Clothianidin

Certified neonicotinoid standards, acetamiprid, clothianidin, dinotefuran, imidacloprid, nitenpyram, thiamethoxam, and thiacloprid, were purchased from FUJIFILM Wako Pure Chemical Corporation. (Osaka, Japan). A standard solution containing ISs of seven neonicotinoids (acetamiprid-d₃, clothianidin-d₃, dinotefuran-d₃, imidacloprid-d₄, nitenpyram-d₃, thiamethoxam-d₃, and thiacloprid-d₄), at a concentration of 10 µg/mL in acetonitrile were purchased from Hayashi Pure Chemical Ind. (Osaka, Japan). The chemical structures of the seven neonicotinoid pesticides and their stable isotope-labeled surrogates are shown in Fig. 1. acetonitrile, methanol, and ultrapure water purchased from Wako were of the pesticide-analysis grade and were used for the extraction and cleanup processes during the analysis.

Oxazosulfyl (>98.0%) and radiolabeled oxazosulfyl (benzoxazolyl-2-¹⁴C, specific activity of 4.83 MBq/mg; purity 98.5%) were synthesized by the Health & Crop Sciences Research Laboratory of Sumitomo Chemical Co., Ltd. Imidacloprid (>98.0%), chlorantraniliprole (>98.0%), clothianidin (>98.0%), and fipronil (>98.0%) were purchased from FUJIFILM Wako Pure Chemical Corp., Japan.
For foliar spray and soil-drench bioassays, test insecticides were diluted in an organic solvent mixture (Acetone : Tween 20=95 : 5 v/v) to prepare a stock solution that was further diluted in deionized water. The test insecticides were diluted in acetone as the solvent carrier for the topical bioassay. At least five concentrations of the test solution (0.003–500 mg a.i./L) or acetone solution (0.0016–63 mg a.i./L) for all insecticides were prepared for each insecticidal bioassay. A surfactant (Shindain 0.05% v/v, Sumitomo Chemical Co., Ltd.) was added to the test solution for all foliar- and leaf-dipping bioassays. A surfactant with a water solution containing no insecticide was used as a blank for the foliar spray bioassays.