β endosulfan

Nineteen certified individual pesticide standards (purity, 96.8–99.55), including α-benzenehexachloride, β-benzenehexachloride, γ-benzenehexachloride, δ-benzenehexachloride, heptachlor, aldrin, heptachlorepoxide, trans-chlordane, cis-chlordane, p,p dichlorodiphenyldichloroethylene, dieldrin, endrin, β-endosulfan, p,p dichlorodiphenyldichloroethane, endrin aldehyde, endosulfan sulphate, p,p dichlorodiphenyltrichloroethane, endrin ketone and methoxychlor were obtained from Sigma Aldrich (Bangalore, India) and were stored at −4 °C. Individual stock standard solutions (1 mg/L) of OCPs were prepared by dissolving an accurate weight of each pesticide in acetonitrile. Analytical grade methanol, hexane, acetone and acetonitrile were supplied by Merck (Mumbai, India). Water was deionized (Riviera, SCHOTT DURAN, Mainz, Germany) and filtered using 0.45-µm Nylon 6,6 membranes (Rankem, New Delhi, India) filtration assembly (Perfit, India). Working standard solutions were prepared daily by serial dilution of the individual stock solution with acetonitrile. An intermediate stock standard mixture was prepared by mixing the appropriate volumes of individual stock solutions and diluted with highly purified water to a required concentration.