Gas Chromatography Uses

[horizon]

Gas chromatography could not be used to:
A. Determine the purity of a sample of perfume.
B. Separate low molecular weight alcohols.
C. Compare the components of two petrol samples.
D. Determine the concentration of aspirin in an analgesic tablet.

Would someone mind explaining why the answer is D? I put down A....

[horizon]

Also, another unrelated question: If unstated, is it assumed that in column chromatography, the stationary phase is non-polar while the mobile phase is polar? What is the general case?

[pi]

From memory, GC can't be used to find concentrations of mixtures, only "relative" concentrations in certain cases (and there is no indication of this from the question stem). Hence, D is the answer.


edit: incorrect info removed

[horizon]

Then this question: I don't get it...

Hexene, hexanol and hexanoic acid were analysed using normal phase column chromatography. 
Which of the following statements is incorrect?

A. the order of the molecules would be eluted form the column is the same in both HPLC and GLC.
B. The order that the molecules would be eluted is: hexene, hexanol, hexanoic acid.
C. The order that the molecules would be eluted is: hexanoic acid, hexanol, hexene.

OK, so obviously its between B or C. The answer says C, but if the mobile phase is a polar solvent, then shouldn't the more polar components be eluted first, thus making C correct and not incorrect?
Is my thinking right or wrong?
Thanks for clarification!

[Lasercookie]

Also, another unrelated question: If unstated, is it assumed that in column chromatography, the stationary phase is non-polar while the mobile phase is polar? What is the general case?

Yep, that's the general case afaik.

Isn't Sillica and Alumina - both polar substances - the most commonly used stationary phases in column chromatography?

[pi]

I thought silica and alumina were non-polar...

/fail


My bad.


edit: Just checked online, yep definitely polar, fixed my above post

[charmanderp]

I'm pretty sure that if we tried to find the concentration of an aspirin tablet using GC we'd just burn the sample. I'm not 100% certain though, it might be volatile.

For the second question, C is incorrect because hexanol is more polar (albeit not very polar at all) than hexanoic acid. Therefore, as we're using a polar mobile phase, it would be eluted first.

However, I'm pretty sure that B would be incorrect in that case too. Perhaps it's something to do with none of them really being polar due to all having large hydrocarbon chains and only a single polar bond or no polar bond at all.