ISO 14181:2000

INTERNATIONAL ISO
STANDARD 14181
First edition
2000-09-15
Animal feeding stuffs — Determination
of residues of organochlorine pesticides —
Gas chromatographic method
Aliments des animaux — Détermination des résidus de pesticides
organochlorés — Méthode par chromatographie en phase gazeuse
Reference number
ISO 14181:2000(E)
©
ISO 2000

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ISO 14181:2000(E)
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ISO 14181:2000(E)
Contents Page
Foreword.iv
1 Scope .1
2 Normative references .1
3 Principle.1
4 Reagents and materials .1
5 Apparatus .3
5.1 Grinder .5
6 Sampling.5
7 Preparation of test sample.5
8 Procedure .5
8.1 General.5
8.2 Test portion .5
8.3 Extraction .5
8.4 Column clean-up.6
8.5 Gas chromatography.6
9 Expression of results .7
9.1 Calculation.7
9.2 Recovery.8
10 Confirmation of identity .8
11 Precision.8
11.1 Interlaboratory test .8
11.2 Repeatability.8
11.3 Reproducibility.8
12 Test report .9
Annex A (informative) Examples of GC operating conditions for organochlorine pesticides.10
Annex B (informative) Results of interlaboratory test.11
Bibliography.20
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ISO 14181:2000(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO
member bodies). The work of preparing International Standards is normally carried out through ISO technical
committees. Each member body interested in a subject for which a technical committee has been established has
the right to be represented on that committee. International organizations, governmental and non-governmental, in
liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical
Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3.
Draft International Standards adopted by the technical committees are circulated to the member bodies for voting.
Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this International Standard may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights.
International Standard ISO 14181 was prepared by Technical Committee ISO/TC 34, Food products,
Subcommittee SC 10, Animal feeding stuffs.
Annexes A and B of this International Standard are for information only.
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INTERNATIONAL STANDARD ISO 14181:2000(E)
Animal feeding stuffs — Determination of residues of
organochlorine pesticides — Gas chromatographic method
1 Scope
This International Standard specifies a gas chromatographic method for the determination of residues of
organochlorine pesticides in animal feeding stuffs.
The method is applicable to animal feeding stuffs containing residues of one or more of the following
organochlorine pesticides and some of their isomers and degradation products: aldrin, op'-DDE, pp'-DDE, op'-DDT,
pp'-DDT, dieldrin, endosulfan, endrin, HCB, �-HCH (�-BHC), �-HCH (�-BHC), �-HCH (�-BHC), �-HCH
(�-BHC), heptachlor, heptachlor epoxide, op'-TDE (op'-DDD), pp'-TDE (pp'-DDD) and methoxychlor.
The lower determination limit for these organochlorine pesticides is 0,005�g/g. However, the lower determination
limit is 0,01 �g/g for op'-DDT and pp'-DDT, and 0,05�g/g for methoxychlor.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of
this International Standard. For dated references, subsequent amendments to, or revisions of, any of these
publications do not apply. However, parties to agreements based on this International Standard are encouraged to
investigate the possibility of applying the most recent edition of the normative document indicated below. For
undated references, the latest edition of the normative documents referred to applies. Members of ISO and IEC
maintain registers of currently valid International Standards.
ISO 3696:1987, Water for analytical laboratory use — Specification and test methods.
ISO 6498, Animal feeding stuffs — Preparation of test samples.
3Principle
A test portion is extracted with acetone. The filtered extract is diluted with water and saturated sodium chloride
solution. The pesticides are partitioned into dichloromethane. The concentrated extract is purified on a
chromatographic column of 10 % water-deactivated silica gel. The pesticide residues are determined by gas
chromatography using an electron capture detector or a mass selective detector.
4 Reagents and materials
Use only reagents of recognized analytical grade and with a purity suitable for pesticide residue analysis.
Check the purity of the reagents by performing a blank test under the same conditions as used in the method. The
chromatogram should not show any interfering impurity.
WARNING — Some of the organic solvents are suspected carcinogens. Use with care.
4.1 Water, complying with at least grade 3 in accordance with ISO 3696.
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ISO 14181:2000(E)
4.2 Hexane.
4.3 Acetone.
4.4 Dichloromethane.
4.5 Silica gel 60, with a mass fraction of water of 10 %.
Activate silica gel 60, particle size 63�mto 200�m, at 130 °C overnight, then cool in a desiccator. After cooling to
room temperature, pour the silica gel into an airtight glass container and add sufficient distilled water to bring the
final mass fraction of water to 10 %. Shake the container mechanically or by hand vigorously for 30 s and allow to
stand for 30 min with occasional shaking. After 30 min the silica gel is ready for use. It should not be stored for
morethan6h.
4.6 Eluting solvent: dichloromethane in hexane, 20 % (by volume).
Mix 1 volume of dichloromethane with 4 volumes of hexane.
4.7 Inert gas, for example nitrogen.
4.8 Sodium sulfate, anhydrous.
4.9 Sodium chloride, saturated solution.
4.10 Pesticide reference standards, as follows:
� aldrin [(1R,4S,4aS,5S,8R,8aR)-1,2,3,4,10,10-hexachloro-1,4,4a,5,8,8a-hexahydro-1,4:5,8-dimethano-
naphthalene];
� op'-DDE [o,p'-(1,1-dichloro-2,2-bis(4-chlorophenyl) ethylene)];
� pp'-DDE [p,p'-(1,1-dichloro-2,2-bis(4-chlorophenyl) ethylene)];
� op'-DDT [o,p'-(1,1,1-trichloro-2,2-bis(4-chlorophenyl) ethane)];
� pp'-DDT [p,p'-(1,1,1-trichloro-2,2-bis(4-chlorophenyl) ethane)];
� dieldrin [(1R,4S,4aS,5R,6R,7S,8S,8aR)-1,2,3,4,10,10-hexachloro-1,4,4a,5,6,7,8,8a-octahydro-6,7epoxy-
1,4:5,8-dimethanonaphthalene];
� endosulfan (6,7,8,9,10,10-hexachloro-1,5,5a,6,9,9a-hexahydro-6,9-methano-2,4,3-benzodioxathiepin 3-oxide);
� endrin [(1R,4S,4aS,5S,6S,7R,8R,8aR)-1,2,3,4,10,10-hexachloro-1,4,4a,5,6,7,8,8a-octahydro-6,7-epoxy-
1,4:5,8-dimethanonaphthalene];
� HCB (hexachlorobenzene);
��-HCH (�-BHC) (�-1,2,3,4,5,6-hexachlorocyclohexane);
��-HCH (�-BHC) (�-1,2,3,4,5,6-hexachlorocyclohexane);
��-HCH (�-BHC; lindane) (�-1,2,3,4,5,6-hexachlorocyclohexane);
��-HCH (�-BHC) (�-1,2,3,4,5,6-hexachlorocyclohexane);
� heptachlor (1,4,5,6,7,8,8-heptachloro-3a,4,7,7a-tetrahydro-4,7-methanoindene);
� heptachlor epoxide (heptachloroepoxy-tetrahydromethanoindene);
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ISO 14181:2000(E)
� op'-TDE (op-DDD) [o,p'-1,1-dichloro-2,2-bis(4-chlorophenyl) ethane];
� pp'-TDE (pp'-DDD) [p,p'-1,1-dichloro-2,2-bis(4-chlorophenyl) ethane];
� methoxychlor [1,1,1-trichloro-2,2-bis(4-methoxyphenyl) ethane].
4.11 Internal standard: mirex (1,3,5-tribromobenzene) or pentachloronitrobenzene.
4.12 Pesticide standard and internal standard solutions.
4.12.1 Stock solutions, of concentration 1 000�g/ml.
Prepare a stock solution of each pesticide reference standard (4.10) and of the internal standard (4.11) as follows.
Weigh, to the nearest 0,1 mg, a mass of a pesticide reference standard (4.10) or the internal standard (4.11) which
will result in a solution with a content of reference standard or internal standard of 1 000�g/ml. While weighing,
observe the cleanness of the standard matrial. Transfer the weighed mass into a volumetric flask, dissolve in
hexane or in an other solvent such as toluene or iso octane. However, dissolve�-HCH in acetone. Dilute to volume
with the same solvent and mix well.
These solutions are stable for 6 months when stored at 4�Cinthedark.
4.12.2 Intermediate solutions, of concentration 10�g/ml.
Pipette 1 ml of each stock solution (4.12.1) into individual 100 ml volumetric flasks. Dilute to volume with hexane.
The solutions are stable for at least 3 months when stored at 4 °C in the dark.
NOTE The stability of properly stored pesticide standards is very widely known. Investigations have shown that all neat
pesticide standards tested are stable for 15 years when stored at –18 °C and that stock solutions of pesticide standards in
toluene of 1mg/ml are stable for at least 3 years when stored at –18 °C.
The following recommended practice may be used for longer storage. Transfer portions of the prepared standard
solutions to amber vials with PTFE-lined screwcaps. Weigh the vials and store at –20 °C. When needed, remove a
vial from the freezer, bring to room temperature and weigh. If the accumulated loss in mass due to evaporation is
10 % or more of the prefrozen net mass, discard the vial. Weigh and refreeze stock standards and intermediate
solutions that are in use for more than 3 months (usually in 25 ml vials). Otherwise the prepared standard solutions
(usually in 2 ml vials) may be stored at 4 °C and shall be discarded after 3 months.
4.12.3 Working solution, of concentration 0,05�g/ml.
Pipette a 0,5 ml of each intermediate solution (4.12.2) into a 100 ml volumetric flask and dilute to volume with
hexane. The solution is stable for 1 month when stored at 4°C in the dark (see 4.12.2).
5 Apparatus
Before use, wash all glassware thoroughly with detergent free of interfering substances. Rinse with water, then with
acetone and dry.
Avoid the use of plastics containers and do not lubricate the stopcocks with grease, otherwise impurities could be
introduced into the solvents.
Usual laboratory equipment and, in particular, the following.
5.1 Separating funnels, of 500 ml capacity with polytetrafluoroethylene (PTFE) stopcocks and stoppers.
5.2 Filtering flasks, of 500 ml capacity.
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ISO 14181:2000(E)
5.3 Büchner funnel, of porcelain, with internal diameter 90 mm.
5.4 Graduated tubes, of 10 ml capacity, with polytetrafluoroethylene (PTFE) stoppers.
5.5 Glass chromatographic tube, about 300 mm in length, 8 mm to 10 mm internal diameter, with coarse fritted
plate of porosity grade P 100 (pore size index 40�mto100�m [2]) or glass wool plug.
5.6 Rotary vacuum evaporator, provided with round-bottom flasks of 100 ml and 500 ml capacities and a water
bath at 40�C � 2 °C.
5.7 Mechanical shaker or high-speed blender.
5.8 Gas chromatographic system consisting of:
� splitless or on-column injection system;
� column;
� electron capture detector or mass selective detector;
� electrometer;
� mV recorder or integrator;
� data handling software and computer system.
Each injection port, column oven and detector shall be provided with an independent heating device controlled to
the nearest 0,1�C.
The chromatographic system shall be adjusted and the parameters optimized according to the characteristics of
the instrument used.
5.8.1 Injection device
An autosampler or any other adequate injection device may be used. For manual injections, use a microsyringe of
1�lto5�l capacity with a needle length suitable for the mode of injection (splitless or on-column).
Before injecting the solution into the gas chromatograph, rinse the syringe 10 times with pure solvent, then 5 times
with solution. After injection, rinse the syringe 5 times with pure solvent.
5.8.2 Column
The use of capillary columns coated with mid-range polarity stationary phases (e.g. SE-30, SE-54, OV-17, or
equivalent) is recommended.
Standard glass columns, of length 2 m to 4 m and of internal diameter 2 mm to 4 mm, packed with a mixture of
2,5 % QF1 + 1 % OV 11 + 0,5 % XE 60 on Chromosorb WHP 0,125 mm to 0,15 mm particle size, or any other
stationary phases and inert supports recommended for organochlorine residue analyses could be used as an
alternative.
The temperature programme for the column shall be chosen to separate the pesticides mixture specified in
clause 1 into individual components (see annex A).
After installing a new column, it shall be conditioned for at least 24 h at a temperature slightly above the maximum
proposed operating temperature, with carrier gas flowing through it and the end of the column disconnected from
the detector.
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ISO 14181:2000(E)
5.8.3 Detector
Use an electron capture detector (ECD) operating either in constant current mode or in constant frequency mode at
the polarization voltage, width, amplitude or frequency of the pulses at which a maximum of 0,05 ng
heptachlor epoxide causes 40 % to 50 % full-scale deflection.
5.8.4 Carrier gas and make-up gas
Pure nitrogen (oxygen-free), pure helium or pure hydrogen, or a mixture of argon and methane [90 + 10, by
volume or (95 + 5) % by volume].
5.9 Grinder
6 Sampling
It is important that the laboratory receive a sample which is truly representative and has not been damaged or
changed during transport or storage.
Sampling is not part of the method specified in this International Standard. A recommended sampling method is
given in ISO 6497 [1].
7 Preparation of test sample
Prepare the test sample in accordance with ISO 6498.
Grind a portion of the well-mixed laboratory sample (dry or low moisture products such as cereals and cereal
products, oilseeds and oilseed meals, mixed feeds, hay, etc.) so that it passes completely through a sieve with
1 mm apertures. Mix thoroughly.
Chop up the high moisture products (e.g. grasses, silages, etc.) and mix thoroughly to obtain homogeneous
samples.
8 Procedure
8.1 General
Carry out steps 8.2 to 8.4 using both the prepared test sample (clause 7) and a blank sample. The blank sample
shall be free of residues at or above the limits of detection found from previous determinations. The blank extract is
used to prepare the matrix-matched standard solution (see 8.5.3).
8.2 Test portion
Weigh, to the nearest 0,1 g, 50 g of the prepared test sample (clause 7) for dry or low moisture products, or 100 g
for high moisture products, into a 1 000 ml conical flask.
8.3 Extraction
Add sufficient water to the test portion so that a total water amount of about 100 g is obtained. Allow the sample to
soak for about 5 min. Add 200 ml of acetone. Close the flask tightly and shake for 2 h on a mechanical shaker or
homogenize for 2 min in a high-speed blender.
Filter the homogenate with suction through a Büchner funnel (5.3) fitted with filter paper of medium porosity, into a
500 ml filtering flask (5.2). Wash the conical flask or the blender cup and the residue on the filter paper with two
25 ml portions of acetone, collecting the washings in the same filtering flask.
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ISO 14181:2000(E)
Measure the volume of the filtrate (V ) and transfer one-fifth of the solution (V ) to a 500 ml separating funnel. Add
1 2
250 ml of water, about 50 ml of saturated sodium chloride solution (4.9) and 100 ml of dichloromethane (4.4) to the
separating funnel. Stopper and shake for 2 min.
Allow the phases to separate and draw off the lower phase (dichloromethane) into a second 500 ml separating
funnel (5.1). Repeat the extraction twice with 50 ml of dichloromethane then combine the extracts in the same
500 ml separating funnel.
Wash the dichloromethane extract with two 100 ml portions of water, discarding the washings.
Filter the dichloromethane extract through a filter paper containing about 20 g of sodium sulfate (4.8) into a 500 ml
flask of a vacuum evaporator. Rinse the separating funnel and the sodium sulfate with two 10 ml portions of
dichloromethane and add to the flask.
Concentrate the solution to about 2 ml under vacuum at a temperature not exceeding 40�C. Transfer the solution
to a 10 ml graduated tube using 1 ml to 2 ml of hexane and concentrate under nitrogen to about 1 ml.
Do not allow the solution to dry completely or losses of pesticides may occur because of volatility or poor solubility.
8.4 Column clean-up
8.4.1 Preparation of the column
Transfer 5 g of silica gel (4.5) to a glass chromatographic tube (5.5). Add 5 g of anhydrous sodium sulfate (4.8) on
the top of the silica gel. Wash the prepared column with 20 ml of hexane.
NOTE Prepacked silica or florisil cartridges (e.g. Millipore-SEP PAK) may be used instead of a silica gel column, after
checking for efficiency and absence of interferences.
8.4.2 Purification
Transfer quantitatively the concentrated extract (8.3) on the top of the column (8.4.1) using 1 ml to 2 ml portions of
hexane.
Elute the organochlorine pesticides with 50 ml of eluting solvent (4.6) and collect the eluate in the 100 ml flask of
the rotary vacuum evaporator (5.6).
Concentrate the eluate to about 2 ml under vacuum at a temperature not exceeding 40 °C. Add about 10 ml of
hexane and concentrate once more to about 1 ml. Repeat two times, leaving about 1 ml of hexane at the final
evaporation. Transfer to a 10 ml graduated tube using 1 ml to 2 ml of hexane. Dilute the sample extract to 10 ml
with hexane for determination by chromatography.
When an internal standard method is used, add 1 ml of the intermediate solution (4.12.2) of the internal standard
(4.11) to the final extract before diluting to 10 ml with hexane. Keep the blank extract to prepare the matrix-matched
standard solution (see 8.5).
8.5 Gas chromatography
8.5.1 Preparation of the system
Equilibrate the gas chromatographic system under the recommended operating conditions (5.8).
If the carrier gas volume flow rate through the column is below 25 ml/min, introduce a supplemental contribution of
gas at the outlet of the column in order to ensure a sufficient flow of gas through the electron capture detector
(make-up gas).
Dry the carrier gas by passing it through 0,5 nm molecular sieve traps, previously activated at 350�C for 4hto8h,
installed in the carrier gas line.
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ISO 14181:2000(E)
Reactivate the molecular sieves each time a new gas cylinder is assembled and as often as needed.
8.5.2 Checking the linearity of the system
Check the linearity of the system from 0,05 ng to 0,5 ng of heptachlor epoxide.
Prepare working solutions with hetachlor epoxide contents ranging from 0,01�g/ml to 0,1�g/ml. Inject 1�l.
Plot the response factor (area/mass, in nanograms, of heptachlor epoxide injected) versus the mass, in nanograms
of heptachlor epoxide injected. The graph shall be straight line parallel to the x-axis. If not, establish the range of
concentrations within which the detector response is linear.
8.5.3 Determination
Inject 1�lto 2�l of working standard solution (4.12.3), then the same volume of the sample extract (8.4.2). Dilute
the sample extract if necessary.
Identify the individual pesticide peaks on the basis of retention times.
Determine the amount of pesticides by comparing the size of the sample peaks with those of the known amount of
the corresponding pesticide peak in the working standard solution.
When the results based on solvent standards indicate residue levels at or above 50 % of the appropriate MRL, a
matrix-matched solution should be used, prepared by adding to the blank extract (8.4.2) appropriate amounts of
intermediate solutions (4.12.2) of those pesticides identified in the sample solution, so that the size of the peaks of
this reference solution is within 25 % of the size of the peaks in the sample solution. Bring to 10 ml with hexane.
Inject into the gas chromatograph the same volume as for the sample solution.
Determine the amount of pesticides by comparing the size of the sample peaks with those of the known amount of
the corresponding pesticide peak in the matrix-matched standard solution.
9 Expression of results
9.1 Calculation
Calculate the residue of each individual pesticide in the test sample by the equation:
A��Am�V�V
si s 2 3
w �
A��Am�V�V
si 1 4
where
w is the content of an individual pesticide residue, in micrograms per gram, in the test sample;
A is the area (or height) of the pesticide peak in the sample solution;
A is the area (or height) of the corresponding standard pesticide peak in the working standard solution or in
s
the matrix-matched standard solution;
A is the area (or height) of the internal standard peak in the sample solution;
i
A is the area (or height) of the internal standard peak in the working standard solution or in the matrix-
si
matched standard solution;
m is the mass, in nanograms, of pesticide in the volume injected into the gas chromatograph;
s
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ISO 14181:2000(E)
V is the total volume of filtrate, in millilitres, obtained in the extraction step;
1
V is the volume of the filtrate, in millilitres, used in the purification step;
2
V is the final volume, in millilitres, of the test solution, taking into account any further dilution that is
3
necessary;
V is the volume, in microlitres, of the sample solution injected into the gas chromatograph;
4
m is the mass, in grams, of the test portion.
9.2 Recovery
Verify the performance of the method by recovery experiments made on fortified blank samples at the 0,05�g/g
level.
Add to the test portion of a blank sample a known amount of pesticide solution. Let it stand for 30 min then analyse
the fortified test portion together with the original blank sample with no added pesticides.
The recovery (%) is calculated for each pesticide as 100 � [(analysed amount in the fortified sample minus the
original amount in the sample)/ (added amount)]
The recovery coefficient for each individual pesticide shall be between 70 % and 110 %.
When a residue exceeding a maximum residue limit (MLR) is to be confirmed, the concurrent recovery level should
be approximately similar to that of the sample.
10 Confirmation of identity
Analyses for confirmation of the identity and quantity of pesticides shall be performed, particularly when the results
obtained correspond to or exceed the maximum residue limits (MRLs), either by chromatography on a second
column of significantly different polarity or, where the apparatus is available, by using GC-MS to quantify and
confirm the identity of the pesticide.
11 Precision
11.1 Interlaboratory test
Details of an interlaboratory test on the precision of the method are given in annex B. The values derived from this
test may not be applicable to concentration ranges and matrices other than those given.
11.2 Repeatability
The absolute difference between two independent single test results, obtained using the same method on identical
test material in the same laboratory by the same operator using the same equipment within a short interval of time,
will in not more than 5 % of cases exceed the repeatability limit r derived from Tables B.1 to B.17.
11.3 Reproducibility
The absolute difference between two single test results, obtained using the same method on identical test material
in different laboratories by different operators using different equipment, will in not more than 5 % of cases exceed
the reproducibility limit R derived from Tables B.1 to B.17.
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ISO 14181:2000(E)
12 Test report
The test report shall specify:
� all information necessary for the complete identification of the sample;
� the sampling method used, if known;
� the test method used, with reference to this International Standard;
� all operating details not specified in this International Standard, or regarded as optional, together with
details of any incidents which may have influenced the test result(s);
� the test result obtained, or the two test results obtained if the repeatability has been checked.
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ISO 14181:2000(E)
Annex A
(informative)
Examples of GC operating conditions for organochlorine pesticides
A.1 Exam
...