Chromatography Forum

Hello everyone

I have just had a discussion with my colleague about shifting retention times. Fact is: She is running a program for quite a while now, and we see retention time shifts of about 1.5 min from one to the other extreme. There are hints that this is correlated to GC measurements running or not running, GC heating up the room by about 6 °C (No, we don't have a good room temperature control).
We use a column oven (set to 25 °C), therefore I don't believe in the temperature fluctuations as a cause (literature says that "his can obviously be avoided when a column thermostat is used", http://ict.ups-tlse.fr/plateforme/HPLC/ ... de_Q_A.pdf).
Anyway, I don't have a better explanation.
Yes we checked: performance of the column oven, pumping rate, gradient mixer etc. The column is also OK, judging from a reference solution.
Any other idea?
Kind regards,
Jörg

Hello

If your column oven is "heating only", 25°C can be too low if it is a hot summer. maybe 35°C are better - hopefully you will never have more than 35° in your lab and this setting will also dampen temperature effects caused by the GC.
Most column ovens(heating only) I know have a temperature range from ambient +5° to 100°

You can also check, if the vent of the GC is in direction to the HPLC - if yes, I would try to move one of these devices.


best regards
Chris

A general rule for isocratic methods is that retention time will change 2% for every 1 degC. We have a fairly well controlled lab temperature so we always try to set our column temp to 30 degC. It is hard to know if the temperature change is feasible without knowing how long your RT range usually is.

For sure, Retention time will Change when temperature changes. Also pH will Change!

not to mention a few more obscure situations: for example, certain nano-flow systems (nano-Acquity from Waters is one) use heat-flow along the solvent-conducting pipe as a way to measure the flow. They are sensitive to wild fluctuations in room temperature, as we've found to much inconvenience when last our heating/air-con went wrong.