## 2 Materials and Methods
### LC-MS/MS Analysis of Mycotoxins  
The study comprises analysis of 14 mycotoxins, including 3-acetyldeoxynivalenol (3-AcDON), 15-acetyldeoxynivalenol (15-AcDON), aflatoxin B1 (AFLB1), aflatoxin B2 (AFLB2), aflatoxin G1 (AFLG1), aflatoxin G2 (AFLG2), deoxynivalenol, fumanisin B1 (FB1), fumanisin B2 (FB2), ochratoxin A (OTA), nivalenol (NIV), T-2 toxin (T-2), HT-2 toxin (HT-2), and zearaleno (ZEA). The mycotoxins were extracted from barley grain samples according to the method described in an earlier publication by the authors [33] based on the method developed by [PERSON] et al. [34]. The method included sample extraction with water (30 min) and acetonitrile (2 h), centrifugation of the sample, and 20-fold dilution of the extract, before instrumental analysis, with LC-phase solution [33]. Instrumental analysis was performed using an LC-MS/MS system consisting of an Eksigent Expert UltraLC 100-XL chromatograph (Eksigent Technologies, Dublin, CA, USA, equipped with a Kinetex C18 100A, 100 mm \(\times\) 2.1 mm, 2.6 \(\upmu\)m core-shell column (Phenomenex, Torrance, CA, USA) kept at 40 \({}^{\circ}\)C, coupled with QTRAP 6500 tandem mass spectrometry (AB Sciex Instruments, Foster City, CA, USA). Data acquisition was conducted using Analyst Software version 1.6.2 (AB Sciex) in multiple reaction monitoring (MRM) mode for 16.0 min and data processing using MultiQuant Software version 3.0.2 (AB Sciex). The LC-MS/MS method used was optimized as described in Reference [33]. The chromatographic parameters were unchanged. Two mobile phases, solvent A, consisting of 0.1% formic acid and 5 mM ammonium formate in water, and solvent B, consisting of 0.1% formic acid and 5 mM ammonium formate in methanol, were used. The gradient elution, at a flow rate of 0.5 mL min\({}^{-1}\), was started at 2% B and held for 1.0 min, then increased to 98% B in 9 min and held for 3.0 min; then, within 0.1 min, the mobile phase composition returned to the initial state, and the column re-equilibration phase was held for 2.9 min. The mass spectrometer, as in previous studies, was used in positive and negative electrospray ionization mode and operated at a capillary voltage of 4500 V or \(-\)4500 V, a desolvation temperature of 500 \({}^{\circ}\)C, an entrance potential (EP) of 10 V or \(-\)10 V, with nitrogen as the curtain gas (CUR), nebulizer (GS1), and auxiliary gas (GS2), at pressures of 30, 60, and 50 psi, respectively, and with nitrogen as the collision gas. For each mycotoxin,the parent ion and two daughter ions were selected with optimized parameters for ion transitions, including collision energy, declustering, and cell exit potential, as well as the determined retention time (RT). All the parameters were presented in the Supplementary Materials of the authors' above-mentioned paper [33]. LC-MS/MS chromatograms of representative barley samples contaminated by mycotoxins are shown in Figure S6 in the Supplementary Materials. For the study, a stock mixture of certified solvent standards (Romer Labs Diagnostic, Tulin, Austria) in acetonitrile was prepared with the following concentrations of individual mycotoxins: AFLB2 and AFLG2 (0.025 \(\upmu\)g mL\({}^{-1}\)); AFLB1 and AFLG1 (0.1 \(\upmu\)g mL\({}^{-1}\)); OTA (0.5 \(\upmu\)g mL\({}^{-1}\)); FB1, FB2, T-2, and HT-2 (5.0 \(\upmu\)g mL\({}^{-1}\)); and ZEA, DON, 3-AcDON, 15-AcDON, and NIV (20 \(\upmu\)g mL\({}^{-1}\)). The stock mixture was diluted by 50-5000-fold with acetonitrile to get working solutions. In addition, the isotopically labelled standard solution of 13C17-aflatoxin B1 (13C17-AB1) in acetonitrile at a concentration of 0.01 \(\upmu\)g mL\({}^{-1}\) was prepared, and its 50-fold dilution was used as an internal standard (ILS). The stock standard mixture and working solutions were kept at -20 \({}^{\circ}\)C.  
Calibration mixtures were prepared from the working mixtures by pipetting 100 \(\upmu\)L of a given concentration of the working standard mixture, 50 \(\upmu\)L of internal standard (ILS), and 850 \(\upmu\)L of LC mobile phase (95% A and 5% B) into the chromatographic vials.