Explanation help Gas-Liquid Chromatography question

[matty.k]

gas liquid chromatography is used to analyse a mixture of methanol (CH3OH), ethanol (C2H5OH) and propanol (C3H7OH)

Q.place the three components in expected order from longest retention time (Rf) value to shortest

agian this is a revision question, how would i go about this question without the rention time? i know that the least soluble compound is swept out first by the gas and is detector by the detector but how do i determine which compound gets swept out first without teh rention time, its not given.

[physics]

it goes according to molar mass so then one with the smallest molar mass comes out first and it increases..i think .. kinda sure

[stonecold]

the larger the molecule gets, the less polar it will be, and the less affinity it will have for the stationary phase.

so the answer would be (longest to shortest):
methanol, ethanol and propanol

i think haha.  my teacher taught us this stuff today, but i think she screwed up on it a little bit...

[happyhappyland]

The compound with the smallest molar mass gets "swept" away fastest by the gases and doesnt adsorb into the stationary phase very much relative to the others with higher molar mass. So in this case it would be CH3OH -> C2H5OH - >C3H7OH. Since all these compounds are from the same functional group, the polarity and its structure in relation to adsorption and desorption in and out of the stationary/mobile phase is expected to be similiar since same functional groups means similiar chemical properties.

[matty.k]

The compound with the smallest molar mass gets "swept" away fastest by the gases and doesnt adsorb into the stationary phase very much relative to the others with higher molar mass. So in this case it would be CH3OH -> C2H5OH - >C3H7OH. Since all these compounds are from the same functional group, the polarity and its structure in relation to adsorption and desorption in and out of the stationary/mobile phase is expected to be similiar since same functional groups means similiar chemical properties.

thank you

[fady_22]

The compound with the smallest molar mass gets "swept" away fastest by the gases and doesnt adsorb into the stationary phase very much relative to the others with higher molar mass. So in this case it would be CH3OH -> C2H5OH - >C3H7OH. Since all these compounds are from the same functional group, the polarity and its structure in relation to adsorption and desorption in and out of the stationary/mobile phase is expected to be similiar since same functional groups means similiar chemical properties.

Wouldn't it depend on the liquid used (i.e. polar or non-polar)? Or all liquids used as the stationary phase in GLC non-polar?
Because these compounds would decrease in solubility in a polar solvent with increasing size, and increase in solubility in non-polar solvents (with increasing size). Right?

[stonecold]

yeah, thats what i thought fady, because as the sample is polar, you would use a polar stationary phase, which is why i gave the answer above.

now i'm confused though lol!

[happyhappyland]

The compound with the smallest molar mass gets "swept" away fastest by the gases and doesnt adsorb into the stationary phase very much relative to the others with higher molar mass. So in this case it would be CH3OH -> C2H5OH - >C3H7OH. Since all these compounds are from the same functional group, the polarity and its structure in relation to adsorption and desorption in and out of the stationary/mobile phase is expected to be similiar since same functional groups means similiar chemical properties.

Wouldn't it depend on the liquid used (i.e. polar or non-polar)? Or all liquids used as the stationary phase in GLC non-polar?
Because these compounds would decrease in solubility in a polar solvent with increasing size, and increase in solubility in non-polar solvents (with increasing size). Right?

The liquid used according to Heinemann book, is a "inert solid coated with high boiling point liquid hydrocarbon or ester called liquid stationary phase". I would think if the compound had a higher mass it would adsorb into this stationary phase more than the Nitrogen gas mobile phase. I think the gases used in the mobile phase are all non polar btw.. not sure on that though; nitrogen, helium and argon are the only gases ive heard being used by GLC.

[fady_22]

The compound with the smallest molar mass gets "swept" away fastest by the gases and doesnt adsorb into the stationary phase very much relative to the others with higher molar mass. So in this case it would be CH3OH -> C2H5OH - >C3H7OH. Since all these compounds are from the same functional group, the polarity and its structure in relation to adsorption and desorption in and out of the stationary/mobile phase is expected to be similiar since same functional groups means similiar chemical properties.

Wouldn't it depend on the liquid used (i.e. polar or non-polar)? Or all liquids used as the stationary phase in GLC non-polar?
Because these compounds would decrease in solubility in a polar solvent with increasing size, and increase in solubility in non-polar solvents (with increasing size). Right?

The liquid used according to Heinemann book, is a "inert solid coated with high boiling point liquid hydrocarbon or ester called liquid stationary phase". I would think if the compound had a higher mass it would adsorb into this stationary phase more than the Nitrogen gas mobile phase. I think the gases used in the mobile phase are all non polar btw.. not sure on that though; nitrogen, helium and argon are the only gases ive heard being used by GLC.

OK, but the substance under analysis doesn't actually adsorb into the mobile phase in gas chromatography, but rather is swept by it.
And you have given both a polar and non-polar stationary phase (ester and hydrocarbon respectively), so I'm still confused.

[stonecold]

these questions are so ambiguous.  and apparently they are the type that may come up on an exam.

[matty.k]

The compound with the smallest molar mass gets "swept" away fastest by the gases and doesnt adsorb into the stationary phase very much relative to the others with higher molar mass. So in this case it would be CH3OH -> C2H5OH - >C3H7OH. Since all these compounds are from the same functional group, the polarity and its structure in relation to adsorption and desorption in and out of the stationary/mobile phase is expected to be similiar since same functional groups means similiar chemical properties.

C3H7OH - > C2H5OH  -> CH3OH

wouldnt this be the right order seeing as C2H7OH would have the longest retention time?

[m@tty]

I think so, as a longer chain will be attracted more to the stationary phase. Was an answer given?

[matty.k]

no i would i have to refer to the answer sheet, but im sure thats the correct order.