Page 109 - Phytochemistry 2 (06-PG 605)
P. 109
Factors affecting separation in adsorption
chromatography
A- Chemical structure of compounds to be separated
B-Nature of adsorbent
1-Particle size of adsorbent (um, mm or mesh). It affects
o Flow rate of m.ph
o Homogenity of st.ph.
o Sharpness of separation
2- Polarity of adsorbent
3- Degree of activation (conditioning)
adsorbent should be activated (removal of water which block the
active sites).
o Partial deactivation is required to increase resolving power of
adsorbent
o In most active adsorbent, all solutes will strongly bound and
no resolution occur.
4-PH of adsorbent
Silica gel is relatively acidic
alumina is relatively basic
o If the compound is acidic and alumina is the adsorbent,
the compound will tightly bound to the adsorbent by ionic
force and difficult to move and resolve.
o The same is true for bases on silica gel
o Bases e.g. alkaloids should be separated on alumina
o Acids and phenols should be separated on silica gel
o Neutral compounds can be separated on either silica or alumina
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