Analysis of acidic pesticide residues in spices with acidified QuEChERS by LC-MS/MS

Klein J., Brand I., Kroschwald J., Büttner S., Witt G.
Analysis of acidic pesticide residues in spices with acidified QuEChERS by LC-MS/MS
Poster im Rahmen des European Pesticide Residue Workshops (EPRW 2022), 19. – 23.09.2022

Acidic pesticide residues can only be insufficiently detected with the established multi method using QuEChERS (extraction step using acetonitrile, e.g. module E7). For this reason, it was necessary to implement a simple method for the determination of acidic pesticide residues which allows a sensitive quantification. Therefore, the existing QuEChERS procedure was modified by changing the extraction step. In this case 1 % formic acid in acetonitrile was used for the reliable determination of the targeted analytes.
This method was developed for 27 acidic pesticide residues in different spices using LC-MS/MS. The  dried herbs (leaf spices) dill and rosemary, and the spices cumin and paprika powder were used for these studies. The d-SPE clean-up materials PSA/C18, EMR-lipid and HLB were compared. The choice of the optimal d-SPE method depends on a variety of conditions and it turned out to be difficult to find a universal clean-up method for different matrices. For the validation of acidified QuEChERS at the levels 0.02 and 0.1 mg/kg, PSA/C18 and EMR-lipid were chosen. These clean-up materials showed the best results for removing interfering ingredients - such as fat-soluble dyes or lipid-rich components - as efficient as possible. In contrast, clean-up with HLB showed poorer precision.
PSA/C18 proved suitable for the recovery range of 70-120 % for dill (100 % of all analytes) and rosemary (67 %). EMR-lipid showed good results (recovery of 70-120 %) for cumin (93 %) and paprika powder (56 %). Especially for paprika powder the active substances of the sulfonylurea group could be poorly detected due to strong matrix influences. Overall, matrix-matched-calibrations are required for the determination.

Referenzen
DIN EN 15662:2018-07 (2018): Foods of plant origin - Multimethod for the determination of pesticide residues using GC- and LC-based analysis following acetonitrile extraction/partitioning and clean-up by dispersive SPE - Modular QuEChERS-method

SANTE/11312/20121 (2022): Guidance document on analytical quality control and method validation procedures for pesticide residues and analysis in food and feed.