This application note describes the use of a quick, easy, cheap, effective, rugged, and safe (QuEChERS) AOAC sample preparation approach for the extraction and cleanup of 13 pesticide residues representing various pesticide classes in spinach. The method involves initial extraction in a buffered aqueous/acetonitrile system, an extraction/partitioning step after the addition of salt, and a cleanup step using dispersive solid-phase extraction (dispersive SPE). A modified method with the addition of toluene was employed to address the significant loss of planar pesticides caused by graphitized carbon black (GCB) in dispersive SPE. The presence of the target pesticides in the spinach extracts were then determined by liquid chromatography coupled to an electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) operating in positive ion multiple reaction monitoring (MRM) mode. The method was validated in terms of recovery and reproducibility for all of the analytes of interest, with a 5 ng/g limit of quantitation (LOQ) for pesticides in spinach. The mean recoveries ranged between 64% and 108% (average of 91.9%), with RSD.
The document details an analytical procedure for extracting and cleaning up 13 pesticide residues from spinach. It utilizes the Agilent Bond Elut QuEChERS AOAC Extraction kit combined with dispersive SPE kits specifically designed for pigmented fruits and vegetables.
To address the loss of planar pesticides often caused by graphitized carbon black (GCB) in standard cleanup, a modified method involving the addition of toluene was employed. The presence of target pesticides was determined using an Agilent 1200 Series HPLC coupled with an Agilent 6410 triple quadrupole LC/MS/MS system.
The procedure recommends placing a 15 g (±0.1g) amount of homogenized spinach into a centrifuge tube.
After adding reagents, the sample tubes must be hand-shaken vigorously for exactly 1 minute.
The method achieves a limit of quantitation as low as 5 ng/g for the target pesticides in spinach.