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Pesticides in Dietary Supplements:

Advantages of QuEChERS vs. PAM 303


By Julie Kowalski, Innovations Chemist, Michelle Misselwitz, Innovations Chemist, Jason Thomas, Innovations Chemist, Jack Cochran, Director of New Business and Technology
  • Simple, cost-effective QuEChERS approach saves time and uses 20x less solvent.
  • GMP-friendly—prepackaged extraction salts and snap-and-shoot standards reduce human error.
  • Cartridge SPE cleanup removes matrix interferences, assuring accurate pesticide determination.
This new QuEChERS-based procedure reduces matrix interferences, as well as sample prep variation among technicians.

Due to safety and efficacy concerns, the FDA now requires the dietary supplement industry to adhere to current Good Manufacturing Practices (cGMPs). To meet these regulations, dietary supplements must be tested for pesticide contaminants, since the products are largely derived from botanical sources. As a result, labs are working to develop and validate methods, an endeavor which is complicated by the wide range of pesticides and matrices to be tested. Many labs begin method development with the FDA's Pesticide Analytical Manual (PAM), which includes procedures for plant materials. While PAM Method 303 is an appropriate starting point, it has several disadvantages, including high solvent consumption, manual procedures that contribute to analytical variation, and the inability to extract polar pesticides. As an alternative, we developed a QuEChERS-based method for analyzing pesticides in dietary supplements that has several advantages, including decreased costs and less variation among technicians (Table I).

Table I  Decrease costs and increase reproducibility with a GMP-friendly QuEChERS approach to analyzing pesticides in dietary supplements.

  PAM 303 Method QuEChERS + cSPE Benefits of QuEChERS + cSPE
Solvent used (mL)1,8509220x less solvent; cleaner, greener, & cost-effective
# of Solvents43
Salt and sorbent used (g)356.65x less salt/sorbent
Glassware/lab equipment
  • Separatory funnel (1L capacity)
  • Filter apparatus
  • Florisil column
  • Centrifuge
  • SPE manifold
Fast, easy batch processing
Manual preparation
  • Salt solution
  • Standards
  • Florisil column
None–prepackaged salts, standards, and cSPE cartridges are ready to use.Highly reproducible; less manual prep means less human error.

To demonstrate the performance of a QuEChERS-based method, we fortified prepared dandelion root with 46 pesticides of varying classes that had been reported in dietary supplements. Samples were extracted using a QuEChERS procedure, and then two possible cleanup methods, dispersive solid phase extraction (dSPE) and cartridge solid phase extraction (cSPE), were compared. We determined that dSPE did not have the sorbent capacity to adequately clean up sample extracts (Figure 1), so cSPE was used for recovery determinations. Samples were analyzed using an Rxi-5Sil MS column and a LECO Pegasus III GC-TOFMS with ChromaTOF software. The method produced very good recoveries for a wide variety of pesticide chemistries, with slightly lower recoveries for some volatile and/or planar compounds. Representative recoveries are shown in Table II; all results and complete analytical details are available in application note PHAN1242A (5.4 mb pdf).

Overall, the chromatography and recovery results seen for a broad range of pesticides in dandelion root powder demonstrate the benefit of the QuEChERS approach for dietary supplement testing. Adopting a QuEChERS method, such as the procedure used here, can be especially advantageous to labs operating under FDA GMPs, as it is highly amenable to batch processing. Analytical benefits include reduced interferences and good recoveries, even of polar pesticides. Other benefits include an overall savings of both materials and prep time compared to the PAM 303 method, and better expected reproducibility due to the straight-forward procedure with fewer manual preparations.

Figure 1  QuEChERS extracts of pesticides in dietary supplements benefit from cSPE cleanup, which minimizes matrix interferences by removing more sugars and fatty acids than dSPE.

dSPE vs. cSPE Sample Cleanup of Dandelion Root Powder (Dietary Supplement) on Rxi-5Sil MS
GC_FF1171
ColumnRxi®-5Sil MS, 30 m, 0.25 mm ID, 0.25 µm (cat.# 13623)
Sampledandelion root powder spiked with 46 pesticides
QuEChERS Internal Standard Mix for GC/MS Analysis (cat.# 33267)
anthracene for quality control (cat.# 33264)
Conc.:80 pg/µL
Injection
Inj. Vol.:1 µL splitless (hold 1.5 min)
Liner:5mm Splitless with wool (cat.# 22975-200.1)
Inj. Temp.:250 °C
Oven
Oven Temp.:90 °C (hold 1.5 min) to 340 °C at 8 °C/min
Carrier GasHe, constant flow
Flow Rate:1.5 mL/min
DetectorMS
Mode:
Analyzer Type:TOF
Source Temp.:225 °C
Electron Energy:70 eV
Ionization Mode:EI
Acquisition Range:45-550 amu
Spectral Acquisition Rate:5 spectra/sec.
InstrumentLECO Pegasus® 4D GCxGC-TOFMS
NotesSample Preparation:
Wetting:1 g of dandelion root powder combined with 9 mL of water, shaken well, fortified with pesticides and QuEChERS Internal Standard Mix for GC/MS Analysis (cat.# 33267), soak for 2 hours.

Extraction: 10 mL acetonitrile added then addition of Q-sep™ Q110 (cat.# 26213), centrifuge with Q-sep™ 3000 Centrifuge (cat.# 26230).

dSPE:cleanup procedure according to EN 15662 method, add control standard anthracene (cat.# 33264) to 1 mL extract, add this to Q-sep™ Q110 dSPE tube (cat.# 26213), shake, centrifuge.

cSPE: add control standard anthracene (cat.# 33264) to 1 mL extract, add magnesium sulfate to cartridge, use 6mL Combo SPE Cartridge containing 500mg CarboPrep® 90/500mg PSA (cat.# 26194), concentrate via evaporation.

Table II  This QuEChERS-based method provides good recoveries for a variety of pesticides found in dietary supplements.

Compound RT (sec) Recovery (%) Class Type
Hexachlorobenzene744.456OrganochlorineImpurity
Pentachloronitrobenzene784.262OrganochlorineFungicide
gamma-BHC791.285OrganochlorineInsecticide
Diazinon816.671OrganophosphorusInsecticide
Chlorothalonil819.2100OrganochlorineFungicide
Pentachlorothioanisole931.266OrganochlorineMetabolite
Chlorpyrifos952.692OrganophosphorusInsecticide
Dacthal958.883OrganochlorineHerbicide
Parathion963.291OrganophosphorusInsecticide
Procymidone1027.4100OrganonitrogenFungicide
Endosulfan1059.890*OrganonitrogenInsecticide
Myclobutanil1100.6100OrganonitrogenFungicide
Oxadixyl1149.4100OrganonitrogenFungicide
Carfentrazone ethyl1188.0110OrganonitrogenHerbicide
Fenhexamid1202.494OrganonitrogenFungicide
4,4'-DDT1203.896OrganochlorineInsecticide
Iprodione1261.0110OrganochlorineFungicide
Cypermethrin1466.898*PyrethroidInsecticide
Pyraclostrobin1538.092OrganonitrogenFungicide
Fluvalinate1541.497*PyrethroidFungicide
Difenoconazole1562.090*TriazoleFungicide
Azoxystrobin1596.093OrganonitrogenFungicide

*Average recovery based on recoveries for individually quantified isomers.