Column adsorption chromatography... (1 Viewer)

[Aerlinn]

In Column adsorption chromatography, polar compounds eg. alcohols and amines, are absorbed more strongly and eluted less readily than the less polar compounds such as halogen compounds, aldehydes, ketones, ethers and hydrocarbons. Can someone tell me why?

 

[xiao1985]

gee... some one has lotsa questions...

depends on the stationary phase and mobile phases you use...

to put it simply: if mobile phase = polar then polar stuff goes quicker and vice versa

 

[Aerlinn]

Ah, ok. Thanx. So in In Column adsorption chromatography, is the mobile phase always polar? And if the mobile phase were non polar, the non polar things travel faster, ya?
Yea, I know, I happen to be in an inquiring mood. heh xD

 

[xiao1985]

true that... often it's possible to alter the polar'ness of the mobile phase: using water:ethanol ratio of 9:1 will be more polar than using it 1:9

 

[Aerlinn]

I see... because, uh, water's more polar than ethanol, so more of water makes the thing more polar? >.<

 

[xiao1985]

/claps
/nod

 

[Aerlinn]

yay ^^
Hang on, just looked back to the question. polar compounds eg. alcohols and amines, are absorbed more strongly and eluted less readily than the less polar compounds such as halogen compounds, aldehydes, ketones, ethers and hydrocarbons.
That means less polar compounds are supposed to be more attracted to the solvent, so the solvent's non-polar.
-- Column adsorption chromatography. Mobile phase= non polar generally? or can you choose what mobile phase you use (??) 'cause the source i got it from seemed to be talking generally

 

[xiao1985]

that is general indeed...

from what it's saying, the stationary phase seem to be more polar than the mobile phase (hence polar substances like to stick and non polar substance tend to go with the mobile phase)

whilst that IS the case in most Column Chromotography i did previously (namely flash chromotography and TLC), i believe that does not have to be the case...

edit: by solvent i assume you mean mobile phase, then you are correct...

 

[Aerlinn]

Yeah, I meant the mobile phase
-----------
I might have done some of this in the past, but I don't remember (in desperate need of revision) but what makes alcohols and amines polar?

 

[xiao1985]

alcohol: the H-O bond

amine the H-N bond

(due to the difference in electronegativity of Hydrogen and some of the most electronegative elemtns out there, namely F, O, N) and we call them hydrogen bonding (an extreme example of polar bonding)

 

[Aerlinn]

Hey I remember this stuff ^^ But Hydrogen bonding, is that the polar bonds between H and F, O, N, (Cl?) only...? I think H-bonds are special in some way, but I dun remember

 

[Riviet]

Hey I remember this stuff ^^ But Hydrogen bonding, is that the polar bonds between H and F, O, N, only...?

That's correct, just remember that chemistry is FON.

 

[Aerlinn]

Kewl, but what about the Cl?

 

[Templar]

There isn't really a special type of bond known as hydrogen bonding. It's just a really strong dipole interaction. So depending on the cut off for interaction, Cl could be borderline classified as well, but in general it's mainly with N, O and F.