retention time shift

[yanyan]

Hello,
I ran some test injections for the FAME standards on our new GC using FID. I noticed there was retention time shift (decreased gradually). Here is an example, the retention time of peak No. x on the first injection was 60.30 min, while it was decreased to 59.97 min for the 6th injection. I ran it as split 1:25. I am running it as split-less now and still seeing the phenomenon. What do you think it might be the cause?

Thanks in advance!

[dblux_]

Hello,
I ran some test injections for the FAME standards on our new GC using FID.

New column as well ?

I noticed there was retention time shift (decreased gradually). Here is an example, the retention time of peak No. x on the first injection was 60.30 min, while it was decreased to 59.97 min for the 6th injection. I ran it as split 1:25. I am running it as split-less now and still seeing the phenomenon. What do you think it might be the cause?

Thanks in advance!

That's 0.5% RT shift. How much would be acceptable for you ?

[rb6banjo]

I wouldn't get too alarmed about that small shift. That doesn't seem like a major shift to me. Do you have other impurities in your sample that will cause you problems if you don't have the same, exact retention time every time?

Those are some long runs. What are your column dimensions?