Analysis of Pesticide Residues in Spinach Using Agilent Bond Elut QuEChERS AOAC Kits by GC/MS

Significance of the topic

The presence of pesticide residues in leafy vegetables poses a significant challenge for food safety and public health. Spinach, with its high chlorophyll content and complex matrix, requires a robust extraction and cleanup approach to quantify low-level residues against stringent maximum residue limits.

Objectives and study overview

This study evaluates the Agilent Bond Elut QuEChERS AOAC sample preparation method coupled with gas chromatography mass spectrometry in selective ion monitoring for analysis of 18 diverse pesticide classes in spinach. A comparison is made between the standard dispersive solid phase extraction cleanup and a modified protocol incorporating toluene to enhance recovery of planar pesticides.

Methodology and instrumentation

Sample preparation follows a buffered acetonitrile extraction with salting out using anhydrous magnesium sulfate and sodium acetate. After centrifugation, the acetonitrile layer is split for two cleanup paths

• Original dispersive SPE containing primary secondary amine graphite carbon black and magnesium sulfate
• Modified dispersive SPE with toluene addition to reduce planar pesticide losses on graphitized carbon black

Extracts are evaporated under nitrogen and reconstituted in acidified acetonitrile prior to analysis.

Used instrumentation

• Agilent 7890A Gas Chromatograph with splitless inlet
• Agilent 5975C Mass Spectrometer operating in SIM mode
• Agilent Bond Elut QuEChERS AOAC extraction and dispersive SPE kits for pigmented produce
• Standard laboratory centrifuges and bottle top dispensers

Main results and discussion

The method achieved limits of quantification of 10 ng per gram for most analytes and 50 ng per gram for folpet. Calibration curves in matrix exhibited correlation coefficients above 0.99 across 10 to 400 ng per gram. Four planar pesticides suffered low recovery with the original cleanup but improved from below 50 percent to above 75 percent when toluene was included. The remaining 14 compounds delivered average recoveries near 88 percent and precision better than 6 percent relative standard deviation across low mid and high spikes.

Benefits and practical applications

The combined QuEChERS AOAC approach offers a streamlined cost effective workflow for multiresidue pesticide screening in pigmented matrices. The addition of toluene addresses recoveries of problematic planar analytes while maintaining overall cleanup efficiency. This strategy supports regulatory compliance monitoring and quality control in agricultural and food testing laboratories.

Future trends and opportunities

Possible developments include integration with tandem mass spectrometry for enhanced selectivity expanded compound panels and automated sample handling. Adaptation of the toluene modified cleanup to other challenging matrices such as berries and spices may broaden the method applicability.

Conclusion

The Agilent Bond Elut QuEChERS AOAC extraction and cleanup kits combined with GC/MS SIM analysis provide a rapid reliable route to quantify multiple pesticide classes in spinach. Incorporating toluene into dispersive SPE successfully restores recovery of planar pesticides without compromising the removal of pigments and coextractives.

References

• Anastassiades M Lehotay SJ Fast and Easy Multiresidue Method Employment Acetonitrile Extraction Partitioning and Dispersive Solid Phase Extraction for the Determination of Pesticide Residues in Produce J AOAC Int 2003 86 412 431
• Lehotay SJ Use of Buffering and Other Means to Improve Results of Problematic Pesticides in a Fast and Easy Method for Residue Analysis of Fruits and Vegetables J AOAC Int 2005 88 615 629
• Lehotay SJ Determination of Pesticide Residues in Foods by Acetonitrile Extraction and Partitioning with Magnesium Sulfate Collaborative Study J AOAC Int 2007 90 485 520
• Zhao L Stevens J Optimizing Recoveries of Planar Pesticides in Spinach Using Toluene and Agilent Bond Elut AOAC QuEChERS Kits with Graphitized Carbon Agilent Technologies publication 5990-4247EN
• Zhao L Stevens J Analysis of Pesticide Residues in Spinach Using Agilent Bond Elut QuEChERS AOAC Kit by LC MS MS Detection Agilent Technologies publication 5990-4248EN
• Database on Pesticide Properties http www herts ac uk aeru footprint en index htm
• Japanese Pesticide Residue Information http www m5 ws001 squarestart ne jp foundation search html
• USDA Pesticide Data Program Summary http www ams usda gov AMSv1 0 getfile dDocName PDP1995Summary
• Wylie PL Meng CK A Method for the Trace Analysis of 175 Pesticides Using the Agilent Triple Quadrupole GC MS MS Agilent Technologies publication 5990-3578EN