Preparation and evaluation of a molecularly imprinted polymer derivatized silica monolithic column for capillary electrochromatography and capillary liquid chromatography

Article abstract of DOI:10.1021/ac061475x

A method for preparation of molecularly imprinted polymer (MIP) derivatized onto the surface of a monolithic silica capillary column was successfully developed. The vinyl groups were first introduced onto the silica monolith by immobilization of γ-methacryloxypropyltrimethoxysilane. Then the MIP coating was copolymerized and anchored onto the surface of the silica monolith. Acetonitrile was selected as porogen (solvent). The other preparation conditions, such as monomer concentration, temperature, and time of polymerization, were systematically studied. The obtained MIP-derivatized silica monolith using L-tetrahydropalmatine (L-THP) and (5S,11S)-(-)-Troeger's base (S-TB) as the imprinted template, respectively, was characterized in terms of the retention behavior of thiourea and toluene. Under the optimized CEC conditions, baseline enantioseparations of THP and TB were achieved in 4 min though the effective length of the columns was 8.5 cm. The result indicates that enough recognition sites were on the surface of silica monolith, resulting in strong recognition ability. Compared with a MIP organic monolith, the MIP-derivatized silica monolith exhibits better column efficiency and stability in CEC. Additionally, the comparison of these two kinds of monolithic columns was performed by capillary liquid chromatography. The separation on MIP-derivatized silica monolith was superior to that on the organic monolith.

Full text of DOI:10.1021/ac061475x

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Anal. Chem. 2007, 79, 639-646
Preparation and Evaluation of a Molecularly
Imprinted Polymer Derivatized Silica Monolithic
Column for Capillary Electrochromatography and
Capillary Liquid Chromatography
Junjie Ou,† Xin Li,† Shun Feng,† Jing Dong,† Xiaoli Dong,†,‡ Liang Kong,† Mingliang Ye,† and
Hanfa Zou*,†
National Chromatographic R & A Center, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian
116023, China, and Department of Chemistry, Xixi Campus, Zhejiang University, Hangzhou 310028, China
applications of molecular imprinting polymers (MIPs) is as chiral
stationary phases for separation of enantiomers by high-perfor-
mance liquid chromatography (HPLC) and capillary electrochro-
matography (CEC).8-13
A method for preparation of molecularly imprinted poly-
mer (MIP) derivatized onto the surface of a monolithic
silica capillary column was successfully developed. The
vinyl groups were first introduced onto the silica monolith
by immobilization of γ-methacryloxypropyltrimethoxy-
silane. Then the MIP coating was copolymerized and
anchored onto the surface of the silica monolith. Aceto-
nitrile was selected as porogen (solvent). The other
preparation conditions, such as monomer concentration,
temperature, and time of polymerization, were systemati-
cally studied. The obtained MIP-derivatized silica mono-
Traditionally, the MIP stationary phases have been prepared
by bulk polymerization, suspension polymerization, multistep
swelling polymerization, and precipitation polymerization methods.
Despite the high yield for these methods, a large number of
template molecules are needed in the preparation process, which
is not cost-efficient. Since Matsui and co-workers14 had employed
an in situ polymerization technique to prepare MIP monolithic
rods, this method has been used to synthesize the MIP in a
stainless steel column or a capillary column without the tedious
procedures of grinding, sieving, and column packing.15-18 How-
ever, the obtained MIP monoliths for both HPLC and CEC often
suffer from low efficiency because of the slow association/
dissociation kinetics of the analytes with the MIP stationary
phases.12,19
lith using L-tetrahydropalmatine (L-THP) and (5S,11S)-
(-)-Tro1ger’s base (S-TB) as the imprinted template,
respectively, was characterized in terms of the retention
behavior of thiourea and toluene. Under the optimized
CEC conditions, baseline enantioseparations of THP and
TB were achieved in 4 min though the effective length of
the columns was 8.5 cm. The result indicates that enough
recognition sites were on the surface of silica monolith,
resulting in strong recognition ability. Compared with a
MIP organic monolith, the MIP-derivatized silica monolith
exhibits better column efficiency and stability in CEC.
Additionally, the comparison of these two kinds of mono-
lithic columns was performed by capillary liquid chroma-
tography. The separation on MIP-derivatized silica mono-
lith was superior to that on the organic monolith.
An alternative approach that may overcome this disadvantage
is to prepare the MIP as a film coating onto the surface of
(3) Andersson, L. I. J. Chromatogr., B 2000, 739, 163-173.
(4) Cunliffe, D.; Kirby, A.; Alexander, C. Adv. Drug Delivery Rev. 2005, 57,
1836-1853.
(5) Haupt, K. Analyst 2001, 126, 747-756.
(6) Mahony, J. O.; Nolan, K.; Smyth, M. R.; Mizaikoff, B. Anal. Chim. Acta 2005,
534, 31-39.
(7) Emgenbroich, M.; Wufll, G. Chem. Eur. J. 2003, 9, 4106-4117.
(8) Wistuba, D.; Schurig, V. J. Chromatogr., B 2000, 875, 255-276.
(9) Kempe, M.; Mosbach, K. J. Chromatogr., A 1995, 694, 3-13.
(10) Schweitz, L.; Spegel, P.; Nilsson, S. Electrophoresis 2001, 22, 4053-4063.
(11) Turiel, E.; Martin-Esteban, A. J. Sep. Sci. 2005, 28, 719-728.
(12) Nilsson, J.; Spegel, P.; Nilsson, S. J. Chromatogr., B 2004, 804, 3-12.
(13) Xu, Y. L.; Liu, Z. S.; Wang, H. F.; Yan, C.; Gao, R. Y. Electrophoresis 2005,
26, 804-811.
(14) Matsui, J.; Kato, T.; Takeuchi, T.; Suzuki, M.; Yokoyama, K.; Tamiya, E.;
Karube, I. Anal. Chem. 1993, 65, 2223-2224.
(15) Schweitz, L.; Andersson, L. I.; Nilsson, S. J. Chromatogr., A 1997, 792, 401-
409.
The molecular imprinting technique has become a well-known
means for the preparation of polymer material with high selectivity,
which has been used in a variety of applications, such as separation
media, artificial antibody mimics, and sensing devices. The
resultant polymers can recognize the imprinted molecules and
show substrate selectivity.1-7 One of the most widely used
* Corresponding author. Tel.: +86-411-84379610. Fax: +86-411-84379620.
E-mail: hanfazou@dicp.ac.cn.
(16) Schweitz, L.; Andersson, L. I.; Nilsson, S. Anal. Chem. 1997, 69, 1179-
1183.
(17) Huang, X. D.; Qin, F.; Chen, X. M.; Liu, Y. Q.; Zou, H. F. J. Chromatogr., B
2004, 804, 13-18.
† Dalian Institute of Chemical Physics.
‡ Zhejiang University.
(1) Owens, P. K.; Karlsson, L.; Lutz, E. S. M.; Andersson, L. I. Trends Anal.
Chem. 1999, 18, 146-154.
(18) Huang, X. D.; Zou, H. F.; Chen, X. M.; Luo, Q. Z.; Kong, L. J. Chromatogr.,
(2) Alexander, C.; Andersson, H. k. S.; Andersson, L. I.; Ansell, R. J.; Kirsch,
N.; Nicholls, I. A.; Mahony, J.; Whitcombe, M. J. J. Mol. Recognit. 2006,
19, 106-180.
A 2003, 984, 273-282.
(19) Quaglia, M.; Sellergren, B.; Lorenzi, E. D. J. Chromatogr., A 2004, 1044,
53-66.
10.1021/ac061475x CCC: $37.00 © 2007 American Chemical Society
Published on Web 12/06/2006
Analytical Chemistry, Vol. 79, No. 2, January 15, 2007 639

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Figure 1. Molecular structure of (a) Tro¨ger’s base and (b) tetrahy-
dropalmatine.
stationary phases. The MIP film coating at the capillary inner wall
for open-tubular CEC (OT-CEC) has been reported.20,21 The MIP
coatings were covalently attached to the capillary by the activation
of the capillary inner surface with vinyl groups. Schweitz22 has
synthesized MIP coatings in fused-silica capillary columns by use
of a surface-coupled radical initiator. Huang et al.23 also prepared
an MIP film based on a 9-ethyladenine cavity for the recognition
of nucleotide bases in OT-CEC. It is well known that the low
sample capacity in OT-CEC is a major disadvantage because of
low surface area. Quaglia et al.24 packed MIP-silica composite
beads into a capillary for enantioseparation of phenylalanine anilide
in CEC. It is a problem to construct reproducible frits, which can
lead to zone broadening and bubble formation.
Figure 2. Schematic representation of preparation procedures of
MIP film-derivatized silica monolithic column. (1) Open-tubular capil-
lary; (2) silica monolith; (3) silanols on the surface of silica monolith;
(4) vinylation on the surface of silica monolith; (5) formation of MIP
film on the surface of silica monolith.
Tanaka and co-workers25,26 pioneered the fabrication of silica
rods via a sol-gel process based on the hydrolytic polymerization
of alkoxysilanes. To date, silica monoliths are widely applied for
many fields of separation by HPLC and CEC.25-27 Compared with
the organic polymer monoliths, silica monoliths are not apt to swell
or shrink in different organic mobile phases.28 In the present study,
the MIP film coating was anchored covalently onto the surface of
silica monolith in capillary. The enantioseparations of tetrahydro-
palmatine (THP) and Tro¨ger’s base (TB) were successfully
acquired by CEC and capillary liquid chromatography (cLC).
(Wuhan, China). Poly(ethylene glycol) (PEG, Mn ) 10 000) was
purchased from Aldrich (Milwaukee, WI). 2,2′-Azobisisobutyroni-
trile (AIBN) was obtained from Shanghai Chemical Plant (Shang-
hai, China) and recrystallized in ethanol before used. γ-Meth-
acryloxypropyltrimethoxysilane (γ-MAPS) was purchased from
Sigma. Fused-silica capillary with 75 µm i.d. × 375 µm o.d. was
purchased from the Yongnian Optic Fiber Plant (Hebei, China).
Water used in all experiments was doubly distilled and purified
by a Milli-Q system (Millipore Inc., Milford, MA). HPLC-grade
acetonitrile (ACN) was used for preparation of electrolyte. Other
chemical reagents used were analytical grade.
EXPERIMENTAL SECTION
Preparation of MIP-Derivatized Silica Monolithic Column.
The procedures for preparation of the MIP-derivatized monolithic
column are illustrated in Figure 2.
Materials. DL-Tetrahydropalmatine (DL-THP) and
L
-tetrahy-
dropalmatine (L-THP) were purchased from the National Institute
for the Control of Pharmaceutical and Biological Products of China
(Beijing, China). (5S,11S)-(-)-Tro¨ger’s base (S-TB) and (5R,11R)-
(+)-Tro¨ger’s base (R-TB) were obtained from Fluka (Buchs,
Switzerland). Their molecular structures are indicated in Figure
1. Ethylene dimethacrylate (EDMA) and trimethylolpropane
trimethacrylate (TRIM) from Sigma (St. Louis, MO) were ex-
tracted with 10% aqueous sodium hydroxide and water and dried
over anhydrous magnesium sulfate. Methacrylic acid (MAA) from
Acros (Geel, Belgium) was distilled under vacuum. Tetramethox-
ysilane (TMOS) was from Chemical Factory of Wuhan University
Prior to the preparation of the silica monolith, the capillary
was rinsed with 1.0 M NaOH for 30 min, water for 30 min, 1.0 M
HCl for 2 h, and water for another 30 min, successively, and then
dried in a GC oven at 110 °C for 12 h. The silica monolithic column
was prepared according to the procedures previously reported.29,30
Briefly, 1.06 g of PEG was dissolved in 10.0 mL of acetic acid
solution (0.01 M). After 4.0 mL of TMOS was added, the whole
solution was violently agitated in an ice bath for 45 min. The
obtained sol was injected into the pretreated capillary and both
ends were sealed, followed by immersing into a thermostat water
bath at 40 °C for 24 h. The mesopores were tailored by treating
the wet gel in 0.01 M ammonium hydroxide solution at 120 °C
for 3 h. The capillary was then placed in a GC oven at 330 °C for
24 h to remove the organic moiety after evaporation of the solvent
in capillary to dry of the gel.
(20) Bruggemann, O.; Freitag, R.; Whitcombe, M. J.; Vulfson, E. N. J. Chromatogr.,
A 1997, 781, 43-53.
(21) Tan, Z. J.; Remcho, V. T. Electrophoresis 1998, 19, 2055-2060.
(22) Schweitz, L. Anal. Chem. 2002, 74, 1192-1196.
(23) Huang, Y. C.; Lin, C. C.; Liu, C. Y. Electrophoresis 2004, 25, 554-561.
(24) Quaglia, M.; Lorenzi, E. D.; Sulitzky, C.; Caccialanza, G.; Sellergren, B.
Electrophoresis 2003, 24, 952-957.
(25) Tanaka, N.; Kobayashi, H.; Ishizuka, N.; Minakuchi, H.; Nakanishi, K.;
Hosoya, K.; Ikegami, T. J. Chromatogr. A 2002, 965, 35-49.
(26) Ishizuka, N.; Kobayashi, H.; Minakuchi, H.; Nakanishi, K.; Hirao, K.; Hosoya,
K.; Ikegami, T.; Tanaka, N. J. Chromatohr. A 2002, 960, 85-96.
(27) Li, W., Fries, D.P., Malik, A., J. Chromatogr., A 2004, 1044, 23-52.
(28) Rieux, L.; Niederlander, H.; Verpoorte, E.; Bischoff, R. J. Sep. Sci. 2005,
28, 1628-1641.
The capillary silica monolith was rinsed with 0.1 M HCl
solution for 1 h, and then with water until the pH value of the
(29) Xie, C. H.; Hu, J. W.; Xiao, H.; Su, X. Y.; Dong, J.; Tian, R. J.; He, Z. K.; Zou,
H. F. Electrophoresis 2005, 26, 790-797.
(30) Xie, C. H.; Hu, J. W.; Xiao, H.; Su, X. Y.; Dong, J.; Tian, R. J.; He, Z. K.; Zou,
H. F. J. Sep. Sci. 2005, 28, 751-756.
640 Analytical Chemistry, Vol. 79, No. 2, January 15, 2007

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purged with dry nitrogen for 15 min to remove oxygen. After the
capillary was full of the polymerization mixtures, both ends of the
capillary were plugged with silicon rubber, and then the capillary
was immersed in a water bath at 55 °C for 12 h. The obtained
MIP monolithic capillary column was washed with ACN/acetic
acid (9/1,v/v) by an HPLC pump to remove the unreacted
reagents. Finally, the prepared polymer monolith was equilibrated
with the running buffer prior to using.
Table 1. Conditions for Preparation of L-THP Imprinted
Polymer Derivatized Silica Monolithic Columns for
Enantioseparation of Racemic THP
amount (mmol)
ACN
T
time perme-
col template MAA EDMA TRIM (mL) (°C) (min) abilitya
1
2
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.4
0.4
0.4
0.4
0.4
0.4
0.4
0.4
0.4
0.4
0
0
0.20
0.20
0.20
0.20
0.20
0.25
0.25
0.25
0.25
0.25
0.2
55
55
55
60
60
55
55
55
60
60
55
55
60
50
low
0
low
3
0
40
good
good
low
good
good
low
good
low
good
low
Instruments and Methods. Electrochromatographic experi-
ments were performed on an Agilent CE system (Hewlett-Packard,
Waldbronn, Germany) equipped with a UV detector. Data were
acquired and processed with ChemStation software. The electro-
lytes composed of ACN with varying concentrations of acetate
buffer were filtered before use. For a silica-based monolithic
column, a detection window was prepared by removing ∼4 mm
of the protecting polymer layer at 8.5 cm from one end of the
capillary. For the organic monolithic column, a detection window
was created by burning out a 2-3-mm segment of the outer
polyimide coating at 8.5 cm from the outlet end of the capillary.
The monolithic capillary column (total length, 33 cm) was placed
in the instrument and equilibrated by applying a voltage of 10 kV
until the baseline signal was stabilized. A pressure of 3 bar was
applied to both inlet and outlet vials simultaneously if not
otherwise stated. The samples were degassed by sonication and
injected electrokinetically by applying a voltage of 5 kV for 4 s in
CEC. The temperature was kept at 25 °C, and the detection
wavelength was set at 214 nm. The resolution is calculated from
the equation Rs ) 2(t2 - t1)/(w1 + w2), where t1 and t2 are the
retention times of the first and second eluted enantiomers,
respectively, and w1 and w2 are the baseline peak widths of the
first and second eluted enantiomers, respectively.
cLC experiments were performed on an Agilent 1100 LC
system (Hewlett-Packard) equipped with a micropump and a UV
detector. The flow rate of pump was set at 60-200 µL/min. For
obtaining a flow rate of nanoliters per minute, a T-union connector
was used to serve as a splitter, with one end connected to the
monolithic column and one end connected to a blank capillary
(50-µm i.d.). The actual flow rate in the monolithic column was
100-400 nL/min, resulting in split ratios from 500:1 to 800:1. A
10-cm-long bare capillary was used to load the samples. After
∼0.44 µL of sample solution was injected into this capillary, the
capillary was connected between the micropump and T-union. So
the sample was also split before injecting into column. The
detection wavelength was set at 214 nm.
4
0
30
5
0
40
6
0
70
7
0
80
8
0
90
9
0
40
10
11
12
0
50
0.2
0.2
150
180
0
0.2
a Permeability represents whether the mobile phase could flow
through the prepared monolithic columns.
outlet solution was 7.0. After subsequent flushing with methanol
for 10 min, it was dried by passage of nitrogen gas in oven. The
solution of γ-MAPS in methanol (1/1, v/v) was injected into the
capillary with a syringe. It was then kept at 40 °C overnight after
both ends were sealed with rubber. Finally, the capillary was
rinsed with methanol and water successively to flush out the
residual reagents and dried again.
The template (L-THP), functional monomer (MAA), cross-
linker (EDMA), and initiator (AIBN) were dissolved in solvent
(ACN) to form a homogeneous solution, in the compositions as
indicated in Table 1, which was sonicated for 10 min and purged
with dry nitrogen for 15 min to remove oxygen. Then the capillary
was filled with the polymerization mixtures. After both ends of
the capillary were plugged with silicon rubber, the polymerization
was initiated thermally by immersing the capillary in a GC oven
at 55 or 60 °C for a few minutes. Then the unreacted mixture
was flushed out by a nitrogen stream with a pressure of 3 bar,
and the remainder of the reagents were further polymerized and
shrunk into a film coating at 55 or 60 °C. The prepared MIP-
derivatized silica monolithic capillary column was washed with
ACN/acetic acid (9/1, v/v) by an HPLC pump to remove the
template molecule and unreacted monomers. Finally, the capillary
with MIP stationary phase was equilibrated with the running buffer
before use.
Scanning electronic microscopic (SEM) images were obtained
by using a JEOL JSM-5600 scanning elctron microscope.
The S-TB imprinted polymer derivatized silica monolith was
prepared according to the procedures described above.
Preparation of
illary Column. The
was also prepared according to the procedures previously re-
ported.31 In brief, the capillary was first immobilized with γ-MAPS
to provide anchoring sites for the polymer and then dried after
being rinsed with methanol and water successively to flush out
L
-THP-Imprinted Organic Monolithic Cap-
RESULTS AND DISCUSSION
L
-THP-imprinted organic monolithic column
Preparation of MIP-Derivatized Silica Monolithic Capil-
lary Column. A silica monolithic capillary column has been
successfully prepared and characterized previously.29 The obtained
silica monolith has the morphology of a continuous skeleton and
large through-pores. For acquiring a stable MIP-derivatized onto
silica monolith, vinylation of the surface of silica monolithic column
must be performed by reaction of silanols and γ-MAPS. Thus,
the MIP can be chemically anchored with the silica monolith by
copolymerization.
the residual reagents. The template (L-THP), functional monomer
(MAA), cross-linker (EDMA), and initiator (AIBN) were dissolved
in porogenic solvents (toluene and dodecanol) to form a homo-
geneous solution. The solution was sonicated for 10 min and
In our case, two basic enantiomers, L-THP and S-TB, were
selected as the imprinted molecules, respectively, which have been
(31) Ou, J. J.; Dong, J.; Tian, R. J.; Hu, J. W.; Ye, M. L.; Zou, H. F. J. Biochem.
Biophys. Methods. In press.
Analytical Chemistry, Vol. 79, No. 2, January 15, 2007 641

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the model analytes for enantioseparation of THP and TB on an
MIP organic monolith by CEC. Likewise, MAA and EDMA/TRIM
were used as functional monomer and cross-linker, respectively.
Although it was reported that ACN was not the best solvent
(porogen) for synthesis of a MIP coating in an open-tubular
capillary by Schweitz,22 in the present work, ACN was still selected
as the solvent/porogen because of its good solubility for a large
number of polar template molecules and its wide use as a
component of electrolyte buffers. As the selectivity and flow-
through property of a monolithic MIP column are very important
in CEC, preparation conditions such as the concentration of
monomers, temperature, and time of polymerization need to be
optimized.
A series of MIP-derivatized silica monolithic columns were
prepared according to the conditions shown in Table 1. The results
indicate that the polymerization temperature and time play very
important roles in the preparation. The flow-through property of
the columns prepared by polymerization at high temperature or
long time would become low. Capillary column (col 1) was
prepared with the polymerization time of 60 min at 55 °C. Even
after applying a pressure of 20 MPa with an HPLC pump, the
column was still in the occluded state and no solvent was flowing
through the column. As the time of polymerization was decreased
to 40 min, the remaining solution in the column (col 3) could be
flushed out by a nitrogen stream. After then, this column would
be used for CEC evaluation. However, further decreasing tem-
perature or time of polymerization led to a reduction of the number
of imprinting sites and resulted in a decrease of selectivity. The
monolith (col 4) prepared by polymerizing at 60 °C for 30 min
also exhibited a good flow-through property. However, both
selectivity factor and resolution for THP obtained on col 4 by CEC
were lower than those on col 3. The result can be explained by
the low temperature of polymerization enhancing the imprinting.
At low temperature, the complex compounds formed by functional
monomer and template molecules in the prepolymerization solu-
tion can be more stable.21
Figure 3. SEM photographs of (A) native silica monolith, (B) MIP-
derivatized silica monolith, and (C) MIP organic monolith.
functional monomer and S-TB, as well as the polymerization
temperature and time. The optimum preparation conditions were
polymerized at 55 °C for 60 min by using 0.025 mmol of S-TB,
0.01 mmol of MAA, and 0.4mmol of EDMA dissolved in 0.20 mL
of ACN.
The effect of amount of solvent (porogen) and another cross-
linker, TRIM, on the preparation was also investigated. As
indicated in Table 1, when the amount of ACN was increased,
the column (col 7) could still have flow-through even though the
polymerization time was extended to 80 min. As the cross-linker
EDMA was substituted by TRIM, the polymerization time was
Characterization of MIP-Derivatized Silica Monolithic
Column. Figure 3A illustrates the SEM photograph of native silica
monolithic column with a diameter of 75 µm. It can be seen that
the silica monolith has medium pores of ∼2 µm and is well linked
to the inner wall of the capillary.29 The denser sol-gel skeleton
not only decreases the mass-transfer resistance from mobile phase
to stationary phase but also increases the surface area of
monolithic material. Compared with the SEM photograph of the
MIP-derivatized silica column shown in Figure 3B, the amount of
mesopores and macropores was decreased, but the skeleton still
existed. Because of the organic MIP derivatized onto the surface
of the silica monolith, the image observed from the radial direction
of the capillary with a microscope became obscure. Additionally,
the morphology of this composite monolith is different from the
particulate structure of an MIP organic monolith, whose SEM
photograph can be seen in Figure 3C. The through-pores of the
organic monolith were also obvious.
extended to 150 min (col 11), but the recognition ability for L-THP
was not increased as the selectivity factor and resolution obtained
on col 11 were lower that those on col 3. Considering both
preparation time and selectivity, the preparation conditions for
col 3 were selected as the optimal conditions.
The relative standard deviation (RSD) for the EOF and
retention times of analytes were less that 2.2% (n ) 3), which
meant good stability of the prepared MIP-derivatized silica
monolithic column. Additionally, both column-to-column and
batch-to-batch reproducibilities for the preparation of a monolithic
column were also evaluated in term of the RSDs for the EOF and
retention times of analytes, and the RSDs were less than 4.7 (n )
3) and 6.3% (n ) 3), respectively. These results indicated that the
prepared monolithic capillary could be easily reproduced.
Similarly, the S-TB imprinted polymer derivatized silica mono-
lithic column was also obtained by changing the molar ratio of
Figure 4A shows the migration times of thiourea and toluene
on the vinyl-derivatized silica monolithic column under CEC by
642 Analytical Chemistry, Vol. 79, No. 2, January 15, 2007