worldwide for CEN national Members.

Foreword
The text of ISO 15681-1:2003 has been prepared by Technical Committee ISO/TC 147 "Water
quality” of the International Organization for Standardization (ISO) and has been taken over as
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 2005, and conflicting national
standards shall be withdrawn at the latest by June 2005.

According to the CEN/CENELEC Internal Regulations, the national standards organizations of
the following countries are bound to implement this European Standard: Austria, Belgium,
Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary,
Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland,
Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.

Endorsement notice
The text of ISO 15681-1:2003 has been approved by CEN as EN ISO 15681-1:2004 without any
modifications.
INTERNATIONAL ISO
STANDARD 15681-1
First edition
2003-12-15
Water quality — Determination of
orthophosphate and total phosphorus
contents by flow analysis (FIA and
CFA) —
Part 1:
Method by flow injection analysis (FIA)
Qualité de l'eau — Dosage des orthophosphates et du phosphore total
par analyse en flux (FIA et CFA) —
Partie 1: Méthode par analyse avec injection en flux (FIA)

Reference number
ISO 15681-1:2003(E)
©
ISO 2003
ISO 15681-1:2003(E)
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ii © ISO 2003 — All rights reserved

ISO 15681-1:2003(E)
Contents Page
Foreword. iv
Introduction . v
1 Scope. 1
2 Normative references. 1
3 Interferences. 2
3.1 General interferences. 2
3.2 Interferences in the determination of total-P . 2
4 Principle. 2
4.1 Determination of orthophosphate . 2
4.2 Total phosphorus with manual digestion. 2
5 Reagents. 2
6 Apparatus. 6
6.1 Flow injection analysis (FIA). 6
6.2 Additional apparatus. 6
6.3 Additional apparatus for the determination of total phosphorus . 6
7 Sampling and sample preparation . 7
8 Procedure. 7
8.1 Analysis preparation. 7
8.2 Instrument performance check. 7
8.3 Reagent blank check . 7
8.4 Calibration. 8
8.5 Check of digestion efficiency for determination of total-P. 8
8.6 Measurement. 8
8.7 Closing down the system. 8
9 Calculation of results. 9
10 Expression of results. 9
11 Test report. 9
Annex A (informative) Example of an FIA system. 10
Annex B (informative) Precision and accuracy . 11
Annex C (informative) Determination of orthophosphate-P and total-P by FIA using ascorbic acid
reduction. 13
Annex D (informative) Replacement of hydrazine sulfate by DEHA (N,N-diethylhydroxylamine) . 18
Bibliography . 19

ISO 15681-1:2003(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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
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.
ISO 15681-1 was prepared by Technical Committee ISO/TC 147, Water quality, Subcommittee SC 2, Physical,
chemical and biochemical methods.
ISO 15681 consists of the following parts, under the general title Water quality — Determination of
orthophosphate and total phosphorus contents by flow analysis (FIA and CFA):
 Part 1: Method by flow injection analysis (FIA)
 Part 2: Method by continuous flow analysis (CFA)
iv © ISO 2003 — All rights reserved

ISO 15681-1:2003(E)
Introduction
Methods of determining water quality using flow analysis automated wet chemical procedures, and are
particularly suitable for the processing of many analytes in water in large sample series at a high analysis
frequency.
[1], [2] [3]
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 part of ISO 15681 describes the FIA method.
The user should be aware that particular problems could require the specification of additional marginal
conditions.
INTERNATIONAL STANDARD ISO 15681-1:2003(E)

Water quality — Determination of orthophosphate and total
phosphorus contents by flow analysis (FIA and CFA) —
Part 1:
Method by flow injection analysis (FIA)
WARNING — Persons using this part of ISO 15681 should be familiar with normal laboratory practice.
This part of ISO 15681 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. Molybdate and antimony waste solutions
should be disposed of properly. It is absolutely essential that tests conducted according to this part of
ISO 15681 be carried out by suitably qualified staff.
1 Scope
This part of ISO 15681 specifies flow injection analysis (FIA) methods for the determination of orthophosphate
in the mass concentration range from 0,01 mg/l to 1,0 mg/l (P), and total phosphorus by manual digestion in
[5], [6]
accordance with ISO 6878 for the mass concentration range from 0,1 mg/l to 10 mg/l (P). The range of
application can be changed by varying the operating conditions.
This part of ISO 15681 is applicable to various types of water (such as ground, drinking, surface, leachate and
waste waters).
This method is also applicable to the analysis of seawater, but with changes in sensitivity, by adaptation of the
carrier and calibration solutions to the salinity of the samples.
2 Normative references
The following reference documents are indispensable for the application 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 on sampling programmes
ISO 5667-2, Water quality — Sampling — Part 2: Guidance on sampling techniques
ISO 5667-3, Water quality — Sampling — Part 3: Guidance on the preservation and handling of water
samples
1)
ISO 6878:— , Water quality — Determination of phosphorus — Ammonium molybdate spectrometric method
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

1) To be published.
ISO 15681-1:2003(E)
3 Interferences
3.1 General interferences
ISO 6878:—, Annex B gives a list of general interferences. In addition, or contrary to the cited standard, the
following guidelines apply.
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 reducing reagent
can be insufficient. In this case it is advisable to remove the oxidizing material prior to digestion.
f) The self-absorption of the sample can be compensated by measuring, in addition to the sample signal
(8.6), 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 (see Clause 9).
3.2 Interferences in the determination of total-P
The interferences from silicate, nitrite, fluoride and iron described for the determination of orthophosphate are
generally not observed, due to the pre-digestion and the higher analytical range.
The efficiency of the digestion can be affected for water samples with a chemical oxygen demand (COD)
value of more than 10 times the highest concentrations of the calibration solutions (5.16). In this case the
sample should be diluted.
4 Principle
4.1 Determination of orthophosphate
The sample is injected into a carrier stream, which is merged with an acidic ammonium molybdate solution.
[4], [5]
The resulting molybdophosphoric acid is reduced by tin(II) chloride to molybdenum blue .
4.2 Total phosphorus with manual digestion
Phosphorus compounds in the sample are oxidized manually with a potassium peroxodisulfate solution, in
accordance with ISO 6878. The resulting orthophosphate is determined by the molybdenum blue reaction as
[5], [6]
in 4.1 .
5 Reagents
Use analytical grade chemicals unless otherwise specified. The phosphate blank value shall be checked (8.3).
Degas carefully all carrier and reagent solutions for the FIA determinations before use, e.g. by vacuum
filtration or purging with helium (for at least 10 min).
2 © ISO 2003 — All rights reserved

ISO 15681-1:2003(E)
5.1 Water, complying to grade 1 of ISO 3696.
5.2 Sulfuric acid, H SO .
2 4
5.2.1 Sulfuric acid (I), ρ = 1,84 g/ml; 98 % (mass fraction).
5.2.2 Sulfuric acid (II), c(H SO ) = 2,45 mol/l.
2 4
To approximately 800 ml of water (5.1) carefully add 136 ml of sulfuric acid (I) (5.2.1) while stirring. Cool and
dilute to 1 000 ml with water (5.1).
5.3 Ammonium heptamolybdate tetrahydrate, (NH ) Mo O ⋅ 4H O.
4 6 7 24 2
5.4 Hydrazine sulfate, N H SO .
2 6 4
5.5 Tin(II) chloride dihydrate, SnCl · 2 H O.
2 2
5.6 Potassium peroxodisulfate, K S O .
2 2 8
5.7 Potassium dihydrogen phosphate, KH PO , dried to constant mass at 105 °C ± 5 °C.
2 4
5.8 Potassium pyrophosphate, K P O .
4 2 7
5.9 Organophosphorus compounds to check the digestion.
5.9.1 Pyridoxal-5-phosphate monohydrate, C H NO P ⋅ H O or alternatively:
8 10 6 2
5.9.2 Disodium phenylphosphate, C H Na PO .
6 5 2 4
5.10 Molybdate solution (R1 in Figure A.1).
Dissolve 35 ml of sulfuric acid (I) (5.2.1) and 10 g of ammonium heptamolybdate tetrahydrate (5.3) in about
800 ml water (5.1), cool and dilute to 1 000 ml.
The solution is stable for 3 months if stored at room temperature.
5.11 Tin (II) chloride reagent (R2 in Figure A.1).
Dissolve 28 ml of sulfuric acid (I) (5.2.1), 200 mg of tin(II) chloride (5.5) and 2 g of hydrazine sulfate (5.4) in
about 800 ml water (5.1), cool and dilute to 1 000 ml. Store at 4 °C ± 2 °C.
The solution is stable for 1 week if stored at 4 °C ± 2 °C.
NOTE Instead of hydrazine sulfate (5.4), N,N-diethylhydroxylamine, DEHA (Annex D) may be used. This change was
not part of the validation in the interlaboratory trial cited in Annex B.
5.12 Carrier solutions
5.12.1 Carrier solution I, for orthophosphate determination (C1 in Figure A.1).
The carrier solution I is water (5.1).
5.12.2 Carrier solution II, for total phosphorus (P) determination after manual digestion (C1 in Figure A.1).
Add 5 ml of sulfuric acid (I) (5.2.1) to 1 000 ml of water (5.1) and mix.
ISO 15681-1:2003(E)
5.13 Orthophosphate stock solution I, ρ = 50,0 mg/l P.
Dissolve 220 mg ± 1 mg of potassium dihydrogenphosphate (5.7) in water (5.1) and dilute to 1 000 ml. Store
in a tightly closed glass bottle.
The solution is stable for 2 months if stored at 4 °C ± 2 °C.
5.14 Orthophosphate stock solution II, ρ = 10,0 mg/l P.
Dilute 20 ml of orthophosphate stock solution I (5.13) to 100 ml with water (5.1).
Prepare freshly each day of use.
5.15 Orthophosphate stock solution III, ρ = 1,00 mg/l P.
Dilute 2 ml of orthophosphate stock solution I (5.13) to 100 ml with water (5.1).
Prepare freshly each day of use.
5.16 Calibration solutions
Prepare at least 5 calibration solutions, evenly distributed over the working range, by diluting solutions 5.13 to
5.15 according to the range required.
Ranges:
For orthophosphate: Range II: 0,01 mg/l to 0,10 mg/l P
Range I: 0,10 mg/l to 1,00 mg/l P

For total phosphorus: Range II: 0,10 mg/l to 1,00 mg/l P
Range I: 1,00 mg/l to 10,0 mg/l P
Tables 1 to 3 give examples for the preparation of 10 calibration solutions for the above-mentioned ranges.
Table 1 — Example for the preparation of 10 calibration solutions for the orthophosphate range II
(0,01 mg/l to 0,10 mg/l P)
Millilitres of orthophosphate stock 1 2 3 4 5 6 7 8 9 10
solution III (5.15) diluted to 100 ml
Concentration of calibration 0,01 0,02 0,03 0,04 0,05 0,06 0,07 0,08 0,09 0,10
solutions, mg/l P
Table 2 — Example for the preparation of 10 calibration solutions for the orthophosphate range I and
total phosphorus range II (0,1 mg/l to 1,0 mg/l P)
Millilitres of orthophosphate stock 1 2 3 4 5 6 7 8 9 10
solution II (5.14) diluted to 100 ml
Concentration of calibration 0,10 0,20 0,30 0,40 0,50 0,60 0,70 0,80 0,90 1,00
solutions, mg/l P
4 © ISO 2003 — All rights reserved

ISO 15681-1:2003(E)
Table 3 — Example for the preparation of 10 calibration solutions for the total phosphorus range I
(1 mg/l to 10 mg/l P)
Millilitres of orthophosphate stock solution I 2 4 6 8 10 12 14 16 18 20
(5.13) diluted to 100 ml
Concentration of calibration solutions, 1,00 2,00 3,00 4,00 5,00 6,00 7,00 8,00 9,00 10,0
mg/l P
Prepare the calibration solutions immediately before use.
5.17 Standards for verifying hydrolysis and digestion efficiency.
5.17.1 Potassium pyrophosphate stock solution, ρ = 100 mg/l P.
Dissolve 533 mg ± 3 mg of potassium pyrophosphate (5.8) in about 800 ml of water (5.1) and dilute to
1 000 ml. Store in a sealed glass container at 4 °C ± 2 °C.
The solution is stable for 6 months.
5.17.2 Potassium pyrophosphate solution I, to check hydrolysis efficiency, ρ = 0,50 mg/l P, for the total-P
working range II (0,10 mg/l to 1,00 mg/l P).
Dilute 0,5 ml of potassium pyrophosphate stock solution (5.17.1) and 100 µl of sulfuric acid (II) (5.2.2) to
100 ml with water (5.1).
The solution is stable for 1 month if stored at 4 °C ± 2 °C.
5.17.3 Potassium pyrophosphate solution II, to check hydrolysis efficiency, ρ = 5,00 mg/l P, for the total-P
working range I (1,00 mg/l to 10,0 mg/l P).
Dilute 5 ml of potassium pyrophosphate stock solution (5.17.1) and 100 µl of sulfuric acid (II) (5.2.2) to 100 ml
with water (5.1).
The solution is stabl
...