Gas/Liquid
Chromatography
Presented by: Eman Jawad
The Structure
How it works
Very small
quantities of the
sample in injected
in the machine
using a small
syringe.
Temperature of thw
injector is set such
that the molecules
have enough energy
to move with the gas
phase
One of the three
things might happen
to a particular
molecule in the
mixture injected into
the column.
It may condense on the stationary phase
A compound with a boiling point higher than the temperature
of the column will obviously tend to condense at the start of
the column.
It may dissolve in the liquid on the
surface of the stationary phase
A component that absorbs most strongly to the stationary
phase will spend more time in the column (will be retained in
the column for the longest time) and will, therefore, have the
longest retention time. It will emerge from the gas phase
chromatograph last.
It may remain in the gas phase
A component that absorbs the least strongly to the stationary
phase will spend the least time in the column (will be retained
in the column for the shortest time), and will, therefore, have
the shortest retention time. It will emerge from the
chromatography first.
Partition
The process where a substance divides itself into two
immiscible solvents because it is more soluble in one than the
other is known as partition.
The detector sends a
signal to the recorder
which results in a peak
on the chart paper. Each
peak repreasents the
compound in the mixture.
RETENTION TIME
This time is measured from the time at which
the sample is injected to the point at which it
shows a maximum peak height for that
compound.
1.Boiling point
The factors
that affect
2.The solubility in the liquid
phase
the retention
time are
3.The temperature of
the column
Determination of the percentage composition of a
mixture by GLC
The important thing here to note is
The area under a peak is proportional to the amount of
a compound present. The peaks are triangular in shape
so their area is
1/2 x base x height
If the peaks are very narrow or have similar base
widths, then peak height may be used instead of peak
area.
FOR EXAMPLE, FOR A MIXTURE OF THREE ESTERS A,B AND C.
FIND THE AMOUNT OF A PRESENT IN THE MIXTURE ?
Carboxylic acid - Most polar
Ketone - Between J and L
Alkene - Most non-polar
18/46+18+28=
19.6%
2
1
3
Thank you!