Abstrakt:
Sulfobetaine zwitterionic monolithic columns were synthesized by in-situ
polymerization (in fused silica capillaries) of a N,N-dimethyl-N-metacryloxyethyl-
N-(3-sulfopropyl) ammonium betaine (MEDSA) functional monomer in
combination with different cross-linking monomers. From among the ten crosslinkers
tested, bisphenol A glycerolate dimethacrylate provides monolithic
capillary columns with best chromatographic efficiency (60 000-70 000
theoretical plates per meter). The respective columns show excellent column-tocolumn
reproducibility of pore morphology, separation selectivity, good
permeability and low mass transfer resistance, so that being suitable for fast and
selective separation of various samples. Monolithic sulfobetaine polymethacrylate
(BIGDMA-MEDSA) micro-columns designed in our laboratory exhibit a dual
retention mechanism, in acetonitrile-rich mobile phase, polar (hydrophilic) interactions control the retention (HILIC separation mode), whereas in more
aqueous mobile phases the column shows essentially non-polar with a major role
of hydrophobic interactions properties (reversed-phase, RP mode). The dual-mode
retention mechanism was investigated and applied to the HILIC and reversedphase
HPLC separations of barbiturates, sulfonamides, nucleobases, nucleosides,
phenolic, and other carboxylic acids, polyphenols, flavonoids plus other lowmolecular
compounds. The separation selectivities in the HILIC and RP
dimensions are highly complementary to each other, so that a zwitterionic
sulfobetaine polymethacrylate micro-column can be used in the first dimension of
two-dimensional LC in alternating RP and HILIC modes, coupled with a short (3-
5 cm) alkyl-bonded core-shell or silica-based monolithic column in the second
dimension, for HILIC×RP and RP×RP comprehensive two-dimensional
separations. During the HILIC×RP period, a programme with the decreasing
acetonitrile gradient is used for separation in the first dimension, so that at the
end of the gradient the polymeric monolithic micro-column is equilibrated with
a highly aqueous mobile phase and is ready for repeated sample injection, in this
case, for separation under reversed-phase gradient conditions with the increasing
concentration of acetonitrile in the first dimension.
