ISO 22018:2021

FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 22018.2
ISO/TC 134
Fertilizers, soil conditioners
Secretariat: ISIRI
and beneficial substances —
Voting begins on:
2021­03­10 Determination of EDTA soluble
phosphorus content in inorganic
Voting terminates on:
2021­05­05
fertilizers
RECIPIENTS OF THIS DRAFT ARE INVITED TO
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
THEY ARE AWARE AND TO PROVIDE SUPPOR TING
DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
Reference number
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
ISO/FDIS 22018.2:2021(E)
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN­
DARDS TO WHICH REFERENCE MAY BE MADE IN
©
NATIONAL REGULATIONS. ISO 2021

---------------------- Page: 1 ----------------------
ISO/FDIS 22018.2:2021(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2021
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH­1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2021 – All rights reserved

---------------------- Page: 2 ----------------------
ISO/FDIS 22018.2:2021(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Reagents . 1
6 Apparatus and materials. 2
7 Test procedure . 3
7.1 General . 3
7.2 Preparation of test sample . 3
7.3 Weigh of test portion . 3
7.4 Extraction of EDTA soluble phosphorus . 3
7.5 Determination of the EDTA soluble phosphorus content . 3
7.6 Blank test . 3
8 Calculation and expression of results . 4
8.1 General . 4
8.2 Precision . 4
8.2.1 Ring test . 4
8.2.2 Repeatability, r .4
8.2.3 Reproducibility, R .4
9 Test report . 4
Annex A (informative) Ring test report . 6
Bibliography .14
© ISO 2021 – All rights reserved iii

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ISO/FDIS 22018.2:2021(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 non­governmental, 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 134, Fertilizers, soil conditioners and
beneficial substances.
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 2021 – All rights reserved

---------------------- Page: 4 ----------------------
ISO/FDIS 22018.2:2021(E)

Introduction
Owing to the variation of basic phosphate component, character and processing technology, traditionally,
different extraction solutions and methods have been utilized for the determination of the phosphorus
content of phosphate fertilizers. Extraction solutions currently employed for phosphorus content
determination include alkaline ammonium citrate (i.e. Petermann’s solution), neutral ammonium
citrate, citric acid, ethylene diamine tetraacetic acid (EDTA) and citric acid, or just EDTA. Each of these
extractants is designed to target specific phosphate components of phosphorus-based fertilizers.
Due to rapid developments in the modern fertilizer industry, especially with the formulation of
compound/complex fertilizers, many phosphate fertilizers may have multiple phosphorus-containing
components. The co-existence of these various phosphorus sources in a compound/complex fertilizer
can complicate the effective extraction and determination of the phosphorus content.
© ISO 2021 – All rights reserved v

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FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 22018.2:2021(E)
Fertilizers, soil conditioners and beneficial substances —
Determination of EDTA soluble phosphorus content in
inorganic fertilizers
1 Scope
This document specifies the method for the determination of the EDTA soluble phosphorus content
of inorganic fertilizers. The method is applicable for fertilizers composed of or blended from multiple
sources such as superphosphate, ammonium phosphate, triple superphosphate, and/or nitrophosphate.
It is not suitable for fertilizers containing calcium magnesium phosphates.
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 proposed standard. For dated references, only the edition cited applies.
For undated references, the latest edition of the referenced document (including any amendments)
applies.
ISO 8157, Fertilizers and soil conditioners — Vocabulary
ISO 8358, Solid fertilizers — Preparation of samples for chemical and physical analysis
ISO 14820­2, Fertilizers and liming materials — Sampling and sample preparation — Part 2: Sample
preparation
ISO 5725­2, Accuracy (trueness and precision) of measurement methods and results — Part 2: Basic method
for the determination of repeatability and reproducibility of a standard measurement method
3 Terms and definitions
For the purposes of this proposed standard, the terms and definitions given in ISO 8157 apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http:// www .electropedia .org/
— ISO Online browsing platform: available at https:// www .iso .org/ obp
4 Principle
The EDTA soluble phosphorus content in inorganic fertilizers (calcium magnesium phosphate excluded)
is extracted by ethylene diamine tetraacetic acid disodium salt solution. Phosphorus content in the
extracting solution in the form of orthophosphate reacts with quimociac reagent in the acid medium
to form yellow quinolinium molybdophosphate precipitate. The EDTA soluble phosphorus content is
determined by gravimetric quinolinium molybdophosphate method.
5 Reagents
WARNING — Nitric acid is both corrosive and toxic. Refer to the applicable safety data sheet
(SDS). Quinoline is irritating to the eyes, skin and respiratory system. Refer to the applicable
SDS. The related operations shall be performed in the fume hood. This document does not point
© ISO 2021 – All rights reserved 1

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ISO/FDIS 22018.2:2021(E)

out all possible safety problems, and the user shall bear the responsibility to take proper safety
and health measures.
NOTE Related laws and regulations of corresponding countries and/or regions can apply to these operations.
Analytical grade reagent (AR) chemicals shall be used in all tests, unless otherwise indicated. The
purity of water used throughout shall be understood to mean reagent water with electrical resistivity
≥ 18,2 MΩ·cm.
5.1 Ethylene diamine tetraacetic acid disodium salt dihydrate (C H N Na O ·2H O) solution
10 14 2 2 8 2
(37,5 g/l, eq. 0,1 mol/l).
Dissolve 37,5 g of EDTA with a certain amount of deionized water in a 1 000 ml beaker. Dilute by adding
deionized water to the 1 000 ml marking. Mix well.
5.2 Quimociac reagent.
The reagents used in the preparation of quimociac reagent:
— sodium molyddate (Na MoO 2H O, CAS: 10102­40­6);
2 4· 2
— citric acid (C H O H O, CAS: 5949­29­1);
6 8 7· 2
— nitric acid (HNO , 65 – 68 %, CAS: 7697­37­2);
3
— quinoline (2-azabicyclo[4.4.0]deca-1(6),2,4,7,9-pentaene, C H N, CAS: 91­22­5);
9 7
— acetone (C H O, CAS: 67­64­1).
3 6
To make solution a, add 70g sodium molybdate (Na MoO ·2H O) into a 400 ml beaker. Add 100 ml water
2 4 2
and stir to dissolve.
To make solution b, add 60 g citric acid (C H O ·H O) into a 1l beaker. Add 100 ml water and stir to
6 8 7 2
dissolve, then add 85 ml nitric acid (HNO , 65 % to 68 %).
3
To make solution c, add solution a into solution b, and mix well.
To make solution d, mix 85 ml nitric acid (HNO , 65 % to 68 %) with 100 ml water in a 400 ml beaker,
3
then add 5 ml quinoline (2-azabicyclo[4.4.0]deca-1(6),2,4,7,9-pentaene, C H N,CAS: 91-22-5). Mix well.
9 7
Add solution d into solution c, mix well and stand overnight. Filter the mixed solution with filter paper,
add 280 ml of acetone into the filtrate, then dilute the solution by adding water to 1 l. The as-prepared
quimociac reagent should be stored in a polyethylene bottle and preserved in a dark place to avoid light
and heat.
NOTE If the colour of quimociac reagent turns to light blue (caused by light), an appropriate amount of
potassium bromate solution (KBr, 10 g/l) can be added into the quimociac reagent until the colour disappears.
5.3 Nitric acid solution (HNO , 1 + 1).
3
Dilute a certain volume of 65 % to 68 % nitric acid (ρ = 1,39 g/ml to 1,40 g/ml) with equal volume of water.
6 Apparatus and materials
6.1 Ordinary laboratory apparatus.
6.2 Electric thermostatic drying oven, temperature can be maintained at 180 ± 2 °C.
6.3 Glass filtering crucible, type IV (pore size: 5μm to15 μm), volume of 30 ml.
2 © ISO 2021 – All rights reserved

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ISO/FDIS 22018.2:2021(E)

6.4 Thermostatic water bath oscillator, equipped with reciprocating oscillator or rotating oscillator
which temperature can be maintained at 60 ± 2 °C.
7 Test procedure
7.1 General
Replicate experiments shall be done for the determination.
7.2 Preparation of test sample
Prepare the test samples for analysis in accordance with ISO 8358 and ISO 14820-2.
7.3 Weigh of test portion
Weigh the appropriate amount of the test portion (accurately to 0,000 2 g) to obtain between 100 mg to
200 mg P O .
2 5
7.4 Extraction of EDTA soluble phosphorus
According to 7.3, weigh the appropriate amount of the test portion on the filter paper and wrap it,
put it into a 250 ml volumetric flask. Add 150 ml EDTA solution (5.1), plug the flask tightly, shake the
volumetric flask to break apart the filter paper and disperse the sample into the solution, then put it in the
thermostatic water bath oscillator (6.4) pre­set at 60 °C ± 2 °C, oscillate for 1 h at constant temperature
(set the oscillation frequency to make the sample in volumetric flask can flip over freely, and to keep the
sample suspended in the extracting solution while avoiding collection of excessive amounts of sample
on the upper portions of the interior of the volumetric flask). Then take the volumetric flask out, cool
down to ambient temperature, dilute the solution by water to scale, mix well and dry filter. Discard
the first part of the filtrate. Label the remaining filtrate as solution I for determining EDTA soluble
phosphorus content.
7.5 Determination of the EDTA soluble phosphorus content
Draw the appropriate amount of solution I (volume of v ) by single-line pipette, place into a 500 ml
1
beaker, add 10 ml nitric acid solution (5.3), dilute by water to 100 ml, heat on the hot plate till boiling,
and hold for 2 min to 3 min, remove and add 35 ml quimociac reagent (5.2), then cover with a watch
glass. Continue heating on the hot plate for 1 min or place covered­beaker into water bath pre­set at
close to boil until the precipitation is complete and the precipitate has settled to the bottom of the
beaker. Remove the beaker from the hot plate or water bath and allow to cool to ambient temperature.
Filter it by glass filter crucible (6.3), which was pre-dried to constant weight in drying oven at
180 °C ± 2 °C beforehand. Filter the supernarant first, and then wash the precipitate by decantation 1
to 2 times, use 25 ml of water each time, then transfer the precipitate to the glass filter crucible with
water and wash with an additional water, the total amount of water was 125 to 150 ml. Place the glass
filter crucible containing the precipitate in the drying oven pre-set at 180 °C ± 2 °C, drying for 45 min
after the temperature reach 180 °C, take it out and transfer it into a desiccator and cool it down to
ambient temperature, weigh the precipitation together with the filter.
7.6 Blank test
Except for not adding samples, the blank test should be carried out exactly the same as the sample test
using the same amount of reagent by identical analysis procedures.
© ISO 2021 – All rights reserved 3

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ISO/FDIS 22018.2:2021(E)

8 Calculation and expression of results
8.1 General
The EDTA soluble phosphorus content (w ) is expressed by a mass fraction percentage of P O as given
1 2 5
in Formula (1):
()mm−×0,03207
12
w = ×100 (1)
1
v
1
m ×
A
250
where
m is the weight of quinolinium molybdophosphate precipitation during the sample test, in g;
1
m is the weight of quinolinium molybdophosphate precipitation during the blank test, in g;
2
m is the weight of test portion used during the sample test for determination of EDTA soluble
A
phosphorus c
...

FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 22018
ISO/TC 134
Fertilizers, soil conditioners
Secretariat: ISIRI
and beneficial substances —
Voting begins on:
2020­01­24 Determination of available
phosphorus content in inorganic
Voting terminates on:
2020­03­20
fertilizers — EDTA extraction method
RECIPIENTS OF THIS DRAFT ARE INVITED TO
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
THEY ARE AWARE AND TO PROVIDE SUPPOR TING
DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
Reference number
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
ISO/FDIS 22018:2020(E)
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN­
DARDS TO WHICH REFERENCE MAY BE MADE IN
©
NATIONAL REGULATIONS. ISO 2020

---------------------- Page: 1 ----------------------
ISO/FDIS 22018:2020(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2020
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH­1214 Vernier, Geneva
Phone: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2020 – All rights reserved

---------------------- Page: 2 ----------------------
ISO/FDIS 22018:2020(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Reagents . 1
5.1 Ethylene diamine tetraacetic acid disodium salt dihydrate (EDTA, C H N Na O
10 14 2 2 8
2H O) solution (37,5 g/l, eq. 0,1 mol/l) . 2
2
5.2 Quimociac reagent . 2
5.3 Nitric acid solution (HNO , 1+1) . 2
3
6 Apparatus and materials. 2
7 Test procedure . 3
7.1 General . 3
7.2 Preparation of test sample . 3
7.3 Weigh of test portion . 3
7.4 Extraction of available phosphorus . 3
7.5 Determination of the available phosphorus content . 3
7.6 Blank test . 3
8 Calculation and expression of results . 4
8.1 General . 4
8.2 Precision . 4
8.2.1 Ring test . 4
8.2.2 Repeatability, r .4
8.2.3 Reproducibility, R .4
9 Test report . 4
Annex A (informative) Ring test report . 6
Bibliography .14
© ISO 2020 – All rights reserved iii

---------------------- Page: 3 ----------------------
ISO/FDIS 22018:2020(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 non­governmental, 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 134, Fertilizers, soil conditioners and
beneficial substances.
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 2020 – All rights reserved

---------------------- Page: 4 ----------------------
ISO/FDIS 22018:2020(E)

Introduction
Owing to the variation of basic phosphate component, character and processing technology,
traditionally, different extraction solutions and methods have been utilized for the determination of
the available phosphorus content of phosphate fertilizers. Extraction solutions currently employed
for phosphorus content determination include alkaline ammonium citrate (i.e. Petermann’s solution),
neutral ammonium citrate, citric acid, EDTA + citric acid, or just EDTA. Each of these extractants is
designed to target specific phosphate components of phosphorus-based fertilizers.
Due to rapid developments in the modern fertilizer industry, especially with the formulation of
compound/complex fertilizers, many phosphate fertilizers can have multiple phosphorus-containing
components. The co-existence of these various phosphorus sources in a compound/complex fertilizer
can complicate the effective extraction and determination of the available phosphorus content.
© ISO 2020 – All rights reserved v

---------------------- Page: 5 ----------------------
FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 22018:2020(E)
Fertilizers, soil conditioners and beneficial substances —
Determination of available phosphorus content in
inorganic fertilizers — EDTA extraction method
1 Scope
This document is applicable for use in the determination of the available phosphorus content of inorganic
fertilizers using an EDTA-based extraction. The method is suitable for fertilizers composed of or
blended from multiple sources such as superphosphate, ammonium phosphate, triple superphosphate,
and/or nitrophosphate. It is not suitable for fertilizers containing calcium magnesium phosphates.
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 8358, Solid fertilizers — Preparation of samples for chemical and physical analysis
ISO 8157, Fertilizers and soil conditioners — Vocabulary
ISO 14820­2:2016, Fertilizers and liming materials — Sampling and sample preparation — Part 2: Sample
preparation
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 8157 apply.
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 Principle
The available phosphorus content in inorganic fertilizers (calcium magnesium phosphate excluded)
is extracted by ethylene diamine tetraacetic acid disodium salt (EDTA) solution. Phosphorus content
in the extracting solution in the form of orthophosphate reacts with quimociac reagent in the acid
medium to form yellow quinolinium molybdophosphate precipitate. The available phosphorus content
is determined by gravimetric quinolinium molybdophosphate method.
5 Reagents
WARNING — Nitric acid is both corrosive and toxic. Refer to the applicable Safety Data Sheet
(SDS). Quinoline is irritating to eyes, skin and respiratory system. Refer to the applicable Safety
Data Sheet (SDS). The related operations shall be performed in the fume hood. This document
does not point out all possible safety problems, and the user shall bear the responsibility to take
proper safety and health measures, and ensure the operations compliant with the conditions
stipulated by the related laws and regulations of corresponding countries/regions.
© ISO 2020 – All rights reserved 1

---------------------- Page: 6 ----------------------
ISO/FDIS 22018:2020(E)

Analytical grade reagent (A.R.) chemicals shall be used in all tests, unless otherwise indicated. The
purity of water used throughout shall be understood to mean reagent water with electrical resistivity
≥18,2 MΩ·cm.
5.1 Ethylene diamine tetraacetic acid disodium salt dihydrate (EDTA, C H N Na O
10 14 2 2 8
2H O) solution (37,5 g/l, eq. 0,1 mol/l)
2
Dissolve 37,5 g of EDTA in 1 000 ml of deionized water in a 1 000 ml beaker. Mix well.
5.2 Quimociac reagent
The reagents used in the preparation of Quimociac reagent:
— sodium molyddate (Na MoO .2H O);
2 4 2
— citric acid (C H O .H O);
6 8 7 2
— nitric acid (HNO , 65 %–68 %);
3
— quinoline (2-azabicyclo[4.4.0]deca-1(6),2,4,7,9-pentaene, C H N , C A S: 91 ­22 ­5 ) .
9 7
Solution a: Add 70 g of sodium molybdate (Na MoO ·2H O) into a 400 ml beaker. Add 100 ml of water
2 4 2
and stir to dissolve.
Solution b: Add 60 g of citric acid (C H O ·H O) into a 1 l beaker. Add 100 ml of water and stir to dissolve,
6 8 7 2
then add 85 ml of nitric acid (HNO , 65 % to 68 %).
3
Solution c: Add solution a into solution b, mix well.
Solution d: Mix 85 ml of nitric acid (HNO , 65 % to 68 %) with 100 ml of water in a 400 ml beaker, then
3
add 5 ml of quinoline (2-azabicyclo[4.4.0]deca-1(6),2,4,7,9-pentaene, C H N,CAS: 91-22-5), mix well.
9 7
Add solution d into solution c, mix well and stand overnight. Filter the mixed solution with filter
paper, add 280 ml of acetone into the filtrate, then dilute the solution by water to 1 L. The as-prepared
quimociac reagent should be stored in a polyethylene bottle and preserved in a dark place to avoid light
and heat.
NOTE If the colour of quimociac reagent turns to light blue (caused by light), appropriate amount of
potassium bromate solution (KBr, 10 g/L) can be added into the quimociac reagent until the colour disappears.
5.3 Nitric acid solution (HNO , 1+1)
3
Dilute a certain volume of 65 % to 68 % nitric acid (ρ = 1,39 g/ml to 1,40 g/ml) with an equal volume
of water.
6 Apparatus and materials
6.1 Ordinary laboratory apparatus.
6.2 Electric thermostatic drying oven, temperature can be maintained at 180 °C ± 2 °C.
6.3 Glass filtering crucible: Type IV (pore size: 5 μm to15 μm), volume of 30 ml.
6.4 Thermostatic water bath oscillator: equipped with reciprocating oscillator or rotating oscillator
which temperature can be maintained at 60 °C ± 2 °C.
2 © ISO 2020 – All rights reserved

---------------------- Page: 7 ----------------------
ISO/FDIS 22018:2020(E)

7 Test procedure
7.1 General
Replicate experiments shall be done for the determination.
7.2 Preparation of test sample
Prepare the test samples for analysis in accordance with ISO 8358 and 14820-2:2016.
7.3 Weigh of test portion
Weigh the appropriate amount of the test portion (accurately to 0,000 2 g) to obtain between 100 mg to
200 mg of P O .
2 5
7.4 Extraction of available phosphorus
According to 7.2, weigh the appropriate amount of the test portion on the filter paper and wrap it,
put it into a 250 ml volumetric flask. Add 150 ml EDTA solution (5.1), plug the flask tightly, shake the
volumetric flask to break apart the filter paper and disperse the sample into the solution, then put
it in the thermostatic water bath oscillator (6.4) pre­set at 60 °C ± 2 °C, oscillate for 1 h at constant
temperature (set the oscillation frequency to make the sample in volumetric flask can flip over freely).
Then take the volumetric flask out, cool down to ambient temperature, dilute the solution by water
to scale, mix well and dry filter. Discard the first part of the filtrate. Label the remaining filtrate as
solution I for determining available phosphorus content.
7.5 Determination of the available phosphorus content
Draw the appropriate amount of solution I (volume of v ) by single-line pipette, place into a 500 mL
1
beaker, add 10 ml nitric acid solution (5.3), dilute by water to 100 mL, heat on the hot plate till boiling,
remove and add 35 mL quimociac reagent, then cover with a watch glass. Continue heating on the hot
plate for 1 min or place covered­beaker into water bath pre­set at close to boil until the precipitation is
complete and the precipitate has settled to the bottom of the beaker. Remove the beaker from the hot
plate or water bath and allow to cool to ambient temperature.
Filter it by glass filter crucible (6.3), which was pre-dried to constant weight in drying oven at
180 °C ± 2 °C beforehand. Filter the supernatant first, and then wash the precipitation by decantation
1 to 2 times, use 25 ml water for each time, transfer the precipitation to the filter, wash it by water
again, use 125 ml to 150 ml water in total. Put the precipitation together with the filter in the drying
oven pre-set at 180 °C ± 2 °C, drying for 45 min after the temperature reach 180 °C, take it out and
transfer it into a desiccator and cool it down to ambient temperature, weigh the precipitation together
with the filter.
7.6 Blank test
Except for not adding samples, the blank test should be carried out exactly the same as the sample test
using the same amount of reagent by identical analysis procedures.
© ISO 2020 – All rights reserved 3

---------------------- Page: 8 ----------------------
ISO/FDIS 22018:2020(E)

8 Calculation and expression of results
8.1 General
The available phosphorus content (w ) are expressed by mass fraction (%) of P O according to
1 2 5
Formula (1) as follows:
()mm−×0,03207
12
w = ×100 (1)
1
v
1
m ×
A
250
where
m is the weight of quinolinium molybdophosphate precipitation during the sample test, g;
1
m is the weight of quinolinium molybdophosphate precipitation during the blank test, g;
2
m is the weight of test portion used during the sample test for determination of available phos­
A
phorus content, g;
v is the volume of test solution I used during the sample test for determination of available
1
phosphorus content, ml;
250 is the total volume of test solution I, ml;
The reported value is the arithmetic average of two parallel determinations using separate solid sample
aliquots and shall be rounded off to two significant figures after the decimal point.
8.2 Precision
8.2.1 Ring test
Details of ring test on the precision of the method are summarized in Annex A.
8.2.2 Repeatabi
...