Ammonium formate hco2nh4

Acetonitrile (ACN), ethyl acetate (EtOAc), methanol (MeOH), chloroform (CHCl₃) and hexane (HPLC gradient grade, 99.9%) were purchased from Fisher Scientific (Madrid, Spain). Deionized water (<18 MΩ cm⁻¹ resistivity) was obtained from a Milli-Q water purification system (Millipore Corp., Bedford, MA, USA). Ammonium formate (HCO₂NH₄, 97%) was supplied by Sigma-Aldrich (St. Louis, MO, USA). Chromatographic solvents and water were degassed for 20 min using a Branson 5200 ultrasonic bath (Branson Ultrasonic Corp., Danbury, CT, USA).

The standards of pesticides were purchased from Dr. Ehrenstorfer GmbH (Augsburg, Germany). For acetamiprid, chlorantraniliprole, and iprovalicarb, the mix DRE-Q60 004725 of 10 µg/mL each was used, while for the other three pesticides, custom individual 10 µg/mL standard solutions in acetonitrile were used, also from Dr. Ehrenstorfer. Dilutions were conducted in acetonitrile to the desired concentrations, and then a final dilution was made by transferring 0.25 mL of the standard solution, adding 10 µL of the internal standard (TPP 5 µg/mL), and then 0.74 mL of ultrapure water. The Quick QuEChERS-Medium Cartridge was purchased from United Chemical Technologies (Bristol, PA, USA); the extraction salts including magnesium sulphate (MgSO₄), sodium chloride (NaCl), acetonitrile, 2-propanol, acetone were from Merck KGaA (Darmstadt, Germany); formic acid (HCOOH; purity ≥ 95%) was from Fisher Chemical; and ammonium formate (HCO₂NH₄) from Sigma Aldrich (St. Louis, MO, USA). Methanol was supplied by HiPerSolv, VWR Chemicals (Radnor, PA, USA). A Kinetex biphenyl chromatography column (2.6 μm, 4.6 × 150 mm) was purchased from Phenomenex (Torrance, CA, USA) and ultrapure water was obtained by a Milli-Q water purification system from Millipore (Bedford, MA, USA).