SIST-TS CEN/TS 16318:2012
(Main)Fertilizers - Determination of trace elements - Determination of chromium(VI) by photometry (method A) and by ion chromatography with spectrophotometric detection (method B)
Fertilizers - Determination of trace elements - Determination of chromium(VI) by photometry (method A) and by ion chromatography with spectrophotometric detection (method B)
This document specifies two methods for the determination of the content of soluble chromate in fertilizers.
Method A specifies the determination of chromate after extraction with water by photometry. This method can be used to determine Cr(VI)-mass fractions in solids higher than 1 mg/kg.
Method B specifies the determination of chromate by alkaline digestion and ion chromatography with spectrophotometric detection. This method can be used to determine Cr(VI)-mass fractions in solids higher than 0,1 mg/kg.
NOTE In case of reducing or oxidizing fertilizer matrix, no valid Cr(VI) content can be reported.
Düngemittel und Calcium-/Magnesium-Bodenverbesserungsmittel - Bestimmung von Elementspuren - Bestimmung von Chrom(VI) mit Photometrie (Verfahren A) und mit Ionenchromatographie mit spektrometrischer Detektion (Verfahren B)
Diese Technische Spezifikation legt zwei Verfahren zur Bestimmung des Gehalts an löslichem Chromat in Düngemitteln fest. Verfahren A legt die Bestimmung von Chromat nach Extraktion mit Wasser durch Photometrie fest. Dieses Verfahren ist anwendbar für die Bestimmung von Chrom(VI)-Massenanteilen von mehr als 1 mg/kg in Feststoffen. Verfahren B legt die Bestimmung von Chromat durch alkalischen Aufschluss und Ionenchromatographie mit spektrometrischer Detektion fest. Dieses Verfahren ist anwendbar für die Bestimmung von Chrom(VI)-Massenanteilen von mehr als 0,1 mg/kg in Feststoffen. ANMERKUNG Bei Vorliegen einer reduzierenden oder oxidierenden Düngemittelmatrix kann der Chrom(VI)-Gehalt nicht zuverlässig ermittelt werden.
Engrais - Dosage des éléments traces - Dosage du chrome (VI) par spectrophotométrie (méthode A) et chromatographie ionique avec détection spectrophotométrique (méthode B)
Cette spécification technique spécifie deux méthodes de détermination de la teneur en chromate soluble dans
les engrais.
La méthode A présente la détermination du chromate après extraction avec de l’eau par spectrophotométrie.
Cette méthode peut être utilisée afin de déterminer les fractions massiques de Cr(VI) supérieures à 1 mg/kg
dans les solides.
La méthode B présente la détermination du chromate par digestion alcaline et chromatographie ionique avec
détection spectrophotométrique. Cette méthode peut être utilisée afin de déterminer les fractions massiques
de Cr(VI) supérieures à 0,1 mg/kg dans les solides.
NOTE En cas de matrice d’engrais oxydante ou réductrice, aucune teneur en Cr(VI) valide ne peut être énoncée.
Gnojila - Določevanje elementov v sledovih - Določevanje kroma (VI) s fotometrijo (metoda A) in z ionsko kromatografijo s spektrofotometrijsko detekcijo (metoda B)
Ta dokument določa dve metodi za določevanje vsebnosti topnega kromata v gnojilih.
Metoda A določa določevanje kromata po vodni ekstrakciji s fotometrijo. Ta metoda se lahko uporablja za določevanje masnih deležev Cr(VI), višjih od 1 mg/kg, v trdnih snoveh.
Metoda B določa določevanje kromata z alkalnim razklopom in ionsko kromatografijo s spektrofotometrijsko detekcijo. Ta metoda se lahko uporablja za določevanje masnih deležev Cr(VI), višjih od 0,1 mg/kg, v trdnih snoveh.
OPOMBA: V primeru zmanjšanja ali oksidacije matrice gnojila ni mogoče poročati o veljavni vsebnosti Cr(VI).
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
SIST-TS CEN/TS 16318:2012
01-junij-2012
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PHWRGD$ LQ]LRQVNRNURPDWRJUDILMRVVSHNWURIRWRPHWULMVNRGHWHNFLMR PHWRGD%
Fertilizers - Determination of trace elements - Determination of chromium(VI) by
photometry (method A) and by ion chromatography with spectrophotometric detection
(method B)
Düngemittel und Calcium-/Magnesium-Bodenverbesserungsmittel - Bestimmung von
Elementspuren - Bestimmung von Chrom(VI) mit Photometrie (Verfahren A) und mit
Ionenchromatographie mit spektrometrischer Detektion (Verfahren B)
Engrais - Dosage des éléments traces - Dosage du chrome (VI) par spectrophotométrie
(méthode A) et chromatographie ionique avec détection spectrophotométrique (méthode
B)
Ta slovenski standard je istoveten z: CEN/TS 16318:2012
ICS:
65.080 Gnojila Fertilizers
SIST-TS CEN/TS 16318:2012 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST-TS CEN/TS 16318:2012
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SIST-TS CEN/TS 16318:2012
TECHNICAL SPECIFICATION
CEN/TS 16318
SPÉCIFICATION TECHNIQUE
TECHNISCHE SPEZIFIKATION
April 2012
ICS 65.080
English Version
Fertilizers - Determination of trace elements - Determination of
chromium(VI) by photometry (method A) and by ion
chromatography with spectrophotometric detection (method B)
Engrais - Dosage des éléments traces - Dosage du chrome Düngemittel - Bestimmung von Elementspuren -
(VI) par spectrophotométrie (méthode A) et Bestimmung von Chrom(VI) mit Photometrie (Verfahren A)
chromatographie ionique avec détection und mit Ionenchromatographie mit spektrometrischer
spectrophotométrique (méthode B) Detektion (Verfahren B)
This Technical Specification (CEN/TS) was approved by CEN on 30 January 2012 for provisional application.
The period of validity of this CEN/TS is limited initially to three years. After two years the members of CEN will be requested to submit their
comments, particularly on the question whether the CEN/TS can be converted into a European Standard.
CEN members are required to announce the existence of this CEN/TS in the same way as for an EN and to make the CEN/TS available
promptly at national level in an appropriate form. It is permissible to keep conflicting national standards in force (in parallel to the CEN/TS)
until the final decision about the possible conversion of the CEN/TS into an EN is reached.
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, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2012 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TS 16318:2012: E
worldwide for CEN national Members.
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SIST-TS CEN/TS 16318:2012
CEN/TS 16318:2012 (E)
Contents Page
Foreword .3
1 Scope .4
2 Normative references .4
3 Terms and definitions .4
4 Sampling and sample preparation .4
5 Method A: Determination by water extraction and spectrophotometric detection .5
6 Method B: Determination by alkaline digestion and ion chromatography with
spectrophotometric detection .8
7 Precision . 15
8 Test report . 15
Bibliography . 16
2
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SIST-TS CEN/TS 16318:2012
CEN/TS 16318:2012 (E)
Foreword
This document (CEN/TS 16318:2012) has been prepared by Technical Committee CEN/TC 260 “Fertilizers
and liming materials”, the secretariat of which is held by DIN.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.
This document has been prepared under a mandate given to CEN by the European Commission and the
European Free Trade Association.
According to the CEN/CENELEC Internal Regulations, the national standards organisations of the following
countries are bound to announce this Technical Specification: 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, Romania, Slovakia, Slovenia,
Spain, Sweden, Switzerland, Turkey and the United Kingdom.
3
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SIST-TS CEN/TS 16318:2012
CEN/TS 16318:2012 (E)
1 Scope
This Technical Specification specifies two methods for the determination of the content of soluble chromate in
fertilisers.
Method A specifies the determination of chromate after extraction with water by photometry. This method can
be used to determine Cr(VI)-mass fractions in solids higher than 1 mg/kg.
Method B specifies the determination of chromate by alkaline digestion and ion chromatography with
spectrophotometric detection. This method can be used to determine Cr(VI)-mass fractions in solids higher
than 0,1 mg/kg.
NOTE In case of reducing or oxidising fertiliser matrix, no valid Cr(VI) content can be reported.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. 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 12944-1:1999, Fertilizers and liming materials and soil improvers — Vocabulary — Part 1: General terms
EN 12944-2:1999, Fertilizers and liming materials and soil improvers — Vocabulary — Part 2: Terms relating
to fertilizers
EN 15192:2006, Characterisation of waste and soil — Determination of Chromium(VI) in solid material by
alkaline digestion and ion chromatography with spectrophotometric detection
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 12944-1:1999 and EN 12944-2:1999
apply.
4 Sampling and sample preparation
Sampling is not part of the methods specified in this Technical Specification. A recommended sampling
method is given in EN 1482-1.
Sample preparation shall be carried out in accordance with EN 1482-2.
Reasonable precautions have to be taken to prevent oxidation of chromate present in the sample. Samples
shall be taken using appropriate devices and placed in containers that do not contain stainless steel
(e.g. plastic, glass).
After digestion, the sample shall be analysed as soon as possible.
4
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SIST-TS CEN/TS 16318:2012
CEN/TS 16318:2012 (E)
5 Method A: Determination by water extraction and spectrophotometric detection
5.1 Principle
Chromate is extracted from the sample with water at room temperature. The chromate concentration in the
extract is measured by colorimetry using 1,5-diphenylcarbazide.
When chromate reduces the 1,5-diphenylcarbazide a magenta coloured complex of 1,5-diphenylcarbazone
and chromium is formed which can be measured colorimetrically at 540 nm.
5.2 Reagents
Use only reagents of recognised analytical grade and water conforming to 5.2.1.
-1
5.2.1 Water, according to EN ISO 3696, grade 2 (electrical conductivity max. 0,1 mS × m equivalent to
resistivity greater than 0,01 MΩ⋅m at 25 °C).
It is recommended that the water used is obtained from a purification system that delivers ultrapure water
having a resistivity greater than 0,18 MΩ⋅m.
5.2.2 Hydrochloric acid, c(HCl) = 12 mol/l; 37 % volume fraction, ρ ≈ 1,18 g/ml.
5.2.3 Hydrochloric acid, diluted, c(HCl) approximately 6 mol/l.
Mix equal volumes of hydrochloric acid (5.2.2) and water (5.2.1).
5.2.4 Diphenylcarbazide solution.
Dissolve 1,0 g Diphenylcarbazide [CO(NHNHC H ) ] in 100 ml acetone and add one drop of acetic acid. If this
6 5 2
solution is stored in a glass bottle in the dark at 4 °C, it may be used for approximately two weeks. This
solution shall be clear without colour. If the diphenylcarbazide solution has become coloured it shall be
discarded and freshly prepared before use.
5.2.5 Chromate standard stock solution, ρ(chromate) = 1 000 mg/l.
Dissolve 2 829 mg potassium dichromate (K Cr O ) in 1 000 ml water (5.2.1) using a volumetric flask. This
2 2 7
solution may be used for two weeks if stored in the dark at 4 °C.
5.2.6 Chromate standard stock solution, ρ(chromate) = 50 mg/l.
Dilute 5 ml chromate stock solution (5.2.5) to 100 ml with water (5.2.1) using a volumetric flask. This solution
shall be freshly prepared on the day of use.
5.2.7 Standard solutions.
Prepare the standard solutions by diluting aliquots of the 50 mg/l chromate standard stock solution (5.2.6) with
water (5.2.1) in 100 ml volumetric flasks. The aliquots and final concentrations of chromate are given in
Table 1. Other volumes and concentrations may be used for the preparation of standard solutions if
appropriate. See 5.4.3 for further instructions on how to prepare the standard solutions.
5
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SIST-TS CEN/TS 16318:2012
CEN/TS 16318:2012 (E)
Table 1 — Aliquots and final concentrations for the preparation of chromate standards from a 50 mg/l
chromate standard stock solution in 100-ml volumetric flasks
Aliquot Final concentration of chromate
ml mg/l
0 0 (calibration blank)
0,05 0,025
0,20 0,10
0,50 0,25
1,00 0,50
1,50 0,75
A blank solution shall be prepared in a separate volumetric flask by adding water (5.2.1) only.
The standard solutions shall be prepared freshly on the day of use.
5.3 Apparatus
5.3.1 Common laboratory glassware.
5.3.2 Analytical balance, capable of weighing to an accuracy of 1 mg.
5.3.3 Membrane filters and vacuum filtration apparatus.
The filters should be made of cellulose nitrate, pore size 5 µm and fit into the vacuum filtration apparatus.
5.3.4 Mechanical shaker.
5.3.5 Pipettes and/or dilutor, pipettes with fixed or variable volume and volumetric glassware to perform
dilutions.
Alternatively a dilutor may be used, which is an instrument used for automated volumetric dilutions. The
precision and accuracy of this equipment for volumetric dilutions shall be proved, controlled, and documented
regularly.
5.3.6 Spectrophotometer, capable to measure transmitted light at 540 nm.
5.3.7 100 ml bottles, made from PE or PP, equipped with watertight caps.
5.4 Procedure
5.4.1 Preparation of the test solution
Weigh approximately 10 g, to the nearest 0,01 g, of the prepared sample and transfer to a suitable extraction
vessel (5.3.7).
Add 40 ml of water (5.2.1). If the sample material (e.g. organic material) absorbs a high amount of water, add
additionally water (5.2.1) to obtain a fluid suspension. Record the amount of additional water added. It may be
necessary to use larger extraction vessels in such cases. Close the cap tightly and shake vigorously for
15 min on a mechanical shaker (5.3.4). Filter the suspension immediately through membrane filters with 5 µm
pore size using the vacuum filtration apparatus (5.3.3).
6
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SIST-TS CEN/TS 16318:2012
CEN/TS 16318:2012 (E)
Pipette 20 ml of the test solution to a 100 ml volumetric flask and continue immediately with the colorimetric
measurement. If the test solution shows a yellow colour, the aliquot should be reduced to minimise
interferences by the colour of organic substances.
The test solution may not be stored. The chromate content shall be analysed on the day of preparation.
5.4.2 Preparation of the blank test solution
Carry out a blank test at the same time as the extraction, with only the reagents and follow the same
procedure as for the samples.
5.4.3 Spectrophotometric measurement
Add approximately 40 ml of water (5.2.1) to all volumetric flasks containing the standard solutions (5.2.7), the
blank test solution (5.4.2) and the sample test solutions (5.4.1). Then add 2 ml diluted hydrochloric acid
(5.2.3). The pH-value of the resulting solution should be between pH 1 and pH 2. Add more diluted
hydrochloric acid (5.2.3) if the pH-value is higher until a pH-value between pH 1 and pH 2 is reached.
Add 2 ml diphenylcarbazide solution (5.2.4) to each volumetric flask and fill up to the mark with water (5.2.1).
Wait 15 min and measure the extinction of the solutions on a spectrophotometer at 540 nm.
5.5 Calculation and expression of the results
5.5.1 Calibration
In the case of a linear calibration curve, the calibration function can be described according to Formula (1).
S = c × b + a (1)
where
S is the net signal for Cr(VI) in a solution;
c is the concentration of Cr(VI) in this solution, in milligrams per litre or in micrograms per litre;
b is the slope of the linear calibration function;
a is the intersection of the linear calibration function.
Calculate the analyte concentration, c , in the filtrate of the test portion using the slope b and the intersection a
f
according to Formula (2):
S − a
f
c = (2)
f
b
where
S is the net signal of the test solution.
f
5.5.2 Calculation of the element content in the sample
Calculate the analyte concentration in the sample or the mass fraction of the analyte, w , expressed in
E
milligrams of analyte per kilogram of fertiliser according to Formula (3).
()c − c
f bl
w = ×V ×1000 (3)
E t
m
7
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SIST-TS CEN/TS 16318:2012
CEN/TS 16318:2012 (E)
where
c is the concentration, in milligrams per litre, of the filtrate of the test portion, as determined according
f
to Formula (2);
c is the concentration, in milligrams per litre, of the blank solution;
bl
m is the mass of the sample, in grams, taken for the extraction, and corrected for water content;
V is the total volume, in litres, of water added to the test portion for extraction.
t
6 Method B: Determination by alkaline digestion and ion chromatography with
spectrophotometric detection
6.1 Principle
6.1.1 Digestion
Cr(VI) is digested from the sample by an alkaline solution.
To quantify the content of Cr(VI) in a solid matrix, the following three criteria shall be satisfied:
1) the digestion solution shall solubilise all species of Cr(VI);
2) the conditions of the digestion shall not induce reduction of native Cr(VI) to Cr(III);
3) the method shall not cause oxidation of native Cr(III) contained in the sample to Cr(VI).
The alkaline digestion described in this document meets these criteria for a wide spectrum of solid matrices.
Under the alkaline conditions, neglect able reduction of Cr(VI) or oxidation of native Cr(III) is expected. The
2+
addition of Mg in a phosphate buffer to the alkaline solution prevents air oxidation of trivalent chromium (see
[7], [8] and [9]).
NOTE Background on methods for the determination of Cr(VI) in solid samples is given in EN 15192:2006, Annex D
and [10], [11], [8].
6.1.2 Determination
The quantification of Cr(VI) in the alkaline digestion solution should be performed using a suitable technique
with appropriate accuracy. For this purpose, ion chromatography is used to separate Cr(VI) from
interferences.
Following this ion chromatographic separation, Cr(VI) is measured spectrophotometrically either at 365 nm
(direct UV detection) or after post-column derivatisation with 1,5-diphenylcarbazide in acid solution at 540 nm.
Post-column derivatisation involves reaction of 1,5-diphenylcarbazide with Cr(VI) to produce trivalent
chromium and diphenylcarbazone. These then combine to form a trivalent chromium-diphenylcarbazone
complex containing the characteristic magenta chromagen (λ = 540 nm).
max
NOTE 1 The choice of detection method is based upon the required sensitivity. Direct UV detection is less sensitive
than detection after post-column derivatisation with 1,5-diphenylcarbazide.
NOTE 2 Hyphenated methods with ion chromatographic separation and detection techniques, such as inductively
coupled plasma-mass spectrometry (ICP-MS) or inductively coupled plasma-atomic emission spectroscopy (ICP-AES),
may be used once validation of the chosen analytical method has been performed.
8
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SIST-TS CEN/TS 16318:2012
CEN/TS 16318:2012 (E)
6.1.3 Interferences and sources of error
Use of ion chromatography is necessary for the separation of Cr(VI) from possible interferences in the alkaline
digestion solution from solid material [12] (see also EN 15192:2006, D.3).
For waste materials or soils, where the Cr(III)/Cr(VI) ratio is expected to be high, Cr(VI) results may be biased
due to method-induced oxidation. This can be particularly expected in soils high in Mn content and amended
with soluble Cr(III) salts or freshly precipitated Cr(OH) [10] (see also EN 15192:2006, D.2).
3
Cr(VI) can be reduced to Cr(III) during digestion from the sample due to reaction with reducing agents such as
e.g. divalent iron. This problem is minimised in the described procedure using alkaline digestion solution [8]
(see also EN 15192:2006, D.2).
Cr(III) can be oxidised to Cr(VI) in hot alkaline solutions. This problem is minimised in the described procedure
by adding magnesium to the alkaline digestion solution [8], [9], [10], [13] (see also EN 15192:2006, D.2).
Overloading the analytical column capacity with high concentrations of anionic species (e.g. chloride) may
cause underestimation of Cr(VI) [6].
6.2 Reagents
Use only reagents of recognised analytical grade, and water as specified in 6.2.1.
-1
6.2.1 Water, a
...
SLOVENSKI STANDARD
kSIST-TS FprCEN/TS 16318:2011
01-november-2011
*QRMLOD'RORþHYDQMHHOHPHQWRYYVOHGRYLK'RORþHYDQMHNURPD 9, VIRWRPHWULMR
PHWRGD$ LQ]LRQVNRNURPDWRJUDILMRVVSHNWURIRWRPHUWLMVNRGHWHNFLMR PHWRGD%
Fertilizers - Determination of trace elements - Determination of chromium(VI) by
photometry (method A) and by ion chromatography with spectrophotometric detection
(method B)
Düngemittel und Calcium-/Magnesium-Bodenverbesserungsmittel - Bestimmung von
Elementspuren - Bestimmung von Chrom(VI) mit Photometrie (Verfahren A) und mit
Ionenchromatographie mit spektrometrischer Detektion (Verfahren B)
Engrais - Dosage des éléments traces - Dosage du chrome (VI) par spectrophotométrie
(méthode A) et chromatographie ionique avec détection spectrophotométrique (méthode
B)
Ta slovenski standard je istoveten z: FprCEN/TS 16318
ICS:
65.080 Gnojila Fertilizers
kSIST-TS FprCEN/TS 16318:2011 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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kSIST-TS FprCEN/TS 16318:2011
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kSIST-TS FprCEN/TS 16318:2011
TECHNICAL SPECIFICATION
FINAL DRAFT
FprCEN/TS 16318
SPÉCIFICATION TECHNIQUE
TECHNISCHE SPEZIFIKATION
September 2011
ICS 65.080
English Version
Fertilizers - Determination of trace elements - Determination of
chromium(VI) by photometry (method A) and by ion
chromatography with spectrophotometric detection (method B)
Engrais - Dosage des éléments traces - Dosage du chrome Düngemittel - Bestimmung von Elementspuren -
(VI) par spectrophotométrie (méthode A) et
Bestimmung von Chrom(VI) mit Photometrie (Verfahren A)
chromatographie ionique avec détection und mit Ionenchromatographie mit spektrometrischer
spectrophotométrique (méthode B) Detektion (Verfahren B)
This draft Technical Specification is submitted to CEN members for formal vote. It has been drawn up by the Technical Committee CEN/TC
260.
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, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland 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 Technical Specification. It is distributed for review and comments. It is subject to change without notice
and shall not be referred to as a Technical Specification.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2011 CEN All rights of exploitation in any form and by any means reserved Ref. No. FprCEN/TS 16318:2011: E
worldwide for CEN national Members.
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kSIST-TS FprCEN/TS 16318:2011
FprCEN/TS 16318:2011 (E)
Contents Page
Foreword .3
1 Scope .4
2 Normative references .4
3 Terms and definitions .4
4 Sampling and sample preparation .4
5 Method A: Determination by water extraction and spectrophotometric detection .5
6 Method B: Determination by alkaline digestion and ion chromatography with
spectrophotometric detection .8
7 Precision . 15
8 Test report . 15
Bibliography . 16
2
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kSIST-TS FprCEN/TS 16318:2011
FprCEN/TS 16318:2011 (E)
Foreword
This document (FprCEN/TS 16318:2011) 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 Formal Vote.
This document has been prepared under a mandate given to CEN by the European Commission and the
European Free Trade Association.
3
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kSIST-TS FprCEN/TS 16318:2011
FprCEN/TS 16318:2011 (E)
1 Scope
This document specifies two methods for the determination of the content of soluble chromate in fertilizers.
Method A specifies the determination of chromate after extraction with water by photometry. This method can
be used to determine Cr(VI)-mass fractions in solids higher than 1 mg/kg.
Method B specifies the determination of chromate by alkaline digestion and ion chromatography with
spectrophotometric detection. This method can be used to determine Cr(VI)-mass fractions in solids higher
than 0,1 mg/kg.
NOTE In case of reducing or oxidizing fertilizer matrix, no valid Cr(VI) content can be reported.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
EN 1482-2, Fertilizers and liming materials — Sampling and sample preparation — Part 2: Sample
preparation
EN 12944-1:1999, Fertilizers and liming materials and soil improvers — Vocabulary — Part 1: General terms
EN 12944-2:1999, Fertilizers and liming materials and soil improvers — Vocabulary — Part 2: Terms relating
to fertilizers
EN 15192:2006, Characterisation of waste and soil — Determination of Chromium(VI) in solid material by
alkaline digestion and ion chromatography with spectrophotometric detection
EN ISO 3696, 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 12944-1:1999 and EN 12944-2:1999
apply.
4 Sampling and sample preparation
Sampling is not part of the methods specified in this Technical Specification. A recommended sampling
method is given in EN 1482-1 [2].
Sample preparation shall be carried out in accordance with EN 1482-2.
Reasonable precautions have to be taken to prevent oxidation of chromate present in the sample. Samples
shall be taken using appropriate devices and placed in containers that do not contain stainless steel (e.g.
plastic, glass).
After digestion, the sample shall be analysed as soon as possible.
4
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kSIST-TS FprCEN/TS 16318:2011
FprCEN/TS 16318:2011 (E)
5 Method A: Determination by water extraction and spectrophotometric detection
5.1 Principle
Chromate is extracted from the sample with water at room temperature. The chromate concentration in the
extract is measured by colorimetry using 1,5-diphenylcarbazide.
When chromate reduces the 1,5-diphenylcarbazide a magenta coloured complex of 1,5-diphenylcarbazone
and chromium is formed which can be measured colorimetrically at 540 nm.
5.2 Reagents
Use only reagents of recognized analytical grade and water conforming to 5.2.1.
5.2.1 Water, conforming to grade 2 of EN ISO 3696.
5.2.2 Hydrochloric acid, c(HCl) = 12 mol/l; 37 % mass/volume, ρ ≈ 1,18 g/ml.
5.2.3 Hydrochloric acid, diluted, c(HCl) approximately 6 mol/l.
Mix equal volumes of hydrochloric acid (5.2.2) and water (5.2.1).
5.2.4 Diphenylcarbazide solution.
Dissolve 1,0 g Diphenycarbazide [CO(NHNHC H ) ] in 100 ml acetone and add one drop of acetic acid. If this
6 5 2
solution is stored in a glass bottle in the dark at 4 °C, it may be used for approximately two weeks. This
solution shall be clear without colour. If the diphenylcarbazide solution has become coloured it shall be
discarded and freshly prepared before use.
5.2.5 Chromate standard stock solution, ρ(chromate) = 1 000 mg/l.
Dissolve 2829 mg potassium dichromate (K Cr O ) in 1 000 ml water (5.2.1) using a volumetric flask. This
2 2 7
solution may be used for two weeks if stored in the dark at 4 °C.
5.2.6 Chromate standard stock solution, ρ(chromate) = 50 mg/l.
Dilute 5 ml chromate stock solution (5.2.5) to 100 ml with water using a volumetric flask. This solution shall be
freshly prepared on the day of use.
5.2.7 Standard solutions.
Prepare the standard solutions by diluting aliquots of the 50 mg/l chromate standard stock solution (5.2.6) with
water in 100 mg/l volumetric flasks. The aliquots and final concentrations of chromate are given in Table 1.
Other volumes and concentrations may be used for the preparation of standard solutions if appropriate.
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Table 1 — Aliquots and final concentrations for the preparation of chromate standards from a 50 mg/l
chromate standard stock solution in 100-ml volumetric flasks
Aliquot Final concentration of chromate
ml mg/l
0 0 (calibration blank)
0,05 0,025
0,20 0,10
0,50 0,25
1,00 0,50
1,50 0,75
A blank solution shall be prepared in a separate volumetric flask by adding water only.
The standard solutions shall be prepared freshly on the day of use.
5.3 Apparatus
5.3.1 Common laboratory glassware.
5.3.2 Analytical balance, capable of weighing to an accuracy of 1 mg.
5.3.3 Membrane filters and vacuum filtration apparatus.
The filters should be made of cellulose nitrate, pore size 5 µm and fit into the vacuum filtration apparatus.
5.3.4 Mechanical shaker.
5.3.5 Pipettes and/or dilutor.
Pipettes with fixed or variable volume and volumetric glassware to perform dilutions. Alternatively a dilutor
may be used, which is an instrument used for automated volumetric dilutions. The precision and accuracy of
this equipment for volumetric dilutions shall be proved, controlled, and documented regularly.
5.3.6 Spectrophotometer, capable to measure transmitted light at 540 nm and equipped with measuring
cells of various dimensions (20 mm, 50 mm).
5.3.7 100 ml bottles, made from PE or PP, equipped with watertight caps.
5.4 Procedure
5.4.1 Preparation of the test solution
Weigh approximately 10 g, to the nearest 0,01 g, of the prepared sample and transfer to a suitable extraction
vessel (5.3.7).
Add 40 ml of water (5.2.1). If the sample material (e.g. organic material) absorbs a high amount of water, add
additionally water to obtain a fluid suspension. It may be necessary to use larger extraction vessels in such
cases. Close the cap tightly and shake vigorously for 15 min on a mechanical shaker (5.3.4). Filter the
suspension immediately through membrane filters with 5 µm pore size using the vacuum filtration apparatus
(5.3.3).
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Pipette 20 ml of the test solution to a 100 ml volumetric flask and continue immediately with the colorimetric
measurement. If the test solution shows a yellow colour, the aliquot should be reduced to minimise
interferences by the colour of organic substances.
The test solution may not be stored. The chromate content shall be analysed on the day of preparation.
5.4.2 Preparation of the blank test solution
Carry out a blank test at the same time as the extraction, with only the reagents and follow the same
procedure as for the samples.
5.4.3 Spectrophotometric measurement
Add approximately 40 ml of water to all volumetric flasks containing the standard solutions (5.2.7), the blank
test solution (5.4.2) and the sample test solutions (5.4.1). Then add 2 ml diluted hydrochloric acid (5.2.3). The
pH-value of the resulting solution should be between pH 1 and pH 2. Add more diluted hydrochloric acid
(5.2.3) if the pH-value is higher until a pH-value between pH 1 and pH 2 is reached.
Add 2 ml diphenylcarbazide solution (5.2.4) to each volumetric flask and fill up to the mark with water. Wait
15 min and measure the extinction of the solutions on a spectrophotometer at 540 nm.
5.5 Calculation and expression of the results
5.5.1 Calibration
In the case of a linear calibration curve, the calibration function can be described as follows.
S = c × b + a (1)
where
S is the net signal for Cr(VI) in a solution;
c is the concentration of Cr(VI) in this solution, in milligrams per litre or in micrograms per litre;
b is the slope of the linear calibration function;
a is the intersection of the linear calibration function.
Calculate the analyte concentration c in the filtrate of the test portion using the slope b and the intersection a
f
found in Equation (1) as follows.
S − a
f
c = (2)
f
b
where
S is the net signal of the test solution.
f
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5.5.2 Calculation of the element content in the sample
Calculate the analyte concentration in the sample or the mass fraction of the analyte, w , expressed in
E
milligrams of analyte per kilogram of fertilizer using Equation (3).
()c − c
f bl
w = ×V (3)
E t
m
where
c is the concentration, in micrograms per litre or in milligrams per litre, of the filtrate of the test portion,
f
as determined using Equation (2);
c is the concentration, in milligrams per litre, of the blank solution;
bl
m is the mass of the sample, in kilograms, taken for the extraction, and corrected for water content;
V is the total volume, in litres, of extract (filtrate of the test portion).
t
6 Method B: Determination by alkaline digestion and ion chromatography with
spectrophotometric detection
6.1 Principle
6.1.1 Digestion
Cr(VI) is digested from the sample by an alkaline solution.
To quantify the content of Cr(VI) in a solid matrix, the following three criteria shall be satisfied:
1) the digestion solution shall solubilise all species of Cr(VI);
2) the conditions of the digestion shall not induce reduction of native Cr(VI) to Cr(III);
3) the method shall not cause oxidation of native Cr(III) contained in the sample to Cr(VI).
The alkaline digestion described in this document meets these criteria for a wide spectrum of solid matrices.
Under the alkaline conditions, neglect able reduction of Cr(VI) or oxidation of native Cr(III) is expected. The
2+
addition of Mg in a phosphate buffer to the alkaline solution prevents air oxidation of trivalent chromium [7],
[8], [9].
NOTE Background on methods for the determination of Cr(VI) in solid samples is given in EN 15192:2006, Annex D
and [10], [11], [8].
6.1.2 Determination
The quantification of Cr(VI) in the alkaline digestion solution should be performed using a suitable technique
with appropriate accuracy. For this purpose, ion chromatography is used to separate Cr(VI) from
interferences.
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Following this ion chromatographic separation, Cr(VI) is measured spectrophotometrically either at 365 nm
(direct UV detection) or after post-column derivatisation with 1,5-diphenylcarbazide in acid solution at 540 nm.
Post-column derivatisation involves reaction of 1,5-diphenylcarbazide with Cr(VI) to produce trivalent
chromium and diphenylcarbazone. These then combine to form a trivalent chromium-diphenylcarbazone
complex containing the characteristic magenta chromagen (λ = 540 nm).
max
NOTE 1 The choice of detection method is based upon the required sensitivity. Direct UV detection is less sensitive
than detection after post-column derivatisation with 1,5-diphenylcarbazide.
NOTE 2 Hyphenated methods with ion chromatographic separation and detection techniques, such as inductively
coupled plasma-mass spectrometry (ICP-MS) or inductively coupled plasma-atomic emission spectroscopy (ICP-AES),
may be used once validation of the chosen analytical method has been performed.
6.1.3 Interferences and sources of error
Use of ion chromatography is necessary for the separation of Cr(VI) from possible interferences in the alkaline
digestion solution from solid material [12] (see also EN 15192:2006, D.3).
For waste materials or soils, where the Cr(III)/Cr(VI) ratio is expected to be high, Cr(VI) results may be biased
due to method-induced oxidation. This can be particularly expected in soils high in Mn content and amended
with soluble Cr(III) salts or freshly precipitated Cr(OH) [10] (see also EN 15192:2006, D.2).
3
Cr(VI) can be reduced to Cr(III) during digestion from the sample due to reaction with reducing agents such as
e.g. divalent iron. This problem is minimised in the described procedure using alkaline digestion solution [8]
(see also EN 15192:2006, D.2).
Cr(III) can be oxidised to Cr(VI) in hot alkaline solutions. This problem is minimised in the described procedure
by adding magnesium to the alkaline digestion solution [8], [9], [10], [13] (see also EN 15192:2006, D.2).
Overloading the analytical column capacity with high concentrations of anionic species (e.g. chloride) may
cause underestimation of Cr(VI) [6].
6.2 Reagents
Use only reagents of recognised analytical grade, and water as specified in 6.2.1.
-1
6.2.1 Water, according to EN ISO 3696, grade 2 (electrical conductivity less than 0,1 mS × m equivalent to
resistivity greater than 0,01 MΩ m at 25 °C).
It is recommended that the water used is obtained from a purification system that delivers ultrapure water
having a resistivity greater than 0,18 MΩ m (usually expressed by manufacturers of water purification systems
as 18 MΩ cm).
6.2.2 Sulfuric acid, concentrated, ρ(H SO ) ~ 1,84 g/ml, w(H SO ) ~ 98 %.
2 4 2 4
6.2.3 Sodium carbonate, anhydrous, w(Na CO ) > 99,9 %.
2 3
6.2.4 1,5-Diphenylcarbazide, w((C H .NH.NH) CO) > 98 %.
6 5 2
6.2.5 Acetone.
6.2.6 Methanol.
...
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