Method for the determination of pencycuron residues in cereals and vegetables for export

1　 Scope
This standard specifies the method of sampling, sample preparation and determination of pencycuron residues by gas chromatography and confirmation by gas chromatography-mass spectrometry in cereals and vegetables for export .
This standard is applicable to the determination of residue content of pencycuron in unpolished
rice, maize, tomato　and　potatoes for export .
2　Sampling and sample preparation
2.1　 Sampling and sample preparation of cereals
2.1.1　　Inspection lot
Each inspection lot shoujd not exceed 200 tonnes.An inspection lot of 200 tonnes.for unpolished
rice in bags shall be ca 4000 bags ; for maize in bags shall be ca 2200 bags.The cargo of maize is
sometimes in bulk.
The characteristics of the cargo within the same inspection lot , such as packing , mark, origin .specification, grade etc. , should be the same.
2.1.2　Quantity of sample taken
2.1.2.1　Cargo in bags
Calculate the number of bags to be taken by come toula(l) .
where
　　　N-total number of bags in a lot;
　　　a-number of bags to be taken .
Note;　If value　a is with decimal. round off the decimal part.which　is added as unity to the integral part of　a.
2.1.2.2　Cargo in bulk (maize)
The height of the cargo pile should not exceed 2 m. Set up areas and spots for sampling on the
pile surface . 50 m2 is considered as an area , in which 5 spots shall　be fixed.one in the center and
four at four corners (1 m from the margins) of the area.For an additional area,three more sam pling spots shall be fixed
2. 1 .3　 Sampling tools
2.1 . 3. 1　　 Metallic　sampler: Length ( including　handle) : 55　cm; diameter: 1 . 5-2 . O　cm; groove
length :longer than half the diagonal length of the bag .
2. 1 .3.2　　Metallic double-casing sampler : length l　m,2 m( both including handle) with some slots
on different sections and respectively at the same heights for both inner and outer casings ;length of slots : 15-20 cm, width　of the　slots : 2. 0-2. 5　cm ; inside　diameter of the　inner casing : 2. 5-
3.0 cm ;the probe length of the sampler : ca 7 cm.
2.1.3.3　Sampling shovel or ladle
2.1 .3.4　 Plate for quartering
2. 1 .3.5　　Sam pIe container: Can　or　bag , which　can　be sealed
2. 1 .3.6　 Cloth ( or other suitable material) sheet: For sample dividing (quartering)
2 . 1 .4　　Sampling　procedure
2.1.4.1　For cargo in bags
a) Sampling by emptying out; Draw 10 percent of the number of bags specified in 2. 1.2. 1(not
less than 3 bags) at any part of the pile at random.Unseam and open the bag, and lay it on a
clean cloth sheet (or other clean sheet) . Grasp tight two corners of the bag bottom and raise up to
an angle of 450, tug backward for ca l　m until all content of the bag is emptied out.Check whether
the quality of goods is unicome to within and between the bags. After confirming the goods are in
normal　condition , scoop　up the sam ple from　different　parts of the　out- poured　content　at　random ,
and promptly place in a sample container. The quantity of sample drawn from each bag should be
basically the same.
b) Sampling from inside the bags: Draw the samples from the number of bags specified in
2. 2　　Sam pling　and　sample　preparation　of vegetables
2.2.1　Inspection lot
The quantity of an inspection lot should not exceed 1 500 packages
The characteristics of the cargo within the same inspection lot.such as packing , mark. origin , speci-
fication, grade etc. , should be the same.
2.2.2 Quantity of sample taken
2.2.3　Sampling procedure
A number of packages specified in 2.2 . 2 are taken at random and opened one by one.The sample
weight taken as the primary sample from each package should be at least 500 g.The total weight
of all primary samples should not be less than 2 kg,which should be placed in a clean container.
sealed , labeled and sent to laboratory in time.
2 .2.4　　Preparation of test sample
The combined primary sample is reduced to ca l kg
vided into two equal portions . Each portion is placed
is then sealed and　labeled .
2.2.5　Storage of test sample
the edible portions are blended.and then din a clean container as the test sample . which
The test samples should be stored below - 180C .
Note :　In the course of sampling and sample preparation . precautions must be taken to avoid contamination　or any
factors that may cause the change of residue content .

3　Method of determination
3 . 1　　 Principle
The pencycuron residues in the test sample are extracted with water-acetone.The extract is con-
centrated and partitioned with dichloromethane. Cleaned up by passing through a on Florisil col-
umn.The analyte is eluted with acetone-n-hexane and the eluate is evaporated. The residue is
leached and made up to a definite volume with acetone . Determination is made by means of a gas
chromatograph equipped with mass selective detector, using external standard method. If neces-
sary,the pencycuron is confirmed by GC-MS .
3.2　Reagents and materials
Unless otherwise specified, all the reagents used should be analytically pure, "water- is distilled
water .
3.2. 1　 Acetone: Redistilled
3.2 .2　　Dichloromethane : Redistilled
3.2.3　 n-hexane: Redistilled
3.2.4　Sodium chloride
3.2.5　　Sodium chloride aqueous solution : 50 g/L
3.2.6　　Anh-/drous sodium sulfate :lgnite at 6500C for 4 h, and keep in a tightly closed container
3.2.7　 Florisil: For chromatography, 100-200 mesh. ignite at 650 C for 5 h. Before use. heat at
130r for 4 h and deactivate by adding 2% ( m/m) water after cooling. Keep in a tightly closed
container.
3.2.8　　 Pencycuron　standard : Purity ? 99 %
3.2.9　Pencycuron standard solution:Accurately weigh an adequate amount of pencycuron stan-
dard and dissolve in a small volume of acetone. Dilute with acetone to form a standard stock solu
tion of l.00 mg/mL in concentration.Then dilute the standard stock solution with acetone to the
required concentration as the standard working solution .
3.3　Apparatus and equipment
3.3. 1　 Gas chromatograph equipped with mass selective detector( MSD)
3.3.2　Homogenizer
3.3.3　Rotary vacuum evaporator
3.3.4　　Column of anhydraus sodium sulfate : 7.5 cm x l.5 cm(i.d. ) , packed with 5 cm　height of
anhydrous sodium sulfate .
3.3.5　　Florisil column : 25 cm x l .5 cm(i. d. ) .add in sequence 2 cm( height) of anhydrous sodium
sulfate, 10 g of Florisil,2 cm( height) of anhydrous sodium sulfate . Rinse the column with 50 mL of
n-hexane before use.
3.3.6　Micro-syringe:10 yL
3.4　Procedure
3.4. 1　　Extraction
Weigh ca 20 g( accurate t0 0. 1　g)　of the test sample into a 250 mL conical flask with stopper, add
40 mL of water and let stand for 2 h.Add 100 mL of acetone and homogenize for 5 min at high
speed . Filter with suction into a 250-mL pear-shaped bo删e . Extract the residue with 50 mL of ace-
tone once more,filter and combine the washings in to the same pear-shaped bo州e.Evaporate to
about 40 mL in a rotary evaporator with a bath temperature below 400C .
Transfer the concentrated solution into a 500-mL separatory funnel, add 200 mL of sodium chloride
aqueous solution and 100 mL of dichloromethane,shake for 3 min and set aside for separating.
Collect the dichloromelhane phase. The water phase is again extracted with 2 x 50 mL of
dichloromethane . Combined the dichloromethane phases,　and let pass through a column of anhy-
drous sodium sulfate to remove the water. Collect the effluent in a 250-mL pear-shaped bottle and
evaporate to near dryness in a rotary evaporator with a bath temperature below 400C . Dissolve the
residue with 10 mL of acetona- n-hexane(5 + 95) .
3 .4.2　 Cleanup
Transfer the above solution into an　Florisil column . Wash the column with 50 mL of acetone- n-
hexane
(5 + 95)　and discard the e俐uent. Then　elute with 50 mL of acetone- n-hexane( 15 + 85) , collect all
the eluates in a 250-mL pear-shaped bottle and evaporate to dryness in a rotary evaporator with a
bath temperature below 400C . Dissolve the residue and dilute exactly t0 5.0 mL with acetone for
GC-MS determination .
3.4.3　Determination
3.4.3. 1　　GC-MS operating condition
a)　Chromatographic column : 30 m x 0.25 mm(i .d. ) .0.25 ym film thickness , DB-17 . silica capillary
column or equivalent;
b)　Column　temperature ; 50 "C ( 2　min) 30 qC/min　200 qC (1
c)　Injection　port　temperature : 270 aC ;
d)　Interface temperature : 2600C ;
e)　Carrier　gas : Helium. purity)99.99 % , 1 .2　mUmin;
f) Injection volume:l yL;
g)　Injection mode : Splitless , purge on after l .5 min ;
h) Electron ionization mode : El;
i) lonization energy:70 eV;
j)　Electronic mulitplier voltage : 1 . 5 kV;
k) Determination mode:SIM mode;
l)　Selected　monitoring　ion　( m/z) : 182 . 183 . 209　u;
m) Solvent protection delay: 5 min .
3.4.3.2　GC-MS determination
min)lOoC/min 2700C ( 5 min)
According to the approximate concentration of the pesticide in the sample solution .sPlect the stan-
dard working solution with similar peak height to that of the sample solution. The responses of
pesticide in the standard working solution and sample solution should be within the linear range of
the instrumental detection . The standard working solution should be randomly injected in-between
the injections of the sample solution of equal volume. Under the above chromatographic condi-
tion . the　retention time of pencycuron　is ca　10 min. For gas ch romatogram　of the standard , see fig-
ure Al in annex A.
3.4.3.3　GC-MS Confirmation
According to the operation condition assigned in 3.4.3. 1 , analyze the standard solution and sam-
ple solution.lf there is any peak of sample solution appeared at the same retention time as such
peak of the standard　solution, it must be confirmed　by selected　monitoring　ions( m/z)　182 , 183 ,
209 (abundance ratio is ca 100: 13 : 79)　with GC-MS.
3.4.4　Blank test
The operation of the blank test is the same as that described in the method of determination but
with　omission　of samDIe addition .
3.5　Calculation and expression of the result
Calculate the content of pencycuron residues in the test sample by GC data processor or according
to tha formula(2) .
where
　　　X-the　residue content　of pencycu rort　in　the test sample, mg/kg ;
　　　h-the peak height of pencycuron in the sample solution, mm ;
　　 hs-the peak height of pencycuron in the standard working solution , mm ;
　　　 c-the concentration of pencycuron in the standard working solution ,yg/mL;
　　　V-the final volume of the sample solution. mL;
　　 m-the corresponding mass of the test sample in the final sample solution.g .
Note : The blank value should be subtracted fram the above result af calculation .
4　Limit of determination and recovery
4. 1　　Limit of determination
The limit of determination of this method is 0.05 mg/kg
4 . 2　　Recovery
4.2 . 1　　According to the experimental　data , the fortifying concentrations of pencycuron　in　unpol-
ished rice and its corre sponding recoveries are:
0 .05 mg/kg , the recovery 92 .2%
0 .50 mg/kg,the recovery 91 .3%
1.0mg/kg , the　recovery 88 . 0%
4.2.2　According to the experimental data.the fortifying concentrations of pencycuron in maize
and its corresponding recoveries are :
0.05 mg/kg,the recovery 92.6% ;
0.50 mg/kg.the recoveW 98 .7% ;
1 .00 mg/kg , the recovery 89 . 5% .
4. 2. 3　　According to the　experimental　data , the fortifying concentration of pencycuron　in tomato
and its corresponding recoveries are :
0.05 mg/kg , the recovery 97.3%
0. 50 mg/kg,the recovery 95.6%
1 .00 mg/kg ,the recovery 92.2%
4.2.4　 According to the experimental data , the fortifying concentrations of pencycuron in potatoes
and its corresponding recoveries are :
0.05 mg/kg,the recovery 96. 1% ;
　　　0.50 mg/kg , the recovery 91 .3% ;
　　　1 .00 mg/kg, the recovery 92.8% .


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