Chromatography Forum

Hi all!

Recently I attended a training session about GC maintenance and the trainer said something that drawed my attention: Polar solvents are not suitable for non polar columns such as a DB-5. OK, that makes sense. Here comes my doubt: Is ethanol considered a polar solvent? It is clearly a polar compound but I would like to know if, using it as a solvent for my preparations, its presence in a DB-5 column could affect to the results, taking into account that I work with a CG-FID.

I also have a fronting peaks issue. I know the solution is reducing the sample volume or increase the split, or dilute the samples. We use 1 uL at a 1:167 split. I think that is quite a high split, isn't it? I don't think I am able to change any of these nowadays (accredited method sets those values). Is it really important to have "ideal" simmetry"?


Thank you!

That split ratio seems very high, but if you cannot deviate from method restrictions than it'll have to do. If sensitivity is an issue you could consider injecting a larger volume. Tailing on the solvent front is only an issue if your compounds of interest elute on top of the solvent tail. If so, you could try different pressures or oven ramps, if allowable. As far as tailing or fronting target peaks, they can be tolerable if their consistent and not so fat and wide as to make integration difficult, especially in complex chromatograms. With a split ratio that high I'm surprised to hear of tailing. I would ask questions about inlet cleanliness, maintenance performed, column installation depth (critical), and health of the column. Verify heated zones for correct temperatures. Restek has an online chromatogram builder you could use to see how your targets should look theoretically under ideal conditions. It's a good place to start.