Analytical methods were optimized for the quantification of insecticides belonging to neonicotinoid, butenolide, and bisamide classes and their metabolites from various plant matrices including nectar, pollen, leaf, and flower samples. Method optimization efforts were primarily focused to obtain sensitive and reproducible analytical results from highly pigmented matrices and lower sample volumes using modified QuEChERS method. The initial optimization efforts were focused on removal of pigments from various sample matrices without compromising the recovery of the planar pesticide, cyantraniliprole. Inclusion of graphitized carbon black (GCB) in the dSPE matrix, that is widely used to remove pigments from the leaf extracts, resulted in &gt;50% loss of cyantraniliprole. The recoveries of other insecticides were less affected by the inclusion of GCB. Multiple alternatives of dSPE sorbents that included additional components to trap pigments without compromising the recovery of planar pesticides were examined. The first sorbent included MgSO4, C18, Chlorofiltr, and primary/secondary amines (PSA) mixed in a ratio of [3:1:1:1]. The second sorbent consisted of MgSO4, Envi-Carb, Z-Sep+, and primary/secondary amines (PSA) mixed in a ratio of [15:1:5:6]. Experimentation showed that although the Chlorofiltr based sorbent provided recoveries of all analytes &gt;85% (&lt;7% CV), it removed &lt;50% of chlorophyll. The Envi-Carb based sorbent removed &gt;80% pigment, and provided recoveries &gt;85% (&lt;5% CV) for all pesticides. The recovery of cyantraniliprole was modeled as an inverse function of the pigment content of sample matrix, where less pigmented matrices resulted in lower recovery of cyantraniliprole. Hence, caution should be exercised in adopting dSPE matrices that specifically target pigment removal for the sample cleanup of non-pigmented sample matrices. The final optimized method for leaf tissue had a method limit of quantitation of 0.16 ppb (&lt;5% RSD) for cyantraniliprole in 500 mg sample.

Method optimization for the trace analysis of planar pesticides in pigmented plant matrices

2019 Fall National Meeting

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