A tea extract was prepared by sonicating two tea bags with a dry weight of 1.75 g each (black tea "Klassik" and rooibos tea "Rooibos Vanille" from Teekanne, Germany) in 100 ml of a water:ethanol solution (50%:50%, v:v) for 25 minutes. Afterwards, the extract was filtered through a Captiva syringe filter (0.2 µm pore size, regenerated cellulose, Agilent Technologies). Blank solutions serving as diluent and negative controls were either a filtered water:ethanol solution (50%:50%, v:v, Blank A), or filtered tea extract that was further diluted 1:10 (Blank B) or 1:100 (Blank C) with Blank A, respectively. The three mixtures from Neochema were pooled together and diluted with Blank A to reach a final concentration of 1000 µ/L for each analyte. The eight submixtures of the comprehensive pesticide mix kit were kept initially separate and diluted with Blank A to final analyte concentrations of 10, 100, and 1000 µ/L, respectively. In addition, all eight pesticide submixtures were pooled together and diluted either with Blank A, B, or C to final concentrations of 1, 2.5, 5, 10, 25, 50, 100, and 1000 µg/L, respectively.