aamc scored #8

[wheatthinners]

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[theonlytycrane]

For "gc trace" they just mean results / graph from the gc. Basically you inject a small liquid sample into a machine and it vaporizes the molecules so the first reading will be the more volatile molecule. For volatility just consider intermolecular forces and molecular weight.

The technique you mentioned is high performance liquid chromatography (hplc) where the normal method is "reverse" in that the polar phase moves and the non-polar phase is stationary. This is opposite from a TLC where the non-polar phase moves and the polar phase is stationary.

 

[aldol16]

What exactly is a "gc trace", and why does the lowest molecular weight go out first? I thought I read on Princeton or something that liquid or gas chromatography was reverse phase which means polar stuff is in the mobile phase so butanol would go out the fastest.

GC is not reverse phase. There is reverse-phase HPLC and you could probably get a reverse phase column for GC but it's not typically run that way (because reverse-phase columns are expensive).

For "gc trace" they just mean results / graph from the gc. Basically you inject a small liquid sample into a machine and it vaporizes the molecules so the first reading will be the more volatile molecule. For volatility just consider intermolecular forces and molecular weight.

The first reading will not necessarily be the more volatile. Otherwise, you're just doing a distillation. What happens after you vaporize it is the molecule is injected into a column. If you open the oven compartment of the GC (not while it's running!) you'll see the column is a coil of "wire" like material that is filled with crushed metal or other material that hinders molecules. That separates the molecules just like any column would and the first reading you'll get is the one that migrates quickest through the column.

The technique you mentioned is high performance liquid chromatography (hplc) where the normal method is "reverse" in that the polar phase moves and the non-polar phase is stationary. This is opposite from a TLC where the non-polar phase moves and the polar phase is stationary.

Just FYI, to make sure nobody gets confused, there's also reverse-phase HPLC where the mobile phase is nonpolar.