Ethoprophos

LC-grade methanol and acetonitrile were purchased from TEDIA. The analytical standards (ethoprophos, coumaphos, profenofos, diazinon, ethion, parathion, phosalone, quinalphos, dicrotophos, purity >95%) were purchased from Sigma Aldrich. Azinphos methyl, tribuphos (purity >95%) were from Dr. Ehrenstorfer Gmbh. Other details are given in Table 1. The analytical-reagent grade anhydrous magnesium sulfate (MgSO4), sodiumchloride (NaCl) was from Kermel. The powder of C18 and primary secondary amine (PSA, 50 μm) were purchased from Agela Technologies. The guarantee dreagent-grade formic acid was purchased from ROE. Ultrapure water was obtained from a Milli Q purification system (Millipore, Molsheim). Individual pesticide stock standard solutions (1000 mg L -1 ) were prepared in methanol and stored at -18°C. A multistandard mixture containing 10 mg L -1 of each pesticide was prepared in methanol and stored at 4°C for less than 3 months. Mixed multi-standard working solutions were prepared fresh to avoid degradation of pesticides. The concentrations of the multi-standard working solutions were 10, 25, 50, 100 and 250 μg kg -1 .