Chromatography Forum

Hello All,

we are using a modified cyclodextrin GC column from MN (Hydrodex beta-TBDA) for chiral analysis of an organic acid.

The sample prep is a liquid/liquid extraction to free the acid from its salt using 1M H2SO4 and MTBE. The organic layer is injected.

Here's the problem: The column is damaged after a few dozen injections when we use the extraction sample prep as opposed to the free acid in MTBE. Trimming off a few meters will temporarily restore the separation.

Obviously, we are injecting something that we shouldn't. The column is not compatible with water and the MTBE could contain up to 15 g/L of water and at an injection volume of 1 µL and a split of 40 that's 0.4 ng water on column per injection. Is that enough water to damage a 0.25mm x 1µm df. GC column? Will the presence of H2SO4 worsen the issue.

We are taking measures to either dry the MTBE before injection and/or achieve a better phase separation using the salting out method.

Still, I would be grateful for any input on this issue. many thanks in advance!

You'd have to try this, but occasionally when I was working, we used anhydrous sodium sulfate granules to pull the water out of organic phases.

We simply put some anhydrous sodium sulfate granules in a 20ml vial, added some of the organic phase, capped it and shook it well, then injected some of the organic phase.

Thank you for the input, Consumer Products Guy,

the question, however, is not how to dry the phase, but if realistically, such a little amount of water can do damage to the GC column.

Using Na2SO4 (or CaCl2) is certainly one good way to dry the solvent.

Upodate: We have had good success with chemically drying the MTBE phase with 2 eq. of dimethoxypropane relative to water in water-saturated MTBE prior to injection - this has solved the column issues.