Determination of pesticides and mycotoxins in feed: Applicability of an analytical method in routine analysis

Abstract

In routine analysis it is often necessary to introduce minor changes in protocols or extend the applicability of previously validated methods to similar matrices. The SANTE guidelines contemplate on-going validation as a quality control process to verify analytical performance through a reduced number of experiments1.In this work, a validated QuEChERS method for the determination of pesticides and mycotoxins in corn and alfalfa was used for the analysis of a large number of different types of feed samples (cereals, pastures, silages). Briefly, 2 g of sample were hydrated with 10 ml H2O (2% CH2O2), followed by extraction and partition with 10 ml acetonitrile, MgSO4/NaCl (4:1). An aliquot of the extract was then cleaned-up using d-SPE with MgSO4, C18 and PSA, prior to analysis by UHPLC-MS/MS2.A modification of the clean-up step had to be introduced due to the large number of samples to be processed and availability of sorbent salts at the time of analysis. Thus, for cereal-based samples only MgSO4/C18 was used while MgSO4/PSA was used for pasture-based samples.Following the concepts of the on-going validation, the mean recovery (Rec%) was evaluated at the same concentration level from validation (100 µg/kg). Precision was evaluated as repeatability and intermediate precision, repeating the test 2 and 3 consecutive days for corn and alfalfa, respectively. The recovery results obtained after the modifications were compared with those from the initial validation through statistical t-tests. Finally, an additional quality control test was done by applying the methodology to a European Union Proficiency Test (EUPT CF18-2014) in wheat flour.As a result, 80% of the studied compounds (117 pesticides and 2 mycotoxins) showed recoveries in the 60-140% range accepted for routine analysis by the SANTE guide, with RSDs <20% in both matrices.From the statistical tests, the Rec% of more than 85% of the studied compounds were not affected by the changes introduced. Moreover, for compounds such as acephate, chlorpyriphos methyl, clethodim, fenthion and metribuzin in corn, and methomyl, metribuzin, thiabendazole, profenofos, spinosad D and terbuphos in alfalfa their Rec% improved with respect to the initial validation. Finally, the results from the EUPT test were compared to the declared concentration through a z-score, verifying the aptitude of the method for the determination of azoxystrobin, epoxiconazole, linuron,pyraclostrobin and carbendazim.