Chromatography Forum

Hi all,

After browsing for some temperature program for GC for our analysis I always noticed that the program is always set to have the initial temperature to be hold for 1 or 2 minutes for example:

initial temperature 70°C, hold 1 minute
Program temperature increase at 10°C/min to final temperature 250°C
hold 250°C for 15 minutes.

I can understand the reason for the hold time for the final temperature.
I know it may sound trivial but I was wondering whats the purpose for the 1 minute hold time for the initial temperature?

Tarapan

This can allow solvent elute from the column with little movement of the anlaytes - other than their beign focused by evaporating solvent.

And, it can take a significant time for everything in the inlet to make it to the column. Assume that your injected sample expands to 2 mL. If your flow rate is 2 mL/minute and you are making a splitless injection, it could take a full minute for the bulk of your samle to pass from the inlet to the column. And, that ignores the fact that there is carrier gas in the inlet at the time of injection and that there will be some diffusion of sample into the carrier following the sample through the inlet.

So your hold time at injection can be to get everything on the column before starting the ramp and/or to obtain solvent focusing.

An isothermal hold is more important in a splitless injection that in a split injection. In a split injection the analytes are swept from the inlet very rapidly, while in a splitless injection the analytes have a significant residence time in the inlet. You want the injection to be complete before you start the temperature ramp.