Clofentezine

L-menthol (natural source, food grade, ≥ 99% purity), BHT (food grade, ≥ 99% purity), formic acid, elevated purity grade solvents (acetonitrile, ethanol), as well as analytical standards of azoxystrobin, boscalid, buprofezin, chlorpyrifos, chlorpyrifos-methyl, clofentezine, dodine, fludioxonil, hexythiazox, methoxyfenozide, myclobutanil, penconazole, propiconazole, pyraclostrobin, pyriproxyfen, pyridaben, spirotetramat, tebuconazole and tebufenpyrad were purchased from Sigma Aldrich-Merck S.r.l. (Milan, Italy). A Milli-Q Plus apparatus (Millipore, Bedford, MA, USA.) was used for obtaining ultrapure water.
Weighted amounts of the analytical standards (OhausDV215CD Discovery semi-micro and analytical balance, 81/210 g capacity, 0.01/0.1 mg readability, Ohaus Corporation, Pine Brook, NJ, USA) were dissolved in methanol or toluene (clofentezine and pyraclostrobin) in volumetric flasks, in order to obtain individual stock solutions at a concentration of 1 mg mL⁻¹.The last ones were diluted in methanol for preparing the multi-standard working solutions at 0.02, 0.5, 1.5, 2.5 and 4 ng μL⁻¹ used for the method validation.

Clofentezine, fenpyroximate and pyridaben with a certified purity >98% were purchased from Sigma-Aldrich Inc. (St. Louis, MO, USA). Stock standard solutions of Clofentezine, fenpyroximate and pyridaben were prepared in Methanol (5.0 mL), with concentration of 1000 mg L⁻¹ and was stored in a freezer at −20 °C. The working standard solutions were prepared daily by diluting the stock solutions with water to the required concentrations. The ultra-pure water was purchased from Shahid Ghazi Pharmaceutical Co. (Tabriz, Iran). Methanol, acetonitrile, phosphate salt (analytical grade), ethylene glycol, n-butanol, glycerol, n-heptanol, n-nonanol and NaCl were obtained from Merck (Darmstadt, Germany). MTOAC with purity higher than 97% were purchased by Aladdin Biochemical Co., Ltd (Shanghai, China).