JA0049 PESTICIDES AND ADULTERANTS IN FOOD PRODUCTS: CHALLENGES AND SOLUTIONS FOR SAMPLE PREPARATION FOR GAS CHROMATOGRAPHY/MASS SPECTROMETRY
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Routine and comprehensive testing of food products is essential to ensure that toxic pesticides or other adulterants are below tolerance levels. This dissertation involves development and validation of simple, rapid, cost-effective, and reliable methods for extraction of adulterants from foods prior to gas chromatography-mass spectrometry (GC-MS) analysis. Sample cleanup is necessary because food contains fatty acids, sugars, proteins, and other endogenous compounds that would otherwise interfere with analysis. Disposable pipette extraction (DPX) involves pulling an aqueous sample into a pipette tip packed with sorbent material and separation of the target compounds from the interferences. Dynamic mixing of DPX sorbent with solutions provides rapid equilibration, partitioning and enhanced contact between analytes and solid phase sorbent. Food adulterants targeted include multiresidue pesticides, fungicides, and two specific contaminants, melamine and cyanuric acid. A reversed phase sorbent (DPX-RP) and mixed-polarity sorbent (DPX-Q) similar to a commercially available product were used for the extraction of organochlorine and organophosphate pesticides, and fungicides, in fruits and vegetables. The hydrophobic nature of the DPX-RP sorbent provides efficient extraction of these slightly polar and non-polar compounds. Although extracts after DPX-Q cleanup contain some interferences, high recoveries were achieved for most pesticides, including very polar pesticides. Suitability for routine analysis was validated by a collaborative study at South Carolina Department of Agriculture with GC/MS and GC/electron capture detection. iv The extraction of organochlorine and organophosphate pesticides in food samples containing 10 to 50% of fat, using weak anion exchange sorbent (DPX- WAX), is also described. The high capacity nature of this sorbent provides easy and quick removal of fatty acids interferences from high fat content samples prior to pesticide analysis. Recent cases of melamine adulteration affected the health of over 50,000 children and caused six deaths in children in China as a result of kidney failure. As with any food adulterants, adequate public and regulatory actions are dependent on the quality of analyses. Cation (DPX-CX) and DPX-WAX cleanup followed by GC-MS is shown to provide the required sensitivity, specificity, and accuracy to meet safety thresholds set by the U.S. Food and Drug Administration for melamine and its analog, cyanuric acid.
Organochlorine, organophosphate pesticides and fungicides in
fruits and vegetables wererapidly analyzed using disposable pipette extraction (DPX)
followed by gaschromatography/mass spectrometry-selected ion monitoring
(GC/MS-SIM). The DPXmethods involved in this study was DPX-RP (reversed phase). DPX’s
rapid intrinsicmixing capability results in fast extractions with analytes being
concentrated, andeliminated the need for solvent evaporation. Extraction of
pesticides from fruits andvegetable using this technique achieved a sample preparation
throughput on the order of afew minutes per sample. Matrix-matched calibrations were
performed, and limits ofdetection (LODs) were determined to be lower than 0.1 ppm.
Coefficients ofdetermination (r2)
were greater than 0.995 for most studied pesticides. The developedmethod exhibited an overall recovery of 72-116% for non-polar and
slightly polarpesticides, with relative standard deviations of the recoveries
below 10%, which indicatesa good accuracy and precision of the proposed method