Water quality - Determination of phosphorus - Ammonium molybdate spectrometric method (ISO 6878:2004)

ISO 6878:2004 specifies methods for the determination of orthophosphate, orthophosphate after solvent extraction, hydrolysable phosphate plus orthophosphate, and total phosphorus after decomposition.
The methods are applicable to all kinds of water including seawater and effluents. Phosphorus concentrations within the range of 0,005 mg/l to 0,8 mg/l may be determined in such samples without dilution.
A solvent extraction procedure allows smaller phosphorus concentrations to be determined with a detection limit of about 0,000 5 mg/l.

Wasserbeschaffenheit - Bestimmung von Phosphur - Photometrisches Verfahren mittels Ammoniummolybdat (ISO/FDIS 6878:2004)

Diese Internationale Norm legt Verfahren für die Bestimmung von
-   Orthophosphat (siehe Abschnitt 4);
-   Orthophosphat nach Lösemittel-Extraktion (siehe Abschnitt 5);
-   hydrolysierbarem Phosphat und Orthophosphat (siehe Abschnitt 6);
-   Gesamtphosphor nach Aufschluss (siehe Abschnitte 7 und 8) fest.
Die Verfahren sind auf alle Wasserarten, einschließlich Meerwasser und Abwässer, anwendbar. Ohne Verdünnung der Proben können Phosphor-Konzentrationen im Bereich von 0,005 mg/l bis 0,8 mg/l Phosphor bestimmt werden.
Ein Extraktionsschritt gestattet es, niedrigere Phosphorkonzentrationen mit einer Nachweisgrenze von etwa 0,000 5 mg/l zu bestimmen.

Qualité de l'eau - Dosage du phosphore - Méthode spectrométrique au molybdate d'ammonium (ISO 6878:2004)

L'ISO 6878:2004 spécifie des méthodes de dosage des orthophosphates, des orthophosphates après extraction au solvant, des phosphates hydrolysables et des orthophosphates, et du phosphore total après décomposition.
Ces méthodes sont applicables à tous les types d'eau, y compris l'eau de mer et les effluents. Des concentrations en phosphore comprises entre 0,005 mg/l et 0,8 mg/l peuvent être déterminées sans dilution pour ces échantillons.
Un mode opératoire d'extraction au solvant permet de déterminer des concentrations en phosphore plus faibles avec une limite de détection d'environ 0,000 5 mg/l.

Kakovost vode - Določevanje fosforja - Spektrometrijska metoda z amonijevim molibdatom (ISO 6878:2004)

General Information

Status
Published
Publication Date
31-May-2004
Technical Committee
Current Stage
9093 - Decision to confirm - Review Enquiry
Due Date
14-May-2009
Completion Date
14-May-2009

RELATIONS

Buy Standard

Standard
EN ISO 6878:2004
English language
23 pages
sale 10% off
Preview
sale 10% off
Preview
e-Library read for
1 day

Standards Content (sample)

SLOVENSKI STANDARD
SIST EN ISO 6878:2004
01-december-2004
1DGRPHãþD
SIST EN 1189:1997
.DNRYRVWYRGH'RORþHYDQMHIRVIRUMD6SHNWURPHWULMVNDPHWRGD]DPRQLMHYLP
PROLEGDWRP ,62
Water quality - Determination of phosphorus - Ammonium molybdate spectrometric
method (ISO 6878:2004)

Wasserbeschaffenheit - Bestimmung von Phosphur - Photometrisches Verfahren mittels

Ammoniummolybdat (ISO 6878:2004)
Qualité de l'eau - Dosage du phosphore - Méthode spectrométrique au molybdate
d'ammonium (ISO 6878:2004)
Ta slovenski standard je istoveten z: EN ISO 6878:2004
ICS:
13.060.50 3UHLVNDYDYRGHQDNHPLþQH Examination of water for
VQRYL chemical substances
SIST EN ISO 6878:2004 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
SIST EN ISO 6878:2004
---------------------- Page: 2 ----------------------
SIST EN ISO 6878:2004
EUROPEAN STANDARD
EN ISO 6878
NORME EUROPÉENNE
EUROPÄISCHE NORM
June 2004
ICS 13.060.50 Supersedes EN 1189:1996
English version
Water quality - Determination of phosphorus - Ammonium
molybdate spectrometric method (ISO 6878:2004)
Qualité de l'eau - Dosage du phosphore - Méthode
spectrométrique au molybdate d'ammonium (ISO
6878:2004)
This European Standard was approved by CEN on 21 May 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 6878:2004: E

worldwide for CEN national Members.
---------------------- Page: 3 ----------------------
SIST EN ISO 6878:2004
EN ISO 6878:2004 (E)
Foreword

This document (EN ISO 6878:2004) 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 December 2004, and conflicting national

standards shall be withdrawn at the latest by December 2004.
This document supersedes EN 1189:1996.

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 6878:2004 has been approved by CEN as EN ISO 6878:2004 without any

modifications.
---------------------- Page: 4 ----------------------
SIST EN ISO 6878:2004
INTERNATIONAL ISO
STANDARD 6878
Second edition
2004-06-01
Water quality — Determination of
phosphorus — Ammonium molybdate
spectrometric method
Qualité de l'eau — Dosage du phosphore — Méthode spectrométrique
au molybdate d'ammonium
Reference number
ISO 6878:2004(E)
ISO 2004
---------------------- Page: 5 ----------------------
SIST EN ISO 6878:2004
ISO 6878:2004(E)
PDF disclaimer

This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but

shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In

downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat

accepts no liability in this area.
Adobe is a trademark of Adobe Systems Incorporated.

Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation

parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In

the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.

© ISO 2004

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,

electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or

ISO's member body in the country of the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii © ISO 2004 – All rights reserved
---------------------- Page: 6 ----------------------
SIST EN ISO 6878:2004
ISO 6878:2004(E)
Contents Page

Foreword............................................................................................................................................................ iv

Introduction ........................................................................................................................................................ v

1 Scope...................................................................................................................................................... 1

2 Interferences.......................................................................................................................................... 1

3 Principle ................................................................................................................................................. 1

4 Determination of orthophosphate ....................................................................................................... 2

5 Determination of orthophosphate after solvent extraction .............................................................. 7

6 Determination of hydrolysable phosphate and orthophosphate..................................................... 9

7 Determination of total phosphorus after peroxodisulfate oxidation ............................................. 11

8 Determination of total phosphorus after nitric acid-sulfuric acid digestion ................................ 14

Annex A (informative) Interferences............................................................................................................... 17

Annex B (informative) Precision data............................................................................................................. 19

Bibliography ..................................................................................................................................................... 21

© ISO 2004 – All rights reserved iii
---------------------- Page: 7 ----------------------
SIST EN ISO 6878:2004
ISO 6878:2004(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 6878 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 6878:1998), which has been technically revised.

iv © ISO 2004 – All rights reserved
---------------------- Page: 8 ----------------------
SIST EN ISO 6878:2004
ISO 6878:2004(E)
Introduction

This International Standard specifies the determination of different forms of phosphorus compounds present in

ground, surface and waste waters in various concentrations in the dissolved and undissolved state.

The user should be aware that particular problems could require the specification of additional marginal

conditions.
© ISO 2004 – All rights reserved v
---------------------- Page: 9 ----------------------
SIST EN ISO 6878:2004
---------------------- Page: 10 ----------------------
SIST EN ISO 6878:2004
INTERNATIONAL STANDARD ISO 6878:2004(E)
Water quality — Determination of phosphorus — Ammonium
molybdate spectrometric method

WARNING — Persons using this International Standard should be familiar with normal laboratory

practice. This International Standard 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. It is absolutely essential

that tests conducted according to this International Standard be carried out by suitably qualified staff.

Molybdate and antimony waste solutions should be disposed of properly.
1 Scope
This International Standard specifies methods for the determination of
 orthophosphate (see Clause 4);
 orthophosphate after solvent extraction (see Clause 5);
 hydrolysable phosphate plus orthophosphate (see Clause 6);
 total phosphorus after decomposition (see Clauses 7 and 8).

The methods are applicable to all kinds of water including seawater and effluents. Phosphorus concentrations

within the range of 0,005 mg/l to 0,8 mg/l may be determined in such samples without dilution.

A solvent extraction procedure allows smaller phosphorus concentrations to be determined with a detection

limit of about 0,000 5 mg/l.
2 Interferences

See Annex A for some known interferences. There may be others and it is recommended to verify whether

any such interferences exist and take action to eliminate them.
3 Principle

Reaction of orthophosphate ions with an acid solution containing molybdate and antimony ions to form an

antimony phosphomolybdate complex.

Reduction of the complex with ascorbic acid to form a strongly coloured molybdenum blue complex.

Measurement of the absorbance of this complex to determine the concentration of orthophosphate present.

Polyphosphate and some organophosphorus compounds are determined if converted to molybdate reactive

orthophosphate formed by sulfuric acid hydrolysis.

Many organophosphorus compounds are converted to orthophosphate by mineralization with peroxodisulfate.

Nitric acid-sulfuric acid mineralization is used if a more vigorous treatment is required.

© ISO 2004 – All rights reserved 1
---------------------- Page: 11 ----------------------
SIST EN ISO 6878:2004
ISO 6878:2004(E)
4 Determination of orthophosphate
4.1 Reagents

During the analysis, use only reagents of recognized analytical grade and only water having a phosphate

content that is negligible compared with the lowest concentration to be determined in the samples.

For low phosphate contents, double-distilled water from an all-glass apparatus is recommended.

4.1.1 Sulfuric acid solution, c(H SO ) ≈ 9 mol/l.
2 4

Add 500 ml ± 5 ml of water to a 2 l beaker. Cautiously add, with continuous stirring and cooling, 500 ml ± 5 ml

of sulfuric acid, ρ = 1,84 g/ml. Mix well and allow the solution to cool to room temperature.

4.1.2 Sulfuric acid solution, c(H SO ) ≈ 4,5 mol/l.
2 4

Add 500 ml ± 5 ml of water to a 2 l beaker. Cautiously add, with continuous stirring and cooling, 500 ml ± 5 ml

of sulfuric acid (4.1.1). Mix well and allow to cool to room temperature.
4.1.3 Sulfuric acid solution, c(H SO ) ≈ 2 mol/l.
2 4

Add 300 ml ± 3 ml of water to a 1 l beaker. Cautiously add 110 ml ± 2 ml of sulfuric acid solution (4.1.1), with

continuous stirring and cooling. In a measuring flask, dilute to 500 ml ± 2 ml with water and mix well.

4.1.4 Sodium hydroxide solution, c(NaOH) = 2 mol/l.

Dissolve 80 g ± 1 g of sodium hydroxide pellets in water, cool and dilute to 1 l with water.

4.1.5 Ascorbic acid solution, ρ = 100 g/l.
Dissolve 10 g ± 0,5 g of ascorbic acid (C H O ) in 100 ml ± 5 ml water.
6 8 6

NOTE The solution is stable for 2 weeks if stored in an amber glass bottle in a refrigerator and can be used as long

as it remains colourless.
4.1.6 Acid molybdate, Solution I.

Dissolve 13 g ± 0,5 g of ammonium heptamolybdate tetrahydrate [(NH ) Mo O ⋅4H O] in 100 ml ± 5 ml of

4 6 7 24 2

water. Dissolve 0,35 g ± 0,05 g of antimony potassium tartrate hemihydrate [K(SbO)C H O ⋅½H O] in

4 4 6 2
100 ml ± 5 ml of water.

Add the molybdate solution to 300 ml ± 5 ml of sulfuric acid (4.1.1) with continuous stirring. Add the tartrate

solution and mix well.

NOTE The reagent is stable for at least 2 months if stored in an amber glass bottle.

4.1.7 Acid molybdate, Solution II.

Cautiously add 230 ml ± 0,5 ml of sulfuric acid (4.1.1) to 70 ml ± 5 ml of water, cool. Dissolve 13 g ± 0,5 g of

ammonium heptamolybdate tetrahydrate [(NH ) Mo O ⋅4H O] in 100 ml ± 5 ml of water. Add to the acid

4 6 7 24 2

solution and mix well. Dissolve 0,35 g ± 0,05 g of antimony potassium tartrate hemihydrate

[K(SbO)C H O ⋅½H O] in 100 ml ± 5 ml of water. Add to the molybdate-acid solution and mix well.

4 4 6 2

This reagent is used when the sample is acidified with sulfuric acid (4.1.2) (see also Clauses 6, 7 and 8).

NOTE The reagent is stable for at least 2 months if stored in an amber glass bottle.

2 © ISO 2004 – All rights reserved
---------------------- Page: 12 ----------------------
SIST EN ISO 6878:2004
ISO 6878:2004(E)
4.1.8 Turbidity-colour compensation solution.

On a volume/volume basis, mix two parts of sulfuric acid (4.1.2) and one part of ascorbic acid (4.1.5).

NOTE The reagent is stable for several weeks if stored in an amber glass bottle in a refrigerator.

4.1.9 Sodium thiosulfate pentahydrate solution, ρ = 12,0 g/l.

Dissolve 1,20 g ± 0,05 g of sodium thiosulfate pentahydrate (Na S O ⋅5H O) in 100 ml ± 5 ml of water. Add

2 2 3 2
0,05 g ± 0,005 g of anhydrous sodium carbonate (Na CO ) as preservative.
2 3

NOTE The reagent is stable for at least 4 weeks if stored in an amber glass bottle.

4.1.10 Orthophosphate stock standard solution, ρ = 50 mg/l.

Dry a few grams of potassium dihydrogen phosphate to constant mass at 105 °C. Dissolve

0,219 7 g ± 0,000 2 g of KH PO in about 800 ml ± 10 ml of water in a 1 000 ml volumetric flask. Add

2 4
10 ml ± 0,5 ml of sulfuric acid (4.1.2) and make up to the mark with water.
Alternatively, use a commercially available stock solution.

The solution is stable for at least 3 months if stored in a well stoppered glass bottle. Refrigeration to about

4 °C is recommended.
4.1.11 Orthophosphate standard solution, ρ = 2 mg/l.

Pipette 20 ml ± 0,01 ml of orthophosphate stock standard solution (4.1.10) into a 500 ml volumetric flask.

Make up to the mark with water and mix well.
Prepare and use this solution each day as required.
NOTE 1 ml of this standard solution contains 2 µg P.
4.1.12 Hydrochloric acid, ρ(HCl) = 1,19 g/ml.
4.1.13 Hydrochloric acid, c(HCl) = 2,5 mol/l.

Cautiously add 200 ml ± 10 ml of hydrochloric acid (4.1.12) to 500 ml ± 10 ml of water. Mix and cool to room

temperature. Make up to 1 000 ml with water.
4.2 Apparatus

4.2.1 Spectrometer, “prism”- or “grating-type” or filter type, capable of accepting optical cells of thickness

10 mm to 50 mm.

The spectrometer chosen shall be suitable for measuring absorbance in the visible and near infra-red regions

of the spectrum. The most sensitive wavelength is 880 nm, but if a loss of sensitivity can be accepted,

absorbance may be measured at 700 nm.

NOTE The detection limit of the method is lower if a spectrometer capable of accepting 100 mm optical cells is

available.
4.2.2 Filter assembly, to hold a membrane filter of nominal pore size 0,45 µm.
4.2.3 Glassware.

Before use, wash all glassware, for example with hydrochloric acid (4.1.13), at approximately 40 °C to 50 °C

and rinse thoroughly with water. Detergents containing phosphate shall not be used.

© ISO 2004 – All rights reserved 3
---------------------- Page: 13 ----------------------
SIST EN ISO 6878:2004
ISO 6878:2004(E)

Preferably the glassware should be used only for the determination of phosphorus. After use, clean it as

described above and keep covered until needed again.

Rinse glassware used for the colour development stage occasionally with sodium hydroxide solution (4.1.4),

followed by thorough rinsing with water (4.1), to remove deposits of the coloured complex which has a

tendency to stick as a thin film on the wall of glassware.
4.3 Sampling and samples
4.3.1 Sampling

Collect the laboratory samples in polyethene, polyvinylchloride or preferably glass bottles. In the case of low

phosphate concentrations, use glass bottles.

The use of sampling bottles with cap lines should be avoided as these may contain phosphorus.

4.3.2 Preparation of the test sample

Filter the laboratory sample (4.3.1) within 4 h after sampling. If the sample has been kept cool in the meantime,

bring to room temperature before filtration.

Wash a membrane filter of nominal pore size 0,45 µm to ensure it is free of phosphate by passing 200 ml of

water, previously heated to approximately 30 °C to 40 °C. Discard these washings. Filter the sample and

reject the first 10 ml of sample filtrate. Collect the remainder in a clean, dry glass bottle for the immediate

determination of orthophosphate (4.4.4).

If the filtrate is not within the range of pH 3 to pH 10, adjust it with sodium hydroxide (4.1.4) or sulfuric acid

solution (4.1.3).

The filtration time should not exceed 10 min. If necessary, a larger diameter filter should be used.

The membrane filter should either be checked for phosphorus content or washed as described. Commercially

available membrane filters that are sold free from phosphorus should be washed as described.

4.4 Procedure
4.4.1 Test portion

Take a volume of test portion not exceeding 40 ml. This maximum volume is suitable for the determination of

orthophosphate concentrations of up to ρ = 0,8 mg/l, when using an optical cell of thickness 10 mm. Smaller

test portions shall be used in order to accommodate higher phosphate concentrations as shown in Table 1.

Similarly, low phosphate concentrations can be determined by measuring the absorbance in an optical cell of

thickness 40 mm or 50 mm.
Table 1 — Sample volumes and concentrations
Orthophosphate concentration Volume of test portion Thickness of optical cell
mg/l ml mm
0,0 to 0,8 40,0 10
0,0 to 1,6 20,0 10
0,0 to 3,2 10,0 10
0,0 to 6,4 5,0 10
0,0 to 0,2 40,0 40 or 50
4 © ISO 2004 – All rights reserved
---------------------- Page: 14 ----------------------
SIST EN ISO 6878:2004
ISO 6878:2004(E)
4.4.2 Blank test

Carry out a blank test in parallel with the determination, by the same procedure, using the same quantities of

all the reagents as in the determination, but using the appropriate volume of water instead of the test portion.

4.4.3 Calibration
4.4.3.1 Preparation of calibration solutions

Transfer, by means of a volumetric pipette, appropriate volumes, for example, 1,0 ml, 2,0 ml, 3,0 ml, 4,0 ml,

5,0 ml, 6,0 ml, 7,0 ml, 8,0 ml, 9,0 ml and 10,0 ml of the orthophosphate standard solution (4.1.11) to 50 ml

volumetric flasks. Dilute with water to about 40 ml. These solutions represent orthophosphate concentrations

ρ = 0,04 mg/l to 0,4 mg/l.

Proceed accordingly for other ranges of phosphate concentrations shown in Table 1.

4.4.3.2 Colour development

Add to each flask, while swirling, 1 ml of ascorbic acid (4.1.5) followed by 2 ml of acid molybdate Solution I

(4.1.6). Make up to the mark with water and mix well.

NOTE Absorbance measured at 700 nm causes a loss of about 30 % of the sensitivity at 880 nm.

4.4.3.3 Spectrometric measurements

Measure the absorbance of each solution using the spectrometer (4.2.1) at 880 nm after a period between

10 min and 30 min, or, if a loss of sensitivity can be accepted, at 700 nm. Use water in the reference cell.

4.4.3.4 Plotting the calibration graph

Plot a graph of absorbance (as the y-axis) against the phosphorus content (as the x-axis) in milligrams of

phosphorus per litre of the calibration solutions. The relationship between absorbance and concentration is

linear. Determine the slope of the graph.

Verify the graph from time to time for linearity, especially if new batches of chemicals are used.

4.4.4 Determination
4.4.4.1 Colour development
4.4.4.1.1 Standard procedure

Pipette the selected volume of test portion (4.4.1), V , into a 50 ml one-mark volumetric flask and, if

necessary, dilute to approximately 40 ml ± 2 ml with water. Proceed as specified in 4.4.3.2.

If the test sample contains arsenate, this should be reduced to arsenite with thiosulfate in acidic medium. The

reduction to arsenite is quantitative for arsenate concentrations up to at least 2 mg/l As, as described below.

Transfer, by means of a volumetric pipette, up to a maximum of 40 ml of the test sample to a 50 ml volumetric

flask. Add 0,4 ml of sulfuric acid (4.1.2), 1 ml of ascorbic acid solution (4.1.5), and 1 ml of thiosulfate solution

(4.1.9). Mix and allow the reduction to proceed for 10 min ± 1 min. Add 2 ml acid molybdate Solution II (4.1.7).

Make up to the mark with water. Mix well. Proceed as described in 4.4.3.3.
© ISO 2004 – All rights reserved 5
---------------------- Page: 15 ----------------------
SIST EN ISO 6878:2004
ISO 6878:2004(E)
4.4.4.1.2 Procedure in case of turbid samples
If the test sample is turbid and/or coloured, proceed as follows.

Add 3 ml of the turbidity-colour compensation reagent (4.1.8) to the selected volume of test portion. Dilute to

50 ml and measure the absorbance. Subtract the absorbance of this solution from the value measured as

specified in 4.4.3.3.
4.4.4.2 Spectrometric measurements
See 4.4.3.3.

If the test portion has been treated with thiosulfate due to interference by arsenate, measurements should be

made within 10 min; otherwise the colour will fade.
4.5 Expression of results
4.5.1 Calculation

Calculate the orthophosphate concentration, ρ , expressed in milligrams per litre, using the equation

()AA− V
0max
ρ =
fV×
where
A is the absorbance of the test portion;
A is the absorbance of the blank test;

f is the slope of the calibration graph (4.4.3.4), expressed in litres per milligram (l/mg);

V is the volume of the volumetric flask (50 ml), expressed in millilitres (ml);
max
V is the actual volume of the test portion, expressed in millilitres (ml).

Report the mass concentrations of phosphorus as follows, but to no more than three significant figures:

 ρ < 0,1 mg/l to the nearest 0,001 mg/l;
 ρ < 10 mg/l to the nearest 0,01 mg/l;
 ρ W 10 mg/l to the nearest 0,1 mg/l.
4.5.2 Precision

The precision data in Table B.1 were obtained in an interlaboratory trial involving 16 laboratories.

NOTE For interferences, see Annex A.
4.6 Test report
The test report shall contain the following information:
a) all information necessary for complete identification of the sample;
b) a reference to this International Standard (ISO 6878:2004);
6 © ISO 2004 – All rights reserved
---------------------- Page: 16 ----------------------
SIST EN ISO 6878:2004
ISO 6878:2004(E)
c) a reference to the method used, and the number of the clause;
d) the results obtained;

e) details of any operations not included in this section or regarded as optional, together with any incidents

likely to have an influence upon the results.
5 Determination of orthophosphate after solvent extraction
5.1 Applicability

This method can be applied only if the phosphate concentration in the sample is less than 0,01 mg/l P. This

method is especially suitable for marine water.
5.2 Reagents
Use the reagents specified in 4.1.5, 4.1.6 and 4.1.10 and in addition:
5.2.1 Hexan-1-ol (C H OH).
6 13
5.2.2 Ethanol (C H OH).
2 5
5.2.3 Orthophosphate, standard solution, ρ = 0,5 mg/l P.

Pipette 5,0 ml ± 0,01 ml of orthophosphate stock standard solution (4.1.10) into a 500 ml one-mark volumetric

flask. Make up to the mark with water and mix well.
Prepare and use this solution each day as required.
5.3 Sampling and samples
See 4.3.
5.4 Procedure
5.4.1 Test portion

Transfer, by means of a measuring cylinder, 350 ml ± 5 ml of the test sample (4.3) to a 500 ml separating

funnel.
5.4.2 Blank test

Carry out a blank test in parallel with the determination, by the same procedure, using the same quantities of

all reagents as in the determination, but using 350 ml of water instead of the test portion.

5.4.3 Calibration
5.4.3.1 Preparation of calibration solutions

Add 300 ml ± 10 ml of water to five individual separating funnels. From a microburette add 1,4 ml, 2,8 ml,

4,2 ml, 5,6 ml and 7,0 ml of orthophosphate standard solution (5.2.3) to each 500 ml separating funnel. Dilute

each solution to 350 ml ± 10 ml with water, stopper, swirl, and mix. These solutions represent orthophosphate

concentrations, ρ , of 0,002 mg/l, 0,004 mg/l, 0,006 mg/l, 0,008 mg/l and 0,01 mg/l respectively.

© ISO 2004 – All rights reserved 7
---------------------- Page: 17 ----------------------
SIST EN ISO 6878:2004
ISO 6878:2004(E)
5.4.3.2 Colour development

To each separating funnel, with swirling, add 7,0 ml ± 0,1 ml of ascorbic acid solution (4.1.5) and

14,0 ml ± 0,1 ml of acid molybdate Solution I (4.1.6).

After 15 min add 40,0 ml ± 0,1 ml of hexan-1-ol (5.2.1) to each separating funnel and stopper. Shake

vigorously for 1 min. Allow the phases to separate and pipette 30 ml ± 0,01 ml of each of the upper hexan-1-ol

extracts into a series of dry 50 ml one-mark volumetric flasks. Add 1,0 ml ± 0,2 ml of ethanol (5.2.2) to each

flask and dilute each solution to the mark with 1-hexanol.
5.4.3.3 Spectrometric measurements

Measure the absorbance of each hexan-1-ol solution at 680 nm in optical cells of thickness 40 mm or 50 mm

against hexan-1-ol in the reference cell.
5.4.3.4 Plotting the calibration graph

Plot a graph of absorbance (as the y-axis) against the phosphorus content (as the x-axis), in milligrams per

litre, of the calibration solutions. Determine the slope of the graph.

Verify the linearity of the calibration curve periodically, especially if new batches of chemicals are used.

5.4.4 Determination
5.4.4.1 Colour development

Treat the test portions (5.4.1) as specified in 5.4.3.2 for the calibration solutions.

5.4.4.2 Spectrometric measurements
See 5.4.3.3.
5.5 Expression of results

Calculate the orthophosphate concentration, ρ , expressed in milligrams per litre (mg/l), using the equation:

A − A
ρ =
where
A is the absorbance of the test portion;
A is the absorbance of the blank test;

f is the slope of the calibration graph (5.4.3.4), in litres per milligram (l/mg).

Report the value to the nearest 0,001 mg/l but give values below 0,000 5 mg/l as ρ < 0,000 5 mg/l.

NOTE For interferences, see Annex A.
5.6 Test report
The test report shall contain the following information:
a) all information necessary for complete identification of the sample;
b) a reference to this International Standard (ISO 6878:2004);
8 © ISO 2004 – All rights reserved
---------------------- Page: 18 ----------------------
SIST EN ISO 6878:2004
ISO 6878:2004(E)
c) a reference to the method used, and the number of the clause;
d) the results obtained;

e) details of any operations not included in this section or regarded as optional, together with any incidents

likely to have an influence upon the result.
6 Determination of hydrolysable phosphate and orthophosphate
6.1 Reagents
Use the reagents specified in 4.1.2, 4.1.4, 4.1.5, 4.1.7 and 4.1.11.
6.2 Apparatus
See 4.2.
6.3 Sampling and samples
6.3.1 Sampling
See 4.3.1.
6.3.2 Preparation of the test sample

Filter the sample (4.3.1) as described in 4.3.2 and analyse as soon as possible after sampling. If the sample

has been kept cool (5 °C to 10 °C) in the meantime, bring to room temperature before filtration.

Add 1 ml of sulfuric acid (4.1.
...

Questions, Comments and Discussion

Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.