Trying to resolve acetaldehyde and methanol

Chromatography Forum: GC Archives: Trying to resolve acetaldehyde and methanol
Top of pagePrevious messageNext messageBottom of pageLink to this message  By Dan MacGregor on Sunday, June 1, 2003 - 05:27 pm:

I am using a HP5890 with electronic pressure control, trying to quantify the amount of fusel oils in an alcoholic beverage. The compounds being analyzed are methanol, acetaldehyde, acetone, ethyl formate, ehtyl acetate, n-propanol, n-butanol, a-amyl alcohol, &sec-butanol.

Initial oven temp: 30oC, hold for 3min
Ramp at 5oC/min to 120oC, hold for 5 min
Final temp 150oC

Inlet temp: 150oC

FID temp: 250oC

Split ratio: 1:20
Head pressure: 10.7psi

Column used, SPB-60

Carrier gas: Nitrogen (Cannot use hydrogen because of company policy)

Solvent: 40% ethanol, 60% demineralized water
Injection volumn: 1uL

My problem is that I cannot achieved resolution for methanol and acetaldehyde (these are the 1st 2 peaks that came out) using a single taper split liner (with deactivated glass wool).Methanol and acetaldehyde coelutes and the acetaldehyde portion show severe tailing. All the other peaks are symetrically and well separated. And the results (area and retention time) for all peaks (even for methanol and acetaldehyde) are reproducible.

But when I use the Cyclosplitter, I can achieved complete resolution for all peaks, but the result is not reproducible. On the next run, all the peak area are either reduced or increased to some extent.

I have tried different temperature and pressure programs, split ratios, inlet leak check, column leak check, new syringe, septa, replaced gold seal but nothing worked. If anyone has any suggestions, I would really appreciate it.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Anonymous on Monday, June 2, 2003 - 04:34 am:

Dan,

First of all, if you are not allowed to use hydrogen as carrier gas, helium is usually a better choice than nitrogen. This is because the optimum flow velocity for helium lies considerably above that for nitrogen-you need to use very low flows with nitrogen to get the optimum performance.
Secondly, acetaldehyde and methanol are easily separated on a DB-Wax column or probably any PEG column, although I used headspace analysis (see Analyst 1992 117 721). I am not sure what your column is (SPB-60). Be careful, especially with PEG phases that the phase has not solidified at your initial temperature-it will not work. To test this, increase the initial column temperature; if increasing the column temperature increases the retention time of compounds (!!!) then the phases might well have solidified at the first temperature.

David McCalley


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Anonymous on Monday, June 2, 2003 - 06:31 am:

I have separated all these analytes except ethyl formate (I do not know its RT) using an Equity 1701 30m 0.25mm 0.25m column at 40C isothermal in aqueous 0.1% v/v solution (each analyte) 1L split 1:10.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By vijay on Friday, July 18, 2003 - 05:19 am:

hai,
interesting i just got this acetaldehyde samples.
i will get back to you dan.


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