Polymers
Polymers consist of many small molecular weight molecules, called monomers, linked together to form very large molecules called macromolecules. A polymer macromolecule may contain ten to one hundred thousand monomer molecules. There are two commonly known types of polymer; the first are the biopolymers such as the carbohydrates and starches, the monomers of which are the pentoses and hexoses and the proteins, the monomers of which are amino acids linked by peptide bonds; the second commonly known types of polymer are the commercial polymers such as polyethylene, the monomer being ethylene, polyvinylchloride the monomer being vinyl chloride and Perspex the monomer being methyl methacrylate. The first commercial polymers were produced in the early 1800s in the form of Vulcanite produced by the vulcanization of rubber and Celluloid produced from low nitrogen-content nitrocellulose. Chromatography equipment utilizes a number of different polymers, Teflon, polytetrafluoroethylene is an extremely inert material that is unaffected by solvents and even by most acids and is used for chromatography in the form of tubes and gaskets.. Neoprene is another polymer that is frequently used as O-ring seals and gaskets in chromatography pumps and valves as it also is resistant to most solvents. Inert polymers, although not very apparent, play a very important part in the manufacture of chromatographs.
Author: RPW Scott
Book:Principles and Practice of Chromatography
Section:Principles Applications Liquid-Chromatography b--blockers
Hosoya et
al. and Kobayashi et al. (17), developed a method for packing
uniformly sized polymer based LC packing materials that provided practically
adequate column efficiency using a copoly-merization technique.
Figure 55 Chromatogram of Some
Polyaromatic Hydrocarbons Separated on the Polymer Based Pickings
The uniformly
sized, polymer-based packing was prepared from mixtures of alkyl methracrylate
and glycerol dimethacrylate by copolymerization techniques using a multistep
swelling and polymerization method. The
Principles Applications Liquid-Chromatography b--blockers
Author: RPW Scott
Book:Gas Chromatography
Section:YES GC-Columns Packed-GC-Column Supports
separations appear to be based largely on exclusion. Macroporous Polymers such
as the packings founded on the co-polymerization of polystyrene and
divinylbenzene are also popular GC adsorbents. The extent of cross-linking
determines its rigidity and the greater the cross-linking the harder the resin
becomes until, at the extreme, the resin formed is very brittle. The
macro-porous resin consists of resin particles a few microns in diameter, which
in turn are composed of a fused mass of polymer micro-spheres, a few Angstroms
in diameter. Consequently, the resin polymer has a relatively high surface area
as well as high porosity. They exhibit strong dispersive type interaction with
solvents and solutes with some polarizability arising from the aromatic nuclei
in the polymer.
Supports for GLC
There have
been a number of materials used as supports for packed GC columns including,
Celite (a proprietary form of a diatomaceous earth), fire-brick (calcined
YES GC-Columns Packed-GC-Column Supports
Author: RPW Scott
Book:The Mechanism of Chromatographic Retention
Section:Retention Exclusion Silica-Gel-Preparation
Initially,
silicic acid is released,
Na2SiO3
+H2O + 2HCl = Si(OH)4 + 2NaCl
However, the
free acid quickly starts to condense with itself with the elimination of water
to form dimers, trimers and eventually polymeric silicic acid.
The
Polymerization of Silicic Acid
The polymer
continues to grow, initially forming polymer aggregates and then polymer
spheres, a few Angstrom in diameter. These polymeric
spheres are called primary silica particles. The primary particles
continue to grow until, at a particular size, the surface silanol groups
(hydroxyl groups attached to the surface silicon atoms) on adjacent primary
polymer particles, start condense. This condensation causes the primary particles to adhere to one another and at this
stage the solution begins to
Retention Exclusion Silica-Gel-Preparation
Author: RPW Scott
Book:Liquid Chromatography
Section:HPLC Macroporous-Polymers
special areas of application
particularly in sample preparation.
Macroporous Polymers
Polymeric ion
exchange materials were developed for chromatography in the early sixties
resulting in the introduction of macro-porous polymers (29-31). The advantages
of this material lay in the macro-porous nature of the resin packing, which
consisted of resin particles a few microns in diameter, which, in turn,
comprised of a fused mass of polymer micro-spheres a few Angstroms in diameter.
The resin polymer micro-spheres play the same part as the silica gel primary
particles, and confer on the polymer a relatively high surface area together
with a high porosity. The high surface area provided increased solute retention
and selectivity together with a superior loading capacity and, consequently, a
wide dynamic range of analysis. The material consists of a highly cross-linked
polystyrene resin with about a 50Å pore diameter. In the case of the ion
exchange materials, inorganic groups of
HPLC Macroporous-Polymers
Author: RPW Scott
Book:Liquid Chromatography
Section:HPLC Stationary-Phases Silica-Gel Irregular
Silica gel is
manufactured by releasing silicic acid from a strong solution of sodium
silicate by hydrochloric acid. (Sodium silicate is prepared by heating sand at
a high temperature in contact with caustic soda or sodium carbonate).
Initially,
silicic acid is released,
Na2SiO3 +H2O +
2HCl = Si(OH)4 + 2NaCl
and then the
free acid quickly starts to condense with itself with the elimination of water
to form dimers, trimers and eventually polymeric silicic acid. The polymer
grows, initially forming polymer aggregates and then polymer spheres, a few
Angstrom in diameter. These polymeric
spheres are called primary silica particles. These primary particles
continue to grow until, at a particular size, the surface silanol groups on
adjacent primary polymer particles, condense with the elimination of water.
This condensation causes the primary particles to adhere to one another and at
this stage the solution begins to gel. During this process, the primary
HPLC Stationary-Phases Silica-Gel Irregular
Author: RPW Scott
Book:Principles and Practice of Chromatography
Section:Principles Applications Gas-Chromatography High-Temperature
a problem. The solute must be
thermally stable so that the partial pressure is sufficiently high to
allow elution in a reasonable time. Nothing can be done with respect
to the solute stability as this is determined by the nature of the
sample.
There are certain
materials hat can be used as stationary phases at remarkably high
temperatures. These materials are based on the polymerization of
carborane substituted siloxanes. An example of the empirical formula
of a carborane silicone polymer is as follows,
where represents the meta–carborane
nucleus.
There are
three commonly used carborane stationary phases, The first a dispersive phase,
Dexsil 300 where the carboranes are linked with a methylsilicone polymer and
can be used up to a temperature of
450˚C (an exceedingly high
temperature for chromatographic separations). Some induced polarizability has
been introduced into the carborane polymer by employing a methyl phenyl
silicone and
Principles Applications Gas-Chromatography High-Temperature