Chromatography Forum

My lab has several very old methods that still use glass, packed columns and over time some of these columns can get some pretty large gaps in the packing/support. I am not sure if this is just inevitable with packed columns or that some of our technicians are removing the column while the GC is still pressurized. Does anyone know what extent does this become a concern? Particularly, I would like some insight into how these gaps can affect peak shape. I suspect the gaps can result in peak broadening but even more specifically I would like to know if these gaps can lead to peak fronting. I am thinking this could very well be possible due to eddy diffusion and different flow paths of a poorly packed column.

Some of these gaps are at the inlet side of the column and are very large which I assume can cause an array of issues. Does anyone have experience with re-mixing of analytes due to large gaps in packed columns?

Thanks!

Hi Rhodium

An interesting query

In general packed columns are surprisingly forgiving.

Yes, the gaps can result in peak broadening for the reasons that you state

more specifically I would like to know if these gaps can lead to peak fronting.

Peak fronting is more likely to be caused by overloading of sample rather than the gaps.

see http://community.asdlib.org/imageandvid ... hic-peaks/

How big are the gaps?
Have you tried gently tapping the column whilst you have a flow/pressure going through it to help compact the packing and remove gaps? - don't use a spanner

Regards

Ralph

these sort of gaps may also occur if the operators load a capillary method while the packed column is installed - the lower pressures settings allow the packing to expand in the same manner as doing inlet maintenance without letting the pressure relax.

Thanks for the responses. I am wondering why we are seeing signs of solute overload by injecting only 0.5 ul on a 6 ft packed column. I would expect the paced column to be able to handle >8000-10000 ng of sample easily. Which leads to my next question. If the solute and stationary phase of the column are very similar in polarity or composition, does that decrease the capacity of the stationary phase? Seems like an obvious yes but I'd like to hear other experiences.

Thanks for the responses. I am wondering why we are seeing signs of solute overload by injecting only 0.5 ul on a 6 ft packed GC column. I would expect the packed column to be able to handle >8000-10000 ng of sample easily. Which leads to my next question. If the solute and stationary phase of the column are very similar in polarity or composition, does that decrease the capacity of the stationary phase? Seems like an obvious yes but I'd like to hear other experiences.

Hi Rhodium

I am wondering why we are seeing signs of solute overload by injecting only 0.5 ul on a 6 ft packed GC column. I would expect the packed column to be able to handle >8000-10000 ng of sample easily. Which leads to my next question. If the solute and stationary phase of the column are very similar in polarity or composition, does that decrease the capacity of the stationary phase?

Rather than going into theoretical discussions about loading, capacity, capacity factor etc Some more information about your column, your sample and an example chromatogram would be more helpful

Kind regards

Ralph