Chromatography Forum

I'm using a HP5890 with a combi-PAL headspace add-on. Empower is the operating system.

I have terrible blanks (DMF) at present... I've change all the 'obvious' (to a green user) things, such as inlet liner etc. I've trimmed the top off the column, increased the purge time or the syringe and it's temperature to minimise backflash. Baked the column out for long periods. All of which has improved the blank but it's still horrible.

Someone suggested adding a syringe wash, but we were unable to work out how to set this up on Empower. So three questions...
1. How do you set up a syringe wash on Empower?
2. Is a syringe wash common practice for GC-Headspace? (Seems to me putting your needle in a liquid is just going to add to the blank problem.)
3. Is washing a 150 degree syringe in say acetone a fire hazard?

Cheers for any help you can give, Pat.

Hi Pat

I am assuming that you have DMF in your headspace vials, and that when you inject headspace you get a chromatogram with a lot of interfering peaks - a "terrible blank".

If these interfering peaks stay the same from run to run they almost certainly come from the DMF. If they reduce from run to run they are very likely contaminants from previous analyses on the instrument.

Try doing a series of injections from an empty vial - if the peaks are still there they are historical contaminants (my gues is that they will vanish).

Try a different batch of DMF.

In GC-headspace you do not "wash" the syringe with solvent - you purge it with clean gas. This might be what was meant by somebody. Trying to wash a hot syringe with acetone would be interesting to watch from a distance, and you are completely right it would only add to the contamination.

I do not have Empower so I can't help with the actual commands.

Good luck

Peter

Forgot to say what I was doing, apologies that was a schoolboy error...
I am trying to quantify the levels of DMSO and nPrOH in an API. DMF is the only solvent I have found that can dissolve the API at a high enough level.

Glad I got one thing right regarding the syringe wash, it is purging with gas for the full length of the analysis time so I can't do more than that. I will try the empty vial experiment and see what happens. (May also try a different system)

Thanks for your help, Pat.

Doing DMSO by headspace is not an easy task.

You might try dimethylacetamide if you wish to try a different solvent but that may elute too closely to DMSO to be of any use.

Depending upon the time and temperature of heating the API and now much water may be present in the API or in the DMF you can form artifacts.

Good luck,

Rod