Comparative Study of Three Sample Preparation Methods for Multi-residue Extraction of Pesticide Residues in Hop Samples

Three sample preparation procedures were compared for a multi-residue analysis of pesticides in hops: (a) modified Hengel’s method based on extraction with acetonitrile in combination with clean-up on a C18 SPE column, (b) miniaturized Biendl’s method based on acetone extraction and PSA SPE sample clean-up, and (c) modified Quick, Easy, Cheap, Effective, Rugged, and Safe (QuEChERS) method which utilizes a specific mixture of three sorbents (PSA, C18, and Z-Sep) for dispersive SPE sample clean-up. The performance of the methods was evaluated and validated for a mixture of 56 pesticides analyzed by the liquid chromatography–high resolution mass spectrometry in compliance with the analytical quality control criteria of the SANTE/11813/2017 guidelines. Strong matrix-dependent signal suppression caused by the co-eluting hop matrix was observed for all sample preparations involved in this method comparison study. The matrix effects in percentages (%ME) were used for the evaluation of the effectiveness of the individual sample clean-up procedures. The recovery experiments were performed by spiking pesticides at the concentration level 0.50 mg/kg into the blank matrix to evaluate the extraction efficiency of the compared methods. Recoveries obtained for the modified Hengel’s method were in the range of 70–120% with RSDs of less than 20% for all studied pesticides. The performances of the methods were tested on the set of 24 samples of hops harvested in the Czech Republic. The method comparison on the determined concentration levels of the pesticide residues clearly showed that the extraction efficiency of the QuEChERS method is significantly less effective for the extraction residues presented in a sample above the level 20 mg/kg. In terms of time consumption, labor, materials, and solvents consumptions, the methods were thoroughly compared, and these demands increase in the following order QuEChERS < modified Hengel’s < miniaturized Biendl’s method.