October 17, 2021, 08:33:32 PM
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Topic: gas chromatography: eluition order  (Read 299 times)

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Offline xshadow

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gas chromatography: eluition order
« on: October 05, 2021, 04:55:50 AM »
I'm studying gas-chromatography but I don't undertand one crucial point.

When I'm in liquid chromatography if I use  a polar compound (-SiOH) as stationary phase the most polar solute will eluite first.
When I use some apolar phase, the less polar solte will eluite first.


I wonder if this difference will occour also in GC...or is the eluition order always defined by the relative vapor pressure (volatility) of the different solutes

i.e: the most volatile solute will always elute first

THANKS :)

Offline Babcock_Hall

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Re: gas chromatography: eluition order
« Reply #1 on: October 05, 2021, 09:40:33 AM »
In the case of alkanes, elution order and volatility are closely related for at least some stationary phases.  I don't have other examples handy at the moment.

Offline xshadow

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Re: gas chromatography: eluition order
« Reply #2 on: October 09, 2021, 06:50:30 AM »
In the case of alkanes, elution order and volatility are closely related for at least some stationary phases.  I don't have other examples handy at the moment.

thanks

Offline Babcock_Hall

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Re: gas chromatography: eluition order
« Reply #3 on: October 09, 2021, 01:31:39 PM »
https://thetruthaboutforensicscience.com/the-top-2-problems-seen-with-gas-chromatography-bac-results/

I did happen to see two chromatograms of ethanol and other simple alcohols (and possibly acetone) recently.  The context was the GC separation and quantitation of ethanol for blood alcohol determination.  The elution order was not identical between two stationary phases.  At the link above, I did not see some information that would be of interests to chemists.

Offline xshadow

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Re: gas chromatography: eluition order
« Reply #4 on: October 10, 2021, 03:44:11 PM »
https://thetruthaboutforensicscience.com/the-top-2-problems-seen-with-gas-chromatography-bac-results/

I did happen to see two chromatograms of ethanol and other simple alcohols (and possibly acetone) recently.  The context was the GC separation and quantitation of ethanol for blood alcohol determination.  The elution order was not identical between two stationary phases.  At the link above, I did not see some information that would be of interests to chemists.
I've read the text...interesting :)


I have a last doubt about a phrase that I've read when it speaks about injection system :

"" A splitless vent opened too earlly causes loss in response of heavier analytes ""

I wonder why....perhaps because the heavier analytes have a lower vapor pressure so if I open the purge valve too early I lost many of those ...

Can make it sense ???
Thanks

BUt i'm not sure because I thought  I was getting a flash vaporization of ALL the samples...p

Offline Babcock_Hall

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Re: gas chromatography: eluition order
« Reply #5 on: October 11, 2021, 08:18:16 AM »
I afraid that such a question exceeds my knowledge of gas chromatography.  However, some of the issues raised in the link I gave are worthy of consideration.  Sample carryover as a source of ghost peaks is a genuine issue.

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