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QuEChERS Made Even Easier: Comprehensive Solutions Simplify Sample Prep and Analysis

 

Save Time and Money with QuEChERS

  • Free-flowing salts in slim packets make extraction a snap.
  • Complete line of easy-to-use QuEChERS products, reference standards, and accessories.
  • Follow up sample prep with a wide range of analytical columns for both LC and GC.
 
 
 

 

Free-flowing Q-sep extraction salts transfer easily and completely;
convenient slim packets fit perfectly into tubes to prevent spills.

 

For years, the QuEChERS approach to sample preparation has been making the lives of food safety scientists easier. Gone are the days of time-consuming, solvent-intensive extraction techniques and multiple solid phase extraction cartridge cleanup steps! Research published by the U.S. Department of Agriculture Eastern Regional Research Center in Wyndmoor, PA, [1] introduced to the world QuEChERS—a method that is Quick, Easy, Cheap, Effective, Rugged, and Safe.

With QuEChERS, a homogenized sample simply undergoes a quick extraction step where the analytes are driven into an organic solvent by the partitioning power of a blend of salts. After extraction, the sample is cleaned up through the use of a dispersive solid phase extraction (dSPE) step that is also quick and easy to perform. This simple, two-stage process offers significant savings in time, materials, and effort, making QuEChERS sample preparation faster and easier than other approaches (Table I).

Since its introduction, the QuEChERS technique has evolved to accom­modate an expanding list of pesticides in an increasingly diverse list of foodstuffs. At Restek, we offer Q-sep products to cover the four major ap­proaches to QuEChERS along with a host of other items to help make your QuEChERS experience simple and successful. We carry a comprehensive line of sample prep supplies, reference standards, and LC and GC columns that will help make QuEChERS even easier whether you are new to the approach or developing a method for a new sample matrix. If you are frustrated with the time and expense of your current pesticide sample cleanup procedure, we suggest you try this simple, economical technique.

Table I: Prepare samples more quickly, easily, and cost effectively with QuEChERS.

 

Mini-Luke or Modified Luke Method

QuEChERS

Savings with QuEChERS

Estimated time to process 6 samples (min)

120

30

4x faster

Solvent used (mL)

60-90

10

6-9x less solvent

Chlorinated waste (mL)

20-30

0

Safer, cheaper, greener

Glassware/specialized equipment

capacity for 200 mL, quartz wool, funnel, water bath, or evaporator

None

Ready to use

 

Quick and Easy...

Prepare Samples for LC or GC Analysis in Two Simple Stages

QuEChERS is primarily a two-stage process, and you’ll select Q-sep products for both stages. Your method may have specific recommendations, but in case you’re not sure what will work, here are some considerations when making your selection.

Stage 1: Sample Extraction

Analytes of interest are extracted from the sample through the addition of an organic solvent and a blend of salts. The salts enhance extraction efficiency and allow the normally miscible organic solvent to separate from the water in the sample. The choice of which extraction technique to use is made principally by considering your analytes of interest. If you’re looking for compounds that aren’t pH sensitive, the original unbuffered method [1] will work great. However, if your analytes of interest are pH sensitive, you will want to select one of the buffered methods—notably, the official EN 15662 method [2], the mini-multiresidue approach [3], or the official AOAC 2007.01 method [4].

Restek’s Q-sep products for the two European approaches, the official EN 15662 method and the mini-multiresidue approach, are the same, so it becomes essentially a choice between a European-developed method and the AOAC method. Both are buffered to lower the pH to a range where most pesticides are stable, and the methods differ only in the specific buffering salts and their ratios. Either would be a good place to start for most analyses. There are a great many studies that highlight specific instances when one buffering technique may outperform another, so a little research into your particular area of study may yield practical suggestions on which extraction method to use.

Step 1: Add acetonitrile and internal standard, then shake vigorously. Step 2: Add extraction salts and shake, then centrifuge to separate the phases.

Stage 2: Sample Cleanup

A subsample of the organic solvent extract from Stage 1 is cleaned up through the use of dSPE. Where the choice of the extraction product was driven largely by the analytes of interest, the choice of cleanup is based on the sample being tested. Restek Q-sep dSPE products are formulated with different sorbents in different ratios so that your dSPE choice can be tailored to the composition of your particular sample type (e.g., fatty, highly pigmented, etc.). Use Table III further below to learn what each sorbent removes and to help select the best dSPE product for your particular sample.

Step 3: Transfer supernatant to dSPE tube.

Step 4: Shake, centrifuge, and transfer to an autosampler vial for analysis by GC or LC.

Effective...

QuEChERS dSPE Cleanup Assures Optimal Results for Pesticide Analysis

  • Removes matrix interferences that obscure target analytes or cause ion suppression.
  • Protects GC inlet, and LC and GC columns from contamination.
  • Improves integration and mass spectral matches
 

Figure 1: QuEChERS dSPE cleanup removes interferences that obscure target pesticides.

Without extract cleanup, hexadecanoic acid from the matrix obscures peaks for all the following pesticides.
(example XIC chromatogram = endosulfan I)

allethrin
buprofezin
cis-chlordane
trans-chlordane
chlorpyrifos
cyprodinil
dacthal

diphenamid
endosulfan I
endosulfan II
fenthion
metolachlor
myclobutanil
oxyfluorfen

pendimethalin
pentachlorothioanisole
pirimiphos methyl
triadimefon
triadimenol

GC_FF01125_1127
ColumnRxi-5Sil MS, 20 m, 0.18 mm ID, 0.18 µm (cat.# 43602)
SampleSweet potato spiked with pesticide mix and extracted with acetonitrile and Q-sep QuEChERS EN Method 15662 extraction salts
Injection
Inj. Vol.:1.0 µL splitless (hold 1 min)
Liner:Single taper (4 mm) w/deact. wool (cat.# 22405)
Inj. Temp.:250 °C
Oven
Oven Temp.:72.5 °C (hold 1 min) to 350 °C at 20 °C/min
Carrier GasHe, constant flow
Flow Rate:1.2 mL/min
DetectorMS
Mode:
Transfer Line Temp.:300 °C
Analyzer Type:TOF
Ionization Mode:EI
Acquisition Range:45-550 amu
InstrumentAgilent/HP6890 GC
NotesA. Extract (without cleanup step) acidified with formic acid to pH 5.
B. Extract with cleanup using Q-sep QuEChERS dSPE cleanup tube (cat.# 26124) acidified with formic acid to pH 5.

Scan range: m/z 60, 73, 87, 129, 256 plotted

Figure 2: QuEChERS dSPE cleanup significantly improves quantification and identification.

Without cleanup, matrix masks Endosulfan I.

GC_FF1222
ColumnRxi-5Sil MS, 20 m, 0.18 mm ID, 0.18 µm (cat.# 43602)
SampleSweet potato spiked with pesticide mix and extracted with acetonitrile and Q-sep QuEChERS extraction salts, then acidified with formic acid to pH 5.
Injection
Inj. Vol.:1 µL splitless (hold 1 min)
Liner:Gooseneck splitless (4 mm) w/deact. wool (cat.# 22405)
Inj. Temp.:250 °C
Oven
Oven Temp.:72.5 °C (hold 1 min) to 350 °C at 20 °C/min
Carrier GasHe, constant flow
Flow Rate:1.2 mL/min
DetectorMS
Mode:
Transfer Line Temp.:300 °C
Analyzer Type:TOF
Ionization Mode:EI
Acquisition Range:45 to 550 amu
InstrumentLECO Pegasus III GC-TOFMS
Notesm/z 60, 195, 197 shown
 

QuEChERS dSPE cleanup improves quantification and identification.
Peak Integration (extracted ion chromatograms)

Optimize Analysis with Sorbent Choice

Choosing a QuEChERS dSPE Sorbent

Primary and secondary amine exchange material (PSA) is the base sorbent used for QuEChERS dSPE cleanup of fruit and vegetable extracts because it removes many organic acids and sugars that might act as instrumental interferences. In addition, C18 or graphitized carbon black (GCB) may be used to remove lipids or pigments, respectively. Choice of sorbent should be based on matrix composition and target analyte chemistry. Most methods make specific recommendations for acidic, basic, and planar pesticides, which may require additional considerations.

As seen in Table II, GCB can have a negative effect on the recoveries of certain pesticides that can assume planar shapes (e.g., chlorothalonil and thiabendazole). The work shown here was done with 50 mg GCB per mL extract, which emphasizes this effect. The EN 15662 QuEChERS method recommends less GCB, which improves recoveries of planar pesticides but still assures the removal of pigments that can degrade GC-MS performance. To simplify and speed up sample prep, Restek QuEChERS tubes are available in the sorbent combinations and amounts specified by EN 15662 and AOAC methods, as well as in other combinations that may provide better results for difficult matrices (Table III).

Table II: Select sorbents based on matrix and target analyte chemistry. (Percent recovery using C18 or GCB, relative to PSA alone).

tR (min)

Pesticide

CAS Number

Action/Use

Classification

C18*

GCB**

9.50

Dichlorvos

62-73-7

insecticide

organophosphorus

111

116

9.67

Methamidophos

10265-92-6

insecticide

organophosphorus

105

107

11.75

Mevinphos

7786-34-7

insecticide

organophosphorus

112

130

12.02

o-phenylphenol

90-43-7

fungicide

unclassified

106

97

12.14

Acephate

30560-19-1

insecticide

organophosphorus

128

147

13.89

Omethoate

1113-02-6

insecticide

organophosphorus

120

119

14.74

Diazinon

333-41-5

insecticide

organophosphorus

108

127

14.98

Dimethoate

60-51-5

insecticide

organophosphorus

124

151

15.69

Chlorothalonil

1897-45-6

fungicide

organochlorine

125

13

15.86

Vinclozolin

50471-44-8

fungicide

organochlorine

102

98

16.21

Metalaxyl

57837-19-1

fungicide

organonitrogen

105

117

16.28

Carbaryl

63-25-2

insecticide

carbamate

114

111

16.60

Malathion

121-75-5

insecticide

organophosphorus

124

160

16.67

Dichlofluanid

1085-98-9

fungicide

organohalogen

122

103

17.51

Thiabendazole

148-79-8

fungicide

organonitrogen

88

14

17.70

Captan

133-06-2

fungicide

organochlorine

88

91

17.76

Folpet

133-07-3

fungicide

organochlorine

108

63

18.23

Imazalil

35554-44-0

fungicide

organonitrogen

115

95

18.39

Endrin

72-20-8

insecticide

organochlorine

104

101

18.62

Myclobutanil

88671-89-0

fungicide

organonitrogen

119

114

19.07

4,4-DDT

50-29-3

insecticide

organochlorine

102

95

19.22

Fenhexamid

126833-17-8

fungicide

organochlorine

118

77

19.40

Propargite 1

2312-35-8

acaricide

organosulfur

110

95

19.43

Propargite 2

2312-35-8

acaricide

organosulfur

121

114

19.75

Bifenthrin

82657-04-3

insecticide

pyrethroid

106

81

20.04

Dicofol

115-32-2

acaricide

organochlorine

98

54

20.05

Iprodione

36734-19-7

fungicide

organonitrogen

118

90

20.21

Fenpropathrin

39515-41-8

insecticide

pyrethroid

113

96

21.32

cis-Permethrin

52645-53-1

insecticide

pyrethroid

106

65

21.47

trans-Permethrin

51877-74-8

insecticide

pyrethroid

109

71

23.74

Deltamethrin

52918-63-5

insecticide

pyrethroid

97

52

*50 mg PSA, 50 mg C18, **50 mg PSA, 50 mg GCB

Strawberry extracts were spiked at 200 ng/mL with pesticides and subjected to dSPE with PSA only. Results were used to generate single-point calibration curves. Spiked extracts were then subjected to additional dSPE sorbents (either C18 or GCB). Results are shown as percent recoveries relative to PSA alone.

Table III: Restek Q-sep dSPE products are formulated with different sorbents in different ratios so that your dSPE choice can be tailored to the composition of your particular sample type (e.g., fatty, highly pigmented, etc.)

Method Sorbent Mass (mg) Product Information

MgSO₄

PSA*

C18-EC

GCB**

 

 

Vial Volume (mL)

 

 

 

 

Cat.#

Removes

Excess water

Sugars, fatty acids, organic acids, anthocyanine pigments

Lipids, nonpolar interferences

Pigments, sterols, nonpolar interferences

Sample Type: General fruits and vegetables
Example: Celery, head lettuce, cucumber, melon

AOAC 2007.01

150

50

-

-

2

26124

Original unbuffered, EN 15662, mini-multiresidue

150

25

-

-

2

26215

AOAC 2007.01

1200

400

-

-

15

26220

Original unbuffered, EN 15662

900

150

-

-

15

26223

Sample Type: Foodstuffs with fats and waxes
Example: Cereals, avocado, nuts, seeds, and dairy

Mini-multiresidue

150

25

25

-

2

26216

-

150

-

50

-

2

26242

AOAC 2007.01

150

50

50

-

2

26125

AOAC 2007.01

1200

400

400

-

15

26221

-

1200

-

400

-

15

26244

-

900

150

150

-

15

26226

Sample Type: Pigmented fruits and vegetables
Example: Strawberries, sweet potatoes, tomatoes
Mini-multiresidue, EN 15662 150 25 - 2.5 2 26217

AOAC 2007.01

150

50

-

50

2

26123

AOAC 2007.01

1200

400

400

400

15

26222

EN 15662

900

150

-

15

15

26224

Sample Type: Highly pigmented fruits and vegetables
Example: Red peppers, spinach, blueberries

Mini-multiresidue, EN 15662

150

25

-

7.5

2

26218

AOAC 2007.01

150

50

50

50

2

26219

EN 15662

900

150

-

45

15

26225

-

900

300

-

150

15

26126

Sample Type: General purpose
Example: Wide range of commodities, including fatty and pigmented fruits and vegetables

-

150

50

50

7.5

2

26243

-

900

300

300

45

15

26245

Note: No entry in the Method column refers to dSPE formulations not specifically included in one of the cited references. These products can be used to accommodate the various needs of specific matrices not directly met by the cited references.

*PSA = primary secondary amine exchange material
**GCB = graphitized carbon black

 

Try QuEChERS risk-free today!

Call Restek or your local Restek representative to request a free sample pack of Q-sep QuEChERS tubes.

 

References

Restek is not able to provide copies of these documents.

  1. M. Anastassiades, S.J. Lehotay, D. Stajnbaher, F.J. Schenck, Fast and easy multiresidue method employing acetonitrile extraction/partitioning and "dispersive solid-phase extraction" for the determination of pesticide residues in produce. J. AOAC Int. 86 (2003) 412-431. http://pubag.nal.usda.gov/pubag/downloadPDF.xhtml?id=555&content=PDF
  2. EN 15662, Foods of Plant Origin—Determination of Pesticide Residues Using GC-MS and/or LC-MS/MS Following Acetonitrile Extraction/Partitioning and Clean-up by Dispersive SPE—QuEChERS method, 2008.
  3. QuEChERS-A Mini-Multiresidue Method for the Analysis of Pesticide Residues in Low-Fat Products, 2004. http://quechers.cvua-stuttgart.de/pdf/reality.pdf
  4. AOAC Official Method 2007.01, Pesticide Residues in Foods by Acetonitrile Extraction and Partitioning with Magnesium Sulfate, 2007.
 
FFSS1183G-UNV

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