Fronting Peaks

Chromatography Forum: GC Archives: Fronting Peaks
Top of pagePrevious messageNext messageBottom of pageLink to this message  By Anonymous on Thursday, January 29, 2004 - 07:54 am:

I am injecting 0.1uL of ethanol (25%) and n-propanol (25%) in water as solvent. The injector is 250degC,head pressure is 12psi and split 100ml/min. The peaks are fronting. I have a 624 type column 30m x 1.8um x 0.32mm.
I would have thought the column would have enough capacity.
Anyone have a feel for this?
If I use 0.53mm and larger film thickness would it help?


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Consumer Products Guy on Thursday, January 29, 2004 - 12:10 pm:

We also assay for ethanol using n-propanol as internal standard. We use a 0.53 mm i.d. column, a split of about 150:1, and our concentrations are about 0.03 g/ml and 0.5 ul injection, where your concentration is about 0.20 g/ml, so you're substantially more concentrated than our samples. I'd say dilute more, or split off more.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Anonymous on Thursday, January 29, 2004 - 12:22 pm:

I'm not familiar with the phase you are using, but from the literature it appears that the 624 phase is 94% polidimethylsiloxane and 6% cyanopropyl. This seems thus like a relative non-polar phase to me. Could it be that you have a mismatch with the polarity of your sample and the stationary phase. This may explain the observed fronting. I would try a more polar phase - a wax type column perhaps? Just make sure the phase is crosslinked otherwise the water may be a problem.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Consumer Products Guy on Thursday, January 29, 2004 - 01:47 pm:

FYI, we use a PEG type phase.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By CCL on Friday, January 30, 2004 - 03:03 am:

We are using that column for residual solvent quantification (among other ethanol) but instead of liquid injection we use Headspace to inject the samples. Under these conditions we can not observe any fronting with the column for ethanol.
I don' t know your column temperature for analysis but the fronting may also arise from the water contained in the sample if the ethanol peak elutes early.
Hope this helps.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Anonymous on Friday, January 30, 2004 - 04:13 am:

The headspace idea seems a good one to me. However, why not dilute the sample with water and see what happens? This might also enable you to avoid injecting such a small volume-can you inject 0.1ul reproducibly? Alternatively a packed porous polymer column might work very well for this separation, if you only have water, ethanol and propanol in your sample. Such columns are almost bomb proof.

David


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