Problems with press-fit

[GT]

Dear All,
I'm analyzing with FID some VOC in solid samples dissolved in propanol wtih splitless mode.
I've installed a pre column (about 1 m for 0.53 ID of empty silica tube connected with universal glass press-fit) in front of 30 m 0.53 ID 1um HP-Innowax for inject dirty samples.
If I compare the areas of standard solutions injected with or without the pre column I can observe a difference of about 20% (with the precolumn I've 20% less than without); is it normal? Where is the problem?
Thanks

[Rafael Chust]

First guess would be a leak...

Sometimes if your column cut is not clean enough, you might have problems fitting it and leakage from there.

[Okkie]

be aware that glass pressfits can have active places which can be responsible for loss of alcohols.
press-fits should be deactivated.
This can be done with DMDCS, procedures can be found in internet

[Peter Apps]

You say that your pre-column is "empty silica tube", if this means that it is not deactivated then you are very probably losing analytes by adsorption to the pre-column. The pre-column has a much larger surface area than the press-fit.

If the pre-column has a non-polar deactivation the propanol solvent will not wet it and you will get peak distortions that might cuase a loss of integrated area.

You need to use a pre-colum with a polar deactivation.

Good luck Peter