combination of sorbents for removal of unwanted sample
components. The sample clean-up also reduces matrix
effects and therefore improves method robustness.
The pesticides analyzed in the cucumber matrix include
mixtures of herbicides, fungicides, organophosphorus
pesticides and pyrethroids. Six extractions of 50 ng/g
spiked level were used for the recovery experiments.
2
Experimental Details
Consumables
Part Number
Column:
TraceGOLD TG-5MS, 30 m x 0.25 mm x 0.25 μm 26098-1420
Septum:
BTO, 17 mm
31303211
Liner:
Splitless Straight Liner, 3 x 8 x 105 mm
45350033
Column ferrules:
100% Graphite ferrules for TRACE injector
29053488
0.1-0.25 mm ID
Graphite/vespel for transfer line 0.1-0.25 mm ID
29033496
Injection syringe:
10 μL Fixed needle syringe for a TriPlus Autosampler
36500525
Thermo Scientific Chromacol 9mm screw 2 mL vial -clear
2-SVW
Thermo Scientific Chromacol 9mm screw caps with PTFE/Silicone/PTFE
9-SC(B)-TST1
Chemicals and Reagents
Part Number
QuEChERS Extraction Stage:
Metalized Pouch containing 6g MgSO
4
,
60105-337
1.5 g sodium chloride, 1.5 g sodium citrate tribasic
dihydrate, 0.75 g sodium citrate dibasic sesquihydrate
and empty centrifuge tube with plug seal cap
QuEChERS Dispersive SPE Stage:
15 mL centrifuge tube with 900 mg MgSO
4
,
60105-227
150 mg PSA, 150 mg C18
Fisher Scientific HPLC grade Acetonitrile
A/0626/17
Sample Preparation
The methodology described in this application note is for the preparation of calibration standards and sample spike
(Figure 1).
an exothermic reaction occurs between the magnesium
sulfate and water. This step may lead to reduced recoveries
of the pesticides. To overcome this problem, the sample
can be weighed directly into an empty centrifuge tube
followed by the addition of acetonitrile.The tube can then
be immersed in an ice bath with slow addition of salts.
The second stage of the QuEChERS method uses
dispersive SPE, which involves transferring a portion of
the acetonitrile extract to a clean-up tube containing a
Figure 1: Flow diagram of QuEChERS methodology used in this application
Extraction Stage
(1)
Add 10 g of homogenized cucumber in 50 mL FEP extraction tube.
Shaken thoroughly
(2)
Add pesticide standard
Sample spike:
Add 10 mL of 50 ng/mL pesticide standard
Add in acetontrile.
Blank:
No pesticide standard added, 10 mL of actonitrile added
(3)
Add the content of the QuEChERS metalized pouch into the
centrifuge tube PN 60105-337 very slowly and under ice bath
(4)
Shake vigorously for 5 minutes and centrifuge for 6 minutes
at 3500 rpm
Dispersive SPE Clean-up
(5)
Transfer 11 mL of acetonitrile extract to QuEChERS extraction
tube P/N 60105-227.
(7)
Transfer 1 mL of sample extract to a GC vial
Calibration standards:
Add 10 µL of 1, 2.5, 5, 10, 25, 50,
100 µg/mL pesticide standard mix into 990 µL
of sample extract.
(6)
Shake vigorously for 5 minutes and centrifuge for 6 minutes
at 3500 rpm
(8)
Add 10 µL of 100 µg/mL internal standard (triphenylphosphine)
to 1 mL of sample extract.
