Chromatography: GLC

CHE 311 "Chromatography"

Gas Liquid Chromatography (glc)

stationary phase = column of non volatile liquid (carbowax

DNP, SE-30, etc.) on solid support.

moving phase = gas

distance after injection

retention time = ---------------------------

chart speed

area A

%A = ------------------------------ X 100%

area A + area B + area C + etc.

area A = height X width (at half height)

applications:

a) analysis of mixture, # of components

(volatile liquids or gases)

b) separation of mg samples

c) identification (retention time)

d) per cent composition

EXPERIMENT: Analysis of Alcohol-Ketone Mixtures

A ketone is a type of organic compound that is represented by the general formula I; it is related to another kind of compound, a secondary alcohol (II).

A ketone can be made from the corresponding alcohol by oxidation; conversely,reduction of a ketone results in the formation of the secondary alcohol. (You need not be overly concerned with the chemistry of these substances now. The relationships just described will be amplified at the appropriate point later in the course.)

When a ketone is prepared from the alcohol, or vice versa, it is possible that not all of the starting material is converted to the end product. The final product may therefore be contaminated with some of the starting material. The difference between the boiling points of the alcohol and the ketone becomes smaller as their molecular weights increase, making it more difficult to separate them by conventional distillation procedures. Analysis by GLC, however, readily indicates the presence of the contaminant.

You will receive a mixture of a ketone and the corresponding secondary alcohol. Carry out a GLC analysis following the general instructions given and whatever special instructions are provided for the instrument available in your laboratory. You will also need to measure the chart speed (inches/minute or cm/min).

If your sample was given to you as an "unknown," compute the approximate percentage composition by measuring the areas of the peaks. If authentic samples of the various possibilities are available, attempt an identification of the components of your mixture. In this case, you need use either an authentic ketone or alcohol, but not both.