Glass wool liner versus other liners

[Charles A. Burger]

To be clear, unless otherwise directed, I prefer glass wool packed liners. It's about trusting that I have vaporized everything in my injection as thoroughly as possible.

Throughout my career I have experimented with other liners and just haven't liked the results I achieved. One of the consistent pieces of data of those experiments is that I could not achieve the same area counts as the injections made using the glass wool liners. Sometimes the drop off using other liners has been up to 50%.

Currently, my analysis is for impurities of a specific Triglyceride. I have a multiple compounds to account for with molecular weights ranging from low to high. Also as it turns out the main compound degrades under the right conditions and switching from a glass wool focus liner to the Cyclosplitter with a double goose-neck has drastically reduced that degradation. However, the area response of the main peak has been cut just about in half.

I am currently screening this new method to optimize the conditions for the best possible sensitivity. But it begs the question, will I be able to find conditions that allow me to vaporize my sample as thoroughly as glass wool and thus regain the close to the same area counts I was getting with glass wool?

I would be grateful for any thoughts or links.

Thanks

Chuck

[CE Instruments]

To even pass much comment you ought to mention split , splitless, PTV, On column, GC supplier, injector conditions , column type etc. For GCs with poor injection design (active sites) degradation can be an issue. Fast transfer through the injector (split) ? Solvent ? You may already be using the best compromise for your sample and set up

[Charles A. Burger]

Fair enough.

Column Rtx-65TG 15m x 0.25mm 0.10µm
Agilent 6890
Plunger speed 20 µl/s
Pre inject delay 3000 ms
Post inject delay 3000 ms
Injector 320°C
Split 25:1
Detector 370°C
FID
Helium carrier
Column 150°C for 1 min
Ramp 1 30°C/min
Column 2 300°C for 0 min
Ramp 2 5°C /min
Column 3 370 for 5 min

Toluene is the solvent.

[CE Instruments]

My guess would be that your losses are due to too little residence time/not enough heat in the liner to completely vapourise the sample. This means more of your sample is going out of the split vent. I would first of all remove the 3 second hold of the syrnge post injection. No point having a nice reactive metal pipe there to encourage degradation. PTV would be the more favoured injector for this sample type but as you only have split I would also look at increasing the injector temperature to increase the energy available to evaporate the sample.
Assume you already use a gold seal at the bottom of the injector ?

[chromatographer1]

The tip of the needle can have great ramifications of the vaporizing of the sample. Hollow point versus taped point, for example.

If the spray from the needle is focused to one side sharply a reduced vaporization can occur. Also if the liquid sample is shot forward into the center of the inlet the liquid may not touch any hot surface before it is sent into the splitter vent. You can see how that would reduce the amount of sample on column.

Such issues are why I always preferred a direct injection to a split injection. I would rather dilute my sample by 5 and inject 5% of the volume I had injected as a split injection to get a 100 : 1 reduction in the amount of sample on the column. This allows more time for the heavy boilers to volatile and refocus on the column, as well as a lower temperature for the injector which is condusive to less degradation of the sample components.

But these things are why it is called research. Do whatever works best for you.

A bonded phase diatomaceous earth packed column might be a choice to experiment with. This technology was not available when the first capillary columns entered the market. Of course, a packed column may not have the resolution needed for your application.

best wishes,

Rod

[Charles A. Burger]

As it turns out, there is a cool on column injector that can be installed. It seems that I have buy in with my supervisor on its use not only for this project, but as a development tool for future projects.

How popular is this technique?

[chromatographer1]

It is useful when discrimination must be avoided at all costs, or the analytes are very sensitive to temperature decomposition.

It is one of those things, which if you need it, price is no problem, but otherwise, people will avoid a costly piece of hardware if they can get by without it.

It is an excellent tool to have at your disposal.

It is like a parachute. When you need it, you need it badly, and price is no object.

best wishes,

Rod