Page 122 - phytochemistry general program

of applications. Commercially available reversed-phase plates are labelled RP-1,
RP-2, RP-8, or RP-18 according to the chain length of the major alkane substituent
attached to silicon. Amino-, cyano-, and diol-modified layers are also interesting

because of their different characteristics to the alkylsiloxane-bonded silica layers.

(3) Alumina, aluminum oxide (Al2O3)
Frequently used for the separation of bases and aromatic compounds.

(4) Kieselguhr (diatomaceous earth) and cellulose
Due to its low activity, kieselguhr is used to dilute silica gel and also used as inert

supports for liquid stationary phases in partition chromatography.
(5) Magnesium silicate (florisil®)

It is used mainly for the separation of lipids.
(6) Ion exchange resins

Such phases are useful for separating polar compounds such as amino acids as
well as anions and cations.

Cation exchangers generally consist of polystyrene–divinylbenzene resins
modified to introduce acidic functional groups. Sulphonic acid (–SO3H), phosphoric

acid (–PO(OH)2), or carboxylic acids (–COOH) are used.
Anion exchangers are formed by introducing polystyrene resins with quaternary

amine groups.

120