Page 325 - Biosystems Engineering

302 Cha pte r Ni ne

The eluting powers of various solvents, that is, their ability to
move a given component down a column is given below:
Hexane
Carbon tetrachloride
Toluene
Benzene Increasing
Increasing
Dichloromethane eluting
eluting
power
Chloroform power
Ethyl acetate
Ethanol
Methanol
Water

Paper Chromatography
In paper chromatography, paper sheets make an ideal support medium
where water is adsorbed between the cellulose fibers and forms a
stationary hydrophilic phase.
The paper strip containing the mixture is suspended in a jar in
such a way that the end of a spotted paper strip is immersed in the
developing solvent. The sample is separated into individual spots as
the solvent ascends the paper (Fig. 9.7). In this case, distribution takes
place between water (adsorbed by the filter paper to an extent of
20 percent) and the mobile solvent. For this reason, it is referred as
liquid partition chromatography. The separation of amino acids can
be done by paper chromatography.
Ion-Exchange Chromatography
Ion-exchange chromatography is the method used to separate the mix-
ture on the basis of adsorption (cation or anion groups on the matrix) in
a column. Generally, the matrix contains charged groups, and the type
of groups defines the nature and strength of ion exchange. These groups
may be either cationic or anionic, according to the nature of their affinity
for either negative or positive ions. There are two different types of ion-
exchange materials: strongly ionized groups, such as SO H, –NR , and
3 3
the weakly ionized groups, such as –COOH, –OH, and –NH . In the
2
strong ion exchange, the resins are completely ionized and exist in
charged form except at extreme pH values. The weak ion-exchange
materials contain a group whose ionization is dependent on the pH and

Ascending Spots of
Descending
Spots of organic organic
compound compound
FIGURE 9.7 Ascending and descending paper chromatography.