I'm searching for a GC-method to determinate the assay of ethanole in beer (especially non-alcoholic-beer. The Determination should be possible without Headspace-GC. A special problem to me is the aqueus matrix.
By Anonymous on Wednesday, February 7, 2001 - 09:31 am:
I've investigated my home brew before. At ~5% EtOH, a fairly large dilution in THF is possible. A low starting oven temp.(~40-50C) separates EtOH from THF without a problem. I believe you can easily get to 0.05% with a splitless injection. The sample solution can still be at least 85% THF so that the aqueous matrix should not be a problem. Good Luck!
By Anonymous on Wednesday, February 7, 2001 - 02:18 pm:
Why not just do a manual headspace injection with a gas-tight syringe at room temperature? You don't need an automated headspace autosampler to do headspace, although it is easier that way. With ambient headspace there is no trouble with the water matrix.
By David McCalley on Thursday, February 8, 2001 - 03:11 am:
You can do the analysis on a packed porous polymer column like Chromosorb 101 or Porapak Q. You need to make an injection directly onto the column. This is possible even with many capillary GC systems (like the Agilent) where you buy a column with a side arm which replaces the liner of the split/splitless injector. You can inject ethanol standards in water on to such a column for evermore without any damage, since the column has no liquid stationary phase. The only problem you will have is that involatile material from the beer will build up on the column and eventually destroy your analysis. This is not the end because the columns are so robust you can simply repack the first few cm. This procedure might be clumsy if you were trying to analyse hundreds of samples per day-but I guess you are not, otherwise you would have invested in a headspace system.
By craig on Thursday, February 8, 2001 - 08:42 am:
We analyze for ethanol in H2O by injecting the H2O directly onto a 0.53 mm DB-WAX column connected to an FID. We get down to 5 ppm in the splitless mode. Make calibrations standards in H2O from neat EtOH and only shoot 1 uL onto a 4mm liner. As mentioned above, start at about 40 deg. C and then ramp to the max temp of the column. It's not the best system, but for something we only do every once in a while it works great.
You're going to have to change your liner frequently, and definately use glass wool. As the previous poster mentioned, if you want high throughput go with headspace.
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