Gas Chromotagraphy

[thestrokes14]

---

Members do not see this ad.

What property of a molecule will determine whether it enters the gas or liquid face in a GC separation? Is it volatility? I am just confused what causes molecules to enter the stationary liquid phase.

Thanks.

 

[DougTPR]

What property of a molecule will determine whether it enters the gas or liquid face in a GC separation? Is it volatility? I am just confused what causes molecules to enter the stationary liquid phase.

It sounds like you have a few things a little confused in GC.

The stationary phase is a solid (usually a polymer or silica/alumina) and polar (at least on the MCAT).

The liquids that are injected are volatilized by heating in the injector and remain so throughout the heated system.

The crux of the technique is that a more polar substance will spend more time adhering to the polar stationary phase and a less polar substance will spend less time Thus, the less polar substance will be swept along with the mobile phase much more quickly and have a shorted retention time.

In short, "Polar is Slower."

 

[thestrokes14]

It sounds like you have a few things a little confused in GC.

The stationary phase is a solid (usually a polymer or silica/alumina) and polar (at least on the MCAT).

The liquids that are injected are volatilized by heating in the injector and remain so throughout the heated system.

The crux of the technique is that a more polar substance will spend more time adhering to the polar stationary phase and a less polar substance will spend less time Thus, the less polar substance will be swept along with the mobile phase much more quickly and have a shorted retention time.

In short, "Polar is Slower."

Thank you very much!

 

[Bernoull]

It sounds like you have a few things a little confused in GC.

The stationary phase is a solid (usually a polymer or silica/alumina) and polar (at least on the MCAT).

The liquids that are injected are volatilized by heating in the injector and remain so throughout the heated system.

The crux of the technique is that a more polar substance will spend more time adhering to the polar stationary phase and a less polar substance will spend less time Thus, the less polar substance will be swept along with the mobile phase much more quickly and have a shorted retention time.

In short, "Polar is Slower."

+1

OP, Just keep in mind the polarity of the column, in GC as opposed to say HPLC, ur separation is chiefly a fn of the column as the mobile phase (He) is inert. In liquid chromatography, u gotta factor both column polarity and the differential suitabilities of ur sample components in the mobile phase & both will affect elution times.

So GC is more straightforward, it's "like dissolves in like" if ur column's nonpolar, then nonpolar substances will have longer retention times and for polar columns, DougTPR has it exactly right, polar compounds will have longer RTs.