Dilute-and-shoot versus clean-up approaches: A comprehensive evaluation for the determination of mycotoxins in nuts by UHPLC-MS/MS.

Mycotoxins are toxic metabolites naturally occurring in foodstuffs stored in warm, humid conditions. Ochratoxin A, aflatoxins B1, B2, G1, and G2 are known for their adverse health effects. Thus, EU permitted levels are set as low as 2 mu g kg 1 for nuts. This study examined solid-liquid extraction (SLE) to isolate mycotoxins from walnuts, followed by UHPLC-MS/MS analysis. However, the strong matrix effect obtained is the main limitation of analyzing mycotoxins in fatty matrices, like nuts. To overcome this problem, 6 clean-ups intended for fatty matrices (PRiME HLB, EMR-Lipid, AFFINIMIP cartridges, Z-sep+, C18, and PSA) were tested in terms of matrix effect, cleanliness of the extract, and co-extractives removal. Nevertheless, none of these clean-ups effectively reduced the strong matrix effects encountered by the SLE. So, the addition of more steps would not be profitable in terms of time, cost, and residues generation. As an alternative, the streamlined, cheap, simple, and fast diluteand-shoot approach was tested. This work shows that by applying 1:100 dilution of SLE extract, obtained matrix effect was soft or negligible. Finally, a 1:100 dilute-and-shoot method was proposed and validated according to EU regulations. LOQs fulfilled EU requirements and satisfactory values were obtained for recovery and precision.

Automated summary

This study examined the extraction of mycotoxins from walnuts using solid-liquid extraction (SLE) and explored various clean-up methods. The main limitation in analyzing mycotoxins in fatty matrices was the strong matrix effect encountered. However, dilution and injection proved to be effective in reducing the matrix effect, and a viable dilute-and-shoot method was proposed.