Chromatography Forum

Hello All,

Signed up to hopefully get some new insight. I have heard that it is possible to, using GC-TCD, collect the separated compounds.

After developing a method that allows for good separation, large volumes of sample, and short retention times, one can simply set up a tube at the exit port that runs into a vial on dry ice. When your peak of interest comes up you put the tube in the vial and collect your product. Repeating this process over and over again can result in a fairly large amount being collected.

Problem is I cant get anything to collect. I have even overloaded the instrument with toluene and still nothing. I tried lowering the make up gas to allow for slower flow but it just doesn't seem to work.

Has anyone here ever heard of this technique? Thanks in advance for any advice.

Like fraction collector https://www.gerstelus.com/products/pfc/ ?

We had GCMS, so need for us to try to to collect fraction by GC.

I did occasionally collect some fractions manually using HPLC, and that did prove useful.

I think I remember someone trying Prepscale GC when I was in college, but not sure how well it worked.

To capture even Toluene, you are going to need a lot of surface area in the collection tube. Have you tried adding glass beads to the collection tube for more surface area. You may also try using liquid nitrogen to make the tube colder.

If using a simple vial you need to do something like add a pipette to the tube for the outgoing gas flow, insert it down to the bottom of the collection vial that is filled with glass beads which is immersed in either liquid nitrogen or a mixture of dry ice and isopropanol which will make better heat transfer from the glass surfaces.

There is GC-based (7890) machine AC Reformulizer.
It has several cold column-like traps which can be heated in subsequent time.
I.e. DHA fractions (PIANO) captured in the traps then released for detailed analysis.

Btw GC x GC with cryogenic modulator is considered most effective.

ISO EN (do not remember the number) on analysis of oxygenates in petrol using GC heartcut implemented with two columns interconnected with Dean's switch.
Appropriate pressure applied at specified time completely stops 1st column flow and separates cut components on 2nd column.

I think I remember someone trying Prepscale GC when I was in college, but not sure how well it worked.

To capture even Toluene, you are going to need a lot of surface area in the collection tube. Have you tried adding glass beads to the collection tube for more surface area. You may also try using liquid nitrogen to make the tube colder.

If using a simple vial you need to do something like add a pipette to the tube for the outgoing gas flow, insert it down to the bottom of the collection vial that is filled with glass beads which is immersed in either liquid nitrogen or a mixture of dry ice and isopropanol which will make better heat transfer from the glass surfaces.

The glass beads are a great idea. I am running to a coil coming off the exit vent that is submerged in dry ice/acetone then into a collection vial that is also cooled.

That is a good setup. But if you want to maximize recovery you have to make the path as tortuous as possible. With a laminar flow, only the edges of the gas stream will be in contact with the cool surface and the warm inner part of the flow will carry the targets away.