Pyriproxyfen

Materials to be

analyzed

Cabbage, cantaloupe, cauliflower, citrus fruit, cottonseed,

cucumber, mustard greens, nutmeats, pome fruit, stone

fruit, summer squash, tomatoes, soil, and water

Instrumentation

Gas chromatograph with nitrogen–phosphorus detector

1

Introduction

Chemical name

(IUPAC )

4-Phenoxyphenyl (RS )-2-(2-pyridyloxy)propyl ether

Structural formula

O

O

O

N

Empirical formula

C

20

H

19

NO

3

Molecular mass

321.4

Melting point

47

◦

C

Vapor pressure

<1×10

−7

mmHg at 22.8

◦

C

Solubility

Water: 0.37 mg L

−1

at 20

◦

C

Hexane: 80 g L

−1

at 20

◦

C

Methanol: 60 g L

−1

at 20

◦

C

Stability

Stable in acidic, neutral and basic aqueous solutions

Other properties

Pale yellowish solid, faint characteristic odor

Flash point: 119

◦

C (Pensky–Martens closed tester)

Use pattern

Pyriproxyfen is an insect growth regulator which acts

both as an ovacide and as an inhibitor of development

(juvenile hormone mimic) against white flies, scale,

and psylla. The specificity of pyriproxyfen, and its low

mammalian toxicity, allow for some variation in appli-

cation timing. For example, the lack of toxicity to bees

allows pyriproxyfen to be applied during bloom on

apple trees, and its low mammalian toxicity allows for

a very short pre-harvest interval on citrus

Regulatory position

The residue definition is for pyriproxyfen alone

Handbook of Residue Analytical Methods for Agrochemicals.

C

2003 John Wiley & Sons Ltd.

Pyriproxyfen

1341

2

Outline of method

2.1

Fruits and vegetables

Residues are extracted with acetone. The extract is rotary evaporated to remove
acetone, the concentrated residue is diluted with 5% aqueous sodium chloride, and
residues are partitioned into dichloromethane. The extract is then concentrated and
purified on a silica gel column. Residues of pyriproxyfen are quantitated by gas
chromatography with nitrogen–phosphorus detection (GC/NPD). For citrus, a
hexane–acetonitrile solvent partition step is required for oil removal prior to the
dichloromethane partition step.

2.2

Ginned cottonseed

Residues are extracted with acetonitrile–water (4 : 1, v/v). The extract is rotary evapo-
rated to remove acetonitrile, and the concentrated residue is diluted with 5% aqueous
sodium chloride prior to partitioning with dichloromethane. The dichloromethane
is removed by rotary evaporation and the sample extract is purified by partition-
ing between hexane–acetonitrile and by silica gel chromatography. Residues of
pyriproxyfen are quantitated by GC/NPD.

2.3

Nutmeats

Residues are extracted with acetone. The extract is then rotary evaporated to remove
acetone, the concentrated residue is diluted with 5% aqueous sodium chloride, and
the residues are partitioned into dichloromethane. The dichloromethane is removed
by rotary evaporation, and the sample extract is purified by partitioning between
hexane–acetonitrile and by silica gel chromatography. A second hexane–acetonitrile
partitioning step is required to remove residual oil, and the residues of
pyriproxyfen are quantitated by GC/NPD.

2.4

Soil

Residues are extracted with methanol–0.1 M sodium hydroxide (NaOH) (4 : 1, v/v).
The extract is rotary evaporated to remove the methanol, the concentrated residue is
diluted with water (at neutral pH), and the residues are partitioned into
dichloromethane. The extract is purified using an alumina column. Pyriproxyfen
residues are quantitated by GC/NPD.

2.5

Water

Residues are partitioned into ethyl acetate. The extract is purified using a Florisil
column, and pyriproxyfen residues are quantitated by GC/NPD.

1342

Individual compounds

3

Apparatus

Buchner funnel, 9-cm diameter
Centrifuge tubes, 15-mL
Centrifuge
Filter paper, 9-cm diameter Whatman GF/A
Filter flask, 500- and 1000-mL
Filter funnel, 10-cm diameter
Gas chromatograph, equipped with a nitrogen–phosphorus detector
Glass chromatography column, 19

× 300 mm with Teflon stopcock

Glass wool (Pyrex)
Linear shaker
OmniMixer, with an adapter for a pint Mason jar
Pasteur pipets
pH indicator paper
Rotary vacuum evaporator, with a 40

◦

C water-bath

Round-bottom flasks, 50-, 100-, 500- and 1000-mL
Separatory funnels, 250- and 500-mL
Ultrasonic water-bath
Vortex mixer

4

Reagents

Acetone, reagent grade
Acetonitrile, reagent grade
Deionized water
Dichloromethane, reagent grade
Diethyl ether, reagent grade
Ethyl acetate, reagent grade
Hexane, reagent grade
Methanol
Phosphoric acid, 85%, reagent grade
Phosphoric acid, 1 M solution
Toluene, reagent grade
Alumina, 150 mesh (Aldrich, Catalog No. 19,996-6)
Florisil, 60–100 mesh
Silica gel, 70–230 mesh (EM Science, Catalog No. 7734-7)
Sodium chloride, reagent grade
Sodium chloride solution, 5% aqueous solution
Sodium hydroxide, reagent grade
Sodium hydroxide solution, 0.1 M aqueous solution
Sodium sulfate, anhydrous

Pyriproxyfen

1343

5

Sampling and preparation

No specific sample preparation or processing is needed for this method. In general,
fruits and vegetables were macerated with dry-ice and placed into freezer storage
prior to extraction.

6

Procedure

6.1

Extraction and cleanup

6.1.1

Fruit and vegetables

Extraction. Homogenize 20 g of sample in a pint Mason jar with 150 mL of acetone

for approximately 5 min using an OmniMixer. Allow the solids to settle and decant
the liquid through a Whatman GF/A glass-fiber filter in a Buchner funnel, collecting
the filtrate in a 500-mL (or 1000-mL) filter flask. Repeat the extraction and filtration
twice with additional 150-mL portions of acetone. Following the third extraction,
transfer the solids onto the filter. Rinse the extraction jar with approximately 20 mL
of acetone and add this rinse to the solids on the Buchner funnel, combining the rinse
with the other extracts. Transfer the filtrate to a 1000-mL round-bottom flask, and
remove the acetone by rotary evaporation under reduced pressure in a

<40

◦

C water-

bath. For citrus samples only, add 250 mL of ethyl acetate to reduce the water volume
to

<5 mL. For the non-oily crops, the volume of water remaining is not critical. For

all samples except citrus, proceed to the dichloromethane partition step. For citrus,
proceed to the hexane–acetonitrile partition step.

Hexane–acetonitrile partition. Add 70 mL of acetonitrile (hexane-saturated) to

the round-bottom flask and briefly sonicate the mixture to dislodge the material on
the glass surface. Transfer the mixture into a 250-mL separatory funnel, add 100 mL
of hexane (acetonitrile-saturated), and shake the funnel vigorously for 1 min. Allow
the phases to separate, then drain the acetonitrile layer into a 500-mL round-bottom
flask. Repeat the partitioning of the hexane layer twice with 70-mL portions of
acetonitrile (hexane-saturated), combining the three extracts in the 500-mL round-
bottom flask. Evaporate the acetonitrile (just to dryness) by rotary evaporation under
reduced pressure with a

<40

◦

C water-bath. Proceed to the dichloromethane partition

step.

Dichloromethane partition. Add 100 mL of 5% sodium chloride solution to the

round-bottom flask, briefly sonicate the flask to dislodge the residues, and transfer
the mixture into a 500-mL separatory funnel. Rinse the round-bottom flask with
150 mL of dichloromethane and transfer the dichloromethane to the separatory fun-
nel. Shake the funnel vigorously (with occasional venting) for 1 min and allow the
phases to separate. Drain the dichloromethane through sodium sulfate (approxi-
mately 50 g suspended on a glass-wool plug in a 10-cm diameter filter funnel) into a
1000-mL round-bottom flask. Once the extract has drained through the sodium sulfate,
rinse the sodium sulfate with approximately 20 mL of dichloromethane. Repeat the

1344

Individual compounds

partition twice with 100-mL portions of dichloromethane, rinsing as before. Rotary
evaporate the combined dichloromethane extract to 20–30 mL under reduced pres-
sure in a

<40

◦

C water-bath. Transfer the residues to a 100-mL round-bottom flask,

rinsing the 1000-mL flask twice with 10-mL portions of ethyl acetate. Continue
the evaporation, and evaporate the sample just to dryness. Add 5 mL of hexane–
ethyl acetate (4 : 1, v/v), stopper the flask, and sonicate the sample to dissolve the
residues.

Silica gel column cleanup. Prepare a silica gel column by placing a glass-wool

plug in the bottom of a glass chromatography column. Slurry 18 g of silica gel with
hexane–ethyl acetate (4 : 1, v/v) and pour the slurry into the column. Rinse the walls
of the column with hexane–ethyl acetate, and add approximately 2 g of sodium sulfate
to the top of the silica gel column. Drain the solvent to the top of the sodium sulfate
layer.

Transfer the sample to the column. Rinse the sample flask sequentially with 5 mL,

5 mL, and then 10 mL of hexane–ethyl acetate (4 : 1, v/v). Allow each rinse to drain
to the top of the sodium sulfate layer before adding the next portion. Discard the
accumulated eluant, place a 100-mL round-bottom flask under the column, and elute
the pyriproxyfen residues with 55 mL of hexane–ethyl acetate (4 : 1, v/v). Evaporate
the eluate by rotary evaporation under reduced pressure in a

<40

◦

C water-bath and

reconstitute the sample in 2.0 mL of toluene with sonication for analysis (Section 6.2).

6.1.2

Cottonseed

Extraction. Homogenize 10 g of a prepared sample in a pint Mason jar with 100 mL

of acetonitrile–water (4 : 1, v/v) for approximately 5 min using an OmniMixer. Filter
the sample through a Whatman GF/A glass-fiber filter in a Buchner funnel, collecting
the filtrate in a 500-mL filter flask. Transfer the filter cake back into the jar and
repeat the extraction and filtration. Rinse the extraction jar twice with approximately
20 mL of acetonitrile, passing each rinse through the solids on the Buchner funnel and
combining the rinses with the other extracts. Transfer the filtrate to a 1000-mL round-
bottom flask, add 150 mL of ethyl acetate to inhibit foaming, and rotary evaporate the
solvent under reduced pressure in a

<40

◦

C water-bath (approximately 20–40 mL of

water will remain).

Dichloromethane partition. Transfer the aqueous extract into a 500-mL separa-

tory funnel and add 150 mL of 5% sodium chloride solution. Rinse the round-bottom
flask with 80 mL of dichloromethane and transfer into the separatory funnel. Shake
the separatory funnel vigorously (with occasional venting) for 1 min and allow
the phases to separate. Drain the lower dichloromethane through sodium sulfate
(approximately 50 g suspended on a glass-wool plug in a 10-cm diameter filter funnel,
pre-rinsed with 25 mL of dichloromethane) into a 500-mL round-bottom flask.
Repeat the partition with another 80-mL portion of dichloromethane. Drain the
dichloromethane through the sodium sulfate as before, and rinse the sodium
sulfate with three 10-mL portions of dichloromethane. Evaporate the combined
dichloromethane extract just to dryness using rotary evaporation under reduced pres-
sure in a

<40

◦

C water-bath.

Pyriproxyfen

1345

Hexane–acetonitrile partition. Add 150 mL of hexane (acetonitrile-saturated) to

the round-bottom flask to reconstitute the sample, and transfer the sample to a 500-mL
separatory funnel. Rinse the round-bottom flask with 100 mL of acetonitrile (hexane-
saturated), and add this rinse to the separatory funnel. Shake the funnel vigorously for
1 min, allow the phases to separate and drain the acetonitrile layer into a clean 500-mL
round-bottom flask. Repeat the partitioning of the hexane layer with a second 100-mL
portion of acetonitrile (hexane saturated), combining the acetonitrile layers. Rotary
evaporate the extract under reduced pressure in a

<40

◦

C water-bath to approximately

40–50 mL. Transfer the extract to a 100-mL round-bottom flask, rinsing the 500-mL
round-bottom flask three times with 5 mL of acetonitrile (hexane-saturated). Continue
the evaporation and take the sample just to dryness. Reconstitute the sample by
sequentially adding 1 mL of toluene and 2 mL of hexane to the 100-mL round-bottom
flask. Sonicate the sample to dissolve any residue adhering to the walls of the flask.

Silica gel column cleanup. Prepare a silica gel column by placing a glass-wool plug

in the bottom of a glass chromatography column. Slurry 15 g of silica gel (deactivated
with 10% water) with hexane, and transfer the slurry to the column. Rinse the walls
of the column with hexane and add 2 g of sodium sulfate to the top of the silica gel
column. Drain the hexane to the top of the sodium sulfate layer.

Transfer the sample to the column and drain the solvent to the top of the sodium

sulfate layer. Rinse the round-bottom flask three times with 3-mL portions of hexane,
adding these rinses sequentially to the column and draining the solvent to the top of
the sodium sulfate layer before the next addition. Pass 90 mL of hexane through the
column, followed by 50 mL of hexane–diethyl ether (15 : 1, v/v). Add each portion
of eluting solvent to the round-bottom flask and sonicate the flask before adding
the solution to the column. Discard the accumulated eluate. Place a 250-mL round-
bottom flask under the column and elute the pyriproxyfen residues with 50 mL of
hexane–diethyl ether (15 : 1, v/v), followed by 20 mL of hexane–acetone (7 : 3, v/v).
As before, add each portion of eluting solvent to the round-bottom flask and sonicate
the flask before adding the solution to the column. Rotary evaporate the combined
eluate under reduced pressure in a

<40

◦

C water-bath to 40–50 mL. Transfer the

sample to a 100-mL round-bottom flask with three 5-mL acetone rinses, and continue
rotary evaporation to take the sample just to dryness. Reconstitute the sample in
1.0 mL of toluene with sonication for analysis (Section 6.2).

6.1.3

Nutmeats

Extraction. Extract 20 g of sample as described for fruit and vegetables. Evaporate

the acetone extract to dryness by rotary evaporation under reduced pressure in a
<40

◦

C water-bath.

Dichloromethane partition. Partition residues into dichloromethane as described

for fruit and vegetables. Evaporate the dichloromethane extract just to dryness by
rotary evaporation under reduced pressure in a

<40

◦

C water-bath.

Hexane–acetonitrile partition. Partition the sample between hexane and acetoni-

trile as described for fruit and vegetables to remove citrus oils. Evaporate the

1346

Individual compounds

dichloromethane extract just to dryness by rotary evaporation under reduced pres-
sure in a

<40

◦

C water-bath.

Silica gel column cleanup. Clean up the sample with a 15-g silica gel column as

described for ginned cottonseed. Evaporate the column eluate just to dryness using
rotary evaporation under reduced pressure in a

<40

◦

C water-bath.

Second hexane–acetonitrile partition. Transfer the sample to a 15-mL glass cen-

trifuge tube by rinsing the round-bottom flask with 2 mL of hexane (acetonitrile-
saturated) followed by 2 mL of acetonitrile (hexane-saturated). Sonicate each rinse
for approximately 15 s before transferring the rinse via a Pasteur pipet to the cen-
trifuge tube. Stopper the centrifuge tube, mix the sample for 30 s using a vortex mixer,
and allow the phases to separate (centrifuge for approximately 2 min, if necessary).
Carefully withdraw the acetonitrile (the lower layer) with a glass syringe or Pasteur
pipet, and transfer the acetonitrile to a 50-mL round-bottom flask. Extract the hexane
layer with two additional 2-mL portions of acetonitrile (hexane-saturated), rinsing
the 250-mL round-bottom flask with each before adding the solvent to the centrifuge
tube. Combine all of the acetonitrile layers in the 50-mL round-bottom flask. Evap-
orate the acetonitrile extract just to dryness by rotary evaporation under reduced
pressure in a

<40

◦

C water-bath. Reconstitute the sample in 2.0 mL of toluene with

sonication for analysis (Section 6.2).

6.1.4

Soil

Extraction. Place 20 g of sample (wet-weight basis) in a pint Mason jar, add 40 mL

of methanol–0.1 M NaOH (4 : 1, v/v), cap the jar, and shake it for approximately
15 min using a linear shaker. Filter the sample through a Whatman GF/A glass-fiber
filter in a Buchner funnel, collecting the filtrate in a 500-mL filter flask. Rinse the jar
with 40 mL of methanol–0.1 M NaOH (4 : 1, v/v) and pass the rinse through the filter
cake, combining the rinse with the extract. Transfer the filter cake back into the jar and
repeat the extraction with a second 40-mL portion of methanol–0.1 M NaOH (4 : 1,
v/v). Filter the sample as before, rinsing the jar again with approximately 20 mL
of methanol–0.1 M NaOH (4 : 1, v/v) and passing the rinse through the filter cake.
Transfer the combined filtrate to a 500-mL round-bottom flask, rinsing the filter flask
twice with 20-mL portions of methanol–0.1 M NaOH (4 : 1, v/v). Reduce the volume
of the extract to approximately 20 mL by rotary evaporation under reduced pressure
in a

<40

◦

C water-bath.

Dichloromethane partition. Add 100 mL of deionized water to the round-bottom

flask. Transfer the sample to a 500-mL separatory funnel and add 1 mL of phos-
phate buffer and 1 g of sodium sulfate. Adjust the pH to 7 with 1 M phosphoric acid
(approximately 0.75 mL), checking that the pH is approximately 7 with pH paper.
Add 100 mL of dichloromethane to the separatory funnel, rinsing the round-bottom
flask with portions of this before addition to the separatory funnel. Shake the sepa-
ratory funnel vigorously (with occasional venting) for 1 min, and allow the phases
to separate. Drain the dichloromethane through sodium sulfate (approximately 50 g

Pyriproxyfen

1347

suspended on a glass-wool plug in a 10-cm diameter filter funnel, pre-rinsed with
25 mL of dichloromethane) into a 500-mL round-bottom flask. Repeat the partition
with another 100-mL portion of dichloromethane. Drain the dichloromethane through
the sodium sulfate as before, and rinse the sodium sulfate with two 10-mL portions
of dichloromethane. Evaporate the dichloromethane extract just to dryness by rotary
evaporation under reduced pressure in a

<40

◦

C water-bath. Reconstitute the sample

in 3 mL of hexane–ethyl acetate (10 : 1, v/v) with sonication.

Alumina column cleanup. Prepare an alumina column by placing a glass-wool plug

in the bottom of a glass chromatography column. Slurry 10 g of alumina with hexane–
ethyl acetate (10 : 1, v/v), and pour the slurry into the column. Rinse the walls of the
column with hexane–ethyl acetate (10 : 1, v/v), and add approximately 2 g of sodium
sulfate to the top of the alumina column. Drain the solvent to the top of the sodium
sulfate layer.

Transfer the sample to the column with a Pasteur pipet and drain the solvent to

the top of the sodium sulfate layer. Rinse the round-bottom flask three times with
3-mL portions of hexane–ethyl acetate (10 : 1, v/v), adding these rinses sequentially
to the column and draining the solvent to the top of the sodium sulfate layer before
the next addition. Discard the accumulated eluate and place a 100-mL round-bottom
flask under the column. Elute the residues with 28 mL of hexane–ethyl acetate (10 : 1,
v/v). Evaporate the column eluate just to dryness by rotary evaporation under reduced
pressure in a

<40

◦

C water-bath. Reconstitute the sample in 2.0 mL of toluene for

analysis (Section 6.2).

6.1.5

Water

Extraction. Transfer 500 mL of the water sample into a 1000-mL separatory funnel.

Add 200 mL of ethyl acetate to the separatory funnel and shake vigorously for 1 min.
Allow the phases to separate and drain the aqueous layer into a 600-mL beaker (or
suitable container). Filter the ethyl acetate through sodium sulfate (approximately 50–
70 g suspended on a glass-wool plug in a 10-cm diameter filter funnel) into a 1000-mL
round-bottom flask. Once the extract has drained through the sodium sulfate, rinse the
sodium sulfate with 10 mL of ethyl acetate. Repeat the partition twice with 100-mL
portions of ethyl acetate, draining each extract through the sodium sulfate and rinsing
the sodium sulfate as before. Evaporate the sample extract just to dryness by rotary
evaporation under reduced pressure in a

<40

◦

C water-bath. Reconstitute the sample

in 10 mL of hexane–ethyl acetate (50 : 1, v/v).

Florisil column cleanup. Prepare a Florisil column by placing a glass-wool plug

in the bottom of a glass chromatography column. Slurry 15 g of Florisil with hexane–
ethyl acetate (50 : 1, v/v) and transfer the slurry into the column. Rinse the walls of the
column with hexane–ethyl acetate (50 : 1, v/v) and add approximately 2 g of sodium
sulfate to the top of the Florisil column. Drain the solvent to the top of the sodium
sulfate layer.

Transfer the sample to the column and drain the solvent to the top of the sodium

sulfate layer. Rinse the round-bottom flask twice with 10-mL portions of hexane–ethyl

1348

Individual compounds

acetate (50 : 1, v/v), adding these rinses sequentially to the column and draining the
solvent to the top of the sodium sulfate layer before the next addition. Wash the
column with an additional 25-mL portion of hexane–ethyl acetate (50 : 1, v/v) and
discard the accumulated eluate. Place a 250-mL round-bottom flask under the column.
Elute the residues with 75 mL of hexane–ethyl acetate (15 : 1, v/v). Reduce the volume
of the eluate to 15–20 mL by rotary evaporation under reduced pressure in a

<40

◦

C

water-bath. Transfer the sample into a 50-mL round-bottom flask, rinsing the 250-mL
round-bottom flask three times with 5-mL portions of hexane–ethyl acetate (15 : 1,
v/v). Evaporate the sample just to dryness. Reconstitute the sample in toluene for
analysis (Section 6.2).

6.2

Determination

6.2.1

Plant material, soil, and water

Inject the sample extract into a gas chromatograph within an analytical sequence,
with calibration standards bracketing and interspersed within the sequence.

Operating conditions
Gas chromatograph

HP5890, Hewlett-Packard

Sample injector

HP7673, Hewlett Packard

Injection port

Split/splitless (approximately 1 : 1 split ratio), 270

◦

C

Injection mode

Splitless, purge on at 0.6 min

Column

DB-17 (J&W Scientific), 30 m

× 0.53-mm i.d., 1.0-µm

film thickness

Column temperature

260

◦

C, 2 min; 10

◦

C min

−1

to 280

◦

C, 6 min (10 min total)

Detector

Nitrogen–phosphorus detector, 300

◦

C

Gas flow rates

Helium carrier gas, 30 mL min

−1

Hydrogen, 3.6 mL min

−1

Air, 110 mL min

−1

Injection volume

1.0 or 2.0 µL

Retention time

2.2 min

Alternative parameters 1
Injection port

Split/splitless (approximately 3 : 1 split ratio), 250

◦

C

Injection mode

Splitless, purge on at 0.6 min

Column

DB-17 (J&W Scientific), 30 m

× 0.53-mm i.d., 1.5-µm

film thickness

Column temperature

265

◦

C, 2.5 min; 10

◦

C min

−1

to 280

◦

C, 6 min (10 min

total)

Detector

Nitrogen–phosphorus detector, 300

◦

C

Gas flow rates

Helium carrier gas, 10 mL min

−1

Helium makeup gas, 20 mL min

−1

Hydrogen, 3.6 mL min

−1

Air, 110 mL min

−1

Injection volume

1.0 µL

Retention time

4.2 min

Pyriproxyfen

1349

Alternative parameters 2
Injection port

Split/splitless (approximately 2 : 1 split ratio), 300

◦

C

Injection mode

Splitless, purge on at 0.6 min

Column

DB-5 (J&W Scientific), 30 m

× 0.53-mm i.d., 1.5-µm film

thickness

Column temperature

250

◦

C, 7 min (isothermal)

Detector

Nitrogen–phosphorus detector, 300

◦

C

Gas flow rates

Helium carrier gas, 20 mL min

−1

Helium makeup gas, 10 mL min

−1

Hydrogen, 3.6 mL min

−1

Air, 110 mL min

−1

Injection volume

1.0 µL

Retention time

3.8 min

7

Evaluation

7.1

Method

Prior to use, the linearity of the gas chromatography system should be verified by
analyzing at least four standards of different concentrations. The linearity standards
should range in concentration from 0.1 to 2.0 µg mL

−1

. A response factor for each

standard is calculated by dividing the response of each standard by its concentration.
The relative standard deviation (RSD) of these response factors should be

<10%.

Quantitation is performed using the external standard calibration technique. The

concentration of the calibration standard is 1.0 µg mL

−1

. The calibration standard

should be injected prior to injection of the treated samples and again after every
second or third injection of treated samples. The analytical sequence should end with
a calibration standard. The RSD of the calibration standards should be

<10%.

7.2

Recoveries, limit of quantitation, and limit of detection

7.2.1

Plant material

Fortification of untreated plant matrices at 0.02 and 0.1 mg kg

−1

gave recoveries

from 67 to 103%. The limit of detection (LOD) is 0.01 mg kg

−1

and the limit of

quantification (LOQ) is 0.02 mg kg

−1

.

7.2.2

Soil

Fortification of blank soil at 0.02 and 0.1 mg kg

−1

gave recoveries from 88 to 95%,

with an LOD of 0.01 mg kg

−1

and an LOQ of 0.02 mg kg

−1

.

7.2.3

Water

Fortification of blank water between 2.0 and 11 µg L

−1

gave recoveries from 87 to

107%, with an LOD of 1.0 µg L

−1

and an LOQ of 2.0 µg L

−1

.

1350

Individual compounds

7.3

Calculation of residues

Pyriproxyfen (mg kg

−1

or µg L

−1

)

=

A

× C × V

B

× S

where

A

= integration counts for pyriproxyfen in the sample

C

= concentration of pyriproxyfen in the calibrating standard (1.0 µg mL

−1

)

V

= final volume of the sample extract (mL)

B

= mean integration counts for the calibration standards

S

= sample weight or volume (g or L)

8

Important points

During evaporation of organic solvents, the temperature of the water-bath should be
kept at 40

◦

C or lower. Once the solvent is evaporated, continued rotary evaporation

may lead to reduced analyte recovery.

In general, pyriproxyfen residues are stable in macerated crop samples. Stability

problems have been observed in summer squash, and this should be extracted within
21 days of harvest.

The variety of cleanup columns included may allow for rapid adaptation to addi-

tional matrices. If using hexane–diethyl ether (15 : 1, v/v) as an eluent, this solution
should be prepared just prior to use. Cleanup with silica gel and hexane–ethyl acetate
(4 : 1, v/v) is recommended for most crop samples.

Each batch of alumina, Florisil, and silica gel used in a cleanup column must be

checked for recovery of pyriproxyfen. If the recovery of pyriproxyfen is

<90%, the

elution volume and/or solvent mixture must be adjusted until suitable recoveries are
obtained.

Cleanup of highly colored samples (e.g., mustard greens) on silica columns may

require that only half of the sample extract be passed through the silica column.

Charles A. Green

Valent USA Corporation, Dublin, CA, USA