Title: Determination of Organophosphate Pesticides in Surface water using Gas

This section method (SM) documents the selected organophosphate pesticides analysis in surface water by all authorized section personnel. 2. Principle: The surface water sample is extracted with methylene chloride. The extract is passed through sodium sulfate to remove residual water. The anhydrous extract is evaporated to almost dryness on a rotary evaporator and diluted to a final volume of I.O mL with acetone. The extract is then analyzed by a gas chromatograph equipped with flame photometric detector (FPD) and any positive result is confirmed by mass selective detector (MSD). The low level diazinon and chlorpyrifos ( RL = 10 ppt) are analyzed only by mass selective detector using the same extract