Baseline increase at the end of running

[nazar_u]

Hai All members,

I have a problem about chromatograph baseline which always increase at the end of running.

I use GC from Varian serial 3800. I usually do hydrocarbon analysis with
carbon number from C5 to C20 or max C25. I operated the GC with condition
as below:

Temperatures;
Injector: 270 Celcius
Detector: 300 Celcius
Column: initial: 40 for 10 minute, and increase to 270 Celcius with ramp 5 Celcius/min and keep 270 Celcius for 19 minute or 44 minute (total time for running 75 minute or 100 minute)

Column pressure: 10 psi

Amount of sample: 0.2 microlitter

Split ratio: 100

Column specification:
Varian capillary column (CP-sil 5 CB), serial CP7690, 50 m x 0.32 mm, ID 5
micrometer

Any suggestions and helps would be appreciated. Thank you very much.

[chromatographer1]

It sounds like you have phase bleed from your 5 micron film column or you have some high molecular weight components of your samples which have coated your column and begin to elute at higher temperatures.

You can carefully condition the column overnight at a temperature 40 degrees below the maximum temperature. Be certain that you do not have any oxygen in your carrier gas or any leak of air in your system or you will damage the phase and it will slow degrade and give excessive bleed at higher temperatures.

I hope your column is not already damaged.

best wishes,

Rod