trace water in inj. on cyclodextrin (MN Hydrodex) GC columns

[Arne]

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!

[Consumer Products Guy]

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.

[Arne]

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.

[Arne]

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.