SIST EN 17547:2022
(Main)Animal feeding stuffs: Methods of sampling and analysis - Determination of vitamin A, E and D content - Method using solid phase extraction (SPE) clean-up and high-performance liquid chromatography (HPLC)
Animal feeding stuffs: Methods of sampling and analysis - Determination of vitamin A, E and D content - Method using solid phase extraction (SPE) clean-up and high-performance liquid chromatography (HPLC)
This European Standard specifies a method for the determination of the content of the total vitamin A (retinol), vitamin E (alpha-tocopherol) and vitamin D (D2 ergocalciferol or D3 cholecalciferol) content in animal feed using solid phase extraction (SPE) clean-up and high performance liquid chromatography (HPLC).
The limit of quantification is XXXX IU vitamin A/kg (using UV-detection), XX IU vitamin A/kg (using fluorescence detection), XX mg vitamin E/kg (using UV-detection), XX mg vitamin E/kg (using
fluorescence detection), XX IU vitamin D/kg (using UV-detection) and XX IU vitamin D/kg (using fluorescence detection).
Futtermittel - Probenahme- und Untersuchungsverfahren - Bestimmung des Gehalts an Vitamin A, E und D - Verfahren mittels Reinigung durch Festphasenextraktion und Hochleistungs-Flüssigchromatographie
Dieses Dokument legt ein Verfahren zur Bestimmung des Gesamtgehalts an Vitamin A (Retinol), Vitamin E (α-Tocopherol) und Vitamin D3 (Cholecalciferol) in Futtermitteln mittels Reinigung durch Festphasenextraktion (SPE; en: solid phase extraction) und Hochleistungs-Flüssigchromatographie (HPLC, en: high performance liquid chromatography) fest.
ANMERKUNG 1 Das Verfahren ermöglicht auch die Bestimmung von Vitamin D2, jedoch unter Verwendung eines anderen internen Standards. Das Verfahren ist nur für Vitamin D3 vollständig validiert.
Das Verfahren wurde in einem Ringversuch für Alleinfuttermittel für Hähnchen, Schweine und Puten, für Vormischungen für Hähnchen und für Ferkel, für Ergänzungsfuttermittel für Kühe sowie für mineralische Futtermittel innerhalb folgender Bereiche erfolgreich geprüft:
— Vitamin A: 4 365 IE/kg – 4 118 352 IE/kg;
— Vitamin E: 22 mg/kg – 13 800 mg/kg
— Vitamin D3: 1 668 IE/kg – 1 638 150 IE/kg.
Üblicherweise sollten Bestimmungsgrenzen von 1 100 IE für Vitamin A/kg (mittels UV-Detektion), 4 mg für Vitamin E/kg (mittels UV-Detektion), 2 mg für Vitamin E/kg (mittels Fluoreszenzdetektion) und 2 000 IE für Vitamin D/kg (mittels UV-Detektion) erreicht werden.
ANMERKUNG 2 Die Bestimmungsgrenzen sind Mindestgrenzen, die nicht im Rahmen der Validierungsstudie bestimmt wurden. Niedrigere Bestimmungsgrenzen sind möglich, müssen jedoch vom Anwender validiert werden.
Aliments des animaux - Méthodes d'échantillonnage et d'analyse - Détermination de la teneur en vitamines A, E et D - Méthode utilisant la purification par extraction en phase solide (SPE) et la chromatographie liquide à haute performance (CLHP)
Le présent document spécifie une méthode de détermination de la teneur totale en vitamine A (rétinol), vitamine E (α-tocophérol) et vitamine D3 (cholécalciférol) dans les aliments pour animaux à l’aide d’une purification par extraction en phase solide (SPE) et d’une chromatographie liquide à haute performance (CLHP).
NOTE 1 Le mode opératoire permet également de déterminer la teneur en vitamine D2 mais en utilisant un autre étalon interne. La méthode est intégralement validée pour la vitamine D3 uniquement.
La méthode a été soumise à essai avec succès lors d’un essai interlaboratoires effectué sur un aliment complet pour poulets, porcs et dindes, sur un prémélange pour poulets et porcelets, sur un aliment complémentaire pour vaches ainsi que sur un aliment minéral dans les gammes suivantes :
vitamine A : 4 365 UI/kg – 4 118 352 UI/kg ;
vitamine E : 22 mg/kg – 13 800 mg/kg ;
vitamine D3 : 1 668 UI/kg – 1 638 150 UI/kg.
Il convient normalement d’atteindre des limites de quantification de 1 100 UI/kg pour la vitamine A (par détection UV), 4 mg/kg pour la vitamine E (par détection UV), 2 mg/kg pour la vitamine E (par détection fluorimétrique) et 2 000 UI/kg pour la vitamine D (par détection UV).
NOTE 2 Les limites de quantification sont les limites minimales qui n’ont pas été déterminées lors de l’étude de validation. Des limites de quantification inférieures peuvent être obtenues, à condition qu'elles soient validées par l'utilisateur.
Krma: metode vzorčenja in analize - Določevanje vitaminov A, E in D - Metoda z ekstrakcijo na trdno fazo (SPE) in tekočinsko kromatografijo visoke ločljivosti (HPLC)
Ta evropski standard določa metodo za določevanje vsebnosti vitamina A (retinol), vitamina E (alfa tokoferol) in vitamina D (D2 ergokalciferol ali D3 holekalciferol) v krmi z ekstrakcijo na trdno fazo (SPE) in tekočinsko kromatografijo visoke ločljivosti (HPLC).
Mejne vrednosti kvantifikacije so: XXXX IU vitamina A/kg (z detekcijo UV), XX IU vitamina A/kg (s fluorescenčno detekcijo), XX mg vitamina E/kg (z detekcijo UV), XX mg vitamina E/kg (s
fluorescenčno detekcijo), XX IU vitamina D/kg (z detekcijo UV) in XX IU vitamina D/kg (s fluorescenčno detekcijo).
General Information
Standards Content (Sample)
SLOVENSKI STANDARD
SIST EN 17547:2022
01-januar-2022
Krma: metode vzorčenja in analize - Določevanje vitaminov A, E in D - Metoda z
ekstrakcijo na trdno fazo (SPE) in tekočinsko kromatografijo visoke ločljivosti
(HPLC)
Animal feeding stuffs: Methods of sampling and analysis - Determination of vitamin A, E
and D content - Method using solid phase extraction (SPE) clean-up and high-
performance liquid chromatography (HPLC)
Futtermittel - Probenahme- und Untersuchungsverfahren - Bestimmung des Gehalts an
Vitamin A, E und D - Verfahren mittels Reinigung durch Festphasenextraktion und
Hochleistungs-Flüssigchromatographie
Aliments des animaux - Méthodes d'échantillonnage et d'analyse - Détermination de la
teneur en vitamines A, E et D - Méthode utilisant la purification par extraction en phase
solide (SPE) et la chromatographie liquide à haute performance (CLHP)
Ta slovenski standard je istoveten z: EN 17547:2021
ICS:
65.120 Krmila Animal feeding stuffs
SIST EN 17547:2022 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST EN 17547:2022
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SIST EN 17547:2022
EN 17547
EUROPEAN STANDARD
NORME EUROPÉENNE
November 2021
EUROPÄISCHE NORM
ICS 65.120
English Version
Animal feeding stuffs: Methods of sampling and analysis -
Determination of vitamin A, E and D content - Method
using solid phase extraction (SPE) clean-up and high-
performance liquid chromatography (HPLC)
Aliments des animaux - Méthodes d'échantillonnage et Futtermittel - Probenahme- und
d'analyse - Détermination de la teneur en vitamines A, Untersuchungsverfahren - Bestimmung des Gehalts an
E et D - Méthode utilisant la purification par extraction Vitamin A, E und D - Verfahren mittels Reinigung durch
en phase solide (SPE) et la chromatographie liquide à Festphasenextraktion und Hochleistungs-
haute performance (CLHP) Flüssigchromatographie
This European Standard was approved by CEN on 27 September 2021.
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, Turkey 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
© 2021 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 17547:2021 E
worldwide for CEN national Members.
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Contents Page
European foreword . 3
Introduction . 4
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Principle . 6
5 Reagents and materials . 8
6 Apparatus . 9
7 Sampling . 10
8 Sample preparation . 11
9 Procedure . 11
10 Expression of results . 21
11 Observations . 24
12 Precision . 25
13 Test report . 26
Annex A (informative) Examples of combinations of weighing, aliquot and dilution to reach
concentrations within the calibration curve . 27
Annex B (informative) Preparation of stock standard solution of vitamin E (α-tocopherol)
from α-tocopherol acetate . 30
B.1 General. 30
B.2 Reagents . 30
B.3 Preparation of stock standard . 30
B.4 Standardization of the vitamin E (α-tocopherol) stock standard solution in
cyclohexane . 30
B.5 Calibration solutions and plotting of calibration graph for vitamins A (retinol) and E
(α-tocopherol) . 31
Annex C (informative) Results of the interlaboratory study . 32
Bibliography . 37
2
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European foreword
This document (EN 17547:2021) has been prepared by Technical Committee CEN/TC 327 “Animal
feeding stuffs - Methods of sampling and analysis”, the secretariat of which is held by NEN.
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 May 2022, and conflicting national standards shall be
withdrawn at the latest by May 2022.
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 has been prepared under a Standardization Request given to CEN by the European
Commission and the European Free Trade Association.
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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Introduction
WARNING — The method described in this document implies the use of reagents that pose a hazard to
health. The standard does not claim to address all associated safety problems. It is the responsibility of
the user of this document to take appropriate measures for the health and safety protection of the
personnel prior to use of the standard and to ensure that regulatory and legal requirements are complied
with.
4
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1 Scope
This document specifies a method for the determination of the content of the total vitamin A (retinol),
vitamin E (α-tocopherol) and vitamin D (cholecalciferol) in animal feed using solid phase extraction
3
(SPE) clean-up and high-performance liquid chromatography (HPLC).
NOTE The procedure also enables determination of vitamin D2 but with the use of another internal standard.
The method is fully validated only for vitamin D .
3
The method has been successfully tested in collaborative trial for complete feed for broilers, pigs, and
turkey, for premixture for broilers and piglets, for complementary feed for cows and mineral feed within
the following ranges:
• vitamin A: 4 365 IU/kg – 4 118 352 IU/kg;
• vitamin E: 22 mg/kg – 13 800 mg/kg;
• vitamin D : 1 668 IU/kg – 1 638 150 IU/kg.
3
The limits of quantification were not determined within the validation study. Quantification limits of
1 100 IU for vitamin A/kg (using UV-detection), 4 mg for vitamin E/kg (using UV-detection), 2 mg for
vitamin E/kg (using fluorescence detection) and 2 000 IU for vitamin D/kg (using UV-detection) should
be normally achieved. Lower limits are possible provided they are validated by the user.
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 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 following terms and definitions 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
3.1
vitamin A content
retinol
content of all-trans- and cis-isomers of retinol determined in accordance with this document
Note 1 to entry: The vitamin A (retinol) content is expressed in International Units per kilogram (IU/kg).
Note 2 to entry: 1 IU of vitamin A (retinol) is equal to 0,300 µg of all-trans-retinol or 0,344 µg all-trans-retinol
acetate or 0,546 µg all-trans-retinol palmitate or 0,359 µg all-trans-retinol propionate.
5
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3.2
vitamin E content
α-tocopherol
content of α-tocopherol determined in accordance with this document
Note 1 to entry: The content of vitamin E (α-tocopherol) can be also expressed as mg α-tocopherol acetate per kg.
Note 2 to entry: 1 mg vitamin E (α-tocopherol acetate) corresponds to 0,91 mg vitamin E (α-tocopherol).
Note 3 to entry: In samples can also be present β-, γ-, δ-tocopherol and α-, β-, γ-, δ-tocotrienol. This method uses
reverse phase separation which does not separate individual forms of tocopherol. Therefore, the content of
vitamin E expressed as α-tocopherol or α-tocopherol acetate includes all forms without taking into account
differences in vitamin activities and the respective proportions of each form. Using a normal phase-column the
separation of α-, β-, γ- and δ-tocopherol is possible (see observation 11.6).
3.3
vitamin D content
3
cholecalciferol
the content of cholecalciferol determined in accordance with this document
Note 1 to entry: The content of vitamin D3 is expressed in International Units per kg (IU/kg). 1 IU corresponds to
an activity of 0,025 µg vitamin D (cholecalciferol).
3
Note 2 to entry: For feeding stuffs, only vitamin D3 is authorized as feed additive pursuant to Regulation
(EC) No 1831/2003 [1]. Addition of vitamin D2 is not allowed. Therefore, the vitamin D2 can be used as internal
standard.
Note 3 to entry: For accurate calculation of the results it is important that the sample does not contain any other
vitamin D2 than that added as internal standard.
4 Principle
The sample is saponified with ethanolic potassium hydroxide solution. In case that vitamin D
3
(cholecalciferol) is to be determined the internal standard is added before saponification. The vitamins
are extracted and purified by SPE column eluting with cyclohexane. The cyclohexane is removed by
evaporation and the residue is dissolved in methanol (for determination of vitamin A (retinol) and
vitamin E (α-tocopherol)) or in n-hexane (for determination of vitamin D (cholecalciferol)).
3
The vitamin A (retinol) and vitamin E (α-tocopherol) concentrations in the methanolic extract are
determined by reversed-phase liquid chromatography using external calibration and HPLC conditions
that give a single peak for all retinol isomers as well as for all tocopherols.
The n-hexane extract for vitamin D determination is purified by semi-preparative normal-phase HPLC
3
on silica gel. The purified extract is separated by reversed phase HPLC using conditions that give a
baseline separation between the vitamin D and vitamin D . Quantification of vitamin D is performed by
2 3 3
external standard calibration taking into account the recovery of the internal standard.
NOTE Figure 1 contains a flowchart for the determination of vitamins A, D and E.
6
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Figure 1 — Flowchart for the determination of vitamins A, D and E
7
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5 Reagents and materials
Use only reagents of recognized analytical grade.
5.1 Water, complying with at least grade 3 in accordance with EN ISO 3696:1995.
5.2 Potassium hydroxide (KOH), w ≈ 850 g/kg.
5.3 Ethanol (C H OH), w = 950 ml/l, or equivalent industrial methylated spirit (ethanol denatured by
2 5
methanol or hexane).
5.4 Ascorbic acid (C H O ).
6 8 6
5.5 Ascorbic acid, solution, ρ = 200 g/l.
5.6 Sodium sulfide (Na S ⋅ 9 H O).
2 2
5.7 Sodium sulfide, alkali solution (see 11.1 observations).
Dissolve 2 000 g of potassium hydroxide (5.2) in 1 200 ml of water (5.1) until as much as possible of KOH
is dissolved. In parallel dissolve 224 g of sodium sulfide (5.6) in 800 ml of water (5.1) in ultrasonic bath.
Mix both solutions together and stir the mixture until the potassium hydroxide (5.2) is dissolved
completely.
5.8 2,6-Di-tert-butyl-4-methylphenol (BHT), (see 11.2 observations).
5.9 Inert gas, e.g. nitrogen.
5.10 Methanol (CH OH), HPLC grade.
3
5.11 Ethanol (CH CH OH), HPLC grade.
3 2
5.12 Cyclohexane (C H ), HPLC grade.
6 12
5.13 2-Propanol (C H OH), HPLC grade.
3 7
5.14 n-Hexane (C H ), HPLC grade.
6 14
5.15 Mobile phase for semi-preparative HPLC-clean up of vitamin D .
3
Mixture of n-hexane (5.14) and propanol (5.13) in the proportions e.g. 980 + 20 (by volume). The ratio of
the mixture must be adapted to the HPLC-column employed. If necessary, filter through a membrane filter
(6.8).
5.16 Mobile phase for analytical HPLC.
Mix together methanol (5.10) and water (5.1) in the proportions 980 + 20 (by volume). The exact ratio
will be determined by the characteristics of the column employed. The use of other mobile phase
composition is allowed provided the separation of vitamins according the scope of this document is
possible. If necessary, filter through a membrane filter (6.8).
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5.17 Vitamin A standard substances.
5.17.1 All-trans-retinol acetate (C H O ), CAS = 127-47-9, MW = 328,49 g/mol, extra pure, of
22 32 2
6
certified activity, e.g. 2,80 × 10 IU/g.
5.17.2 All-trans-retinol palmitate (C H O ), CAS = 79-81-2, MW = 524,86 g/mol, extra pure, of
36 60 2
6
certified activity, e.g. 1,80 × 10 IU/g.
5.18 Vitamin E standard substance.
5.18.1 DL-α-tocopherol (C H O ), CAS = 10191-41-0, MW = 430,72 g/mol, extra pure, of certified
29 50 2
purity.
5.19 Vitamin D standard substances.
5.19.1 Vitamin D (ergocalciferol; C H O), CAS = 50-14-6, MW = 384,62 g/mol, extra pure, of certified
2 28 44
6
activity, e.g. 40 × 10 IU/g.
5.19.2 Vitamin D (cholecalciferol; C H O), CAS = 67-97-0; MW = 384,62 g/mol, extra pure, of certified
3 27 44
6
activity, e.g. 40 × 10 IU/g.
5.20 Celite for SPE column
Base material coarse-grained kieselguhr (also known as diatomaceous earth, hydromatrix, celite);
particle size: max. 10 % < 100 μm, max. 90 % < 500 μm, max. 5 % > 800 μm; large pore size, high pore
volume, constantly high batch-to-batch quality.
6 Apparatus
Usual laboratory equipment and, in particular, the following:
6.1 Boiling water bath with magnetic stirrer or electrical heating device with stirring (for hot
saponification).
6.2 Overhead rotating shaker (for cold saponification).
6.3 Amber glassware (see observation 11.3).
6.3.1 Flat bottom - or conical flasks, 250 ml and 500 ml, with ground-glass socket.
6.3.2 Allihn condenser, jacket length 300 mm, with ground-glass joint, with adapter for gas feed pipe.
6.3.3 Graduated flasks with ground-glass stoppers, narrow-necked, 20 ml, 25 ml, 50 ml and 100 ml.
6.3.4 Pear shaped flask with ground-glass stoppers, 100 ml.
6.4 Vials, suitable for sample concentrator.
1
6.5 Column for SPE, filled with celite (e.g. Chromabond XTR , 70 ml volume) which is able to adsorb
the water phase from the saponification solution (9.4.2) and release the vitamins A, E and D completely
1
Chromabond XTR is an example of a suitable product available commercially. This information is given for the
convenience of users of this document and does not constitute an endorsement by CEN of this product.
9
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by elution with organic solvents. The column shall have a capacity of not less than 20 ml aqueous solution
and possibly closed by a valve at the outlet.
6.6 Rotary vacuum evaporator, with water bath at 40 °C.
6.7 Sample nitrogen concentrator, heated to 50 °C.
2
6.8 Membrane filter, compatible with methanol, 0,45 μm pore size; e.g. Chromafil PET - 45/15 MS or
suitable filter with smaller pore size.
6.9 Syringe filter, with a Nylon or PVDF membrane, 0,2 μm (or 0,45 µm) pore size or equivalent, i.e.
fully chemical compatibility with methanol and adaptable on 2-5ml syringes .
6.10 HPLC system semi-preparative, for the clean-up of vitamin D, consisting of:
6.10.1 HPLC pump, set to deliver a constant eluent volume flow rate of e.g. 2,5 ml/min.
6.10.2 HPLC injection device, injection volume of 500 µl.
6.10.3 HPLC semi-preparative normal phase column with guard column (see 9.7.2).
6.10.4 Column oven, set to provide a constant column temperature.
6.10.5 UV-Detector
6.11 HPLC-system for analytical separation, consisting of the following:
6.11.1 HPLC-pump, set to deliver a constant eluent volume flow rate of e.g. 1 ml/min.
6.11.2 HPLC injection devices, injection volume of 20 µl and 100 µl.
6.11.3 HPLC reversed-phase column, with guard column (see 9.8.1).
6.11.4 Column oven, set to provide a constant column temperature.
6.11.5 Detectors for UV- and fluorescent detection.
6.11.6 Integrator / data handling system.
6.12 UV (or UV-Visible) spectrophotometer, capable of measuring absorbance at the wavelengths
defined in 9.2.1.4, 9.2.2.4 and 9.2.3.5, equipped with cells of 10 mm path length.
7 Sampling
It is important that the laboratory receive a sample which is truly representative and has not been
damaged or changed during transport or storage. Sampling is not part of the method specified in this
document. A recommended sampling method is given in EN ISO 6497 [2].
Store the sample in such a way that deterioration and change in its composition are prevented.
2
Chromafil PET is an example of a suitable product available commercially. This information is given for the
convenience of users of this document and does not constitute an endorsement by CEN of this product.
10
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8 Sample preparation
Samples are grinded at the day of analysis as recommended in the guidelines for sample preparation as
in EN ISO 6498.
Grind a representative portion of the dry laboratory sample so that it passes through a sieve with 1 mm
apertures. Prevent to heat up.
Grinding of sample(s) with adequate particle size distribution (e.g. premixtures and concentrates) may
not be necessary if homogeneity is ensured.
Semi-moist pet foods (canned pet foods) can be homogenized by mincing.
Samples can be ground before the day of analysis. In this case the storage conditions must prevent any
degradation, e.g. freeze the ground sample and defrost it in a fridge a night before analysis.
9 Procedure
9.1 General
Because of the sensitivity of vitamin A, E and D to UV radiation and air, perform all operations away from
natural and strong fluorescent light and as rapidly as is consistent with accurate working. Use amber
glassware (6.3) where possible (see observation 11.3).
9.2 Preparation and standardization of standard solutions
9.2.1 Vitamin A (retinol)
9.2.1.1 General
For preparation of vitamin A (retinol) standard solutions use all-trans-retinol acetate (5.17.1) or all-
trans-retinol palmitate (5.17.2).
NOTE Standard substance of retinol itself is less stable then retinol palmitate or retinol acetate and therefor it
is usual to use these esters for preparation of standard solution of vitamin A. Nevertheless, use of standard
substance retinol is also possible.
9.2.1.2 Stock standard solution of vitamin A (retinol)
Weigh to the nearest 0,1 mg an amount of vitamin A (retinol acetate) (5.17.1) or vitamin A (retinol
palmitate) (5.17.2) containing approximately 100 000 IU of vitamin A (retinol) into a 250 ml flat bottom
or conical flask (6.3.1) and continue with saponification according to 9.4.2.1 or 9.4.2.2 and extraction
according to 9.5.
Collect the eluate from the SPE column (6.5) in a 100 ml graduated flask (6.3.3) and fill up to the mark
with cyclohexane (5.12).
The nominal concentration of stock standard solution of vitamin A (retinol) in cyclohexane is
approximately 75 IU per ml.
The exact content has to be calculated from exact concentration of working standard solution of vitamin
A (retinol) (9.2.1.3) determined according to 9.2.1.4.
The stock standard solution of vitamin A (retinol) is stable for 6 months in dark at 4°C and can be used
for preparation of working standard solution according to 9.2.1.2 during this period.
9.2.1.3 Working standard solution of retinol
Pipette 10,0 ml of the vitamin A (retinol) stock standard solution (9.2.1.2) into a 100 ml graduated flask
and fill up to the mark with cyclohexane (5.12).
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The nominal concentration of the working standard solution is 7,5 IU vitamin A (retinol) per ml.
The exact concentration of vitamin A (retinol) in working standard solution has to be determined
according to 9.2.1.4.
The working standard solution of vitamin A (retinol) is stable for at least 2 months in dark at 4°C but the
real concentration shall be checked before use.
9.2.1.4 Standardization of the vitamin A (retinol) working standard solution (9.2.1.3)
The exact concentration of vitamin A (retinol) in working standard solution (9.2.1.3) is determined by
spectrometric measurement. Measure the UV spectrum of this solution against cyclohexane (5.12) in the
spectrophotometer (6.12) at the absorption maximum between 325 nm and 327 nm.
The vitamin A (retinol) concentration can be calculated with Formula (1).
33 333××AA33 333
wSTD wSTD
CA19,212× (1)
A wSTD
A 1 735
325
where
C is the vitamin A (retinol) concentration, in IU/ml;
A
33 333 is the concentration of vitamin A (retinol) corresponding to 10000 µg/ml, in IU/ml;
A is the absorbance of working standard solution (9.2.1.3);
wSTD
A is the absorption coefficient of vitamin A (retinol) in cyclohexane at 325 nm.
325
1%
NOTE The absorption coefficient of vitamin A (retinol) in cyclohexane A at 325 nm is 1 735, i.e.
1cm
33 333 IU/ml provide absorbance 1 735, so the absorbance of 7,5 IU/ml is 0,3904.
9.2.2 Vitamin E (α-tocopherol)
9.2.2.1 General
For preparation of vitamin E (α-tocopherol) standard solutions use DL-α-tocopherol (5.18.1).
NOTE It is also possible to use as standard DL-α-tocopherol acetate, see Annex B. Preparation from DL-α-
tocopherol is preferable because in this case is not necessary to apply saponificantion.
9.2.2.2 Stock standard solution of vitamin E (α-tocopherol)
Weigh 50 mg of vitamin E (DL-α-tocopherol) (5.18.1) to the nearest 0,1 mg, into a 100 ml graduated flask
(6.3.3). Dissolve in ethanol (5.11) and make up to the mark with the same solvent.
The nominal concentration of this solution is 500 μg vitamin E (α-tocopherol) per ml.
The exact concentration of vitamin E (α-tocopherol) in stock standard solution (9.2.2.2) has to be
calculated from exact concentration of working standard solution of vitamin E (α-tocopherol) (9.2.2.3).
The stock standard solution of vitamin E (α-tocopherol) in ethanol is stable at least for six months in dark
at 4 °C and can be used for preparation of working standard solution according to 9.2.2.3 during this
period.
9.2.2.3 Working standard solution of vitamin E (α-tocopherol) in ethanol
Pipette 10,0 ml of the vitamin E (α-tocopherol) stock standard solution (9.2.2.2) into a 100 ml graduated
flask and fill up to the mark with ethanol (5.11).
The nominal concentration of the working standard solution is 50 μg vitamin E (α-tocopherol) per ml.
12
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The exact concentration of vitamin E (α-tocopherol) in working standard solution has to be determined
according to 9.2.2.4.
The working standard solution of vitamin E (α-tocopherol) is stable for at least 2 months in dark at 4 °C
but the real concentration shall be checked before use.
9.2.2.4 Standardization of the vitamin E (α-tocopherol) working standard solution in ethanol
(9.2.2.3)
The exact concentration of vitamin E (α-tocopherol) in working standard solution (9.2.2.3) is determined
by spectrometric measurement absorbance of working standard solution (9.2.2.3) in ethanol (5.11).
Measure the UV spectrum of this solution against ethanol (5.11) in the spectrophotometer (6.12) at the
absorption maximum between 250 nm and 320 nm. The absorption maximum shall be at 292 nm for
ethanol (5.11).
The vitamin E (α-tocopherol) content in ethanol (5.11) can be calculated with Formula (2).
10 000× A
wSTD
C 131, 9× A (2)
E wSTD
A
292
where
C is the vitamin E concentration in ethanol (5.11), in μg/ml;
E
10 000 is the concentration of vitamin E (α-tocopherol) corresponding to 10000 µg/ml, in μg/ml;
A is the absorbance of working standard solution (9.2.2.3);
wSTD
A is the absorption coefficient of vitamin E (α-tocopherol) in ethanol at 292 nm.
292
1%
NOTE The absorption coefficient of vitamin E (α-tocopherol) in ethanol (5.11) at 292 nm A is 75,8, i.e.
1cm
1 000 mg/100 ml provide absorbance 75,8, so the absorbance of 50 µg/ml is 0,379.
9.2.3 Vitamin D
9.2.3.1 Stock internal standard solution of vitamin D (ergocalciferol)
2
Weigh 50 mg vitamin D (ergocalciferol) (5.19.1) to the nearest 0,1 mg into a 100 ml graduated flask
2
(6.3.3), dissolve it in ethanol (5.11) and fill up to 100 ml with ethanol (5.11).
Nominal concentration of this solution is 20 000 IU of vitamin D (ergocalciferol) per ml.
2
The exact content of vitamin D (ergocalciferol) in stock internal standard solution has to be determined
2
according to 9.2.3.5.
The stock internal solution of vitamin D (ergocalciferol) is stable for at leas
...
SLOVENSKI STANDARD
oSIST prEN 17547:2020
01-oktober-2020
Krma: metode vzorčenja in analize - Določevanje vitaminov A, E in D - Metoda z
ekstrakcijo na trdno fazo in tekočinsko kromatografijo visoke ločljivosti
Animal feeding stuffs: Methods of sampling and analysis - Determination of vitamin A, E
and D content - Method using solid phase extraction clean-up and High Performance
Liquid Chromatography
Futtermittel - Probenahme- und Untersuchungsverfahren - Bestimmung des Gehalts an
Vitamin A, E und D - Verfahren mittels Reinigung durch Festphasenextraktion und
Hochleistungs-Flüssigchromatographie
Aliments des animaux - Méthodes d'échantillonnage et d'analyse - Détermination de la
teneur en vitamines A, E et D - Méthode utilisant la purification par extraction en phase
solide et la chromatographie liquide à haute performance
Ta slovenski standard je istoveten z: prEN 17547
ICS:
65.120 Krmila Animal feeding stuffs
oSIST prEN 17547:2020 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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oSIST prEN 17547:2020
DRAFT
EUROPEAN STANDARD
prEN 17547
NORME EUROPÉENNE
EUROPÄISCHE NORM
August 2020
ICS 65.120
English Version
Animal feeding stuffs: Methods of sampling and analysis -
Determination of vitamin A, E and D content - Method
using solid phase extraction clean-up and High
Performance Liquid Chromatography
Aliments des animaux - Méthodes d'échantillonnage et Futtermittel - Probenahme- und
d'analyse - Détermination de la teneur en vitamines A, Untersuchungsverfahren - Bestimmung des Gehalts an
E et D - Méthode utilisant la purification par extraction Vitamin A, E und D - Verfahren mittels Reinigung durch
en phase solide et la chromatographie liquide à haute Festphasenextraktion und Hochleistungs-
performance Flüssigchromatographie
This draft European Standard is submitted to CEN members for enquiry. It has been drawn up by the Technical Committee
CEN/TC 327.
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
© 2020 CEN All rights of exploitation in any form and by any means reserved Ref. No. prEN 17547:2020 E
worldwide for CEN national Members.
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Contents Page
European foreword . 4
Introduction . 5
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
4 Principle . 7
5 Reagents and materials . 9
6 Apparatus . 10
7 Sampling . 11
8 Sample preparation . 11
9 Procedure. 11
9.1 General . 11
9.2 Preparation and standardization of standard solutions . 11
9.2.1 Vitamin A (retinol) . 11
9.2.2 Vitamin E (α-tocopherol). 13
9.2.3 Vitamin D . 14
9.3 Calibration . 15
9.3.1 General . 15
9.3.2 Calibration solutions and plotting of calibration graph for vitamins A (retinol) and E
(α-tocopherol) . 15
9.3.3 Calibration solution and plotting of calibration graph for vitamins D2 and D3 . 16
9.4 Analysis of the sample . 17
9.4.1 Preparation of test samples . 17
9.4.2 Saponification . 18
9.5 Extraction of vitamin A (retinol), vitamin E (α-tocopherol) and vitamin D
3
(cholecalciferol) by SPE . 18
9.6 Preparation of the test solution for HPLC separation . 18
9.6.1 Vitamin A (retinol) and vitamin E (α-tocopherol) . 18
9.6.2 Vitamin D (cholecalciferol) . 19
3
9.7 Semi-preparative HPLC clean-up for determination of vitamin D . 19
3
9.7.1 Determination of retention time window for vitamin D /D fraction . 19
2 3
9.7.2 Conditions for semi-preparative HPLC clean-up . 19
9.7.3 Collection of the vitamin D fraction . 20
9.8 High-performance liquid chromatography . 20
9.8.1 Conditions for analytical HPLC . 20
9.8.2 Determination . 21
10 Expression of results . 21
10.1 Result calculation for vitamin A (retinol) . 21
10.2 Result calculation for vitamin E (α-tocopherol) . 22
10.3 Result calculation for vitamin D (cholecalciferol) . 22
3
10.4 Recovery of vitamin D. 23
11 Observations . 24
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12 Precision . 24
12.1 Interlaboratory study . 24
12.2 Repeatability . 25
12.3 Reproducibility . 25
13 Test report . 26
Annex A (informative) Examples of combinations of weighing, aliquot and dilution to reach
concentrations within the calibration curve . 27
Annex B (informative) Preparation of stock standard solution of vitamin E (α-tocopherol)
from α-tocopherol acetate . 30
B.1 General . 30
B.2 Reagents . 30
B.3 Preparation of stock standard . 30
B.4 Standardization of the vitamin E (α-tocopherol) stock standard solution in
cyclohexane . 30
B.5 Calibration solutions and plotting of calibration graph for vitamins A (retinol) and E
(α-tocopherol) . 31
Annex C (informative) Results of the interlaboratory study . 32
Bibliography . 38
3
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European foreword
This document (prEN 17547:2020) has been prepared by Technical Committee CEN/TC 327 “Animal
feeding stuffs: Methods of sampling and analysis”, the secretariat of which is held by NEN.
This document is currently submitted to the CEN Enquiry.
This document has been prepared under a standardization request given to CEN by the European
Commission and the European Free Trade Association.
4
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Introduction
WARNING — The method described in this document implies the use of reagents that pose a hazard to
health. The standard does not claim to address all associated safety problems. It is the responsibility of
the user of this document to take appropriate measures for the health and safety protection of the
personnel prior to use of the standard and to ensure that regulatory and legal requirements are complied
with.
5
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1 Scope
This document specifies a method for the determination of the content of the total vitamin A (retinol),
vitamin E (α-tocopherol) and vitamin D (cholecalciferol) content in animal feed using solid phase
3
extraction (SPE) clean-up and high-performance liquid chromatography (HPLC).
NOTE 1 The procedure enables also determination of vitamin D but with the use of another internal standard.
2
The method is fully validated only for vitamin D .
3
The method has been successfully tested in collaborative trial for complete feed for broilers, pigs, and
turkey, for premixture for broilers and piglets, for complementary feed for cows and mineral feed within
the following ranges:
— vitamin A: 4 365 IU/kg – 4 118 352 IU/kg;
— vitamin E: 22 mg/kg – 13 800 mg/kg
— vitamin D : 1 668 IU/kg – 1 638 150 IU/kg.
3
Quantification limits of 1 100 IU for vitamin A/kg (using UV-detection), 4 mg for vitamin E/kg (using UV-
detection), 2 mg for vitamin E/kg (using fluorescence detection) and 2 000 IU for vitamin D/kg (using
UV-detection) should be normally achieved.
NOTE 2 The limits of quantification are minimum limits which were not determined within the validation study.
Lower limits of quantification are possible but is validated by the user.
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 ISO 3696:1995, Water for analytical laboratory use - Specification and test methods (ISO 3696:1987)
EN ISO 6498, Animal feeding stuffs - Guidelines for sample preparation (ISO 6498)
3 Terms and definitions
For the purposes of this document, the following terms and definitions 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/
3.1
vitamin A (retinol) content
content of all-trans-retinol and cis-isomers determined in accordance with this standard
Note 1 to entry: The vitamin A (retinol) content is expressed in International Units per kilogram (IU/kg).
Note 2 to entry: 1 IU of vitamin A (retinol) is equal to 0,300 µg of all-trans-retinol or 0,344 µg all-trans-retinol
acetate or 0,546 µg all-trans-retinol palmitate or 0,359 µg all-trans-retinol propionate.
6
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3.2
vitamin E (α-tocopherol) content
content of α-tocopherol determined in accordance to this document
Note 1 to entry: The content of vitamin E (α-tocopherol) could be also expressed as mg α-tocopherol acetate per
kg.
Note 2 to entry: 1 mg vitamin E (α-tocopherol acetate) corresponds to 0,91 mg vitamin E (α-tocopherol).
Note 3 to entry: In samples can also be present β-, γ-, δ-tocopherol and α-, β-, γ-, δ-tocotrienol. This method uses
reverse phase separation which does not separate individual forms of tocopherol. Therefore, the content of
vitamin E expressed as α-tocopherol or α-tocopherol acetate includes all forms without taking into account
differences in vitamin activities and the respective proportions of each form. Using a normal phase-column the
separation of α-, β-, γ- and δ-tocopherol is possible (see observation 11.6).
3.3
vitamin D3 (cholecalciferol) content
the content of cholecalciferol determined in accordance with this standard
Note 1 to entry: The content of vitamin D is expressed in International Units per kg (IU/kg). 1 IU corresponds to
3
an activity of 0,025 µg vitamin D (cholecalciferol).
3
Note 2 to entry: For feeding stuffs, only vitamin D3 is authorized as feed additive pursuant to Regulation
(EC) No 1831/2003 [1]. Addition of vitamin D2 is not allowed. Therefore, the vitamin D2 can be used as internal
standard.
Note 3 to entry: For accurate calculation of the results it is important that the sample does not contain any other
vitamin D2 than that added as internal standard.
4 Principle
The sample is saponified with ethanolic potassium hydroxide solution. In case that vitamin D
3
(cholecalciferol) is to be determined the internal standard is added before saponification. The vitamins
are extracted and purified by SPE column eluting with cyclohexane. The cyclohexane is removed by
evaporation and the residue is dissolved in methanol (for determination of vitamin A (retinol) and
vitamin E (α-tocopherol)) or in n-hexane (for determination of vitamin D (cholecalciferol)).
3
The vitamin A (retinol) and vitamin E (α-tocopherol) concentrations in the methanolic extract are
determined by reversed-phase liquid chromatography using external calibration and HPLC conditions
that give a single peak for all retinol isomers as well as for all tocopherols.
The n-hexane extract for vitamin D determination is purified by semi-preparative normal-phase HPLC
3
on silica gel. The purified extract is separated by reversed-phase HPLC using conditions that give a
baseline separation between the vitamin D and vitamin D . Quantification of vitamin D is performed by
2 3 3
external standard calibration taking into account the recovery of the internal standard.
NOTE Figure 1 contains a flowchart for the determination of vitamins A, D and E.
7
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Figure 1 — Flowchart for the determination of vitamins A, D and E
8
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5 Reagents and materials
Use only reagents of recognized analytical grade.
5.1 Water, complying with at least grade 3 in accordance with EN ISO 3696:1995.
5.2 Potassium hydroxide (KOH), w ≅ 85 %.
5.3 Ethanol (C H OH), w = 95 % (by volume), or equivalent industrial methylated spirit (ethanol
2 5
denatured by methanol or hexane).
5.4 Ascorbic acid (C H O ).
6 8 6
5.5 Ascorbic acid, solution, ρ = 200 g/l.
5.6 Sodium sulphide (Na S × 9 H O).
2 2
5.7 Sodium sulphide, alkali solution (see 11.1 observations).
Dissolve 2 000 g of potassium hydroxide (5.2) in 1 200 ml of water (5.1). Dissolve 224 g of sodium
sulphide (5.6) in 800 ml of water (5.1) in ultrasonic bath. Mix both solutions together.
NOTE Dissolution of KOH is a slow procedure. It is necessary to mix the solution until as much as possible of
KOH is dissolved. After addition of sodium sulphide solution, the residuum of KOH is dissolved.
5.8 2,6-Di-tert-butyl-4-methylphenol (BHT), (see 11.2 observations).
5.9 Inert gas, e.g. nitrogen.
5.10 Methanol (CH OH), HPLC grade.
3
5.11 Ethanol (CH CH OH), HPLC grade.
3 2
5.12 Cyclohexane (C H ), HPLC grade.
6 12
5.13 2-Propanol (C H OH), HPLC grade.
3 7
5.14 n-Hexane (C H ), HPLC grade.
6 14
5.15 Mobile phase for semi-preparative HPLC-clean-up of vitamin D .
3
Mixture of n-hexane (5.14) and propanol (5.13) in the proportions e.g. 98 + 2 (by volume). The ratio of
the mixture shall be adapted to the HPLC-column employed. If necessary, filter through a membrane filter
(6.8).
5.16 Mobile phase for analytical HPLC.
Mix together methanol (5.10) and water (5.1) in the proportions 980 + 20 (by volume). The exact ratio
will be determined by the characteristics of the column employed. The use of other mobile phase
composition is allowed provided the separation of vitamins according the scope of this standard is
possible. If necessary, filter through a membrane filter (6.8).
5.17 Vitamin A standard substances.
5.17.1 All-trans-retinol acetate (C H O ), CAS = 127-47-9, MW = 328,49 g/mol, extra pure, of
22 32 2
6
certified activity, e.g. 2,80 × 10 IU/g.
5.17.2 All-trans-retinol palmitate (C H O ), CAS = 79-81-2, MW = 524,86 g/mol, extra pure, of
36 60 2
6
certified activity, e.g. 1,80 × 10 IU/g.
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5.18 Vitamin E standard substance.
5.18.1 DL-α-tocopherol (C H O ), CAS = 10191-41-0, MW = 430,72 g/mol, extra pure, of certified
29 50 2
purity.
5.19 Vitamin D standard substances.
5.19.1 Vitamin D (ergocalciferol; C H O), CAS = 50-14-6, MW = 384,62 g/mol, extra pure, of certified
2 27 44
6
activity, e.g. 40 × 10 IU/g.
5.19.2 Vitamin D (cholecalciferol; C H O), CAS = 67-97-0; MW = 384,62 g/mol, extra pure, of certified
3 27 44
6
activity, e.g. 40 × 10 IU/g.
5.20 Celite for SPE column
Base material coarse-grained kieselguhr (also known as diatomaceous earth, hydromatrix, celite);
particle size: max. 10 % < 100 μm, max. 90 % < 500 μm, max. 5 % > 800 μm; large pore size, high pore
volume, constantly high batch-to-batch quality.
6 Apparatus
Usual laboratory equipment and, in particular, the following:
6.1 Boiling water bath with magnetic stirrer or electrical heating device with stirring (for hot
saponification).
6.2 Overturning rotating stirrer (for cold saponification).
6.3 Amber glassware (see observation 11.3).
6.3.1 Flat bottom - or conical flasks, 250 and 500 ml, with ground-glass socket.
6.3.2 Allihn condenser, jacket length 300 mm, with ground-glass joint, with adapter for gas feed pipe.
6.3.3 Graduated flasks with ground-glass stoppers, narrow-necked, 20 ml, 25 ml, 50 ml and 100 ml.
6.3.4 Pear shaped flask with ground-glass stoppers, 100 ml.
6.4 Vials, suitable for sample concentrator.
6.5 Column for SPE, filled with celite (e.g. Chromabond XTR, 70 ml volume) which is able to adsorb
the water phase from the saponification solution (9.4.2) and release the vitamins A, E and D completely
by elution with organic solvents. The column shall have a capacity of not less than 20 ml aqueous solution
and possibly closed by a valve at the outlet.
6.6 Rotary vacuum evaporator, with water bath at 40 °C.
6.7 Sample nitrogen concentrator, heated to 50 °C.
6.8 Membrane filter, compatible with methanol, 0,45 μm pore size; e.g. Chromafil PET - 45/15 MS or
suitable filter with smaller pore size.
6.9 HPLC system semi-preparative, for the clean-up of vitamin D, consisting of:
6.9.1 HPLC pump, set to deliver a constant eluent volume flow rate of e.g. 2,5 ml/min.
6.9.2 HPLC injection device, injection volume of 500 µl.
6.9.3 HPLC semi-preparative normal phase column with guard column (see 9.7.2).
6.9.4 Column oven, set to provide a constant column temperature.
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6.9.5 UV-Detector
6.10 HPLC-system for analytical separation, consisting of the following:
6.10.1 HPLC-pump, set to deliver a constant eluent volume flow rate of e.g. 1 ml/min.
6.10.2 HPLC injection devices, injection volume of 20 µl and 100 µl.
6.10.3 HPLC reversed-phase column, with guard column (see 9.8.1).
6.10.4 Column oven, set to provide a constant column temperature.
6.10.5 Detectors for UV- and fluorescent detection.
6.10.6 Integrator / data handling system.
6.11 UV (or UV-Visible) spectrophotometer, capable of measuring absorbance at the wavelengths
defined in 9.2.1.3, 9.2.2.3 and 9.2.3.5, equipped with cells of 10 mm path length.
7 Sampling
It is important that the laboratory receive a sample which is truly representative and has not been
damaged or changed during transport or storage. Sampling is not part of the method specified in this
European Standard. A recommended sampling method is given in EN ISO 6497 [2].
Store the sample in such a way that deterioration and change in its composition are prevented.
8 Sample preparation
Samples are grinded at the day of analysis as recommended in the guidelines for sample preparation as
in EN ISO 6498.
Grind a portion of the well-mixed dry laboratory sample so that it passes through a sieve with 1 mm
apertures. Prevent to heat up.
Do not grind the sample(s) if the particle size distribution is adequate (e.g. premixtures and
concentrates).
Semi-moist pet foods (canned pet foods) can be homogenized by mincing.
Samples can be ground before the day of analysis. In this case the storage conditions shall prevent any
degradation, e.g. freeze the ground sample and defrost it in a fridge a night before analysis.
9 Procedure
9.1 General
Because of the sensitivity of vitamin A, E and D to UV radiation and air, perform all operations away from
natural and strong fluorescent light and as rapidly as is consistent with accurate working. Use amber
glassware (6.3) where possible (see observation 11.3).
9.2 Preparation and standardization of standard solutions
9.2.1 Vitamin A (retinol)
9.2.1.1 General
For preparation of vitamin A (retinol) standard solutions use all-trans-retinol acetate (5.17.1) or all-
trans-retinol palmitate (5.17.2).
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NOTE Standard substance of retinol itself is less stable then retinol palmitate or retinol acetate and therefor it
is usual to use these esters for preparation of standard solution of vitamin A. Nevertheless, use of standard
substance retinol is also possible.
9.2.1.2 Stock standard solution of vitamin A (retinol)
Weigh to the nearest 0,1 mg an amount of vitamin A (retinol acetate) (5.17.1) or vitamin A (retinol
palmitate) (5.17.2) containing approximately 100 000 IU of vitamin A (retinol) into a 250 ml flat bottom
or conical flask (6.3.1) and continue with saponification according to 9.4.2.1 or 9.4.2.2 and extraction
according to 9.5.
Collect the eluate from the SPE column (6.5) in a 100 ml graduated flask (6.3.3) and fill up to the mark
with cyclohexane (5.12).
The nominal concentration of stock standard solution of vitamin A (retinol) in cyclohexane is
approximately 75 IU per ml.
The exact content shall be calculated from exact concentration of working standard solution of vitamin A
(retinol) (9.2.1.2) determined according to 9.2.1.3.
The stock standard solution of vitamin A (retinol) is stable for 6 months in dark at 4°C and can be used
for preparation of working standard solution according to 9.2.1.2 during this period.
9.2.1.3 Working standard solution of retinol
Pipette 10,0 ml of the vitamin A (retinol) stock standard solution (9.2.1.2) into a 100 ml graduated flask
and fill up to the mark with cyclohexane (5.12).
The nominal concentration of the working standard solution is 7,5 IU vitamin A (retinol) per ml.
The exact content of vitamin A (retinol) in working standard solution shall be determined according to
9.2.1.3.
The working standard solution of vitamin A (retinol) is stable for at least 2 months in dark at 4°C but the
real shall be checked before use.
9.2.1.4 Standardization of the vitamin A (retinol) working standard solution (9.2.1.2)
The exact content of vitamin A (retinol) in working standard solution (9.2.1.2) is determined by
spectrometric measurement. Measure the UV spectrum of this solution against cyclohexane (5.12) in the
spectrophotometer (6.11) at the absorption maximum between 325 nm and 327 nm.
The vitamin A (retinol) content can be calculated with Formula (1).
33 333××AA33 333
wSTD wSTD
CA19,212× (1)
A wSTD
A 1 735
325
where
C is the vitamin A (retinol) content, in IU/ml;
A
33 333 is the concentration of retinol corresponding to 1 % solution, in IU/ml;
A is the absorption of working standard solution (9.2.1.3);
wSTD
A is the absorption coefficient of retinol in cyclohexane at 325 nm.
325
1%
NOTE The absorption coefficient of vitamin A (retinol) in cyclohexane 𝐴𝐴 at 325 nm is 1 735, i.e.
1𝑐𝑐𝑐𝑐
33 333 IU/ml provide absorption 1 734, so the absorption of 7,5 IU/ml is 0,3904.
12
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