Why are the following procedures invalid? (a) To minimize the ...

[luminitza]

Why are the following procedures invalid?
  (a) To minimize the time required for an analysis, the temperature of a GC instrument is
  increased above the boiling points of the components in the mixture.
  (b) To increase the retention times and thus maximize the separation between peaks, the gas
  flow is adjusted to a very low value.

Question 2

Again consider the TLC plate illustrated in Problem 12.8. Would the Rf of Compound B be different if the solvent system used to develop the plate was 100 hexanes? If so, would it be
  lower or higher?

[mariahkathleeen]

Answer to Question 1

(a) The gaseous compounds will not reach a liquid-vapor equilibrium with the liquid adsor
bent on the inert packing of the column.
(b) The peaks would becomevery broad by diffusion so tthat no advantage is gained.

Answer to Question 2

The Rf of Compound B would be different. It would be lower because 100 hexanes is a less
polar solvent (and thus less powerful eluter) than is 90 hexanes10 ethyl acetate.