Howard College Ion- Exchange Chromatography Lab Report

Experiment 24 – Ion Exchange ChromatographyChromatography
Separation (purification) of a mixture using a stationary phase and a
mobile phase. Components of a mixture are carried through the
stationary phase by the flow of the mobile phase, and separations are
based on differences in migration rates among the mobile phase
components.
Column Chromatography
The stationary phase is held in a narrow tube, and the mobile phase
is forced through the tube either by pressure or gravity.
Separating Ions by Ion Exchange Chromatography
Ion exchange is a process by which ions held on porous insoluble
solids are exchanged for ions in a solution that is brought in contact
with the solid.
Most solids used today are synthetic high molecular weight polymers
that contain large numbers of functional groups per molecule. Cation
exchange resins contain acidic groups, whereas anion exchange
resins have basic groups. This experiment calls for the use of the
cationic exchange resin AG1-X8.
Ion exchange separations are usually performed under conditions in
which one ion predominates in both phases. The separation of the
two cations of Ni and Co is based on differences in their tendency to
form anionic complexes. In the example under consideration, it can
be seen that by adding chloride ion as the eluent, an anionic complex
of cobalt is formed (equation 2) which will have affinity for the cationic
sites on the resin, Thus, it will be retained on the column, whereas
the nickel complex is cationic and will move down the column (called
elution). After all the nickel has been eluted, the addition of water to
the column will shift the equilibrium shown in eq 2 to the left, thereby
reforming the cobalt cationic complex which will be repelled by the
cationic sites on the resin and will therefore elute. In this manner, the
two ions can be separated.
Equations 3 and 4 (page 24-2) show the spot tests one would use to
identify the nickel and cobalt ions after they have been eluted from
the column. Notice that each complex has a unique color.
The assignment for this exercise is given below in the form of
questions.
1) What is the objective of this experiment?
2) When packing the column, what must be avoided (2 factors)?
3) Which cationic complex will elute first? Why?
4) Which cationic complex will elute next? Why?
5) What is the equation for the nickel spot test? What color would
you expect to observe?
6) What is the equation for the cobalt spot test? What color would
you expect to observe?
7) Explain the meaning of the following terms:
a) Elution
b) Mobile Phase
c) Stationary Phase
8) Which experimental factors will most influence the outcome of this
separation? In other words, what steps (or factors) in the procedure
are most important in order to obtain the desired results?
9) What is the basic principle which allows for the separation of these
two cations by this method?
10) If it was desired to separate a mixture containing a much larger
amount of the two cations, what changes would be required?