Thin Layer Chromatography
Gas Chromatography-Mass Spectrometry
(Adapted from Mohrig, pp. 118-121)
is a technique used when separating a mixture of two liquids that do not
"behave" well enough to use simple distillation. In this case simple distillation
would not be enough to fully separate the two liquids. The distillate
would contain a majority of one liquid but would still contain a little
of the second. To further separate this resulting distillate, one would
need to redistill this mixture. Depending on the two liquids in question,
many simple distillations would be required to obtain pure liquid.
essentially performs these "redistillations" automatically in a portion
of the fractional distillation apparatus called the fractionating column.
As the mixture boils, it turns to vapor and rises up the column. It reaches
a certain point up the column and condenses. It then turns to vapor again
and rises a little bit further up the column. This continues until the
vapor rises all the way up the column and condenses in the condenser.
At this point, the liquid has been completely purified.
The procedure for fractional distillation is very similar to that of simple
distillation. Once you have set up your fractional distillation apparatus,
place the liquid to be distilled in the distilling flask. The flask should
be no more than two-thirds full at the start of the distillation because
the contents may foam and boil over. Remember to place one or two boiling
stones in the flask to promote even boiling. Ensure that all joints are
tight. Turn on the water for the condenser. Only a small stream of water
is needed; too much water pressure will cause the tubing to pop off. Turn
on the Variac and the distillation can begin. As always, never boil the
flask to dryness because, in some cases, high-boiling explosive peroxides
can become concentrated. Stop the distillation when a small amount of
liquid is left in the distilling flask. Turn off the Variac and remove
the heating mantle to allow the flask to cool more quickly.