Chromatography Forum

Hello,

we have a Shimadzu GC equipped with a BID (barrier discharge ionization detector). We make manual injections with the following parameters:

Column: ShinCarbon 2m
Split injection with a split ratio of 4
Injector: 150 C
Flow control with a flow of 7mL/min (pressure 276.4kPa, linear velocity 30.3cm/s)

Oven temperature is constant 100C and detector is at 280C. The whole program takes 6 minutes and the injection medium is H2 in Ar.

The injection is made every 10 minutes and after let's say 5 injections the baseline starts to fluctuate. If I heat the oven to 200C then will come a big peak and things will go back to normal for some time.

I assume that not all of the gases are eluted through the column as long as there is no higher temperature. Would it help if I increase the column flow?

How can I solve this issue?

Thanks a lot in advance!

If baking it out removes the interference you may want to set up a run program where after the last peak of interest elutes isothermal you ramp the temperature up for a couple minutes (or long enough to clear the column of interferences). It will add a few minutes to the run in total but you shouldn't have to stop every 5 samples to do the clean step so in the long run it may increase the number of samples you can run per day.

Thanks a lot! That's what I thought would be a solution. I will give it a try and hopefully it will work.