Fertilizers - Determination of sulfates content using three different methods

This document specifies three different methods (Methods A, B and C) for the determination of sulfur present in fertilizer extracts in the form of sulfates. Method A specifies the gravimetric method. Method B specifies the method using inductively coupled plasma optical spectrometry (ICP-OES). Method C specifies the method using ion chromatography (IC).

Düngemittel - Bestimmung von Sulfat mit drei verschiedenen Verfahren

Dieses Dokument legt drei verschiedene Verfahren (Verfahren A, B und C) für die Bestimmung des in Dünge¬mittelextrakten vorliegenden Schwefels in Form von Sulfaten fest. Als Verfahren A ist das gravimetrische Verfahren festgelegt. Als Verfahren B ist die Bestimmung mittels optischer Emissionsspektrometrie mit induktiv gekoppeltem Plasma (ICP OES) festgelegt. Als Verfahren C ist die Vorgehensweise mittels Ionen¬chromatographie (IC) festgelegt.

Engrais - Dosage des sulfates selon trois méthodes différentes

Le présent document spécifie trois méthodes différentes (méthodes A, B et C) pour le dosage du soufre présent dans les extraits d’engrais sous forme de sulfates. La méthode A utilise la gravimétrie. La méthode B emploie la spectrométrie d’émission optique par plasma à couplage inductif (ICP-OES). La méthode C a recours à la chromatographie ionique (IC).

Gnojila - Določevanje sulfatov s tremi različnimi metodami

Ta evropski standard določa metodo za določevanje količine izboljševalcev tal, razen materialov za apnenje in rastnih substratov v razsutem in zapakiranem stanju. Ta dokument se uporablja za material v trdni obliki, vendar ne v obliki blokov, ki se prodaja po dimenzijah, in ki presega omejitev velikosti delcev v standardu EN 12580 ter kjer je deklarirana nazivna velikost delcev večja od 60 mm.

General Information

Status
Published
Publication Date
09-Aug-2022
Current Stage
6060 - Definitive text made available (DAV) - Publishing
Start Date
10-Aug-2022
Due Date
05-Sep-2021
Completion Date
10-Aug-2022

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SLOVENSKI STANDARD
SIST EN 15749:2023
01-marec-2023
Nadomešča:
SIST EN 15749:2010
Gnojila - Določevanje sulfatov s tremi različnimi metodami
Fertilizers - Determination of sulfates content using three different methods
Düngemittel - Bestimmung von Sulfat mit drei verschiedenen Verfahren
Engrais - Dosage des sulfates selon trois méthodes différentes
Ta slovenski standard je istoveten z: EN 15749:2022
ICS:
65.080 Gnojila Fertilizers
SIST EN 15749:2023 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN 15749:2023

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SIST EN 15749:2023


EN 15749
EUROPEAN STANDARD

NORME EUROPÉENNE

August 2022
EUROPÄISCHE NORM
ICS 65.080 Supersedes EN 15749:2009
English Version

Fertilizers - Determination of sulfates content using three
different methods
Engrais - Dosage des sulfates selon trois méthodes Düngemittel - Bestimmung von Sulfat mit drei
différentes verschiedenen Verfahren
This European Standard was approved by CEN on 3 July 2022.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.

This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

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





EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2022 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 15749:2022 E
worldwide for CEN national Members.

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SIST EN 15749:2023
EN 15749:2022 (E)
Contents Page
European foreword . 3
Introduction . 4
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Principle . 5
5 Sampling and sample preparation . 6
6 Method A – Gravimetric method . 6
7 Method B – ICP-OES method . 7
8 Method C – IC method . 11
9 Precision of methods A, B and C . 17
10 Test report . 19
Annex A (informative) Statistical results of the inter-laboratory tests. 20
Annex B (informative) Statistical results of the inter-laboratory tests of VDLUFA . 23
Annex C (informative) Statistical results of the inter-laboratory tests of Spanish Proficiency
Testing Program . 26
Bibliography . 28

2

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SIST EN 15749:2023
EN 15749:2022 (E)
European foreword
This document (EN 15749:2022) has been prepared by Technical Committee CEN/TC 260 “Fertilizers
and liming materials”, the secretariat of which is held by DIN.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by February 2023, and conflicting national standards shall
be withdrawn at the latest by February 2023.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN 15749:2009.
In comparison with the previous edition, the following technical modifications have been made:
— update of the normative references;
— Formula (18) has been corrected;
— addition of more data as result of inter-laboratory tests, Annex B and Annex C.
Any feedback and questions on this document should be directed to the users’ national standards body.
A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organisations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia,
Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland,
Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of North
Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United
Kingdom.
3

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SIST EN 15749:2023
EN 15749:2022 (E)
Introduction
This document specifies three different methods for the determination of sulfur. Based on the statistical
results of the inter-laboratory tests, obtained with the same samples, the three methods produce
equivalent results, therefore all three methods can be used, depending on the decision of the user and the
availability of equipment.
4

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SIST EN 15749:2023
EN 15749:2022 (E)
1 Scope
This document specifies three different methods (Methods A, B and C) for the determination of sulfur
present in fertilizer extracts in the form of sulfates. Method A specifies the gravimetric method. Method B
specifies the method using inductively coupled plasma optical spectrometry (ICP-OES). Method C
specifies the method using ion chromatography (IC).
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.
EN 1482-2, Fertilizers and liming materials - Sampling and sample preparation - Part 2: Sample
preparation
EN 12944-1, Fertilizers and liming materials and soil improvers - Vocabulary - Part 1: General terms
EN 12944-2, Fertilizers and liming materials and soil improvers - Vocabulary - Part 2: Terms relating to
fertilizers
EN 15925, Fertilizers - Extraction of total sulfur present in various forms
EN 15926, Fertilizers - Extraction of water soluble sulfur where the sulfur is in various forms
EN 15960, Fertilizers - Extraction of total calcium, total magnesium, total sodium and total sulfur in the
forms of sulfates
EN 15961, Fertilizers - Extraction of water-soluble calcium, magnesium, sodium and sulfur in the form of
sulfates
EN ISO 3696:1995, Water for analytical laboratory use - Specification and test methods (ISO 3696:1987)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in EN 12944-1 and EN 12944-2 apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at https://www.electropedia.org/
— ISO Online browsing platform: available at https://www.iso.org/obp
4 Principle
4.1 Method A: Gravimetric method
Sulfur is extracted from the sample according to the methods described in EN 15925, EN 15926,
EN 15960 or EN 15961 and determined based on the gravimetric determination as barium sulfate.
4.2 Method B: ICP-OES
Sulfur is extracted from the sample according to the methods described in EN 15925, EN 15926,
EN 15960 or EN 15961 and its concentration in the extract is measured by inductively coupled plasma-
optical emission spectrometry (ICP-OES).
5

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SIST EN 15749:2023
EN 15749:2022 (E)
4.3 Method C: IC
Sulfur is extracted from the fertilizer according to the methods described in EN 15925, EN 15926,
EN 15960 or EN 15961 in the form of sulfate. The sulfate concentration of the extract is measured by ion
chromatography (IC) equipped with a suppressor device and a conductivity detector.
5 Sampling and sample preparation
Sampling is not part of the methods specified in this document. A recommended sampling method is given
in EN 1482-1 [1].
Sample preparation shall be carried out in accordance with EN 1482-2.
6 Method A – Gravimetric method
6.1 Reagents
Use only reagents of recognized analytical grade.
6.1.1 Water, distilled or demineralized (grade 3 according to EN ISO 3696:1995).
6.1.2 Diluted hydrochloric acid.
Mix one volume of mass concentration ρ(HCl) = 1,18 g/ml with one volume of water.
6.1.3 Barium chloride solution, ρ(BaCl .2 H O) = 122 g/l.
2 2
6.1.4 Silver nitrate solution, ρ(AgNO ) = 5 g/l.
3
6.2 Apparatus
6.2.1 Porcelain crucibles.
6.2.2 Hot water bath.
6.2.3 Drying oven, set at (105 ± 1) °C.
6.2.4 Electric oven, set at (800 ± 50) °C.
6.3 Procedure
6.3.1 Sampling of the solution
Pipette an aliquot part of one of the extraction solutions containing between 20 mg and 100 mg of sulfur
or 50 mg and 250 mg of SO .
3
Place this aliquot in a beaker of suitable capacity. Add 20 ml of diluted hydrochloric acid (6.1.2). Make up
to about 300 ml with water.
6.3.2 Preparation of the precipitate
Bring the solution to the boil. Add, drop by drop, about 20 ml of the barium chloride solution (6.1.3) while
stirring the solution vigorously. Boil for a few minutes.
Place the beaker, covered with a watch glass, in a boiling hot water bath (6.2.2) for approximately 1 h.
Then leave standing hot (approximately 60 °C) until the supernatant liquor is clear. Decant the clear
solution through a slow filtration ash-free filter. Wash the precipitate several times with hot water.
6

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SIST EN 15749:2023
EN 15749:2022 (E)
Continue to wash the precipitate on the filter until the filtrate is chloride free. This can be checked by
using a silver nitrate solution (6.1.4).
6.3.3 Incineration and weighing of the precipitate
Place the filter paper and precipitate in a porcelain crucible (6.2.1) previously weighed to the nearest
0,1 mg.
Dry in the oven (6.2.3) and ash at approximately 800 °C for approximately half an hour (6.2.4). Allow to
cool in a desiccator and weigh to 0,1 mg.
6.4 Calculation and expression of the result
1 mg of barium sulfate corresponds to 0,137 mg of sulfur or to 0,343 mg of SO .
3
Calculate the sulfates content expressed as sulfur, w , as mass fraction in percent of the fertilizer
S
according to Formula (1):
V
1
wm=××0,0137 (1)
S1
Vm×
22
where
m is the mass of the barium sulfate precipitate, in mg;
1
m is the mass of the test portion, in g;
2
V is the volume of the extraction solution, in ml;
1
V is the aliquot volume, in ml.
2
Calculate the SO content, w , as mass fraction in percent of the fertilizer according to Formula (2):
3 SO3
ww×2,5 (2)
SO3 S
7 Method B – ICP-OES method
7.1 Reagents
Use only reagents of recognized analytical grade.
Stock solutions shall be replaced after a maximum of one year, but the standard solution shall be freshly
prepared monthly as a minimum.
7.1.1 Water, conforming to grade 2 of EN ISO 3696:1995.
7.1.2 Hydrochloric acid, ρ approximately 1,18 g/ml.
7.1.3 Diluted hydrochloric acid.
Mix 40 ml of hydrochloric acid (7.1.2) in 1 l of water.
7
=

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SIST EN 15749:2023
EN 15749:2022 (E)
7.1.4 Sulfur stock solution, corresponding to 1 000 mg/l sulfur.
Dry in a pre-treatment step a sufficient quantity of sodium sulfate (Na SO ) at 105 °C for approximately
2 4
1 h in order to dispose of at least the necessary amount of dried sodium sulfate (Na SO ). Let cool in a
2 4
desiccator. Weigh to the nearest 0,1 mg, approximately 4,437 5 g of sodium sulfate (Na SO ). Dissolve the
2 4
weighted mass in a small quantity of water in volumetric flasks of nominal capacity of 1 000 ml, fill to the
mark with water.
The solution is stable for several months if stored at 4 °C to 6 °C.
Sulfur stock solution of 1 000 mg/l is also readily available commercially, and may be used instead.
7.2 Apparatus
Common laboratory equipment and glassware, and in particular the following.
7.2.1 Analytical balance, capable of weighing to an accuracy of 0,1 mg.
7.2.2 Inductively coupled plasma optical emission spectrometer.
Inductively coupled plasma optical emission spectrometer (ICP-OES) with radial viewing of the plasma
and simultaneous measurement of emission signals.
For measuring sulfur at wavelengths below 190 nm, the optical system shall be evacuated or be filled or
continuously flushed with an inert gas as recommended by the instrument manufacturer to obtain high
and stable signal intensities.
The instrument shall be equipped with radial plasma as a minimum requirement; axial plasma is equally
acceptable, as long as it can be shown that the results are statistically equal to the results obtained with
radial plasma. Background correction shall also be performed. Settings of the working conditions (e.g.
viewing height, gas flows, radio frequency or plasma power, sample uptake rate, integration time, number
of replicates) shall be optimized according to the manufacturer’s instructions.
7.3 Preparation of the extract
The sulfur is extracted from the sample according to one of the methods described in EN 15925,
EN 15926, EN 15960 or EN 15961.
7.4 Procedure
7.4.1 General
Calibration shall be performed by means of the standard addition technique. This method allows the
analysis of fertilizers with unknown matrix composition or with a matrix that cannot be synthetically
imitated easily.
7.4.2 Preparation of the test solution
Dilute the extraction solution with the diluted hydrochloric acid (7.1.3) to obtain a concentration between
10 mg/l and 150 mg/l of sulfur.
7.4.3 Preparation of the blank test solution
Carry out a blank test at the same time as the extraction, with only the reagents.
8

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SIST EN 15749:2023
EN 15749:2022 (E)
7.4.4 Preparation of the calibration solutions
The standard additions to the test solution, prior to the dilution step, should be about 20 %, 50 % and
100 % of the expected sulfur content. After the standard additions, dilute each of the samples with the
diluted hydrochloric acid (7.1.3).
A (external) calibration curve method can also be used instead of the standard addition method where
the analytical results are demonstrated to be statistically equal. Appropriate matrix matching of the
calibration solutions shall be performed if an (external) calibration method is used.
7.5 Determination
7.5.1 General
Set up the instrument (7.2.2) according to the manufacturer’s instructions using appropriate conditions,
and with the suitable background correction system in operation.
For each instrument used, selectivity, limits of detection and quantification, precision, linear working
area, and interference shall be established separately.
7.5.2 Determination by ICP-OES
The general analytical conditions for the sulfur determination by ICP-OES are listed in Table 1.
Aspirate the blank test solution (7.4.3), the test solution (7.4.2) and the various standard additions (7.4.4)
in ascending order separately into the plasma, and measure the emission of sulfur. Perform at least two
replicates and average the values if the values fall within an accepted range. After each measurement,
aspirate water or diluted hydrochloric acid (7.1.3).
The following special procedures can be used to obtain high precision and accuracy necessary to analyse
high sulfur contents in fertilizers:
a) optimized instrument settings;
b) simultaneous measurement of the signals of analyte and an appropriate internal standard element;
c) adjustment of the matrix of calibration solutions to the sample matrix;
d) consistent identical treatment of samples and calibration solutions during preparation and
measurement, or use gravimetric dilution instead of volumetric dilution;
e) correction of instrumental drift and background (if required).
Table 1 — General analytical conditions for sulfur determination by ICP-OES
181,978
Wavelength, nm
alternatives:

180,676

182,568

Yes
Background correction
Working range, mg/l 1 to 150
Possible internal standard: 202,030 nm
Molybdenum
281,615 nm
9

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SIST EN 15749:2023
EN 15749:2022 (E)
7.6 Calculation and expression of the results
7.6.1 Calculation
NOTE Net signal is defined as the number of counts per time unit at the selected wavelength, corrected for
background contributions.
In case of several standard additions, regression techniques on the linear model of variable y as a function
of variable x, shall be used to determine the sulfur concentration of the test solution. Generally, this model
can be written as:
y = a + b × x (3)
i i
In this particular case of three standard additions:
y = S (i = 0, 1, 2, 3) (4)
i i
x = ρ × V (i = 0, 1, 2, 3) (5)
i s i
where
ρ is the concentration, in mg/l, of the standard solution;
s
V are the various volumes, in l, of the standard solution added;
i
S are the net signals after the various standard additions.
i
Calculate the values of a and b as follows:
n×∑xy−∑x∑y
ii i i
b= (6)
2
2
nx×∑ − ∑x
( )
ii
∑y−b×∑x
ii
a= (7)
n
where
n is the number of solutions measured (n = 4 in case of three standard additions).
Calculate the sulfur concentration ρ , in mg/l, of the filtrate of the test portion using the following formula:
f
a
b
ρ = (8)
f
V
f
where
V is the volume, in l, of the filtrate of the test portion used to prepare the test solution.
f
10

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SIST EN 15749:2023
EN 15749:2022 (E)
7.6.2 Expression of the sulfur content in the sample
The sulfur content in the sample or mass fraction of sulfur, w , expressed in mg of sulfur per kg of
S
fertilizer, is determined using the following formula:
ρρ−
( )
f bl
wV× (9)
St
m
where
ρ is the concentration, in mg/l, of the filtrate of the test portion, as determined using
f
Formula (8);
ρ is the concentration, in mg/l, of the blank solution;
bl
m is the mass of sample, in kg, taken for the extraction, and corrected for water content;
V is the total volume, in l, of extract (filtrate of the test portion).
t
Sulfur contents of secondary nutrient fertilizers are to be expressed in the oxide form (SO ) or the
3
elemental form (S). As the results of the determination are expressed as sulfur (S), the following
conversion factor shall be used:
S = 0,400 × SO
3
8 Method C – IC method
8.1 Reagents
Use only reagents of recognized analytical grade.
Stock solutions shall be replaced after a maximum of one year, but the standard solution shall be renewed
monthly as a minimum.
8.1.1 Water, conforming to EN ISO 3696:1995, grade 2.
8.1.2 Hydrochloric acid, ρ approximately 1,18 g/ml.
8.1.3 Sulfate stock solution, corresponding to 1 000 mg/l SO .
4
Dry to constant weight in an oven at (150 ± 2) °C a sufficient quantity of anhydrous sodium sulfate
(Na SO ) in order to dispose of at least the necessary amount of dried product.
2 4
Allow to cool in a desiccator. Weigh to the nearest 0,1 mg, approximately 1,479 0 g of the dried sodium
sulfate (Na SO ). Dissolve and make up to the mark with water in a 1 000 ml volumetric flask.
2 4
The solution is stable for several months if stored at 4 °C to 6 °C.
Sulfate stock solution of 1 000 mg/l is also readily available commercially, and may be used instead.
.
8.1.4 Sulfate standard solution of 100 mg/l SO4
Prepare a tenfold dilution of
...

SLOVENSKI STANDARD
oSIST prEN 15749:2021
01-maj-2021
Gnojila - Določevanje sulfatov s tremi različnimi metodami
Fertilizers - Determination of sulfates content using three different methods
Düngemittel - Bestimmung von Sulfat mit drei verschiedenen Verfahren
Engrais - Dosage des sulfates selon trois méthodes différentes
Ta slovenski standard je istoveten z: prEN 15749
ICS:
65.080 Gnojila Fertilizers
oSIST prEN 15749:2021 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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oSIST prEN 15749:2021

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oSIST prEN 15749:2021


DRAFT
EUROPEAN STANDARD
prEN 15749
NORME EUROPÉENNE

EUROPÄISCHE NORM

May 2021
ICS 65.080 Will supersede EN 15749:2009
English Version

Fertilizers - Determination of sulfates content using three
different methods
Engrais - Dosage des sulfates selon trois méthodes Düngemittel - Bestimmung von Sulfat mit drei
différentes verschiedenen Verfahren
This draft European Standard is submitted to CEN members for enquiry. It has been drawn up by the Technical Committee
CEN/TC 260.

If this draft becomes a European Standard, 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.

This draft European Standard was established by CEN in three official versions (English, French, German). A version in any other
language made by translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC
Management Centre has the same status as the official versions.

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

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 supporting documentation.

Warning : This document is not a European Standard. It is distributed for review and comments. It is subject to change without
notice and shall not be referred to as a European Standard.


EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2021 CEN All rights of exploitation in any form and by any means reserved Ref. No. prEN 15749:2021 E
worldwide for CEN national Members.

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oSIST prEN 15749:2021
prEN 15749:2021 (E)
Contents Page
European foreword . 3
Introduction . 4
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Principle . 5
5 Sampling and sample preparation . 6
6 Method A – Gravimetric method . 6
7 Method B – ICP-OES method . 7
8 Method C – IC method . 11
9 Precision of methods A, B and C . 16
10 Test report . 18
Annex A (informative) Statistical results of the inter-laboratory tests. 19
Annex B (informative) Statistical results of the inter-laboratory tests of VDLUFA . 22
Annex C (informative) Statistical results of the inter-laboratory tests of Spanish Proficiency
Testing Program . 25
Bibliography . 27

2

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oSIST prEN 15749:2021
prEN 15749:2021 (E)
European foreword
This document (prEN 15749:2021) has been prepared by Technical Committee CEN/TC 260 “Fertilizers
and liming materials”, the secretariat of which is held by DIN.
This document is currently submitted to the CEN Enquiry.
This document will supersede EN 15479:2009.
In comparison with the previous edition, the following technical modifications have been made:
• update of the normative references;
• Formula 18 has been corrected;
• addition of more data as result of inter-laboratory tests, Annex B and Annex C.
3

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oSIST prEN 15749:2021
prEN 15749:2021 (E)
Introduction
This document specifies three different methods for the determination of sulfur. Based on the statistical
results of the inter-laboratory tests, obtained with the same samples, the three methods produce
equivalent results, and hence can be used all three methods on decision of the user and availability of
equipment.
4

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oSIST prEN 15749:2021
prEN 15749:2021 (E)
1 Scope
This document specifies three different methods (Methods A, B and C) for the determination of sulfur
present in fertilizers extracts in the form of sulfates. Method A specifies the gravimetric method.
Method B specifies the method using inductively coupled plasma optical spectrometry (ICP-OES).
Method C specifies the method using ion chromatography (IC).
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.
EN 1482-2, Fertilizers and liming materials — Sampling and sample preparation — Part 2: Sample
preparation
EN 12944-1, Fertilizers and liming materials and soil improvers — Vocabulary - Part 1: General terms
EN 12944-2, Fertilizers and liming materials and soil improvers — Vocabulary - Part 2: Terms relating to
fertilizers
EN 15925, Fertilizers — Extraction of total sulfur present in various forms
EN 15926, Fertilizers — Extraction of water soluble sulfur where the sulfur is in various forms
EN 15960, Fertilizers — Extraction of total calcium, total magnesium, total sodium and total sulfur in the
forms of sulfates
EN 15961, Fertilizers — Extraction of water-soluble calcium, magnesium, sodium and sulfur in the form of
sulfates
EN ISO 3696, Water for analytical laboratory use - Specification and test methods (ISO 3696)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in EN 12944-1 and EN 12944-2 apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
• IEC Electropedia: available at http://www.electropedia.org/
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4 Principle
4.1 Method A: Gravimetric method
Sulfur is extracted from the sample according to the methods described in EN 15925, EN 15926,
EN 15960 or EN 15961 and determined based on the gravimetric determination as barium sulfate.
4.2 Method B: ICP-OES
Sulfur is extracted from the sample according to the methods described in EN 15925, EN 15926,
EN 15960 or EN 15961 and its concentration in the extract is measured by inductively coupled plasma-
optical emission spectrometry (ICP-OES).
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4.3 Method C: IC
Sulfur is extracted from the fertilizer according to the methods described in EN 15925, EN 15926,
EN 15960 or EN 15961 in the form of sulfate. The sulfate concentration of the extract is measured by ion
chromatography (IC) equipped with a suppressor device and a conductivity detector.
5 Sampling and sample preparation
Sampling is not part of the methods specified in this document. A recommended sampling method is given
in EN 1482-1 [1].
Sample preparation shall be carried out in accordance with EN 1482-2.
6 Method A – Gravimetric method
6.1 Reagents
Use only reagents of recognized analytical grade and distilled or demineralized water (grade 3 according
to EN ISO 3696).
6.1.1 Diluted hydrochloric acid.
Mix one volume of mass concentration ρ(HCl) = 1,18 g/ml with one volume of water.
6.1.2 Barium chloride solution, ρ(BaCl .2 H O) = 122 g/l.
2 2
6.1.3 Silver nitrate solution, ρ = 5 g/l.
6.2 Apparatus
6.2.1 Porcelain crucibles.
6.2.2 Hot water bath.
6.2.3 Drying oven, set at (105 ± 1) °C.
6.2.4 Electric oven, set at (800 ± 50) °C.
6.3 Procedure
6.3.1 Sampling of the solution
Pipette an aliquot part of one of the extraction solutions containing between 20 mg and 100 mg of sulfur
or 50 mg and 250 mg of SO .
3
Place this aliquot in a beaker of suitable capacity. Add 20 ml of diluted hydrochloric acid (6.1.1). Make up
to about 300 ml with water.
6.3.2 Preparation of the precipitate
Bring the solution to the boil. Add, drop by drop, about 20 ml of the barium chloride solution (6.1.2) while
stirring the solution vigorously. Boil for a few minutes.
Place the beaker, covered with a watch glass, in a boiling hot water bath (6.2.2) for approximately 1 h.
Then leave standing hot (approximately 60 °C) until the supernatant liquor is clear. Decant the clear
solution through a slow filtration ash-free filter. Wash the precipitate several times with hot water.
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Continue to wash the precipitate on the filter until the filtrate is chloride free. This can be checked by
using a silver nitrate solution (6.1.3).
6.3.3 Incineration and weighing of the precipitate
Place the filter paper and precipitate in a porcelain crucible (6.2.1) previously weighed to the nearest
0,1 mg.
Dry in the oven (6.2.3) and ash at approximately 800 °C for approximately half an hour (6.2.4). Allow to
cool in a desiccator and weigh to 0,1 mg.
6.4 Calculation and expression of the result
1 mg of barium sulfate corresponds to 0,137 mg of sulfur or to 0,343 mg of SO .
3
Calculate the sulfates content expressed as sulfur, w , as mass fraction in percent of the fertilizer
S
according to Formula (1):
v
1
w=m××0,0137 (1)
S 1
vm×
22
where
m is the mass of the barium sulfate precipitate, in mg;
1
m is the mass of the test portion, in g;
2
v is the volume of the extraction solution, in ml;
1
v is the aliquot volume, in ml.
2
Calculate the SO content, w , as mass fraction in percent of the fertilizer according to Formula (2):
3 SO3
ww× 2,5 (2)
SO3 S
7 Method B – ICP-OES method
7.1 Reagents
Use only reagents of recognized analytical grade, and water conforming to grade 2 of EN ISO 3696.
Stock solutions shall be replaced after a maximum of one year, but the standard solution shall be freshly
prepared monthly as a minimum.
7.1.1 Hydrochloric acid, ρ approximately 1,18 g/ml.
7.1.2 Diluted hydrochloric acid.
Mix 40 ml of hydrochloric acid (7.1.1) in 1 l of water;
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7.1.3 Sulfur stock solution, corresponding to 1 000 mg/l sulfur.
Dry in a pre-treatment step a sufficient quantity of sodium sulfate (Na SO ) at 105 °C for approximately
2 4
1 h in order to dispose of at least the necessary amount of dried sodium sulfate (Na SO ). Let cool in a
2 4
desiccator. Weigh to the nearest 0,1 mg, approximately 4,437 5 g of sodium sulfate (Na SO ). Dissolve the
2 4
weighted mass in a small quantity of water in volumetric flasks of nominal capacity of 1 000 ml, fill to the
mark with water.
The solution is stable for several months if stored at 4 °C to 6 °C.
Sulfur stock solution of 1 000 mg/l is also readily available commercially, and may be used instead.
7.2 Apparatus
Common laboratory equipment and glassware, in particular equipment according to 7.2.1 to 7.2.2.
7.2.1 Analytical balance, capable of weighing to an accuracy of 0,1 mg.
7.2.2 Inductively coupled plasma optical emission spectrometer.
Inductively coupled plasma optical emission spectrometer (ICP-OES) with radial viewing of the plasma
and simultaneous measurement of emission signals.
For measuring sulfur at wavelengths below 190 nm the optical system shall be evacuated or be filled or
continuously flushed with an inert gas as recommended by the instrument manufacturer to obtain high
and stable signal intensities.
The instrument shall be equipped with radial plasma as a minimum requirement; axial plasma is equally
acceptable, as long as it can be shown that the results are statistically equal to the results obtained with
radial plasma. Background correction shall also be performed. Settings of the working conditions (e.g.
viewing height, gas flows, RF or plasma power, sample uptake rate, integration time, number of
replicates) shall be optimized according the manufacturer’s instructions.
7.3 Preparation of the extract
The sulfur is extracted from the sample according to one of the methods described in EN 15925,
EN 15926, EN 15960 or EN 15961.
7.4 Procedure
7.4.1 General
Calibration shall be performed by means of the standard addition technique. This method allows the
analysis of fertilizers with unknown matrix composition or with a matrix that cannot be synthetically
imitated easily.
7.4.2 Preparation of the test solution
Dilute the extraction solution with the diluted hydrochloric acid (7.1.2) to obtain a concentration between
10 mg/l and 150 mg/l of sulfur.
7.4.3 Preparation of the blank test solution
Carry out a blank test at the same time as the extraction, with only the reagents.
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7.4.4 Preparation of the calibration solutions
The additions to the test solution, prior to the dilution step, should be about 20 %, 50 % and 100 % of the
expected sulfur content. After the additions, dilute each of the samples with the diluted hydrochloric acid
(7.1.2).
A (external) calibration curve method can also be used instead of the standard addition method where
the analytical results are demonstrated to be statistically equal. Appropriate matrix matching of the
calibration solutions shall be performed if an (external) calibration method is used.
7.5 Determination
7.5.1 General
Set up the instrument (7.2.2) according to the manufacturer’s instructions using appropriate conditions,
and with the suitable background correction system in operation.
For each instrument used, selectivity, limits of detection and quantification, precision, linear working
area, and interference shall be established separately.
7.5.2 Determination by ICP-OES
The general analytical conditions for the sulfur determination by ICP-OES are listed in Table 1.
Aspirate the blank test solution (7.4.3), the test solution (7.4.2) and the various additions (7.4.4) in
ascending order separately into the plasma, and measure the emission of sulfur. Perform at least two
replicates and average the values if the values fall within an accepted range. After each measurement,
aspirate water or diluted hydrochloric acid (7.1.2).
The following special procedures can be used to obtain high precision and accuracy necessary to analyse
high sulfur contents in fertilizers:
a) optimized instrument settings;
b) simultaneous measurement of the signals of analyte and an appropriate internal standard element;
c) adjustment of the matrix of calibration solutions to the sample matrix;
d) consistent identical treatment of samples and calibration solutions during preparation and
measurement, or use gravimetric dilution instead of volumetric dilution;
e) correction of instrumental drift and background (if required).
Table 1 — General analytical conditions for sulfur determination by ICP-OES
181,978
Wavelength, nm
alternatives:

180,676

182,568

Yes
Background correction
Working range, mg/l 1 to 150
Possible internal standard: 202,030 nm
Molybdenum
281,615 nm
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7.6 Calculation and expression of the results
7.6.1 Calculation
NOTE Net signal is defined as the number of counts per time unit at the selected wavelength, corrected for
background contributions.
In case of several additions, regression techniques on the linear model of variable y as a function of
variable x, shall be used to determine the sulfur concentration of the test solution. Generally, this model
can be written as:
y = a + b × x (3)
i i
In this particular case of three standard additions:
y = S (i = 0, 1, 2, 3) (4)
i i
x = ρ × V (i = 0, 1, 2, 3) (5)
i s i
where
ρ is the concentration, in mg/l, of the standard solution;
s
V are the various volumes, in l, of the standard solution added;
i
S are the net signals after the various additions.
i
Calculate the values of a and b as follows:
n ×∑xy − ∑x∑y
ii i i
b= (6)
2
2
nx ×∑ − ∑x
( )
ii
∑yb −  ×∑x
i i
(7)
a=
n
where
n is the number of solutions measured (n = 4 in case of three additions).
Calculate the sulfur concentration ρ, in mg/l, of the filtrate of the test portion using the following
f
equation:
a
b
ρ = (8)
f
V
f
where
V is the volume, in l, of the filtrate of the test portion used to prepare the test solution.
f
7.6.2 Expression of the sulfur content in the sample
The sulfur content in the sample or mass fraction of sulfur, w , expressed in mg of sulfur per kg of
S
fertilizer, is determined using the following equation:
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ρρ −
( )
f bl
wV× (9)
St
m
where
ρ is the concentration, in mg/l, of the filtrate of the test portion, as determined using
f
Formula (8);
ρ is the concentration, in mg/l, of the blank solution;
bl
m is the mass of sample, in kg, taken for the extraction, and corrected for water content;
V is the total volume, in l, of extract (filtrate of the test portion).
t
Sulfur contents of secondary nutrient fertilizers are to be expressed in the oxide form (SO ) or the
3
elemental form (S). As the results of the determination are expressed as sulfur (S), the following
conversion factor shall be used:
S = 0,400 × SO
3
8 Method C – IC method
8.1 Reagents
Use only reagents of recognized analytical grade.
Stock solutions shall be replaced after a maximum of one year, but the standard solution shall be renewed
monthly as a minimum.
8.1.1 Water, conforming to EN ISO 3696, grade 2.
8.1.2 Hydrochloric acid, ρ approximately 1,18 g/ml.
8.1.3 Sulfate stock solution, corresponding to 1 000 mg/l SO .
4
Dry to constant weight in an oven at (150 ± 2) °C a sufficient quantity of anhydrous sodium sulfate
(Na SO ) in order to dispose of at least the necessary amount of dried product.
2 4
Allow to cool in a desiccator. Weigh to the nearest 0,1 mg, approximately 1,479 0 g of the dried sodium
sulfate (Na SO ). Dissolve and make up to the mark with water in a 1 000 ml volumetric flask.
2 4
The solution is stable for several months if stored at 4 °C to 6 °C.
NOTE Sulfate stock solution of 1 000 mg/l is also readily available commercially, and can be used instead.
8.1.4 Sulfate standard solution of 100 mg/l SO .
4
Prepare a tenfold
...

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