Applications of Size Exclusion Chromatography
Relative molecular mass distributions for components of biochemical and polymer systems can be
determined with a 10% accuracy using standards. With biochemical materials, where both simple and
macro-molecules may be present in an electrolyte solution, desalting is commonly employed to isolate
the macromolecules. Inorganic salts and small molecules are eluted well after such materials as
peptides, proteins, enzymes and viruses. Desalting is most efficient if gels with relatively small pores
are used, the process being more rapid than dialysis. Dilute solutions of macro-molecules can be
concentrated and isolated by adding dry gel beads to absorb the solvent and low RMM solutes.
4.4—
Electrophoresis
Summary
Principles
Separation mainly of charged materials by differential migration across a surface or through a column
in an applied potential gradient; migration rates dependent upon size, shape and charge of species.
Apparatus and Instrumentation
Traditional electrophoresis: paper, cellulose acetate or polymeric gels used as a supporting medium for
the electrolyte solution; enclosed tank with electrodes and buffer reservoirs; dc power supply.
Capillary electrophoresis: narrow-bore fused-silica capillary tube; injection system; detector; recorder
or VDU.
Applications
Qualitative and quantitative characterization of biologically active materials; especially useful for
clinical and forensic work where small amounts of complex samples may be involved. Nanogram to 3
femtogram scale separations by capillary electrophoresis.
Disadvantages
Mobilities very sensitive to supporting medium and precision poor for quantitative work by traditional
methods (5–20%); 0.5–3% for capillary methods.
Traditional electrophoresis involves the differential migration of charged species in an electrolyte
solution under the influence of an applied potential gradient. The rate of migration of each species is a
function of its charge, shape and size. In traditional zone electrophoresis, the electrolyte solution is
retained by an inert porous supporting medium, usually paper or gel, in the form of a sheet or column.
Application of a dc potential across the solution for a period of time results in the components of a
mixture, originally placed