1971L0250 — EN — 26.05.1999 — 003.001 — 1
This document is meant purely as a documentation tool and the institutions do not assume any liability for its contents
►B FIRSTCOMMISSIONDIRECTIVE
of15June1971
establishingCommunitymethodsofanalysisfortheofficial controloffeeding-stuffs
(71/250/EEC)
(OJ L 155, 12.7.1971, p. 13)
Amended by:
Official Journal
No page date
►M1Commission Directive 81/680/EEC of 30 July 1981 L 246 32 29.8.1981
►M2Commission Directive 98/54/EC of 16 July 1998 L 208 49 24.7.1998
►M3Commission Directive 1999/27/EC of 20 April 1999 L 118 36 6.5.1999
Corrected by:
►C1Consolidated text of corrigenda to instruments published in Special
Editions 1952-72, p. 89 (71/250/EEC)
▼B
FIRSTCOMMISSIONDIRECTIVE
of15June1971
establishingCommunitymethodsofanalysisfortheofficialcontrol
offeeding-stuffs
(71/250/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 on the intro-
duction of Community methods of sampling and analysis for the
official control of feeding-stuffs,(1) and in particular Article 2 thereof;
Whereas that Directive requires that official controls of feeding-stuffs
be carried out using Community methods of sampling and analysis forthe purpose of checking compliance with requirements arising underthe provisions laid down by law, regulation or administrative actionconcerning the quality and composition of feeding-stuffs;
Whereas all the necessary methods of analysis should be established as
soon as possible; whereas the establishment of methods for the deter-
mination of hydrocyanic acid, calcium, carbonates, crude ash, ashinsoluble in HCl, chlorine from chlorides, mustard oil, lactose, potas-sium, sodium, sugars, theobromine and urea, and the determination ofalkaloids in lupins and the estimation of the urease activity of products
derived from soya are a first stage in this process;
Whereas the measures provided for in this Directive are in accordance
with the Opinion of the Standing Committee for Feeding-stuffs;
HAS ADOPTED THIS DIRECTIVE:
Article 1
The Member States shall require that analyses for official controls of
feeding-stuffs as regards their levels of hydrocyanic acid, calcium,carbonates, crude ash, ash insoluble in HCl chlorine from chlorides,►
M3 ◄lactose, potassium, sodium, sugars
►M3 ◄and urea, ►M2 ◄and the esti-
mation of the urease activity of products derived from soya be carried
out using the methods set out in the Annex to this Directive.
The general rules contained in Part 1 of the Annex shall apply to the
methods of analysis adopted pursuant to Council Directive 70/373/EEC.
Article 2
The Member States shall, not later than 1 July 1972, bring into force
the laws, regulations or administrative provisions necessary to comply
with this Directive. They shall forthwith inform the Commission
thereof.
Article 3
This Directive is addressed to the Member States.1971L0250 — EN — 26.05.1999 — 003.001 — 2
(1) OJ No L 170, 3.8.1970, p. 2.▼M1
▼B
▼B
ANNEX
METHODS OF ANALYSIS OF THE COMPONENTS OF FEEDING-
STUFFS
1.GENERAL PROVISIONS ON METHODS OF ANALYSIS FOR
FEEDINGSTUFFS
A. PREPARATION OF SAMPLES FOR ANALYSIS
1.Purpose
The procedures described below concern the preparation for analysis of
final samples, sent to the control laboratories after sampling in accordance
withth e provisions laid down by First Commission Directive 76/371/EEC
of 1 March 1976 establishing Community methods of sampling for the offi-
cial control of feedingstuffs(1).
These samples must be prepared in such a way that the amounts weighed
out, as provided for in the methods of analysis, are homogeneous and
representative of the final samples.
2.Precautionstobetaken
All the necessary operations must be performed in such a way as to avoid
as far as possible contamination of the sample and changes of its composi-
tion. Grinding, mixing and sieving should be carried out as quickly as
possible with minimal exposure of the sample to the air and light. Mills
and grinders likely to appreciably heat the sample should not be used.
Manual grinding is recommended for feedingstuffs which are particularly
sensitive to heat. Care should also be taken to ensure that the apparatus
itself is not a source of contamination of trace elements.
If the preparation cannot be carried out without significant changes in the
moisture content of the sample, determine the moisture content before and
after preparation according to the method laid down in Part 1 of the Annex
to Second Commission Directive 71/393/EEC of 18 November 1971 estab-
lishing Community methods of analysis for the official control of
feedingstuffs(2), as amended by Commission Directive 73/47/EEC of 5
December 1972(3).
3.Procedure
Mix thoroughly the final sample either mechanically or manually. Divide
the sample into two equal portions (the quartering method should be used
where applicable). Keep one of the portions in a suitable clean, dry
container, fitted with an air-tight stopper, and prepare the other portion or
a representative part of it, of at least 100 g, as indicated below.
3.1.Feedingstuffs which can be ground as such
Unless otherwise specified in the methods of analysis, sieve the whole
sample through a sieve with a square mesh of 1 mm side (in accordance
withrecommendation ISO R565) after grinding, if necessary. Avoid any
overgrinding.
Mix the sieved sample and collect it in a suitable clean, dry container fitted
with an air-tight stopper. Mix again, immediately before weighing out the
amount for analysis.
3.2.Feedingstuffs which can be ground after drying
Unless otherwise specified in the methods of analysis, dry the sample to
bring its moisture content down to a level of 8 to 12 %, according to the
preliminary drying procedure described under point 4.3 of the method of
determination of moisture mentioned in section 2 above. Then proceed as
indicated in section 3.1.1971L0250 — EN — 26.05.1999 — 003.001 — 3
(1) OJ No L 102, 15. 4. 1976, p. 1.
(2) OJ No L 279, 20. 12. 1971, p. 7.
(3) OJ No L 83, 30. 3. 1973, p. 35.▼M1
▼M1
3.3.Liquid or semi-liquid feedingstuffs
Collect the sample in a suitable clean, dry container, fitted with an air-tight
stopper. Mix thoroughly immediately before weighing out the amount for
analysis.
3.4.Other feedingstuffs
Samples which cannot be prepared according to one of the above proce-
dures should be treated by any other procedure which ensures that the
amounts weighed out for the analysis are homogeneous and representative
of the final samples.
4.Storageofsamples
Samples must be stored at a temperature that will not alter their composi-
tion. Samples intended for the analysis of vitamins or substances which are
particularly sensitive to light should be stored in brown glass containers.
B. PROVISIONS RELATING TO REAGENTS AND APPARATUS USED IN
METHODS OF ANALYSIS
1. Unless otherwise specified in the methods of analysis, all analytical
reagents must be analytically pure (a.p.). When determining trace elements,
the purity of the reagents must be checked by a blank test. Depending upon
the results obtained, further purification of the reagents may be required.
2. Any operation involving preparation of solutions, dilution, rinsing or
washing, mentioned in the methods of analysis without indication as to
the nature of the solvent or diluent employed, implies that water must be
used. As a general rule, water should be demineralized or distilled. In parti-
cular cases, which are indicated in the methods of analysis, it must be
submitted to special procedures of purification.
3. In view of the equipment normally found in control laboratories, only those
instruments and apparatus which are special or require specific usage are
referred to in the methods of analysis. They must be clean, especially
when very small amounts of substances have to be determinded.
C. APPLICATION OF METHODS OF ANALYSIS AND EXPRESSION OF
THE RESULTS
1. In general a single method of analysis is established for the determination
of each substance in feedingstuffs. Where several methods are given, the
particular method used by the control laboratory must be indicated on the
analysis report.
2. The result given in the analysis report shall be the average value obtained
from at least two determinations, carried out on separate portions of the
sample, and of satisfactory repeatability.
This result shall be expressed in the manner laid down in the method of
analysis to an appropriate number of significant figures and shall be
corrected, if necessary, to the moisture content of the final sample prior to
preparation.1971L0250 — EN — 26.05.1999 — 003.001 — 4
▼B
2.DETERMINATIONOFHYDROCYANICACID
1.Purposeandscope
This method makes it possible to determine the level of hydrocyanic acid,
free and combined in the form of glycosides, in feeding-stuffs and in parti-
cular in products derived from flax seed, manioc flour and certain species of
beans.
2.Principle
The sample is suspended in water. The hydrocyanic acid is released by the
action of enzymes, entrained by steam distillation and collected in a specific
volume of acidified silver nitrate solution. The silver cyanide is separated by
filtration and the excess silver nitrate is titrated with a solution of ammonium
thiocyanate.
3Reagents
3.1. A suspension of sweet almonds: crushtwenty blanch ed sweet almonds
in 100 ml of water at 37 to 40 ºC. Check that there is no hydrocyanic
acid in 10 ml of the suspension using sodium picrote paper or by
carrying out a blank test as described in the last paragraph of 5.
3.2. 10% solution (w/v) of sodium acetate, neutral to phenolphthalein.
3.3. Anti-foaming emulsion (e.g. silicone).
3.4. Nitric acid, d: 1·40.
3.5. Silver nitrate solution: 0·02 N.
3.6. Ammonium thiocyanate solution: 0·02 N.
3.7. Saturated solution of ammonium ferric sulphate.
3.8. Ammonia, d: 0·958.
4.Apparatus
4.1. Oven withth ermostat set at 38 ºC.
4.2. Apparatus for distillation by entrainment in steam fitted witha
condenser witha curved extension piece.
4.3. 1000 ml flat-bottomed flasks withground-glass stoppers.
4.4. Oil bath.
4.5. Burette graduated in 1/20 ml.
5.Procedure
Weigh 20 g of the sample to the nearest 5 mg, place in 1 litre flat-bottomed
flask and add 50 ml of water and 10 ml of sweet almond suspension (3.1.).
Stopper the flask and transfer to the oven for sixteen hours at 38 ºC. Next,
cool to room temperature and add 80 ml of water, 10 ml of sodium acetate
solution (3.2) and a drop of anti-foaming emulsion (3.3).
Connect the flask to the steam distillation apparatus and place in an oilbath
which has first been brought to a temperature slightly above 100 ºC. Distil
200 to 300 ml of liquid by passing a powerful current of steam through the
flask and gently heating the oil-bath. Collect the distillate in an Erlenmeyer
flask protected from the light and containing exactly 50 ml of silver nitrate
solution 0·02 N (3.5) and 1 ml of nitric acid (3.4). Make sure that the
condenser's extension piece is immersed in the silver nitrate solution.
Transfer the contents of the Erlenmeyer flask to a 500 ml volumetric flask,
make up to volume withwater, stir and filter. Remove 250 ml of th e filtrate,
add approximately 1 ml solution of ammonium ferric sulphate (3.7) and
back-titrate the excess silver nitrate with the solution of ammonium thiocya-
nate 0·02 N (3.6) taken from the burette graduated in 1/20 ml.
A blank test may, if required , be carried out by applying the same procedure
to 10 ml of sweet almond suspension (3.1), omitting the sample to be
analysed.
6.Calculationofresults
If the blank test indicates that silver nitrate solution 0.02 N has been
consumed, subtract the value of this from the volume consumed by the distil-1971L0250 — EN — 26.05.1999 — 003.001 — 5
▼B
late of the sample. 1 ml of AgNO30·02 N corresponds to 0·54 mg of HCN.
Express the result as a percentage of the sample.
7.Observation
If the sample contains a large quantity of sulphides (e.g. beans), a black
precipitate of silver sulphide is formed which is filtered together with the
silver cyanide deposit. The formation of this precipitate causes a loss of
silver nitrate solution 0·02 N, the volume of which must be subtracted from
the volume used to calculate the HCN content. To do this, proceed as
follows:
Treat the deposit left on the filter with 50 ml of ammonia (3.8) in order to
dissolve the silver cyanide. Wash the residue in dilute ammonia and then
determine its silver content. Convert the value obtained into ml of silver
nitrate solution 0·02 N.
The sample's HCN content may also be determined by titrating the acidified
ammoniacal filtrate withnitric acid.
3.DETERMINATIONOFCALCIUM
1.PurposeandScope
The method makes it possible to determine the total calcium content of
feeding-stuffs.
2.Principle
The calcium is ashed, the ash treated with hydrochloric acid and the calcium
precipitated as calcium oxalate. Dissolve the precipitate in sulphuric acid and
titrate the oxalic acid which forms with a solution of potassium permangante.
3.Reagents
3.6. Hydrochloric acid A.R., d: 1·143.2. Nitric acid A.R., d: 1·40
3.3. Sulphuric acid A.R., d: 1·13
3.4. Ammonia A.R., d: 0·98
3.5. Cold saturated solution of ammonium oxalate A.R.
3.6. 30% solution (w/v) of citric acid A.R.
3.7. 5% solution (w/v) of ammonium chloride A.R.
3.8. 0·04% solution (w/v) of bromo-cresol green
3.9. Solution of potassium permanganate 0·1 N
4.Apparatus
4.1. Electric muffle-furnace withair circulation and th ermostat.
4.2. Platinum, silica or porcelain crucibles for ashing.
4.3. Glass filter crucibles of G
4porosity.
5.Procedure
Weigh approximately 5 g of the sample (or more if necessary) to the nearest
mg, calcine at 550 ºC and transfer the ash to a 250 ml beaker.
Add 40 ml of hydrochloric acid (3.1), 60 ml of water and a few drops of
nitric acid (3.2). Bring to the boil and keep at boiling point for thirty
minutes. Cool and transfer the solution to a 250 ml volumetric flask. Rinse,
bring the volume up to the mark with water, homogenise and filter.
Using a pipette, remove to a 250 ml beaker an aliquot amount containing 10
to 40 mg of calcium according to the assumed calcium content. Add 1 ml of
citric acid solution (3.6) and 5 ml of ammonium chloride solution (3.7).
5. Make the volume up to approximately 100 ml with water. Bring to the boil,
add eight to ten drops of bromo-cresol green solution (3.8) and 30 ml of a
warm solution of ammonium oxalate (3.5). If a precipitate forms, dissolve it
by adding a few drops of hydrochloric acid (3.1).
Neutralise very slowly withammonia (3.4), stirring continuously until a pH
reading of 4.4 to 4.6 is obtained (i.e. when the indicator changes colour).1971L0250 — EN — 26.05.1999 — 003.001 — 6
▼B
Place the beaker in a boiling water bath and keep there for thirty minutes to
allow the precipitate which has formed to settle. Remove the beaker from the
water bath. Leave it to stand for an hour and filter through a G4filter
crucible.
Wash the beaker and the crucible with water until the excess ammonium
oxalate is completely removed (the absence of chloride in the washing water
indicates that they have been sufficiently washed).
Dissolve the precipitate on the filter in 50 ml of warm sulphuric acid (3.3).
Rinse the crucible with warm water and make the filtrate up to approxi-
mately 100 ml. Bring the temperature up to 70—80 ºC and titrate drop by
drop witha solution of potassium permanganate (3.9) until a pink colour is
obtained which lasts for one minute.
6.Calculationofresults
1 ml of potassium permanganate 0·1 N corresponds to 2·004 mg of calcium.
Express the result obtained as a percentage of the sample.
7.Observations
7.1. For very low contents of calcium proceed as follows: filter the calcium
oxalate precipitate through an ash-free filter paper. After washing, dry
the filter and ash at 550 ºC in a platinum crucible. Redissolve the
residue in a few drops of sulphuric acid (3.3), evaporate until dry,
calcine again at 550 ºC and weigh. If W is the weight of the calcium
sulphate obtained, the calcium content of the aliquot amount taken as a
sample = W × 0·2944.
7.2. If the sample consists solely of mineral substances, dissolve in hydro-
chloric acid without ashing it first. In the case of products such as
calcium-aluminium phosphate which are difficult to dissolve in acid,
melt as follows by an alkaline process before dissolving: mix the sample
to be analysed thoroughly in a platinum crucible with a mixture five
times its weight, consisting of equal amounts of potassium carbonate
and sodium carbonate. Heat carefully until the mixture is completely
melted. Cool, and dissolve in hydrochloric acid.
7.3. If the magnesium content of the sample is high, precipitate the calcium
oxalate a second time.
4.DETERMINATIONOFCARBONATES
1.PurposeandScope
This method makes it possible to determine the amount of carbonates,
conventionally expressed as calcium carbonate, in most feeding-stuffs.
However in certain cases (for example, withiron carbonate) a special meth od
must be used.
2.Principle
The carbonates are decomposed in hydrochloric acid; the carbon dioxide
released is collected in a graduated tube, and its volume compared withth at
released under the same conditions by a known quantity of calcium carbonate
A.R.
3.Reagents
3.1. Hydrochloric acid, d: 1·10.
3.2. Calcium carbonate, A.R.
3.3. Sulphuric acid, approximately 0·1 N, coloured with methyl red.
4.Apparatus
Scheibler-Dietrich apparatus (see diagram) or equivalent apparatus.
5.Procedure
According to the sample's carbonate content, weigh a portion of the sample
as shown below:
0·5 g for products containing from 50 to 100 % of carbonates, expressed
as calcium carbonate;1971L0250 — EN — 26.05.1999 — 003.001 — 7
▼B
1 g for products containing from 40 to 50% of carbonates, expressed as
calcium carbonate;
2 to 3 g for other products.
Place the portion of the sample in the special flask (4) of the apparatus, fitted
with a small tube of unbreakable material containing 10 ml of hydrochloricacid (3.1), and connect the flask to the apparatus. Turn the three-way cock
(5) so that the tube (1) connects with the outside. Using the mobile tube
(2), which is filled with coloured sulphuric acid (3.3) and connected to the
graduated tube (1), bring the level of the liquid up to the zero mark. Turn
the cock (5) in order to connect up tubes (1) and (3) and check that the level
is at zero.
Run the hydrochloric acid (3.1) slowly over the portion of the sample, tilting
the flask (4). Make the pressure equal by lowering the tube (2). Shake the
flask (4) until the release of carbon dioxide has stopped completely.
Restore pressure by bringing the liquid back to the same level in tubes (1)
and (2). After a few minutes , when the volume of gas has become constant,
take the reading.
Carry out a control test in the same conditions on 0·5 g of calcium carbonate
(3.2).
6.Calculationofresults
The content in grammes of carbonates, expressed as calcium carbonate, as a
percentage of the sample, is calculated by using the formula:
V/C2100
T/C22W
where:
V = ml of CO2released by the portion of the sample.
T = ml of CO2released by 0·5 g of CaCO3A.R.
W = weight, in grammes, of the portion of the sample.
7.Observations
7.1. When the portion of the sample weighs more than 2 g, first place 15 ml
of distilled water in the flask (4) and mix before beginning the test. Use
the same volume of water for the control test.
7.2. If the apparatus used has a different volume from that of the Scheibler-
Dietrich apparatus, the portions taken from the sample and from the
control substance and the calculation of the results must be adapted
accordingly.1971L0250 — EN — 26.05.1999 — 003.001 — 8
▼B
SCHEIBER-DIETRICH APPARATUS FOR THE DETERMINATION OF CO2
(measuredinmm)
5.DETERMINATIONOFCRUDEASH
1.PurposeandScope
This method makes it possible to determine the crude ash content of feeding-
stuffs.
2.Principle
The sample is ashed at 550 ºC; the residue is weighed.
3.Reagents
20% solution (w/v) of ammonium nitrate.
4.Apparatus
4.1. Hot-plate.
4.2. Electric muffle-furnace withth ermostat.4.3. Crucibles for ashing made of platinum or an alloy of platinum and gold
(10% Pt, 90 Au), either rectangular (60 × 40 × 25 mm) or circular
(diameter: 60 to 75 mm, height: 20 to 25 mm).1971L0250 — EN — 26.05.1999 — 003.001 — 9
▼B
5.Procedure
Weigh out to the nearest mg approximately 5 g of the sample (2·5 in the case
of products which have a tendency to swell) and place in a crucible for
ashing which has first been calcined and tared. Place the crucible on the
hot-plate and heat gradually until the substance carbonises. Put the crucible
into the muffle-furnace set at 550 ºC ± 5 ºC. Keep at this temperature until
white, light grey or reddish ash is obtained which appears to be free from
carbonaceous particles. Place the crucible in a desiccator, leave to cool and
weighimmediately.
6.Calculationofresults
Calculate the weight of the residue by deducting the tare.Express the result as a percentage of the sample.
7.Observations
7.1. The ash of substances which are difficult to ash must be subjected to an
initial ashing of at least three hours, cooled and then a few drops of 20%
solution of ammonium nitrate added to it (carefully, to avoid dispersal
of the ash or the formation of lumps). Continue calcining after drying
in the oven. Repeat the operation as necessary until ashing is complete.
7.2. In the case of susbstances resistant to the treatment described under 7.1,
proceed as follows: after ashing for three hours, place the ash in warm
water and filter through a small, ash-free filter. Ash the filter and its
contents in the original crucible. Place the filtrate in the cooled crucible,
evaporate until dry, ashand weigh .
7.3. In the case of oils and fats , weighaccurately a sample of approximately
25 g in a suitably sized crucible. Carbonise by setting light to the
substance witha strip of ash -free filter paper. After combustion, moisten
withas little water as possible. Dry and ashas described under 5.
6.DETERMINATION OF ASH WHICH IS INSOLUBLE IN HYDRO-
CHOLORICACID
1.PurposeandScope
This method makes it possible to determine the level in feeding-stuffs of
mineral substances which are insoluble in hydrochloric acid. Two methods
can be used, depending on the nature of the sample.
1.1.Method A: applicable to straight organic feeding-stuffs and to most
compound feeding-stuffs;
1.2.Method B: applicable to mineral compounds and mixtures and to
compound feeding-stuffs whose content in substances insoluble in
hydrochloric acid, as determined by Method A, is greater than 1 %.
2.Principle
2.1.Method A: the sample is ashed, the ash boiled in hydrochloric acid and
the insoluble residue filtered and weighed.
2.2.Method B: the sample is treated with hydrochloric acid. The solution is
filtered, the residue ashed and the ash thus obtained treated in accor-
dance withMeth od A.
3.Reagents
3.1. Hydrochloric acid 3 N.
3.2. 20% solution (w/v) of trichloroacetic acid.
3.3. 1% solution (w/v) of trichloroacetic acid.
4.Apparatus
4.1. Hot plate.4.2. Electric muffle-furnace withth ermostat.
4.3. Crucibles for ashing made of platinum or an alloy of platinum and gold
(10% Pt, 90% Au), either rectangular (60 × 40 × 25 mm) or circular
(diameter 60 to 75 mm, height: 20 to 25 mm).1971L0250 — EN — 26.05.1999 — 003.001 — 10
▼B
5.Procedure
5.1.Method A:
Ash the sample using the method described for the determination of
crude ash. Ash obtained from that analysis may also be used.
Place the ash in a 250 to 400 ml beaker using 75 ml of hydrochloric
acid 3 N (3.1). Bring slowly to the boil and boil gently for fifteen
minutes. Filter the warm solution through an ash-free filter paper and
wash the residue with warm water until the acid reaction is no longer
visible. Dry the filter containing the residue and ash in a tared crucible
at a temperature of not less than 550 ºC and not more than 700 ºC. Cool
in a desiccator and weigh.
5.2.Method B
Weigh 5 g of the sample to the nearest mg and place in a 250 to 400 ml
beaker. Add 25 ml of water and 25 ml of hydrochloric acid 3 N (3.1)
successively, mix and wait for effervescence to cease. Add a further
50 ml of hydrochloric acid 3 N (3.1). Wait for any release of gas to
cease then place the beaker in a boiling water bath and keep it there
for thirty minutes or longer, if necessary, in order to hydrolyse thor-
oughly any starch which may be present.
Filter while warm through an ash-free filter and wash the filter in 50 ml
of warm water (see observation 7). Place the filter containing the residue
in a crucible for ashing, dry and ash at a temperature of not less than
550 ºC and not more than 700 ºC. Place the ash in a 250 to 400 ml
beaker using 75 ml of hydrochloric acid 3 N (3.1); continue as described
in the second subparagraph of 5.1.
6.Calculationofresults
Calculate the weight of the residue by deducting the tare. Express the result
as a percentage of the sample.
7.Observation
If filtration proves difficult recommence the analysis, replacing the 50 ml of
hydrochloric acid 3 N (3.1) by 50 ml of 20% trichloroacetic acid (3.2) and
washing the filter in a warm solution of 1% trichloroacetic acid (3.3).
7.DETERMINATIONOFCHLORINEFROMCHLORIDES
1.PurposeandScope
This method makes it possible to determine the amount of chlorine in chlor-
ides which are soluble in water, conventionally expressed as sodium chloride.
It is applicable to all feeding-stuffs.
2.Principle
The chlorides are dissolved in water. If the product contains organic matter it
is clarified. The solution is slightly acidified with nitric acid and the chlor-
ides precipitated in the form of silver chloride by means of a solution of
silver nitrate. The excess silver nitrate is titrated with a solution of ammo-
nium thiocyanate, by Volhard's method.
3.Reagents
3.1. Solution of ammonium thiocyanate 0.1 N.3.2. Solution of silver nitrate 0.1 N.
3.3. Saturated solution of ammonium ferric sulphate.
3.4. Nitric acid, d: 1.38.3.5. Diethyl ether A.R.3.6. Acetone A.R.
3.7. Carrez I solution: dissolve in water 21.9 g of zinc acetate, Zn (CH
3COO)2·2 H2O and 3 g of glacial acetic acid. Make up to 100 ml with
water.
3.8. Carrez II solution: dissolve in water 10·6 g of potassium ferrocynaide K4Fe (CN)6·3 H2O. Make up to 100 ml withwater.
3.9. Active carbon A.R., free from chlorides and not absorbing them.1971L0250 — EN — 26.05.1999 — 003.001 — 11
▼B
4.Apparatus
Mixer (tumbler): approximately 35 to 40 rpm.
5.Procedure
5.1.Preparation of the solution
According to the nature of the sample, prepare a solution as shown
under 5.1.1, 5.1.2 or 5.1.3.
At the same time carry out a blank test omitting the sample to be
analysed.
5.1.1. Samples free from organic matter
Weigh to the nearest mg a sample of not more than 10 g and
containing not more than 3 g of chlorine in the form of chlorides.
Place with400 ml of water in a 500 ml volumetric flask at
approximately 20 ºC. Mix for thirty minutes in the tumbler, bring
up to volume, homogenise and filter.
5.1.2. Samples containing organic matter, excluding the products listed
under 5.1.3.
Weigh approximately 5 g of the sample to the nearest mg and
place with1 g of active carbon in a 500 ml volumetric flask.
Add 400 ml of water at approximately 20 ºC and 5 ml of Carrez
solution I (3.7), stir then add 5 ml of Carrez solution II (3.8). Mix
for thirty minutes in the tumbler, bring up to volume, homogenise
and filter.
5.1.3. Cooked feeding-stuffs, flax cakes and flour, products rich in flax
flour and other products rich in mucilage or in colloidal
substances (for example, dextrinated starch)
Prepare the solution as described under 5.1.2 but do not filter.
Decant (if necessary centrifuge), remove 100 ml of the superna-
tant liquid and transfer to a 200 ml measuring flask. Mix with
acetone (3.6) and bring up to volume with this solvent, homoge-
nise and filter.
5.2.Titration
Using a pipette, transfer to an Erlenmayer flask from 25 ml to 100 ml of
the filtrate (according to the assumed chlorine content) obtained as
described under 5.1.1, 5.1.2 or 5.1.3. The aliquot portion must not
contain more than 150 mg of chlorine (Cl). Dilute if necessary to not
less than 50 ml with water, add 5 ml of nitric acid (3.4.), 20 ml of satu-
rated solution of ammonium ferric sulphate (3.3) and two drops of
ammonium thiocyanate solution (3.1) transferred by means of a burette
filled up to the zero mark. Using a burette, transfer the silver nitrate
solution (3.2) in sucha way th at an excess of 5 ml is obtained. Add
5 ml of diethyl ether (3.5) and shake hard to coagulate the precipitate.
Titrate the excess silver nitrate with the ammonium thiocyanate solution
(3.1) until the reddish-brown tint has lasted for one minute.
6.Calculationofresults
The amount of chlorine (w), expressed as sodium chloride, present in the
volume of filtrate taken for titration is calculated by using the following
formula:
W = 5·845 (V1−V2)m g
where: V1= ml of silver nitrate solution C·1 N added
V2= ml of ammonium thiocyanate solution 0·1 N used for titration.
If the blank test indicates that silver nitrate solution 0·1 N has been
consumed deduct this value from the volume (V1−V2).
7.Observations
7.1. Titration may also be carried out by potentiometry;
7.2. In the case of products which are very rich in oils and fats, first de-fat
with diethyl ether or light petroleum;
7.3. In the case of fish-meal, titration may be carried out by Mohr's method.1971L0250 — EN — 26.05.1999 — 003.001 — 12
▼M3
9.DETERMINATIONOFLACTOSE
1.Purposeandscope
This method makes it possible to determine the level of lactose in feeding-
stuffs containing more than 0·5% of lactose.
2.Principle
The sugars are dissolved in water. The solution is subjected to fermentation
by the yeast Saccharomyces cerevisiae which leaves the lactose intact. After
clarification and filtration the lactose content of the filtrate is determined by
the Luff-Schoorl method.
3.Reagents
3.1. Suspension of Saccharomyces cerevisiae: suspend 25 g of freshyeast in
100 ml of water The suspension will keep for a maximum period of one
week in a refrigerator.
3.2. Carrez solution I: dissolve in water 21·9 g of zinc acetate Zn (CH3COO)2·2 H2O and 3 g of glacial acetic acid. Make up to 100 ml with
water.
3.3. Carrez solution II: dissolve in water 10·6 g of potassium ferrocyanide
►C1K4Fe (CN)6·3 H2O◄. Make up to 100 ml withwater.
3.4. Luff-Schoorl reagent:
Stirring carefully, pour the citric acid solution (3.4.2) into the sodium
carbonate solution (3.4.2). Add the copper sulphate solution (3.4.1) and
make up to 1 litre with water. Leave to settle overnight and filter. Check
the normality of the reagent thus obtained (Cu 0·1 N; Na2CO32N). The
solution's pH should be approximately 9·4.
3.4.1. Copper sulphate solution: dissolve 25 g of copper sulphate A.R.
Cu SO4·5 H2O, free from iron, in 100 ml of water.
3.4.2. Citric acid solution: dissolve 50 g of citric acid A.R. C6H8O7·
H2O in 50 ml of water.
3.4.3. Sodium carbonate solution: dissolve 143·8 g of anhydrous sodium
carbonate A.R. in approximately 300 ml of warm water. Leave to
cool.
3.5. Granulated pumice stone boiled in hydrochloric acid, washed in water
and dried.
3.6. 30% solution (w/v) of sodium iodide.
3.7. Sulphuric acid 6 N.
3.8. Solution of sodium thiosulphate 0·1 N.
3.9. Starchsolution: add a mixture of 5 g of soluble starchin 30 ml of water
to 1 litre of boiling water. Boil for three minutes, leave to cool, and if
necessary add 10 mg of mercuric iodide as a preservative.
4.Apparatus
Water bathwithth ermostat set at 38-40 ºC.
5.Procedure
Weigh 1 g of the sample to the nearest mg and place this portion of the
sample in a 100 ml volumetric flask. Add 25 to 30 ml of water. Place the
flask in a boiling water bath for thirty minutes and then cool to approxi-
mately 35 ºC. Add 5 ml of yeast suspension (3·1) and homogenise. Leave
the flask to stand for two hours in a water bath, at a temperature of 38-
40 ºC. Cool to approximately 20 ºC.
Add 2·5 ml of Carrez solution I (3.2) and stir for thirty seconds, then add
2·5 ml of Carrez solution II (3.3) and again stir for thirty seconds. Make up
to 100 ml withwater, mix and filter. Using a pipette, remove an amount of
filtrate which does not exceed 25 ml and whichpreferably contains from 40
to 80 mg of lactose and transfer it to a 300 ml Erlenmeyer flask. If necessary,
make up to 25 ml withwater.
Carry out a blank test in the same way with 5 ml of yeast suspension (3.1).1971L0250 — EN — 26.05.1999 — 003.001 — 13
▼B
▼B
Determine the lactose content according to Luff-Schoorl, as follows: add
exactly 25 ml of Luff-Schoorl reagent (3.4) and two granules of pumice stone
(3.5). Stir by hand-while heating over a free flame of medium height and
bring the liquid to the boil in approximately two minutes. Place the Erlen-
meyer immediately on an asbestos-coated wire gauze witha h ole
approximately 6 cm in diameter under which a flame has been lit. The flame
shall be regulated in such a way that only the base of the Erlenmeyer is
heated. Fit a reflux condenser to the Erlenmeyer flask. Boil for exactly ten
minutes. Cool immediately in cold water and after approximately five
minutes titrate as follows:
Add 10 ml of potassium iodide solution (3.6) and immediately afterwards
(carefully, because of the risk of abundant foaming) add 25 ml of sulphuric
acid 6 N (3.7). Titrate with sodium thiosulphate solution 0·1 N (3.8) until a
dull yellow colour appears, add the starch indicator (3.9) and complete titra-
tion.
Carry out the same titration on an accurately measured mixture of 25 ml of
Luff-Schoorl reagent (3.4) and 25 ml of water, after adding 10 ml of potas-
sium iodide solution (3.6) and 25 ml of sulphuric acid 6 N (3.7) without
boiling.
6.Calculationofresults
Using the attached table, establish the amount of lactose in mg which corre-
sponds to the difference between the results of the two titrations, expressed in
ml of sodium thiosulphate 0·1 N.
Express the result as parts of anhydrous lactose as a percentage of the
sample.
7.Observation
For products containing more than 40% of fermentable sugar, use more than
5 ml of yeast suspension (3.1).
Tableofvaluesfor25mlofLuff-Schoorlreagent
ml of Na2S2O30·1 N, two minutes' heating, ten minutes' boiling
Na2S2O30·1 NGlucose, fructose invert
sugars
C6H12O6Lactose
G12H22O11Maltose
C12H22O11Na2S2O30·1 N
ml mg difference mg difference mg difference ml
1 2·4 2·4 3·6 3·7 3·9 3·9 1
2 4·8 2·4 7·3 3·7 7·8 3·9 2
3 7·2 2·5 11·0 3·7 11·7 3·9 3
4 9·7 2·5 14·7 3·7 15·6 4·0 45 12·2 2·5 18·4 3·7 19·6 3·9 5
6 14·7 2·5 22·1 3·7 23·5 4·0 6
7 17·2 2·6 25·8 3·7 27·5 4·0 78 19·8 2·6 29·5 3·7 31·5 4·0 8
9 22·4 2·6 33·2 3·8 35·5 4·0 9
10 25·0 2·6 37·0 3·8 39·5 4·0 1011 27·6 2·7 40·8 3·8 43·5 4·0 1112 30·3 2·7 44·6 3·8 47·5 4·1 12
13 33·0 2·7 48·4 3·8 51·6 4·1 13
14 35·7 2·8 52·2 3·8 55·7 4·1 1415 38·5 2·8 56·0 3·9 59·8 4·1 15
16 41·3 2·9 59·9 3·9 63·9 4·1 16
17 44·2 2·9 63·8 3·9 68·0 4·2 1718 47·1 2·9 67·7 4·0 72·2 4·3 18
19 50·0 3·0 71·7 4·0 76·5 4·4 19
20 53·0 3·0 75·7 4·1 80·9 4·5 2021 56·0 3·1 79·8 4·1 85·4 4·6 2122 59·1 3·1 83·9 4·1 90·0 4·6 22
23 62·2 88·0 94·6 231971L0250 — EN — 26.05.1999 — 003.001 — 14
▼B
10.DETERMINATIONOFPOTASSIUM
1.Purposeandscope
This method makes it possible to determine the level of potassium in
feeding-stuffs.
2.Principle
The sample is ashed and the ash dissolved in hydrochloric acid. The
►C1potassium ◄content of the solution is determined by flame photo-
metry in the presence of caesium chloride and aluminium nitrate. The
addition of these substances largely eliminates interference from disturbing
elements.
3.Reagents
3.1. Hydrochloric acid A.R., d: 1.12.
3.2. Caesium chloride A.R.3.3. Aluminium nitrate ►
C1Al (NO3)3·9H2O◄, general purpose
reagent.
3.4. Potassium chloride A.R., anhydrous.
3.5. Loading agent: dissolve in water 50 g of caesium chloride (3.2) and
250 g of aluminium nitrate (3.3), make up to 1 litre withwater and
homogenise. Store in plastic bottles.
3.6. Standard solution of potassium: dissolve in water 1·907 g of potassium
chloride (3.4), add 5 ml of hydrochloric acid (3.1), make up to 1 litre
with water and homogenise. Store in plastic bottles. 1 ml of this solution
contains 1·00 mg of potassium
4.Apparatus
4.1. Platinum, silica or porcelain crucibles for ashing, provided if necessary
withlids.
4.2. Electric muffle-furnace withth ermostat.4.3. Flame photometer.
5.Procedure
5.1.Analysis of sample
As a general rule, weigh out 10 g of the sample to the nearest 10 mg,
place in a crucible and ash at 450 ºC for three hours. After cooling
transfer the ash quantitatively to a 500 ml graduated flask, using 250 to
300 ml of water and then 50 ml of hydrochloric acid (3.1). When all
release of carbon dioxide has ceased, heat the solution and keep at a
temperature of about 90 ºC for two hours, stirring occasionally. After
cooling to room temperature, make up to the mark with water, shake
and filter. Transfer to a 100 ml graduated flask an aliquot part of the
filtrate containing a maximum of 1·0 mg of potassium, add 10·0 ml of
loading agent (3.5), make up to the mark with water and homogenise. In
the case of higher levels of potassium dilute the solution to be analysed
in suitable proportions before adding the loading agent.
The table below is given as a guide for a sample of about 10 g.
Assumed potassium content of the
sample (% K)Dilution factor Aliquot part in ml of the solution
up to 0·1 — 50
0·1 to 0·5 — 100·5 to 1·0 — 5
1·0 to 5·0 1: 10 10
5·0 to 10·0 1: 10 5
10·0 to 20·0 1: 20 5
Measure by flame photometry at a wavelength of 768 nm. Calculate the
result by means of a calibration curve.1971L0250 — EN — 26.05.1999 — 003.001 — 15
▼B
5.2.Calibration curve
Place exactly 10 ml of the standard solution (3.6) in a 250 ml graduated
flask, make up to the mark with water and homogenise. Place in 100 ml
graduated flasks exactly 5, 10, 15, 20 and 25 ml of this solution, corre-
sponding respectively to amounts of potassium of 0·2, 0·4, 0·6, 0·8 and
1·0 mg. Complete the series with a blank flask containing no standard
solution. Add 10 ml of loading agent (3.5) to eachflask, make up to
the mark with water and homogenise. Carry out the measurements as
indicated in 5.1. The calibration curve is generally linear up to a potas-
sium concentration of 1 mg in 100 ml of solution.
6.Calculationofresults
Express the result as a percentage of the sample.
7.Observations
It is not always necessary to add loading agent (3.5) in order to eliminate the
interference of disturbing elements.
11.DETERMINATIONOFSODIUM
1.Purposeandscope
This method makes it possible to determine the level of sodium in feedings-
stuffs.
2.Principle
The sample is ashed and the ash dissolved in hydrochloric acid. The sodium
content of the solution is determined by flame photometry in the presence of
caesium chloride and aluminium nitrate. The addition of these substances
largely eliminates interference from disturbing elements.
3.Reagents
3.1. Hydrochloric acid A.R., d: 1.12.
3.2. Caesium chloride A.R.3.3. Aluminium nitrate ►
C1Al◄(NO3)3·9H2O, general purpose reagent
3.4. Sodium chloride A.R., anhydrous.
3.5. Loading agent: dissolve in water 50 g of caesium chloride (3.2) and
250 g of aluminium nitrate (3.3), make up to 1 litre withwater and
homogenise. Store in plastic bottles.
3.6. Standard solution of sodium: dissolve in water 2·542 g of sodium
chloride (3.4), add 5 ml of hydrochloric acid (3.1), make up to 1 litre
with water and homogenise Store in plastic bottles, 1 ml of this solution
contains 1·00 mg of sodium.
4.Apparatus
4.1. Platinum, silica or porcelain crucibles for ashing, provided if necessary
withlids.
4.2. Electric muffle-furnace withth ermostat.
4.3. Flame photometer.
5.Procedure
5.1.Analysis of sample
As a general rule, weigh out 10 g of the sample to the nearest 10 mg,
place in a crucible (4.2) and ash at 450 ºC for three hours. Avoid over-
heating (ignition). After cooling transfer the ash quantitatively to a
500 ml graduated flask, using 250 to 300 ml of water and then 50 ml
of hydrochloric acid (3.1). When all release of carbon dioxide has
ceased,heat the solution and keep at a temperature of about 90 ºC for
two hours, stirring occasionally. After cooling to room temperature,
make up to the mark with water, shake and filter. Transfer to a 100 ml
graduated flask an aliquot part of the filtrate containing a maximum of
1·0 mg of sodium, add 10·0 ml of loading agent (3.5), make up to the
mark with water and homogenise. In the case of higher levels of
sodium, dilute the solution to be analysed in suitable proportions before
adding the loading agent.1971L0250 — EN — 26.05.1999 — 003.001 — 16
▼B
The table below is given as a guide for a sample of about 10 g.
Assumed sodium content of the
sample (% Na)Dilution factor Aliquot part in ml of the solution
up to 0·1 — 50
0·1 to 0·5 — 100·5 to 1·0 — 51·0 to 5·0 1: 10 10
5·0 to 10·0 1: 10 5
10·0 to 20·0 1: 20 5
Measure by flame photometry at a wavelength of 589 nm. Calculate the
result by means of a calibration curve.
5.2.Calibration curve
Place exactly 10 ml of the standard solution (3.6) in a 250 ml graduated
flask, make up to the mark with water and homogenise. Place in 100 ml
graduated flasks exactly 5, 10, 15, 20 and 25 ml of this solution, corre-
sponding respectively to amounts of sodium of 0·2, 0·4, 0·6, 0·8 and
1·0 mg. Complete the series with a blank flask containing no standard
solution. Add 10 ml of loading agent (3.5) to eachflask, make up to
the mark with water and homogenise. Carry out the measurements as
indicated in 5.1. The calibration curve is generally linear up to a sodium
concentration of 1 mg in 100 ml of solution.
6.Calculationofresults
Express the result as a percentage of the sample.
7.Observations
7.1. For products containing more than 4% of sodium, it is preferable to ash
the substance for two hours in a crucible with a lid. After cooling, add
water, bring the ash into suspension by means of a platinum wire, dry
and ash again for two hours in the crucible with a lid.
7.2. If the sample consists solely of mineral substances, dissolve without
prior ashing.
12.DETERMINATIONOFSUGAR
1.Purposeandscope
This method makes it possible to determine the amount of reducing sugars
and total sugars after inversion, expressed as glucose or where appropriate
as sucrose, converting by the factor 0·95. It is applicable to compound
feeding-stuffs. Special methods are provided for other feeding-stuffs. Where
necessary, lactose should be measured separately and taken into account
when calculating the results.
2.Principle
The sugars are extracted in dilute ethanol; the solution is clarified with
Carrez solutions I and II. After eliminating the ethanol, the quantities before
and after inversion are determined by the Luff-Schoorl method.
3.Reagents
3.1. 40% ethanol (v/v) d: 0·948 at 20 ºC, neutralised to phenolphthalein.
3.2. Carrez solution I: dissolve in water 21·9 g of zinc acetate Zn (CH
3COO)2·2 H2O and 3 g of glacial acetic acid. Make up to 100 ml with
water.
3.3. Carrez solution II: dissolve in water 10·6 g of potassium ferrocyanide
►C1K4Fe (CN)6·3 H2O◄. Make up to 100 ml withwater.
3.4. 0·1% solution (w/v) of methyl orange.
3.5. Hydrochloric acid 4 N.3.6. Hydrochloric acid 0·1 N.
3.7. Sodium hydroxide solution 0·1 N.
3.8. Luff-Schoorl reagent:1971L0250 — EN — 26.05.1999 — 003.001 — 17
▼B
Stirring carefully, pour the citric acid solution (3.8.2) into the sodium
carbonate solution (3.8.3). Add the copper sulphate solution (3.8.1) and
make up to 1 litre withwater. Leave to settle overnigh t and filter.
Check the normality of the reagent thus obtained (Cu 0·1 N; Na2CO32 N). The solution's pH should be approximately 9·4.
3.8.1. Copper sulphate solution: dissolve 25 g of copper sulphate A.R.,
Cu SO4·5 H2O, free from iron, in 100 ml of water.
3.8.2. Citric acid solution: dissolve 50 g of citric acid A.R., C6H8O7·
H2O in 50 ml of water.
3.8.3. Sodium carbonate solution: dissolve 143·8 g of anhydrous
sodium carbonate A.R. in approximately 300 ml of warm water.
Leave to cool.
3.9. Sodium thiosulphate solution 0·1 N.3.10. Starchsolution: add a mixture of 5 g of soluble starchin 30 ml of
water to 1 litre of boiling water. Boil for three minutes, leave to cool
and if necessary add 10 mg of mercuric iodide as a preservative.
3.11. Sulphuric acid 6 N.
3.12. 30% solution (w/v) of potassium iodide.3.13. Granulated pumice stone boiled in hydrochloric acid, washed in water
and dried.
3.14. 3-methylbutan-l-ol.
4.Apparatus
Mixer (tumbler): approximately 35 to 40 rpm.
5.Procedure
5.1.Extraction of sample
Weigh 2.5 g of the sample to the nearest mg and place in a 250 ml volu-
metric flask. Add 200 ml of ethanol (3.1) and mix in the tumbler for one
hour. Add 5 ml of Carrez solution I (3.2) and stir for one minute. Add
5 ml of Carrez solution II (3.3) and again stir for one minute. Make up
to volume with ethanol (3.1), homogenise and filter. Remove 200 ml of
the filtrate and evaporate to approximately half volume in order to elim-
inate most of the ethanol. Transfer the evaporation residue quantitatively
to a 200 ml volumetric flask using warm water, cool, bring up to
volume with water, homogenise and filter if necessary. This solution
will be used to determine the amount of reducing sugars and, after
inversion, of total sugars.
5.2.Determination of reducing sugars
Using a pipette, remove not more than 25 ml of the solution containing
less than 60 mg of reducing sugars expressed as glucose. If necessary,
make up to 25 ml withdistilled water and determine th e content of
reducing sugars by the Luff-Schoorl method. The result is expressed as
the percentage content of glucose in the sample.
5.3.Determination of total sugars after inversion
Using a pipette take 50 ml of the solution and transfer to a 100 ml volu-
metric flask. Add a few drops of methyl orange solution (3.4) then,
carefully and stirring continuously, add hydrochloric acid 4 N (3.5) until
the liquid turns a definite red. Add 15 ml of hydrochloric acid 0·1 N
(3.6), immerse the flask in a fast boiling water bath and keep there for
thirty minutes. Cool rapidly to approximately 20 ºC and add 15 ml of
sodium hydroxide solution 0·1 N (3.7). Make up to 100 ml with water
and homogenise. Remove not more than 25 ml containing less than60 mg of reducing sugars expressed as glucose. If necessary, make up
to 25 ml withdistilled water and determine th e content of reducing
sugars by the Luff-Schoorl method. The result is expressed as the
percentage of glucose or, where appropriate, sucrose, by multiplying by
the factor 0·95.
5.4.Titration by the Luff-Schoorl method
Using a pipette, take 25 ml of Luff-Schoorl reagent (3.8) and transfer to
a 300 ml Erlenmeyer flask; add exactly 25 ml of the clarified sugar
solution. Add 2 granules of pumice stone (3.13), heat, stirring by hand,
over a free flame of medium height and bring the liquid to the boil in
approximately two minutes. Place the Erlenmeyer immediately on an
asbestos-coated wire gauze witha h ole approximately 6 cm in diameter1971L0250 — EN — 26.05.1999 — 003.001 — 18
▼B
under which a flame has been lit. The flame shall be regulated in such a
way that only the base of the Erlenmeyer is heated. Fit a reflux
condenser to the Erlenmeyer flask, Boil for exactly ten minutes. Cool
immediately in cold water and after approximately five minutes titrate
as follows:
Add 10 ml of potassium iodide solution (3.12) and immediately after-
wards (carefully, because of the risk of abundant foaming), add 25 ml
of sulphuric acid 6 N (3.11). Titrate with sodium thiosulphate solution
0·1 N (3.9) until a dull yellow colour appears, add the starch indicator
(3.10) and complete titration.
Carry out the same titration on an accurately measured mixture of 25 ml
of Luff-Schoorl reagent (3.8) and 25 ml of water, after adding 10 ml of
potassium iodide solution (3.12) and 25 ml of sulphuric acid 6 N (3.11)
without boiling.
6.Calculationofresults
Using the table establish the amount of glucose in mg which corresponds to
the difference between the values of the two titrations, expressed in mg of
sodium thiosulphate 0·1 N.
Express the result as a percentage of the sample.
7.Specialprocedures
7.1. In the case of feeding-stuffs which are rich in molasses and other
feeding-stuffs which are not particularly homogeneous, weigh out 20 g
and place with500 ml of water in a 1 litre volumetric flask. Mix for one
hour in the tumbler. Clarify using Carrez 1 (3.2) and II (3.3) reagents as
described under 5.1, this time however using four times the quantities of
eachreagent. Bring up to volume with80% eth anol (v/v).
Homogenise and filter. Eliminate the ethanol as described under 5.1. If
there is no dextrinised starch, bring up to volume with distilled water.
7.2. In the case of molasses and straight feeding-stuffs which are rich in
sugar and almost starch-free (carobs, dried beetroot cossettes etc.),
weighout 5 g, place in a 250 ml volumetric flask, add 200 ml of
distilled water and mix in the tumbler for one hour, or more if neces-
sary. Clarify using Carrez I (3.2) and II (3.3) reagents as described
under 5.1. Bring up to volume withcold water, h omogenise and filter.
In order to determine the amount of total sugars, continue as described
under 5.3.
8.Observations
8.1. In order to prevent foaming it is advisable to add (irrespective of the
volume) approximately 1 ml of 3-methylbutan-l-ol (3.14) before boiling
withLuff-Sch oorl reagent.
8.2. The difference between the content of total sugars after inversion,
expressed as glucose, and the content of reducing sugars, expressed as
glucose, multiplied by 0·95, gives the percentage content of sucrose.
8.3. In order to determine the content of reducing sugars, excluding lactose,
two methods may be adopted:
8.3.1. for an approximate calculation, multiply by 0·675 the lactose
content established by a different method of analysis and subtact
the result obtained from the content of reducing sugars.
8.3.2. For an accurate calculation of reducing sugars, excluding lactose,
the same sample must be used for the two final determinations.
One of the analyses is carried out on part of the solution obtained
under 5.1, the other on part of the solution obtained during the
determination of lactose by the method laid down for that
purpose (after fermenting the other types of sugar and clarifying).
In both cases the amount of sugar present is determined by the Luff-
Schoorl method and calculated in mg of glucose. One of the values issubtracted from the other and the difference is expressed as a percentage
of the sample.
ExampleThe two volumes taken correspond, for each determination, to a sample
of 250 mg.1971L0250 — EN — 26.05.1999 — 003.001 — 19
▼B
In the first case 17 ml of sodium thiosulphate solution 0·1 N corre-
sponding to 44·2 mg of glucose is consumed; in the second, 11 ml,
corresponding to 27·6 mg of glucose.
The difference is 16·6 mg of glucose.
The content of reducing sugars (excluding lactose), calculated as
glucose, is therefore:
4/C216/C16
10¼6/C164%
Tableofvaluesfor25mlofLuffSchoorlreagent
ml of Na2S2O30·1 N, two minutes'heating, ten minutes' boiling
Na2S2O30·1 NGlucose, fructose invert
sugars
C6H12O6Lactose
C12H22O11Maltose
C12H22O11Na2S2O30·1 N
ml mg difference mg difference mg difference ml
1 2·4 2·4 3·6 3·7 3·9 3·9 1
2 4·8 2·4 7·3 3·7 7·8 3·9 2
3 7·2 2·5 11·0 3·7 11·7 3·9 34 9·7 2·5 14·7 3·7 15·6 4·0 4
5 12·2 2·5 18·4 3·7 19·6 3·9 5
6 14·7 2·5 22·1 3·7 23·5 4·0 67 17·2 2·6 25·8 3·7 27·5 4·0 78 19·8 2·6 29·5 3·7 31·5 4·0 8
9 22·4 2·6 33·2 3·8 35·5 4·0 9
10 25·0 2·6 37·0 3·8 39·5 4·0 1011 27·6 2·7 40·8 3·8 43·5 4·0 11
12 30·3 2·7 44·6 3·8 47·5 4·1 12
13 33·0 2·7 48·4 3·8 51·6 4·1 1314 35·7 2·8 52·2 3·8 55·7 4·1 14
15 38·5 2·8 56·0 3·9 59·8 4·1 15
16 41·3 2·9 59·9 3·9 63·9 4·1 1617 44·2 2·9 63·8 3·9 68·0 4·2 1718 47·1 2·9 67·7 4·0 72·2 4·3 18
19 50·0 3·0 71·7 4·0 76·5 4·4 19
20 53·0 3·0 75·7 4·1 80·9 4·5 2021 56·0 3·1 79·8 4·1 85·4 4·6 21
22 59·1 3·1 83·9 4·1 90·0 4·6 22
23 62·2 88·0 94·6 23
14.DETERMINATIONOFUREA
1.Purposeandscope
This method makes it possible to determine the level of urea in feeding-
stuffs.
2.Principle
The sample is suspended in water with a clarifying agent. The suspension is
filtered. The urea content of the filtrate is determined after the addition of 4-
dimethylaminobenzaldehyde (4-DMAB) by measuring the optical density at a
wavelengthof 420 nm,
3.Reagents
3.1. Solution of 4-dimethylaminobenzaldehyde: dissolve 1·6 g of 4-DMAB
A.R. in 100 ml of 96% ethanol and add 10 ml of hydrochloric acid
A.R. (d: 1·19). This reagent keeps for a maximum period of two weeks.
3.2. Carrez solution I: dissolve in water 21·9 g of zinc acetate ►C1Zn
(CH3COO)2·2 H2O◄and 3 g of glacial acetic acid. Make up to
100 ml withwater.1971L0250 — EN — 26.05.1999 — 003.001 — 20
▼M3
▼B
▼B
3.3. Carrez solution II: dissolve in water ►C110·6 g of potassium ◄
ferrocyanide, K4Fe (CN)6·3 H2O. Make up to 100 ml withwater.
3.4. Active carbon A.R. which does not absorb urea (to be checked).
3.5. 0·1% solution (w/v) of urea A.R.
4.Apparatus
4.1. Mixer (tumbler): approximately 35 to 40 rpm.
4.2. Test tubes: 160 × 16 mm withground-glass stoppers.
4.3. A spectrophotometer.
5.Procedure
5.1.Analysis of sample
Weigh out 2 g of the sample to the nearest mg and place with 1 g of
active carbon (3.4) in a 500 ml volumetric flask. Add 400 ml of water
and 5 ml of Carrez solutions I (3.2) and II (3.3). Mix for thirty minutes
in the tumbler. Make up to volume with water, shake and filter.
Remove 5 ml of the transparent colourless filtrates, place in test tubes
withground-glass stoppers, add 5 ml of 4-DMAB solution (3.1) and
mix. Place the tubes in a hot-water bath at 20 ºC. After fifteen minutes
measure the optical density of the sample solution with the spectrophot-
ometer at 420 nm. Compare with the blank test solution of the reagents.
5.2.Calibration curve
Remove volumes of 1, 2, 4, 5 and 10 ml of the urea solution (3.5), place
in 100 ml volumetric flasks and make up the volume with water.
Remove 5 ml from eachsolution, add 5 ml of 4-DMAB solution (3.1)
to each of them, homogenise and measure the optical density as shown
above in comparison witha control solution containing 5 ml of 4-
DMAB and 5 ml of water free from urea. Plot the calibration curve.
6.Calculationofresults
Determine the amount of urea in the sample using the calibration curve.
Express the result as a percentage of the sample.
7.Observations
7.1. In the case of contents of urea exceeding 3%, reduce the sample to 1 g
or dilute the original solution so that there are not more than 50 mg of
urea in 500 ml.
7.2. In the case of low contents of urea, increase the sample as long as the
filtrate remains transparent and colourless.
7.3. If the sample contains simple nitrogenous compounds such as amino
acids, the optical density should be measured at 435 nm.
16.ESTIMATION OF THE UREASE ACTIVITY OF PRODUCTS
DERIVEDFROMSOYA
1.Purposeandscope
This test makes it possible estimate the urease activity of products derived
from soya and to show whether these products have been cooked for a suffi-
cient lengthof time.
2.Principle
Urease activity is estimated by the amount of ammoniacal nitrogen liberated
per 1 g of product per minute at 30 ºC from a solution of urea.
3.Reagents
3.1. Hydrochloric acid 0·1 N.
3.2. Solution of sodium hydroxide 0·1 N.1971L0250 — EN — 26.05.1999 — 003.001 — 21
▼M2
▼B
▼B
3.3. Loading agent of phosphate 0·05 M, containing, per 1000 ml, 4·45 g of
disodium phosphate (Na2HPO4·2 H2O) and 3·40 g of monopotassium
phosphate (KH2PO4).
3.4. Freshly-prepared urea loading agent containing 30·0 g of urea per
1000 ml of loading agent (3.3); pH 6·9-7·0.
4.Apparatus
4.1. Potentiometric titration apparatus or high sensitivity pH-meter (0·02 pH)
withmagnetic stirrer.
4.2. Water bathfitted withth ermostat set at 30 ºC exactly.
4.3. Test-tubes withground-glass stoppers, 150 × 18 mm.
5.Procedure
Crush about 10 g of the sample (for example in a coffee mill) so that it
passes through a sieve with a mesh of 0·2 mm. Weigh out 0·2 g of the
crushed sample to the nearest mg, place in a test tube with a ground-glass
stopper and add 10 ml of urea loading agent (3.4). Stopper immediately and
shake vigorously. ►C1 ◄Place the tube in a water bath set
at 30 ºC exactly and keep there for exactly thirty minutes. Immediately add
10 ml of 0·1 N hydrochloric acid (3.1), cool rapidly to 20 ºC and transfer the
contents of the tube quantitatively to a titration vessel, rinsing twice with 5 ml
of water. Using a glass electrode (4.1) titrate immediately and rapidly to pH
4·7 with the 0·1 N sodium hydroxide solution (3.2) by electrometry.
Carry out a blank test as follows:Quickly place a sample of 0·2 g weighed to the nearest mg in a test tube with
a ground-glass stopper, add 10 ml of 0·1 N hydrochloric acid (3.1) and then
10 ml of urea loading agent (3.4). Cool the tube immediately in ice-water
and leave there for thirty minutes. Under the conditions indicated above,
transfer the contents of the tube to the titration vessel using the 0·1 N sodium
hydroxide solution (3.2) up to pH 4·7.
6.Calculation
The urease activity is calculated by using the formula:
mg N
g minat 30 ºC ¼1/C14b/C0a ðÞ
30/C1E
where: a = ml of 0·1N sodium hydroxide solution consumed by the sample,
b = ml of 0·1N sodium hydroxide solution consumed in the blank
test,
E = weight of sample in g.
7.Observation
7.1. This method is suitable for a urease activity of up to 1 mg of N/g/min at
30 ºC. For more active products, the size of the sample can be reduced
to 50 mg.
7.2. Products containing more than 10% of crude fatty substance must first
be defatted cold.1971L0250 — EN — 26.05.1999 — 003.001 — 22