Acetonitrile (polar) is NOT a preferred solvent, if you are using non-polar capillary column (for example DB-5 or DB-1701) on GC-ECD.  You may want to transfer the analytes (organochlorine pesticides) to non-polar solvent such as hexane. You can do this in two ways.  (1) hexane-water patitioning method or (2) evaporate the acetonitrile extract (close to dryness- do not dry too much- you may lose your analytes) by using gentle stream of ultra high purity nitrogen gas and add desired volume (1ml or 2 mL) hexane.  Inject 1uL of this hexane extract.

I would recommend two choices to try out.

1) do the solvent exchange from acetonitrile to acetone or toluene.

2) if you want to do acetonitrile, you can try to use spit injection with split ratio of 1:1 or 1:3. Jack Cochran from Restek has a paper that you would not loose sensitivity much. However, acetonitrile may give the response to the ECD so if you need to use ECD, I would do the solvent exchange.

ACN is not a good solvent for ECD. For GC/ECD analysis of OC pesticides you should use non-polar column and less polar solvent  for final extract as well.  The easiest way is to evaporate ACN almost to dryness and dissolve the residue in hexane.

Acetonitrile can be used if you for instance you a Zebron ZB-5 column (5 % phenyl-95 % dimethylpolysiloxane). Please see the attached paper as it directly describes extraction and analyses of chlorinated pesticides (insecticides and fungicides) using QuEChERS and GC-ECD.

Use solvent exchange method. Evaporate the final extract to dryness using rota vapor at 40 degrees or Nitrogen air blower to dryness and add 1-2 ml n-hexane to exchange, then take to vial for injection.