Validation and application of a liquid chromatography-tandem mass spectrometry based method for the assessment of the co-occurrence of mycotoxins in maize silages from dairy farms in NW Spain.

The first objective of this study was the validation of an efficient multi-analyte method for the simultaneous detection and quantification of mycotoxins in maize silage, by reverse-phase liquid chromatography coupled with electrospray ionisation triple quadrupole mass spectrometry (LC-HESI-MS/MS). A simple liquid/solid extraction was performed either with clean-up on Mycospin 400 columns or without any clean-up. Almost all the target mycotoxins showed highly-suppressed signals in the presence of a matrix, emphasising the need to quantitate mycotoxins by means of matrix-matched calibrations. An alternative validation method based on ISO 11843 and on a single factor balanced design was implemented. The achieved average recoveries from spiked samples at three levels ranged from 60% to 122% with relative standard deviations (rsd) below 11%. Limits of Detection (LODs) and Limits of Quantification (LOQs) were between 0.02-17.1 µg kg-1 and 0.06-57 µg kg-1. The calculated repeatability and within-lab reproducibility ranged from 5.2 to 23.2% and from 7.2 to 23.9%, respectively. Finally, the decision limit and detection capacity, CCα and CCβ, were calculated for all mycotoxins having regulated/recommended contents in feed. The validated method was applied to 148 samples collected over two years in 19 dairy farms from Galicia (NW Spain). Of the analysed samples, 62% contained at least one mycotoxin. Zearalenone (ZEA), deoxynivalenol (DON), fumonisins B1 and B2, roquefortine C, α-zearalenol, β-zearalenol, enniatins B and B1, andrastin A, marcfortine A, verruculogen and mycophenolic acid were quantified, the highest average detection frequency being for enniatin B (51%). DON, mycophenolic acid and ZEA plus metabolites (α-zearalenol, β-zearalenol) were the most abundant mycotoxins.