Problems with retention times on my BP column

General discussion of factors that affect chromatographic resolution, peak shape, and noise in the raw data.
Post Reply
User avatar
Mad Hatter
Posts: 4
Joined: Tue Dec 08, 2015 9:07 pm

Problems with retention times on my BP column

Post by Mad Hatter » Tue Dec 08, 2015 9:34 pm

I understand the issues with retention time instability on PLOT columns but my retention times on the BP column seem to vary a lot. This causes a lot of identification problems because some of the separations are not baseline separations. Does anyone else see this or know what might be causing it?

User avatar
White Rabbit
Posts: 3
Joined: Tue Dec 08, 2015 8:35 pm

Re: Problems with retention times on my BP column

Post by White Rabbit » Tue Dec 08, 2015 9:41 pm

Dear Hatter,
Nice hair! It depends on just how bad they are changing and to some degree how old your system is. We generally look at the relative standard deviation (RSD) for each peak across the entire day and see only 0.02-0.03 on the BP column. Problems like leaks in the dean's switch or at the thermal desorber could cause this but often if it is an older system is is more likely a problem with the oven temperature control. There is not much you can compare it to since the PLOT column is generally affected by moisture in the sample or carrier gas and is generally far less stable. GC temperature control is generally a function of either a bad oven thermocouple or a bad vent door or fan. Check to see that the vent flapper door is not binding or not opening the same each time. The muffin fan on the vent can also get week and cause oven temperatures to vary.

Post Reply