*2.2. Chemicals*

Analytical-grade (98–99.9% purity) standards of pesticides were supplied by Sigma-Aldrich (Steinheim, Germany) and are listed in Appendix A (Table A1). Pesticide-grade solvents, Supel™ QuE Citrate Extraction Tubes and Supel™ QuE PSA/C18 (EN) Cleanup Tubes were used to extract and purify samples and were purchased from Sigma-Aldrich (Steinheim, Germany). High purity water was prepared using a Milli-Q water purification system (Millipore, Milford, MA, USA). Single standard solutions were prepared in methanol at a concentration of 1000 mg/L. The working standard solutions were prepared by mixing the appropriate amounts of single standard solutions and diluting with methanol to a final concentration of 10 and 1 mg/L. All solutions were stored in the dark in 10 mL amber bottles at −20 ◦C.
