Planar Pesticide Quantitation from Green Food Matrices Using QuEChERS Cleanup With a Novel Graphitized Carbon Black and Zirconia-based Adsorbent

Klaus Buckendahl, Merck/Sigma-Aldrich Chemie GmbH, Taufkirchen, Germany
Patrick Myers, Milliporesigma/supelco, Bellefonte, Pa, U.s.a.
Bill Betz, Milliporesigma/supelco, Bellefonte, Pa, U.s.a.
Bill Ozanich, Milliporesigma/supelco, Bellefonte, Pa, U.s.a.
Jennifer Claus, Milliporesigma/supelco, Bellefonte, Pa, U.s.a.
Michael Ye, Milliporesigma/supelco, Bellefonte, Pa, U.s.a.

Pesticides with planar structures, such as hexachlorobenzene and chlorothalonil, are commonly used during the cultivation of spinach and other leafy, green crops. The extraction and analysis of these residues is often complicated by the presence of chlorophyll in green food matrices. In both GC/MS and LC/MS/MS analyses. Large pigment molecules, such as chlorophyll accumulate in the inlet and degrade column performance in GC/MS.  Chlorophyll is also known to contaminate the LC/MS/MS source.  Method EN15662 recommends the use of Graphitized Carbon Black (GCB) in sample cleanup methods for the removal of chlorophyll and other pigment interferences. While traditional GCB efficiently removes pigment molecules, it also retains planar pesticides as a result of π-π interactions between the graphitic carbon and the planar structures of the pesticides. A near linear inverse relationship between pigment removal and recovery of planar pesticides is shown in previous work. Recommendations to alleviate this problem include the addition of toluene to the extraction solvent to minimize binding to the GCB as well as the use of smaller amounts of GCB to balance recovery of planar pesticides with color removal. Data shows that neither of these solutions is completely satisfactory. Supel QuE Verde, a unique QuEChERS cleanup mix that contains a zirconia-containing adsorbent, Z-Sep+, in combination with proprietary GCB, provides recoveries ranging from 70% to 120% of challenging planar pesticides while maintaining >95% chlorophyll removal in green matrices. The use of Supel QuE Verde to remove chlorophyll while maintaining high recovery of planar and non-planar pesticide residues in spinach and other green matrices will be discussed herein. Color removal will be demonstrated using a UV-Vis spectrophotometer.  Planar and non-planar pesticide recovery will be determined using a GC/MS/MS Triple Quad.  The effects of quantity and surface areas of GCB on color removal and pesticide recovery will also be examined.