There is no single way for determination of residues for all pesticides. I can only talk about herbicides. For herbicides, depending on the chemical, you can go through the herbicide handbook published annually by the Weed Science Society of America (WSSA). You can also get ideas in the "Residue Review". Or, you can get a hold of the manufacturer. It is very important to have the right column and the materials to detect the herbicide residues by GC.

@ Hossein ghadiri thanks alot , i need help in organophosphorus and organochlorine pesticide residue in food of plant origin

QuEChERS method, you can ask to Steven Lehotay ([email protected]) and he can give you information

For Organochlorine and Organophosphate you can try this method for extraction of residue.

Representative sample of (5-20 g ) is dipped in 100 ml of acetone and kept over night. The extracted samples is re-extracted with 50 ml of acetone and filtered. Finally, a washing is given to the beaker with acetone to remove traces of residues of parents’ compound and its metabolites.

The extract is transferred to a separatory funnel of 1litre capacity and diluted with 500 ml of 2 per cent aqueous solution of sodium chloride. To this 75 ml of dichloromethane is added and shaken gently for one minute. The contents are allowed to stand till a clear separation of two phases is obtained. The lower layer of dichloromethane is drained into a 500 ml beaker through one and half-inch layer of anhydrous sodium sulphate supported on a pre-washed glass wool in a funnel. The aqueous layer is re-extracted with75 ml of dichloromethane and twice with75 ml of hexane each time and the upper organic phase is passed through the same anhydrous sodium sulphate and combined with the contents already obtained. The sodium sulphate is washed with an additional 25 ml of dichloromethane. If the sample has some colour, then 0.5 g of activated charcoal is added in the beaker and shake it for 1 hr. on orbital shaker.Concentrated the cleaned up extract under vacuum at30 C to about 2 to 5 mL and stored in a 15 mL stoppered centrifuge tube for further estimation on gas chromatography.

QuEChERS is the most widely used multi-residue method for analysis of different kinds of pesticide residues in foods. The information is easily available on the internet and the procedure is very effective. Barring a few pesticides and high fat foods, the method works well for most of the pesticides.

Quechers

if u want Standard method means can u go through the AOAC (Method 970.02) methods the have described lot of methods for food analysis (pesticide : ocp opp Herbicides )

in water matrix you can follow APHA and USEPA Methods

few USEPA methods are

EPA 508 (OCP-GC-ECD)

EPA 525.2 (PESTCIDE - GCMS)

EPA 8141A ( PESTICISES OPP/HERBICIDES) IN GC-NPD/PID