1973L0046 — EN — 19.08.1981 — 001.001 — 1
This document is meant purely as a documentation tool and the institutions do not assume any liability for its contents
►B FOURTHCOMMISSIONDIRECTIVE
of5December 1972
establishingCommunitymethodsofanalysisfortheofficial controloffeedingstuffs
(73/46/EEC)
(OJ L 83, 30.3.1973, p. 21)
Amended by:
Official Journal
No page date
►M1Commission Directive 81/680/EEC of 30 July 1981 L 246 32 29.8.1981
▼B
FOURTHCOMMISSIONDIRECTIVE
of5December 1972
establishingCommunitymethodsofanalysisfortheofficialcontrol
offeedingstuffs
(73/46/EEC)
THE COMMISSION OF THE EUROPEAN COMMUNITIES,
Having regard to the Treaty establishing the European Economic
Community;
Having regard to the Council Directive of 20 July 1970(1) on the intro-
duction of Community methods of sampling and analysis for the
official control of feedingstuffs, as amended by the Directive No 72/275/EEC of 20 July 1972(
2), and in particular Article 2 thereof;
Whereasthat Directive requiresthat official controlsof feedings tuffs
be carried out using Community methods of sampling and analysis for
the purpose of checking compliance with requirements arising underthe provisions laid down by law, Regulation or administrative actionconcerning the quality and composition of feedingstuffs;
WhereasDirectivesNo 71/250/EEC of 15 June 1971(
3), No 71/393/
EEC of 18 November 1971(4) and No 72/199/EEC of 27 April
1972(5) have already established a number of Community methods of
analysis; whereas the progress of work since then makes it advisable toadopt a fourth set of methods;
Whereasthe meas uresprovided for in thisDirective are in accordance
with the Opinion of the Management Committee for Feedingstuffs;
HAS ADOPTED THIS DIRECTIVE:
Article 1
The Member States shall require that analyses for official controls of
feedingstuffs as regards moisture contents of animal and vegetablefats and oils and magnesium and crude fibre contents of feedingstuffsbe carried out according to the methodsdes cribed in Annex I to thisDirective.
Article 2
The Member States shall require that analyses for official controls of
feedingstuffs as regards their contents of retinol (vitamin A), thiamine
(aneurine, vitamin B1), ascorbic and dehydroascorbic acids (vitamin C)
be carried out according to the methodsdes cribed in Annex II to thisDirective.
Article 3
The Member Statess hall, not later than 1 January 1974, bring into
force the laws, regulations or administrative provisions necessary tocomply with this Directive. They shall forthwith notify the Commissionthereof.1973L0046 — EN — 19.08.1981 — 001.001 — 2
(1) OJ No L 170, 3. 8. 1970, p. 2.
(2) OJ No L 171, 29. 7. 1972, p. 39.
(3) OJ No L 155, 12. 7. 1971, p. 13.
(4) OJ No L 279, 20. 12. 1971, p. 7.
(5) OJ No L 123, 29. 5. 1972, p. 6.▼M1
▼B
▼M1
▼B
▼B
Article 4
This Directive is addressed to the Member States.1973L0046 — EN — 19.08.1981 — 001.001 — 3
▼B
ANNEX I
1.DETERMINATION OF MOISTURE IN ANIMAL AND VEGETABLE
FATSANDOILS
1.PurposeandScope
This method makes it possible to determine the water and volatile substances
content of animal and vegetable fatsand oils .
2.Principle
The sample is dried to constant weight at 103 ºC. The loss in mass is deter-
mined by weighing.
3.Apparatus
3.1. Flat-bottomed dish, of a corrosion-resistant material, 8 to 9 cm in
diameter and approximately 3 cm high.
3.2. Mercury thermometer with a strengthened bulb and expansion tube at
the top end, graduated from approximately 80 ºC to at least 110 ºC,
and approximately 10 cm in length.
3.3. Sand bath or electric hot-plate.3.4. Desiccator, containing an efficient drying agent.
3.5. Analytical balance.
4.Procedure
Weigh out to the nearest mg approximately 20 g of the homogenized sample
into the dry, weighed dish (3.1) containing the thermometer (3.2). Heat on
the sand bath or hot-plate (3.3), stirring continuously with the thermometer,
so that the temperature reaches 90 ºC in about 7 minutes.
Reduce the heat, watching the frequency with which bubblesris e from the
bottom of the dish. The temperature must not exceed 105 ºC. Continue to
stir, scraping the bottom of the dish, until bubbles stop forming.
In order to ensure complete elimination of moisture, reheat several times to
103 ºC ± 2 ºC, cooling to 93 ºC between successive heatings. Then leave to
cool to room temperature in the desiccator (3.4) and weigh. Repeat this
operation until the loss in mass between two successive weighings no longer
exceeds2 mg.
N.B.An increase in the mass of the sample after repeated heating indicates
an oxidation of the fat, in which case calculate the result from the
weighing carried out immediately before the mass began to increase.
5.Calculationofresults
The moisture content, as a percentage of the sample, is given by the
following formula:
M
1/C0M2 ðÞ /C1100
Mo
where:
Mo= mass, in grammes, of the test sample;
M1= mass, in grammes, of the dish with its contents before heating;
M2= mass, in grammes, of the dish with its contents after heating.
Results lower than 0·05 % must be recorded as ‘lower than 0·05 %’.
Repeatability
The difference in moisture between the results of two parallel determinations
carried out on the same sample must not exceed 0·05 %, in absolute value.1973L0046 — EN — 19.08.1981 — 001.001 — 4
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2.DETERMINATIONOFMAGNESIUM
— by atomic absorption spectrophotometry —
1.PurposeandScope
This method makes it possible to determine the quantity of magnesium in
feeding stuffs. It is particularly appropriate for determining magnesium
contentslower than 5 %.
2.Principle
The sample is ashed and dissolved in dilute hydrochloric acid. If it contains
no organic substances, it is dissolved directly in dilute hydrochloric acid. The
solution is diluted and the magnesium content determined by atomic absorp-
tion spectrophotometry at 285·2 nm, by comparison with standard solutions.
3.Reagents
3.1. Hydrochloric acid a.p. d: 1·16.
3.2. Concentrated hydrochloric acid a.p. d: 1·19.3.3. Magnesium ribbon or wire, or magnesium sulphate heptahydrate, dried
at room temperature.
3.4. Strontium salt solution (chloride or nitrate) at 2·5 % (w/v) strontium
(= 76·08 g SrC1
2·6 H2O a.p., or 60·38 g Sr (NO3)2a.p.).
3.5. Standard magnesium solution: weigh out to the nearest mg 1 g magne-
sium (3.3) which has previously had its oxide coating carefully
removed, or the corresponding quantity (10·143 g) of magnesium
sulphate heptahydrate (3.3). Place in a 1 000 ml graduated flask, add
80 ml hydrochloric acid (3.1), leave to dissolve and make up to
1 000 ml with water. 1 ml of thiss olution contains1·000 mg magne-
sium.
4.Apparatus
4.1. Platinum, silica or porcelain ashing crucibles.
4.2. Thermostatically controlled electric muffle furnace.
4.3. Atomic absorption spectrophotometer.
5.Procedure
5.1.Preparationof the sample solution
5.1.1.Feeding stuffs composed exclusively of mineral substances
Weigh out to the nearest mg 5 g of the sample into a 500 ml
graduated flask with 250 to 300 ml water. Add 40 ml hydro-
chloric acid (3.1), bring to the boil and keep the liquid gently
boiling for 30 minutes. Leave to cool, make up to volume with
water, mix and filter into a dry beaker through a dry pleated
filter. Discard the first 30 ml of the filtrate. In the presence of
silica, treat 5 g of sample with a sufficient quantity (15—30 ml)
of hydrochloric acid (3.2), evaporate to dryness on a water bath
and transfer to an oven at 105 ºC for one hour. Proceed as from
the third sentence of 5.1.2.
5.1.2.Feeding stuffs composed predominantly of mineral substances
Weigh out to the nearest mg 5 g of the sample into a crucible and
ash at 550 ºC in the muffle furnace until an ash which is free
from carbonaceousparticlesisobtained, and leave to cool. In
order to eliminate silica, add to the ash a sufficient quantity
(15—30 ml) of hydrochloric acid (3.2), evaporate to dryness on
a water bath and transfer to an oven at 105 ºC for one hour. Treat
the residue with 10 ml hydrochloric acid (3.1) and transfer to a
500 ml graduated flask using warm water. Leave to cool and
make to volume with water. Mix and filter into a dry beaker
through a dry pleated filter. Discard the first 30 ml of the filtrate.
5.1.3.Feedingstuffs composed predominantly of organic substances
Weigh out to the nearest mg 5 g of the sample into a crucible and
ash at 550 ºC in the muffle furnace until an ash which is free
from carbonaceousparticlesisobtained. Treat the as h with 5 ml
hydrochloric acid (3.2), evaporate to dryness on a water bath and
then dry for one hour in the oven at 105 ºC in order to render the1973L0046 — EN — 19.08.1981 — 001.001 — 5
▼B
silica insoluble. Treat the ash with 5 ml hydrochloric acid (3.1),
transfer to a 250 ml graduated flask using warm water, bring to
the boil, leave to cool and make up to volume with water. Mix
and filter into a dry beaker through a dry pleated filter. Discard
the first 30 ml of the filtrate.
5.2.Measurement by atomic absorption
By diluting the standard solution (3.5) with water, prepare at least 5
reference solutions of increasing concentration, corresponding to the
optimal measuring range of the spectrophotometer. Add to each solution
10 ml strontium salt solution (3.4) and then make up the volume to
100 ml with water. Dilute with water one aliquot part of the filtrate
obtained from 5.1.1, 5.1.2 or 5.1.3, so as to obtain a magnesium concen-
tration which iswithin the limitsof concentration of the reference
solutions. The hydrochloric acid concentration of this solution must not
exceed 0·4 N. Add 10 ml strontium salt solution (3.4) and then make up
the volume to 100 ml with water. Measure the absorption of the solution
to be determined and of the reference solutions at 285·2 nm.
6.Calculationofresults
Calculate the quantity of magnesium in the sample by relation to the refer-
ence solutions. Express the result as a percentage of the sample.
Repeatability
The difference between the results of two parallel determinations carried out
on the same sample must not exceed 5 %, in relative value.
3.DETERMINATIONOFCRUDEFIBRE
1.PurposeandScope
This method makes it possible to determine in feeding stuffs the quantity of
fat-free organic substances which are insoluble in acid and alkaline media
and are conventionally described as crude fibre.
2.Principle
The sample, defatted where necessary, is treated successively with boiling
solutions of sulphuric acid and potassium hydroxide of specified concentra-
tions. The residue is separated by filtration in the presence of asbestos,
washed, dried, weighed and ashed at 900 ºC. The loss of weight resulting
from ashing corresponds to the crude fibre present in the test sample.
3.Reagents
3.1. Sulphuric acid 0·26 N.
3.2. Treated asbestos: add to asbestos of the type used with a Gooch crucible
approximately 5 timesitsweight of dilute hydrochloric acid (1 volume
hydrochloric acid, d: 1·19 + 3 volumesof water). Boil the mixture for
approximately 45 minutes, leave to cool and filter through a Buchner
funnel. Wash the residue first with water until hydrochloric acid has
disappeared from the washing water, and then with acetone (3.6). Dry
the asbestos in the drying oven and then ash for 2 hours at 900 ºC.
Leave to cool and keep in a stoppered flask. Asbestos treated in this
way may be used several times. It must meet the specifications given
in 5. regarding the blank test.
3.3. Antifoaming emulsion (eg silicone).
3.4. Potassium hydroxide solution 0·23 N.
3.5. Hydrochloric acid 0·5 N.
3.6. Acetone.
3.7. Diethyl ether.
4.Apparatus
4.1. Beakers of at least 600 ml capacity, with measuring marks at the 200 ml
level.
4.2. Porcelain discs approximately 80 mm in diameter and approximately
4 mm thick, perforated with approximately 32 holes, each approximately
4 mm in diameter.1973L0046 — EN — 19.08.1981 — 001.001 — 6
▼B
4.3. Rubber-stoppered vacuum flasks of approximately 2 litre capacity, with
measuring marks at the 800 ml level and fitted with glass funnels
120 mm in diameter.
4.4. Filter platesapproximately 40 mm in diameter and approximately 4 mm
thick, with slanting edges to fit the cone of the funnel (4.3), perforated
with approximately 16 holes, each approximately 4 mm in diameter, and
covered by a wire mesh, the mesh size being approximately 1 mm. Both
plates and wire mesh must be resistant to acids and alkalis.
4.5. Platinum or silica ashing crucibles.
4.6. Thermostatically controlled electric muffle furnace.
4.7. Desiccator.4.8. Asbestos filter: Suspend 2·0 g asbestos (3.2) in 100 ml water.
Filter under vacuum over a filter plate covered with a wire mesh (4.4) and
placed in the funnel of a vacuum flask (4.3). Collect the filtrate and filter
once more through the same filter. Discard the filtrate.
5.Procedure
Weigh out to the nearest mg 3 g of the sample and 2 g treated asbestos (3.2)
into a beaker (4.1), add 200 ml sulphuric acid (3.1) and a few drops of anti-
foaming emulsion (3.3). Bring rapidly to the boil and leave to boil for
exactly 30 minutes. To keep a constant volume, cover the beaker with a
cooling device such as a 500 ml round-bottomed flask in which cold water
iscirculated. Stop boiling by adding approximately 50 ml cold water and
filter immediately under vacuum through an asbestos filter previously
prepared ass hown in 4.8.
Wash the residue with 5 lots of approximately 100 ml of very hot water to
obtain a final volume of filtrate of 800 ml. Transfer the residue quantitatively
to the beaker (4.1) which has first been fitted with a porcelain disc (4.2) to
regulate the boiling. Add 200 ml potassium hydroxide solution (3.4). Bring
rapidly to the boil and leave to boil for exactly 30 minutes. Add approxi-
mately 50 ml cold water and filter immediately under vacuum through a
fresh asbestos filter previously prepared as shown in 4.8. Wash the residue
with very hot water until the washing water is neutral (test with litmus
paper), then 3 timeswith acetone (3.6) (approximately 100 ml acetone in all).
Transfer the residue quantitatively to an ashing crucible (4.5), break up if
necessary and dry to constant weight in the drying oven at 130 ºC.
Leave to cool in the desiccator (4.7) and weigh rapidly.
Place the crucible in the muffle furnace (4.6) and leave to ash for 30 minutes
at 900 ºC. Leave to cool in the desiccator (4.7) and weigh rapidly,
Carry out a blank test applying the same procedure to the treated asbestos
(3.2), but without the sample. Loss of weight resulting from ashing of the
6 g asbestos must not exceed 10 mg.
6.Calculationofresults
The crude fibre content, asa percentage of the s ample, isgiven by the ratio:
a/C0b ðÞ /C1 100
3
where:
a = loss of weight after ashing during the determination;
b = loss of weight after ashing during the blank test.
RepeatabilityThe difference between the results of two parallel determinations carried out
on the same sample must not exceed:
0·3, in absolute value, for crude fibre contents lower than 10 %;3 %, in relative value, for crude fibre contentsequal to or greater than 10 %.
7.Observations
7.1. Feedingstuffs containing more than 10 % oils and fats must be defatted
prior to analysis with diethyl ether (3.7). To do this, place the test
sample (3 g weighed to the nearest mg) on an asbestos filter (4.8).
Cover 3 timeswith approximately 50 ml diethyl ether (3.7) and each1973L0046 — EN — 19.08.1981 — 001.001 — 7
▼B
time filter carefully under vacuum. Transfer the defatted test sample and
the asbestos quantitatively to a beaker (4.1) and continue the analysis as
shown in 5.
7.2. Feedingstuffs containing oils and fats which cannot be extracted directly
must be, defatted as shown in 7.1 and defatted a further time after the
acid attack has been washed from the residue.
To do this, wash this attack from the residue 3 times with acetone (3.6)
(100 ml in all), then 3 timeswith 50 ml diethyl ether (3.7). Then
transfer the residue quantitatively to a beaker (4.1) and continue the
analysis as shown in the second paragraph of 5 (treatment with potas-
sium hydroxide solution).
7.3. If the feedingstuffs are rich in calcium (more than 2 % calcium), place
the test sample (3 g weighed to the nearest mg) in a beaker (4.1) with
100 ml hydrochloric acid 0·5 N (3.5) and leave to stand in a cool
temperature for 5 minutes. Filter immediately and wash in cold water.
Use as a filtration aid the 2·0 g asbestos specified for boiling with
sulphuric acid. If filtration proves difficult, dilute the suspension with
acetone (3.6). Then proceed ass hown in 5.1973L0046 — EN — 19.08.1981 — 001.001 — 8
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ANNEX II
1.DETERMINATIONOFRETINOL(VITAMINA)
1.PurposeandScope
This method makes it possible to determine the quantity of retinol (Vitamin
A) in feedingstuffs, concentrates and premixes. The lower limit of the deter-
mination is10 000 IU/kg for highly pigmented feedsand 4 000 IU/kg for
others(1). Products are classified in two groups, according to their presumed
retinol content:
Group A: contentslower than 200 000 IU/kg;
Group B: contentsequal to or greater than 200 000 IU/kg.
2.Principle
The sample is hydrolised when hot with a potassium hydroxide solution in an
ethanol medium and in the presence of an antioxidant or in a nitrogen atmo-
sphere. The mixture is extracted with 1,2-dichlorethane. The extract is
evaporated to dryness and treated with light petroleum. The solution is chro-
matographed on a column of aluminium oxide (forGroup B products,
chromatography is only required in certain cases). For Group A products
the retinol isdetermined by s pectrophotometry at 610 nm after development
of a coloured complex according to the Carr-Price reaction; for Group B
productsby s pectrophotometry in the UV at 325 nm.
3.Reagents
(a)used for analysing products of Groups A and B
3.1. 96 % (v/v) ethanol.
3.2. 10 % (w/v) sodium ascorbate solution a.p., or3.3. Purified nitrogen.3.4. 50 % (w/v) potassium hydroxide solution a.p.
3.5. Potassium hydroxide solution 1 N a.p.
3.6. Potassium hydroxide solution 0·5 N a.p.3.7. 1,2-dichlorethane a.p.3.8. Light petroleum, boiling range: 30—50 ºC. If necessary, purify as
follows: stir 1 000 ml light petroleum with 20 ml lots of concen-
trated sulphuric acid until the acid remains colourless. Remove
the acid and wash the light petroleum successively with 500 ml
water, twice with 250 ml of 10 % (w/v) sodium hydroxide solution
and three timeswith 500 ml water. Remove the aqueouslayer, dry
the light petroleum for 1 hour over active carbon and anhydrous
sodium sulphate, filter and distil.
3.9. Aluminium oxide, standardized according to Brockmann: ash for 8
hours at 750 ºC, cool in a desiccator and keep in a brown glass
bottle fitted with a ground-glass stopper. Before use in chromato-
graphy moisten as follows: place in a brown glass bottle 10 g
aluminium oxide and 0·7 ml water, seal with a stopper, reheat for
5 minutesin a boiling water bath while s haking. Leave to cool.
Verify the activity of the aluminium thusprepared by s ubjecting a
known quantity of retinol (3.17) (ca. 500 IU) to the procedure of
5.3 and 5.4 and checking recovery.
3.10. Basic aluminium oxide, degree of activity 1 (Woelm, Merck or
equivalent).
3.11. Pure diethyl ether. Remove peroxidesand tracesof water by chro-
matography on a column of basic aluminium oxide (3.10). (25 g
aluminium oxide per 250 ml diethyl ether.)
3.12. Light petroleum solutions (3.8) at 4, 8, 12, 16 and 20 % (v/v)
diethyl ether (3.11).
3.13. Sodium sulphide solution 0·5 molar in 70 % (v/v) glycerine,
prepared from sodium sulphide a.p.1973L0046 — EN — 19.08.1981 — 001.001 — 9
(1) 1 IU = 0·3 µg of retinol.
▼B
(b)used exclusively for analysing Group A products
3.14. Crystallizable benzene a.p.
3.15. Chloroform a.p. Remove the ethanol, phosgene and traces of water
by chromatography on a column of basic aluminium oxide (3.10)
(50 g aluminium oxide per 200 ml chloroform; it isadvis able to
chromatograph the first 50 ml of the eluate a second time).
3.16. Carr-Price reagent: stir approximately 25 g antimony trichloride
a.p. (kept in a desiccator) with 100 ml chloroform (3.15) until the
solution is saturated. A slight deposit of antimony trichloride
causes no problem. Add 2 ml acetic anhydride a.p. Keep in a
refrigerator in a brown glass bottle with ground-glass stopper. The
solution keeps for several weeks.
3.17. Retinol — standardized spectrophotometrically.
(c)used exclusively for analysing Group B products
3.18. Isopropanol, for chromatography.
4.Apparatus
4.1. Water bath.
4.2. Vacuum evaporation apparatus with round flasks of different capacities.4.3. Glass chromatography tubes (length: 300 mm; internal diameter: about
13 mm).
4.4. Spectrophotometer with 10 mm cells. Measurements in the UV require
silica cells.
4.5. UV lampss uitable for 365 nm.
5.Procedure
N.B.All operations must be carried out away from direct light, if necessary
in brown glass equipment.
5.1.Test Sample
From the finely divided sample, take a test sample proportional to the
presumed retinol content, thus:
0·1—1·0 g for concentrates(contentsgreater than 20 000 IU/g);
3·0—5·0 g for premixes(contentsof between 400 and 20 000 IU/g);
10—20 g for mineral mixtures;
30 g for Group A products.Immediately place the test sample in a 500 ml flask with a ground-glass
stopper.
5.2.Hydrolysis and extraction (
1)
Add successively to the test sample 40 ml ethanol (3.1), 2 ml sodium
ascorbate solution (3.2)(2), 10 ml potassium hydroxide solution (3.4)
and 2 ml sodium sulphide solution (3.13).
Heat for 30 minutesat 70—80 ºC under a reflux condens er and then
leave to cool under a stream of water. Add 50 ml ethanol (3.1) and
100 ml 1,2-dichlorethane (3.7) (taken with a pipette). Shake vigorously
and then decant the supernatant liquid into a decanting container. Add to
the container 150 ml potassium hydroxide solution (3.5), shake for 30
seconds and leave to stand until the layers are separated. Collect the
dichlorethane layer (lower layer) in a decanting container, add 40 ml
potassium hydroxide solution (3.6), shake for 10 seconds and leave to
stand until the layers are separated. Collect the dichlorethane layer in a
decanting container and wash 6—8 times with 40 ml lots of water until
free of alkali (phenolphthalein test). Collect the dichlorethane layer and
remove the last traces of water using strips of filter paper.1973L0046 — EN — 19.08.1981 — 001.001 — 10
(1) For milk feedsand productswith a tendency to agglomerate or s well, double the quan-
tity of the reagents shown in the first and second paragraphs of 5.2.
(2) Sodium ascorbate need not be added when hydrolysis is carried out in a nitrogen atmo-
sphere.
▼B
Evaporate to dryness an aliquot part of the solution under vacuum and
on the water bath at 40 ºC. Rapidly treat the residue with 5 ml light
petroleum (3.8).
For Group A products, chromatograph ass hown in 5.3.1.
For Group B products, transfer the solution to a 50 ml graduated flask,
make up to volume with light petroleum (3.8), mix and measure the
optical density as shown in 5.4.2.
5.3.Chromatography
5.3.1.Group A products
Fill a chromatography tube (4.3) to a height of 200 mm with 10 g
aluminium oxide (3.9) previously slurried with light petroleum
(3.8). Place in the tube the solution obtained in 5.2 and immedi-
ately add 20 ml light petroleum (3.8). Elute successively with
10 ml lotsof the light petroleum s olutionsat 4, 8, 12, 16 and
20 % diethyl ether (3.12) under pressure or partial vacuum, the
rate of flow being 2 to 3 dropsper s econd.
The carotene iseluted firs t(1). The retinol isgenerally eluted with
the light petroleum solution at 20 % diethyl ether (3.12). The
elution isfollowed under UV light (brief irradiation of the
column with the mercury lamp). The fluorescent zone of the
retinol isclearly s eparated from the yellow xanthophyll zones
following it. Collect the eluate fraction containing the retinol in
an Erlenmeyer flask.
5.3.2.Group B products
Chromatography must only be carried out if the optical density
measurements obtained in 5.4.2 do not conform to the require-
mentsgiven in 5.4.2.
If chromatography proves necessary, place in the chromatography
column an aliquot part of the solution in the light petroleum
obtained in 5.2, containing approximately 500 IU of retinol, and
chromatograph ass hown in 5.3.1.
5.4.Measurement of the optical density
5.4.1.Group A products
Evaporate to dryness under vacuum the eluate containing the
retinol obtained in 5.3.1. Treat the residue with 2 ml benzene
(3.14). Take 0·3 ml of thiss olution and add 3 ml of the Carr-
Price reagent (3.16). A blue colouring develops. Measure the
optical density with the spectrophotometer at 610 nm exactly 30
seconds after the reaction has begun. Determine the retinol
content by reference to a standard curve obtained from benzene
solutions of increasing retinol-standard concentrations treated
with Carr-Price reagent (2 to 16 IU retinol-standard (3.17) per
0·3 ml benzene (3.14) +3 ml Carr-Price reagent (3.16)). The stan-
dard curve must be checked regularly and frequently using the
standard and a freshly prepared Carr-Price reagent solution.
5.4.2.Group B products
Take an aliquot part of the solution in light petroleum obtained in
5.2 containing approximately 200 IU retinol. Evaporate to
dryness under vacuum and treat the residue with 25 ml isopro-
panol (3.18). Measure the optical density in the
spectrophotometer at 325, 310 and 334 nm. The absorption
maximum islocated at 325 nm. The retinol content of the s olu-
tion iscalculated asfollows :
E325· 18·30 = IU of retinol/ml
However, the ratio of the optical densities
E310:E325and E334:E325
must be 6 : 7 = 0·857.
If one of these ratios differs appreciably from this value (< 0·830
or > 0·880), the measurement of the optical densities must be1973L0046 — EN — 19.08.1981 — 001.001 — 11
(1) Carotene content may be determined by optical density measurement at 450 nm;
E1%
1c m¼2600
▼B
preceded by chromatography in accordance with the method
given in 5.3.2. If the measurement of the optical densities carried
out after chromatography shows that the abovementioned ratios
still differ appreciably from the value of 0·857 (< 0·830 or
> 0·880), the determination must be carried out in accordance
with the method given for Group A products.
6.Calculationofresults
Calculate the retinol content of the sample taking into account the weight of
the test sample and the dilutions carried out in the course of analysis. Express
the results in IU of retinol per kg of feedingstuff or per kg of concentrate or
premix.
Repeatability
The difference between the results of two parallel determinations carried out
on the same sample must not exceed:
— 20 %, in relative value, for retinol contentslower than 75 000 IU/kg;
— 15 000 IU for contentsbetween 75 000 and 150 000 IU/kg;— 10 %, in relative value, for contentsbetween 150 000 and 250 000 IU/kg;
— 25 000 IU for contentsbetween 25 000and 500 000 IU/kg;
— 5 %, in relative value, for contentsgreater than 500 000 IU/kg.
2.DETERMINATIONOFTHIAMINE(VITAMINB
1,ANEURINE)
1.PurposeandScope
This method makes it possible to determine the quantity of thiamine
(aneurine, Vitamin B1) in feeding stuffs, concentrates and premixes. The
lower limit of the determination is5 ppm.
2.Principle
The solution is treated when hot with dilute sulphuric acid and then hydro-
lysed enzymatically. The solution obtained is subjected to alkaline oxidation.
The thiochrome formed isextracted with is obutanol and determined by
fluorimetry.
3.Reagents
3.1. 100 µg/ml standard thiamine solution: dissolve 112·3 mg thiamine
hydrochloride, previoulsly dried under vacuum to constant weight, in
1 000 ml sulphuric acid 0·2 N (3.2). If stored in a cool, dark place,
thiss olution keepsfor one month.
3.2. Sulphuric acid 0·2 N.
3.3. Pure sodium bisulphite.
3.4. 20 % (w/v) potassium ferricyanide solution a.p.
3.5. 25 % (w/v) potassium hydroxide solution a.p.
3.6. Oxidizing mixture: mix 2 ml potassium ferricyanide solution (3.4) with
48 ml potassium hydroxide solution (3.5). This mixture does not keep
for more than 4 hours.
3.7. Isobutanol a.p.
3.8. Sodium acetate solution 2·5 N.
3.9. Multienzymatic preparation containing protease, phosphatase and
amylase (eg, Clarase).
3.10. 96 % (v/v) ethanol.
4.Apparatus
4.1. Water bath.
4.2. Centrifuge (3 500 rpm) with 30 to 50 ml tubesfitted with ground-glas s
stoppers.
4.3. Fluorimeter.1973L0046 — EN — 19.08.1981 — 001.001 — 12
▼B
5.Procedure
5.1.Enzymatic hydrolysis
Place in each of two 250 ml graduated flasks, A and B, identical
amountsof the finely divided s ample containing approximately 100 µg
thiamine and 125 ml sulphuric acid (3.2). Also add, to flask A only,
1·0 ml standard solution (3.1) (internal standard).
Shake the flasks vigorously, place on a boiling water bath and keep
there for 15 minutes, shaking occasionally. Leave to cool to approxi-
mately 45 ºC. Add to each flask 20 ml sodium acetate solution (3.8)
and 0·5 g multienzymatic preparation (3.9), then leave to stand for 20
minutes at room temperature. Add 20 ml sodium acetate solution (3.8),
make up to volume with water, homogenize and filter. Collect filtrates
A and B after having discarded the first 15 ml. Prepare the following
solutions:
5.1.1.Reference solution T
Place in a centrifuge tube (4.2) 5 ml filtrate A and approximately
10 mg sodium bisulphite (3.3). Immerse the tube in a boiling
water bath for 15 minutesand then leave to cool to room
temperature.
5.1.2.Solutions A (internal standard) and B (sample)
Place 5 ml filtrate A in a centrifuge tube (4.2) and 5 ml filtrate B
in another centrifuge tube (4.2).
5.2.Oxidation
Add to solutions T, A and B 5 ml of the oxidising mixture (3.6) and,
one minute later, 10 ml isobutanol (3.7). Stopper the tubes and shake
vigorously for 5 seconds. Leave to stand for one minute and centrifuge
so as to separate the layers. From each tube transfer 5 ml of the super-
natant isobutanol layer to each of the 25 ml graduated flasks, make up
to volume with ethanol (3.10) and homogenize (= extractsT, A and B).
5.3.Measurement of fluorescence
Carry out the measurements at the wavelength for which the fluorimeter
gives an optimal response to the fluorescence of the thiochrome.
Irradiate at approximately 365 nm.
Adjust the instrument to zero using extract T. Measure the intensity of
fluorescence of extracts A and B.
6.Calculationofresults
The thiamine content in mg/kg of the sample is given by the ratio:
d/C1b
a/C0b ðÞ c
where:
a = intensity of fluorescence of extract A (internal standard);
b = intensity of fluorescence of extract B (sample);
c = weight of the test sample in g;
d = amount of thiamine in µg added to the test sample (internal standard).
RepeatabilityThe difference between the results of two parallel determinations carried out
on the same sample must not exceed:
10 %, in relative value, for contentslower than 500 mg/kg, and
5 %, in relative value, for contentsequal to or greater than 500 mg/kg.
3.DETERMINATION OF ASCORBIC ACID AND DEHYDROAS-
CORBICACID
(VITAMINC)
1.PurposeandScope
This method makes it possible to determine the total quantity of ascorbic and
dehydroascorbic acids (Vitamin C) in feedingstuffs, concentrates and
premixes. The lower limit of the determination is 5 ppm. Products are classi-
fied in two groups, according to their presumed Vitamin C content:1973L0046 — EN — 19.08.1981 — 001.001 — 13
▼B
Group A: contentslower than 10 g/kg;
Group B: contentsequal to or greater than 10 g/kg.
2.Principle
The sample is suspended in a dilute solution of metaphosphoric acid and
extracted with chloroform. The aqueous phase is treated with a solution of
2,6-dichlorophenol-indophenol in order to transform the ascorbic acid into
dehydroascorbic acid, and then with a solution of 2,4-dinitrophenylhydrazine.
The hydrazone formed isextracted with a mixture of ethyl acetate, glacial
acetic acid and acetone. The solution is chromatographed on a column of
silica gel, the eluate evaporated to dryness and the residue dissolved in dilute
sulphuric acid. The optical density of the solution is measured by a spectro-
photometer at 509 nm.
For Group A products the eluate resulting from chromatography on the
column is further subjected to thin layer chromatography to isolate the hydra-zone.
3.Reagents
3.1. Standard solution of 0·05 % L-ascorbic acid: dissolve 50 mg L-
ascorbic acid a.p. in approximately 20 ml metaphosphoric acid solution
(3.2) and make up to 100 ml with water. Prepare immediately beforeuse.
3.2. 10 % (w/v) metaphosphoric acid solution: after grinding it in a mortar,
dissolve in water 200 g metaphosphoric acid a.p. and make up to
2 000 ml with water. Keep at 4 ºC. Thisiss table for one week.
3.3. Chloroform a.p.
3.4. Solution of 0·5 % (w/v) 2,6-dichlorophenol-indophenol a.p. Prepare
immediately before use.
3.5. Filtration aid (S. and S. No 121 or equivalent).
3.6. Acid solution of 2 % (w/v) 2,4-dinitrophenylhydrazine: dissolve 2 g
2,4-dinitrophenylhydrazine in 100 ml dilute sulphuric acid (25 ml
sulphuric acid a.p., d: 1·84, diluted by making up to 100 ml with
water). Stored at a cool temperature thiss olution keepsfor one week.
3.7. Nitrogen, or
3.8. Carbon dioxide.3.9. Mixture of ethyl acetate a.p./glacial acetic acid/acetone a.p.: 96/2/2 in
volume.
3.10. Mixture of dichloromethane a.p./glacial acetic acid: 97/3 in volume.3.11. Silica gel, particle size: 0·05 to 0·2 mm.
3.12. Stahl grade silica gel H, for thin layer chromatography.
3.13. Dilute sulphuric acid: place 105 ml water in a 200 ml graduated flask,
make up to volume with sulphuric acid a.p., d: 1·84.
3.14. Eluting solvent for thin layer chromatography: mix 75 ml diethyl ether
a.p., 25 ml ethyl acetate a.p. and 4·0 ml 96 % (w/v) acetic acid a.p.
Renew after 2 to 3 chromatographies.
4.Apparatus
4.1. Water bath fitted with a thermostat set at 20 ºC.
4.2. Centrifuge (3 500 rpm) with 40 to 50 ml tubesfitted with ground-glas s
stoppers.
4.3. Rotary vacuum evaporator with 250 ml flasks.
4.4. Glass chromatography tubes (length: 100 mm, internal diameter: 20 mm),
with a sintered disc (eg Allihn tubes).
4.5. Spectrophotometer or colorimeter with filterswith 10 mm cells .
4.6. Apparatusfor thin layer chromatography, with s ilica gel plates(3.12)
coated to a depth of 0·5 to 0·6 mm. (Ready-made platesare appropriate.)
Dry the platesfor 2½ to 3 hoursin the drying oven at 120 to 130 ºC.
Leave to cool and then keep in a desiccator for at least 24 hours before
use.
4.7. Drying oven set at 120 to 130 ºC.1973L0046 — EN — 19.08.1981 — 001.001 — 14
▼B
5.Procedure
5.1.Extraction
Place in each of two 250 ml graduated flasks (with ground-glass stop-
pers), A and B, identical quantities of the finely divided sample
containing about 200 µg vitamin C. Add to flask A only 0·4 ml standard
solution (3.1) and mix, shaking gently (internal standard).
Add to each flask 30 ml chloroform (3.3) and 25 ml metaphosphoric
acid solution (3.2) at 4 ºC. Shake briefly and then leave to stand for 10
to 15 minutes. Add 25 ml water, stopper the flasks, shake vigorously for
10 seconds and leave to stand for 10 to 15 minutes in the water bath
(4.1). Centrifuge to separate the aqueous phase from the chloroform
phase. Carry out the operations simultaneously, as described below, on
the aqueousextractsA (internal s tandard) and B.
5.2.Oxidation
Using a pipette, transfer 40 ml of the supernatant aqueous solution
(slightly cloudy) obtained in 5.1 to a reaction tube fitted with a
ground-glass stopper, add 0·5 to 1 ml 2,6-dichlorophenol-indophenol
solution (3.4) and mix. A red colouring develops which should remain
for at least 15 minutes. Then add approximately 300 mg filtration aid
(3.5), shake and filter through a dry pleated filter. The filtrate need not
necessarily be clear.
5.3.Reaction with 2,4-dinitrophenylhydrazine and hydrazone extraction
Using a pipette, transfer 10 ml of the filtrate obtained in 5.2 to a centri-
fuge tube (4.2), add 2 ml 2,4-dinitrophenylhydrazine solution (3.6) and
mix. Pass a stream of nitrogen (3.7) or carbon dioxide (3.8) rapidly into
the tube, stopper the tube and immerse it for approximately 15 hours
(overnight) in the water bath (4.1).
Then add 3 ml water, 20 ml of the ethyl acetate/glacial acetic acid/
acetone mixture (3.9) and approximately 800 mg filtration aid (3.5).
Stopper the tube, shake vigorously for 30 seconds and centrifuge. Place
15 ml of the supernatant phase in an evaporation flask and evaporate
under reduced pressure in the rotary evaporator (4.3) until an oily
residue is obtained. Dissolve the residue in 2 ml of the ethyl acetate/
glacial acetic acid/acetone mixture (3.9) by re-heating at 50 ºC, leave
to cool, add 10 ml of the dichloromethane/glacial acetic acid mixture
(3.10) and mix.
5.4.Chromatography ona column
Fill a chromatography tube (4.4) up to a level of 30 mm with the
dichloromethane/glacial acetic acid mixture (3.10). Suspend (shaking
vigorously) 5 g silica gel (3.11) in 30 ml of the dichloromethane/glacial
acetic acid mixture (3.10); pour the suspension into the tube. Leave to
stand and then compress under nitrogen (3.7) at low pressure. Decant
into the tube the solution obtained in 5.3, rinse the flask with a small
quantity of the dichloromethane/glacial acetic acid mixture (3.10) and
decant into the tube, then fill the latter with the mixture (3.10) and
proceed to wash the column with the same mixture (3 to 4 lots of
approximately 5 ml) until a colourless eluate is obtained. Discard the
part of the eluate which iscoloured yellow.
Elute the reddish zone at the top of the column with the ethyl acetate/
glacial acetic acid/acetone mixture (3.9), collect the eluate and evaporate
to dryness.
5.4.1.For Group A products (contents in vitamin C lower than 10 g/
kg),dissolve the residue in 2·0 ml of the ethyl acetate/glacial
acetic acid/acetone mixture (3.9) and chromatograph immediately
on a thin layer ass hown in 5.5.
5.4.2.For Group B products (contents in vitamin C equal to or greater
than10 g/kg), treat the oily residue with 4·0 ml dilute sulphuric
acid (3.13), shake vigorously to dissolve the residue completely
and measure the optical density as shown in 5.6.
5.5.Thinlayer chromatography
Carry out in duplicate the operations described as follows. Place in a
thin line on the plate (4.6) 0·5 ml of the solution obtained in 5.4.1.
Using the eluting solvent (3.14) develop for at least 20 minutes in a
tank saturated with solvent vapour, until the pink-coloured hydrazone
zone isclearly s eparated. Leave to dry in the open. Mark out the limit
of the pink zone, scrape away the zone with a spatula and quantitatively
transfer the powder into a chromatography tube (4.4).1973L0046 — EN — 19.08.1981 — 001.001 — 15
▼B
Elute successively once with 2 ml and twice with 1·5 ml of the ethyl
acetate/glacial acetic acid/acetone mixture (3.9). Collect the eluate in a
small flask (the last part must be colourless). Evaporate to dryness, treat
the oily residue with 4·0 ml dilute sulphuric acid (3.13), shake vigor-
ously to dissolve the residue completely and measure the optical density.
5.6.Measurement of the optical density
Measure the optical density with a spectrophotometer at 509 nm 20 to
30 minutes after dissolving the residue in sulphuric acid. Carry out the
measurements by comparison with dilute sulphuric acid (3.13).
5.7.Blank test
Carry out a blank test applying the same procedure but without the
sample.
6.Calculationofresults
The vitamin C content of the sample in g per kg is given by the ratio:
c/C0a ðÞ /C1 2
b/C0c ðÞ /C1 10d
where:
a = optical density of the blank;
b = optical density of the internal standard solution;
c = optical density of the sample solution;d = weight, in grammes, of the test sample.
Repeatability
The difference between the results of two parallel determinations carried out
on the same sample must not exceed:
10 %, in relative value, for vitamin C contentslower than 10 g/kg and
5 %, in relative value, for contentsequal to or greater than 10 g/kg.1973L0046 — EN — 19.08.1981 — 001.001 — 16