Introduction to Soil Chemistry

178 chromatography
Table 9.1. Fundamental Types of Chromatography
Type of Stationary
Types of
Compounds
Amenable
Chromatography Phase Mobile Phase to Separation
Gas (also GLC a High-boiling Gas Compounds to be
and GSC b ) liquid separated must
be in gaseous
HPLC
phase
c
Solid Solvent, aqueous, Compounds or ions
aqueous solution; must be soluble in
solvant, or mixture mobile phase and
of solvants have appreciable
attraction to
solid phase
TLCd Solid Solvent, aqueous, Compounds or ions
aqueous solution; must be soluble in
solvant, or mixture mobile phase and
of solvants have appreciable
attraction to
solid phase
Electrophoresis Solid or Curerent Compounds or ions
semisolid in must be ionized
a buffer
solution
to be separated
a Gas–liquid chromatography.
b Gas–solid chromatography.
c High-performance liquid chromatography.
d Thin-layer chromatography.
9.2.2. Mobile Phases
In gas chromatography common mobile phases are hydrogen, argon, helium,
and nitrogen gases and air; helium and nitrogen are the most commonly used.
Because gas chromatographic detectors are extremely sensitive and it is desirable
to keep the noise level as low as possible, it is always advisable to use
very high-purity gas as the mobile phase.
9.2.3. Stationary Phases
Chromatographic stationary phases are either solids or liquids coating or
bonded to solids. Common stationary phases are listed in Table 9.2. For gas
chromatography the solids are activated carbon of various sorts, polymers,
molecular sieves, or similar materials, and the chromatography may be
referred to as gas–solid chromatography (GSC). This type of stationary phase