Chromatography Forum

Hi,

I'm trying to optimize a custom-designed GC that I'm building myself, and I've run into a strange issue.

With a 3 ft packed 1/8" (ca. 2mm ID) column packed with untreated bentonite (80-100 mesh) i get baseline separation between n-propane and n-butane (the standard i use since the column is at room temp.)

with a 4 ft "micro-packed" 1/16" (ca. 1mm id) packed column with same stationary phase I get no separation at all.



I know it's a difficult thing to comment on, given nothing is from a commercial GC system, but what could I have missed?

There's quite a bit of dead space in my detector, could the decreased sample throughput of the smaller column mean the components have time to diffuse together again after the column, before the detector?


both columns were run at 30 PSI head pressure at which the 1/8" column have a flow of 25 ml/min

The detector is a 4-element TCD built into compression fitting Tee's.

Thanks in advance!
-Chris

Both columns are activated?

Activated how? They'll be untreated bentonite, so very polar and not deactivated.

I've made no attempt at conditioning them.

My plan is to develop different liquid phases to coat them with later, but I wanted a non-treated standard to compare to. I just noticed the difference, and activation or not, it's the same batch of stationary phase used in both columns.

Thanks!