GC/MS P&T - High CO2 - Low compound recovery

[ALS]

HI,
I'm running a GC/MS P&T method using a 6890N, 5975B and a velocity XPT. When I run fresh water samples with a volume of 5ml i get a large CO2 peak and a low target analyte recovery. When I run QC, purged H2O, samples or soil samples, extracted in MeOH, I get a smaller hit for CO2 and analyte recovery is fine.
Because I am not getting large CO2 hits for all samples, I don't think it is a problem with the trap.

Can anyone help me?

cheers

[JI2002]

There is CO2 desolved in almost all water samples, it's no surprise to see a big CO2 peak in the front. On the other hand, there is little CO2 in the purged water, CO2 peak is much smaller in your QC samples. CO2 has nothing to do with your problem. If QC is ok and you only have problem with matrix spike, it could be matrix interference or the way how you prepare the sample spike solution. Can't comment further without detail information.