High performance capillary electrophoresis - T.E.A.M.
High performance capillary electrophoresis - T.E.A.M.
High performance capillary electrophoresis - T.E.A.M.
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Modes<br />
the stationary phase in LC. Surfactants can be anionic,<br />
cationic, non-ionic, zwitterionic, or mixtures of each (table<br />
14). In each category, alkyl chain length or structure can<br />
also be varied. In addition, MEKC can be performed using<br />
bile salts or microemulsions. In all cases, variations in<br />
buffer concentration, pH, temperature, or use of additives<br />
such as urea, metal ions, or chiral selectors can also be used<br />
to affect selectivity.<br />
Biological detergents CMC Aggregation<br />
(mM) number<br />
Anionic SDS 8.2 62<br />
Cationic DTAB 14 50<br />
CTAB 1.3 78<br />
Non Ionic Octylglucoside — —<br />
n-Dodecyl-b-D-maltoside 0.16 —<br />
Triton X-100 0.24 140<br />
Zwitterionic CHAPS 8 10<br />
CHAPSO 8 11<br />
Table 14<br />
Surfactants<br />
Bile Salt Cholic acid 14 2– 4<br />
Deoxycholic acid 5 4 –10<br />
Taurocholic acid 10 –15 4<br />
As in chromatography, organic modifiers can be added to<br />
manipulate solute-micelle interaction. Modifiers such as<br />
methanol, acetonitrile, and 2-propanol have all been used<br />
successfully. Added to the running buffer in concentrations<br />
from a few percent up to 50 % (v/v) can lessen hydrophobic<br />
interactions between the solute and micelle. They can also<br />
decrease the hydrophobic interactions which maintain<br />
micellar structure, allowing more rapid chromatographic<br />
kinetics.<br />
Surfactants used for MEKC can also interact with the<br />
<strong>capillary</strong> wall and have dramatic effects on the EOF as well<br />
as solute-wall interactions. The direction of solute and<br />
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