Biomedical Engineering Reference
In-Depth Information
Fig. 3 Schematic of the
partial filling technique
(reproduced with permission
from [ 79 ])
3.2 Capillary Electrochromatography
CEC is a hybrid separation technique that combines the high efficiency typical of
capillary electrophoresis with the phase selectivity of a high-performance liquid
chromatography [ 73 ]. An interesting aspect of this technique is the possibility to
use a so-called pseudostationary phase (PSP). Different from a common stationary
phase, PSPs are interaction phases that move with (or against) the mobile phase and
are continuously replaced, without needing to be packed [ 74 - 77 ]. To be suitable for
this purpose, MIP NPs have to possess certain properties, such as: (a) able to form
stable suspensions and exhibit enough selectivity in the electrolyte solutions used as
mobile phases; (b) be charged, in order not to co-elute with the electroosmotic flow;
(c) have a uniform velocity to avoid peak broadening; (d) exhibit high-surface areas
and low mass-transfer resistance; and (e) not interfere with the detection mecha-
nism [ 78 ]. A “partial filling” technique has been exploited for use of MIP NPs in
CEC, whereby a fraction of nanoparticles suspension is injected before the sample
(Fig. 3a ). The analytical sample will be separated during the run by passing through
the more slowly moving “plug” of nanoparticles when the voltage is applied,
arriving at the detection window before the nanoparticles (Fig. 3b ), thus avoiding
scattering from the PSP during UV detection (Fig. 3c )[ 74 , 76 , 79 ].
Schweitz and coauthors successfully synthesized and used 200-500 nm MIP
nanoparticles in CEC separation of propranolol enantiomers [ 58 ]. The authors used
UV-initiated precipitation polymerization at
26 C to strengthen the interactions
between the template and the functional monomer. Under optimized conditions,
racemic resolution was achieved in slightly more than 1 min, even for multiple
racemic mixtures of atenolol, pindolol, and propranolol [ 76 ]. The same group
performed the simultaneous CEC resolution of two different racemic analytes,
propranolol and ropivacaine, either by injecting two different types of MIP
nanoparticles at the same time, or by using MIP nanoparticles which were simulta-
neously imprinted for the two templates [ 59 ]. In the first case it was possible to
separate the racemic mixtures of the two different templates in a single run (Fig. 4 ).
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