Preparation of a β-cyclodextrin-based open-tubular capillary electrochromatography column and application for enantioseparations of ten basic drugs

Article abstract of DOI:10.1371/journal.pone.0146292

An open-tubular capillary electrochromatography column was prepared by chemically immobilized β-cyclodextrin modified gold nanoparticles onto new surface with the pre-derivatization of (3-mercaptopropyl)-trimethoxysilane. The synthesized nanoparticles and the prepared column were characterized by transmission electron microscopy, scanning electron microscopy, infrared spectroscopy and ultraviolet visible spectroscopy. When the column was employed as the chiral stationary phase, no enantioselectivity was observed for ten model basic drugs. So β-cyclodextrin was added to the background electrolyte as chiral additive to expect a possible synergistic effect occurring and resulting in a better separation. Fortunately, significant improvement in enantioselectivity was obtained for ten pairs of drug enantiomers. Then, the effects of β-cyclodextrin concentration and background electrolyte pH on the chiral separation were investigated. With the developed separation mode, all the enantiomers (except for venlafaxine) were baseline separated in resolutions of 4.49, 1.68, 1.88, 1.57, 2.52, 2.33, 3.24, 1.63 and 3.90 for zopiclone, chlorphenamine maleate, brompheniramine maleate, dioxopromethazine hydrochloride, carvedilol, homatropine hydrobromide, homatropine methylbromide, venlafaxine, sibutramine hydrochloride and terbutaline sulfate, respectively. Further, the possible separation mechanism involved was discussed.

Full text of DOI:10.1371/journal.pone.0146292

RESEARCH ARTICLE
Preparation of a β-Cyclodextrin-Based Open-
Tubular Capillary Electrochromatography
Column and Application for
Enantioseparations of Ten Basic Drugs
Linlin Fang, Jia Yu, Zhen Jiang, Xingjie Guo*
Department of Pharmaceutical Analysis, School of Pharmacy, Shenyang Pharmaceutical University, Ministry
of Education, Shenyang, Liaoning Province, P. R. China
*
syykdx410@163.com
Abstract
An open-tubular capillary electrochromatography column was prepared by chemically
immobilized β-cyclodextrin modified gold nanoparticles onto new surface with the prederi-
vatization of (3-mercaptopropyl)-trimethoxysilane. The synthesized nanoparticles and the
prepared column were characterized by transmission electron microscopy, scanning elec-
tron microscopy, infrared spectroscopy and ultraviolet visible spectroscopy. When the col-
umn was employed as the chiral stationary phase, no enantioselectivity was observed for
ten model basic drugs. So β-cyclodextrin was added to the background electrolyte as chiral
additive to expect a possible synergistic effect occurring and resulting in a better separation.
Fortunately, significant improvement in enantioselectivity was obtained for ten pairs of drug
enantiomers. Then, the effects of β-cyclodextrin concentration and background electrolyte
pH on the chiral separation were investigated. With the developed separation mode, all the
enantiomers (except for venlafaxine) were baseline separated in resolutions of 4.49, 1.68,
OPEN ACCESS
Citation: Fang L, Yu J, Jiang Z, Guo X (2016)
Preparation of a β-Cyclodextrin-Based Open-Tubular
Capillary Electrochromatography Column and
Application for Enantioseparations of Ten Basic
Drugs. PLoS ONE 11(1): e0146292. doi:10.1371/
journal.pone.0146292
Editor: Jonghoon Choi, Hanyang University,
REPUBLIC OF KOREA
Received: August 17, 2015
Accepted: December 14, 2015
Published: January 15, 2016
1
.88, 1.57, 2.52, 2.33, 3.24, 1.63 and 3.90 for zopiclone, chlorphenamine maleate, brom-
pheniramine maleate, dioxopromethazine hydrochloride, carvedilol, homatropine hydrobro-
mide, homatropine methylbromide, venlafaxine, sibutramine hydrochloride and terbutaline
sulfate, respectively. Further, the possible separation mechanism involved was discussed.
Copyright: © 2016 Fang et al. This is an open
access article distributed under the terms of the
Creative Commons Attribution License, which permits
unrestricted use, distribution, and reproduction in any
medium, provided the original author and source are
credited.
Data Availability Statement: All relevant data are
within the paper.
Introduction
The development of chiral separation methods increased vastly during the past decades for the
fact that enantiomers have different biological, physiological and pharmacological behaviors
on human body. Usually, only eutomer has the desired effect, whereas the uneutomer has
unwanted effects such as side effects or toxic effecs [1–3]. In order to separate racemic mix-
tures, various analytical methods have been developed for chiral separation including HPLC
Funding: This work was supported by the National
Natural Science Foundation of China (No.81473178).
The funders had no role in study design, data
collection and analysis, decision to publish, or
preparation of the manuscript.
[4–5], GC [6–7] and CE [8–10]. Recently, capillary electrochromatography (CEC), which
Competing Interests: The authors have declared
that no competing interests exist.
exploits both the high efficiency of CE and the high selectivity of liquid chromatography
PLOS ONE | DOI:10.1371/journal.pone.0146292 January 15, 2016
1 / 11

β-CD-GNPs Modified Column and Its Application on Enantioseparation
stationary phase, emerged as a fairly novel enantiomeric separation technique [11–12]. In gen-
eral, CEC experiments can be performed with particle packed capillaries, monolithic capillary
columns, and open-tubular capillaries (OT-CEC) [13]. In the case of OT-CEC, the chiral selec-
tor is coated onto the inner wall of the capillary as stationary phase. OT-CEC is viewed as a
promising approach to avoid various problems associated with packed column CEC, such as
the difficulties of end-frit fabrication and obtaining uniformly packed columns. Its evident dis-
advantage, however, is the low separation capability that arises from the low phase ratio on the
limited surface area [14–17].
Recently, the use of gold nanoparticles as supports in OT-CEC has aroused the interest of
analytical chemists because the gold nanoparticles have larger surface area to enhance the
phase ratio [18–20]. O’mahony et al prepared OT-CEC by immobilisation of dodecanethiol
gold nanoparticles on prederivatised fused-silica capillaries and applied the columns to sepa-
rate pyrethroid pesticides [21]. Liu and co-workers described the preparation of OT-CEC col-
umns through the self-assembly of alkanethiols onto AuNP-coated capillaries and investigated
their use for the separation of neutral steroid drugs [22]. Besides, β-cyclodextrin-modified
GNPs were immobilized onto the inner wall of the fused-silica capillaries and applied as special
stationary phases for OT-CEC to separate polyaromatic hydrocarbons and three drug enantio-
mers [23].
Herein, we first present the preparation of an OT-CEC column by chemically immobilized
β-cyclodextrin modified gold nanoparticles (β-CD-GNPs) onto new surface of prederivatised
fused-silica capillary. Then, the work was focused on the combined use of the chiral OT-CEC
column and β-CD as background electrolyte (BGE) additive in CEC for the enantiomeric sepa-
rations of (1) zopiclone, (2) chlorphenamine maleate, (3) brompheniramine maleate, (4) diox-
opromethazine hydrochloride, (5) carvedilol, (6) homatropine hydrobromide, (7)
homatropine methylbromide, (8) venlafaxine, (9) sibutramine hydrochloride and (10) terbuta-
line sulfate. The chemical structures of the 10 chiral analytes are shown in Fig 1. The influences
of BGE pH and the concentration of β-CD additive on the enantioseparation efficiency were
examined. Finally, the possible separation mechanism was discussed.
Materials and Methods
Materials
(RS)-Zopiclone, (RS)-chlorphenamine maleate, (RS)-dioxopromethazine hydrochloride, (RS)-
carvedilol, (RS)-homatropine hydrobromide, (RS)-homatropine methylbromide, (RS)-venla-
faxine, (RS)-sibutramine hydrochloride and (RS)-terbutaline sulfate were purchased from the
National Institute for the Control of Pharmaceutical and Biological Products (Beijing, China).
(RS)-brompheniramine maleate was obtained from Sigma Chemical Co. (St. Louis, MO, USA).
β-Cyclodextrin (β-CD) was purchased from Bodi Chemical Holding Co., Ltd. (Tianjin, China).
β-CD-SH was obtained from Shandong Binzhou Zhiyuan Bio-technology Co., Ltd. (Shandong,
China). Potassium tetrachloroaurate (III) and (3-mercaptopropyl) trimethoxysilane (MPTMS)
were purchased from Shanghai Energy Technology Co., Ltd. (Shanghai, China). Analytical
grade sodium hydroxide, phosphoric acid and thiourea were obtained from Shenyang Chemi-
cal Regent Factory Co., Ltd. (Shenyang, China). Trisodium citrate dihydrate and tris (hydroxy-
methyl) aminomethane (Tris) were supplied by Bodi Chemical Holding Co., Ltd. (Tianjin,
China).
Apparatus
All analyses were performed on an HPCE apparatus (CL1030, Beijing Huayang Limin Instru-
mental Co., Beijing, China), equipped with a power supply, a HW-2000 chromatography
PLOS ONE | DOI:10.1371/journal.pone.0146292 January 15, 2016
2 / 11

β-CD-GNPs Modified Column and Its Application on Enantioseparation
Fig 1. The chemical structures of the ten chiral analytes.
doi:10.1371/journal.pone.0146292.g001
workstation and a UV-visible detector. The uncoated fused-silica capillary column (Yongnian
Ruifeng Chromatographic Device Co. Ltd, Hebei, China) with a total length of 49 cm (effective
length 40 cm to detector) × 50 μm i.d. was used for modification. A modified fused-silica capil-
lary column was used for separations throughout the experiments. UV-visible (UV) and FT-IR
(
IR) spectra of the synthesised GNPs were recorded with a Shimadzu UV-2201 scanning elec-
tron microscopy (SEM) and FT-IR Spectrometer Paragon 1000, respectively. Transmission
electron microscopy (TEM) was performed using a JEM 1200 EX TEMSCAN, and SEM pic-
tures of capillaries were obtained using a Hitachi S4000 SEM microscope. The oven used for
modifying the capillary was a component of a gas chromatograph 7890A series (Agilent Tech-
nologies, Santa Clara, CA, USA).
Each day, the modified capillary was rinsed successively with 0.1mol/L NaOH for 15 min,
water for 10 min, and running BGE for 10 min. Between each injection, it was purged with
0
.1mol/L NaOH for 2 min, water for 2 min, running BGE for 2 min. An applied voltage 20 kV
PLOS ONE | DOI:10.1371/journal.pone.0146292 January 15, 2016
3 / 11

β-CD-GNPs Modified Column and Its Application on Enantioseparation
Fig 2. (A) TEM micrograph of gold nanoparticles dispersed in hexane, on a carbon film 400-mesh
copper grid; (B) Visible absorption spectrum of gold nanoparticles dispersed in hexane. λmax = 519
nm.
doi:10.1371/journal.pone.0146292.g002
was used for optimization of the resolution during the separation. Samples were injected into
the capillary by hydrodynamic flow at a height differential of 10 cm for 5s. Thiourea was used
as a neutral marker to determine the electroosmotic flow (EOF).
A concentration of 25 mM Tris-H PO was used as BGE buffer and the desired pH was
3
4
adjusted with 1.0 mol/L H PO . Sample stock solutions were prepared in methanol at 1.0
3
4
mg/mL and were stored in a refrigerator. The stock solutions were further diluted into 0.1
mg/mL with distilled water. All the solutions were filtered with a pore size of 0.22 μm filter
membranes.
Preparation of OT-CEC column
Prior to prepare OT-CEC column, the gold nanoparticles was synthesized according to to pub-
lished procedure [24]. The synthesized GNPs dispersed in hexane were characterized by TEM
and UV-visible spectroscopy (Fig 2A and 2B), respectively. The TEM image (200 kV × 120.0 K
magnification) showed the dispersed phase of the GNPs in hexane consisted of spherical particles
with an average size of 13 nm (2–3 nm size range). The UV-Vis spectrum of GNPs exhibited
plasmon resonance absorption at 519 nm which further confirmed their nanoparticles diameter.
The preparation of capillary column coated with a monolayer of β-CD-GNPs was proposed
by a method described by O’Mahony [21] with some modification. A capillary column of 49
PLOS ONE | DOI:10.1371/journal.pone.0146292 January 15, 2016
4 / 11

β-CD-GNPs Modified Column and Its Application on Enantioseparation
cm in length was firstly placed in the Beckman P/ACE MDQ capillary electrophoresis system
(
1
Fullerton, CA, USA) and then washed by 1.0 M of NaOH under a pressure rinsing (20 psi) for
h at 25°C followed by deionized water for 10 min. Upon rinsing with acetone for 30 min, the
capillary column was dried in the oven under nitrogen at 60°C for 2 h. After removing acetone,
MPTMS solution prepared in ethanol(1%) was then pumped (20 psi) through the capillary
under 25°C for 1 h and allowed it to stand overnight. The capillary column was sealed and
annealed at 100°C in the oven for 24 h. The synthesized GNPs solution (in water) was pumped
(
20 psi) through the column at 25°C for 1 h and left to stand for 1 h. The excess GNPs were
removed from the capillary with distilled water. Then, the capillary column was flushed with
ethanol at 20 psi for 1 h and then allowed to stand for 1 h. After that, a solution of 2 mg/mL of
β-CD-SH in 50% ethanol solution was pumped through the capillary column for 1 h at 25°C by
the pressure of 20 psi and then left to stand for 1 h. Finally, the excess β-CD-SH solution was
removed from the capillary column by pumping with 50% ethanol and then flushing with
ethanol.
To investigate whether the β-CD-GNPs have been successfully attached onto the capillary,
the typical transmission FT-IR spectrums of SH-β-CD and β-CD-GNPs modified OT-CEC
-
1
column were compared. As shown in Fig 3A and 3B, strong peaks at 3300–3500 cm
and
νOH)
(
-
1
2
920 cm
are attributed to the O-H and C-H stretching vibrations of CD. The typical and
νCH)
(
-
1
weak S-H stretching band at 2500–2600 cm shown in Fig 3A preliminary proved the presence
of β-CD-SH, while this peak disappeared in the event of the formation of Au-S bond described
in Fig 3B. To further prove the existence of β-CD-GNPs etched to the bare capillary, the SEM
image of bare capillary shown in Fig 3C (5 kV × 1.0 K magnification) and etched β-CD-GNPs
capillary shown in Fig 3D (5 kV × 50.0 K magnification) were also determined. Fig 3C showed
a smooth capillary wall, yet a rough capillary wall was obtained in Fig 3D, indicating that the
coverage of β-CD-GNPs on the column wall is quite extensive. The above results guarantee
that β-CD-GNPs have been successfully attached onto the surface of capillary column.
EOF flow is the main driving force in capillary electrophoresis. In the present study, we
investigated the EOF value of the bare capillary in the varied pH from 3.0 to 6.0 (other condi-
tons: 25 mM Tris-H PO buffer solution, 20 kV). From Fig 4(A), it can be seen that EOF
3
4
mobility of bare capillary increase greatly with the increase of pH from 3.0 to 6.0 which is gen-
erated by electrical double layer on the inner surface determined by its surface charge density.
Meanwhile, as shown in Fig 4(B), under the same buffer conditions, β-CD-GNPs based capil-
lary displays a similar mobility profile to that of an untreated capillary and as expected the μeo
values of the modified capillary was lower than the bare capillary due to silanol blocking.
Results and Discussion
Enantioseparation of ten basic drugs
In our preliminary work, the separation conditions of the 10 drug enantiomers, zopiclone,
chlorphenamine maleate, brompheniramine maleate, dioxopromethazine hydrochloride, car-
vedilol, homatropine hydrobromide, homatropine methylbromide, venlafaxine, sibutramine
hydrochloride and terbutaline sulfate were optimized on the OT-CEC column. Tris-H PO
3
4
buffer with concentration of 25 mM and pH varying from 2.0 to 3.0 was used as the running
buffer. It was found that the migration time of all analytes decreased as the pH increased,
mainly due to increased electroosmotic mobility (EOF). However, no chiral recognition was
observed for any of the studied basic analytes. In order to improve the efficiency of separation,
β-CD (5.0 mM) was added to the BGE as chiral additive. As expected, significantly improve-
ment in enanotiomeric separation was achieved. In this case, the effects of BGE pH and added
CD concentration on the enantioseparation were studied.
PLOS ONE | DOI:10.1371/journal.pone.0146292 January 15, 2016
5 / 11

β-CD-GNPs Modified Column and Its Application on Enantioseparation
Fig 3. FT-IR spectra of (A) free SH-β-CD and (B) β-CD-GNPs based capillary; SEM photographs of (C)
bare capillary and (D) etched β-CD-GNPs capillary.
doi:10.1371/journal.pone.0146292.g003
PLOS ONE | DOI:10.1371/journal.pone.0146292 January 15, 2016
6 / 11

β-CD-GNPs Modified Column and Its Application on Enantioseparation
3 4
Fig 4. The effect of pH on the EOF mobility. BGE: pH 2.5, 25 mM Tris-H PO buffer solution, 20kV. (a)
blank capillary; (b) β-CD-GNPs based capillary. OTCEC conditions: 49 cm × 50 μm i.d., Sample: thiourea,
Separation voltage, 20 kV.
doi:10.1371/journal.pone.0146292.g004
The effect of the BGE pH on the enantioseparation was investigated over the range of 2.0–
3
.0 using 25 mM Tris-H PO buffer containing 5.0 mM β-CD at an applied voltage of 20 kV.
3 4
As can be seen in Fig 5A, the chiral resolutions of studied drugs apparently increased with
increasing the pH range from 2.0 to 2.5, then decreased at a pH 3.0 (except for sibutramine
hydrochloride). This decreased resolution might be due to the decreased interaction opportu-
nity between chiral selector and analyte resulting from the enhancement of EOF at pH 3.0.
Therefore, pH 2.5 was chosen as the optimized pH value for the chiral separation of the studied
drugs (for sibutramine hydrochloride, pH 2.0 was selected).
To investigate the influence of the β-CD concentration on the resolutions of the ten drugs,
the concentration of β-CD was varied from 3.0 to 10.0 mM when the other conditions were as
follows: 25 mM Tris-H PO buffer at pH 2.5 (sibutramine hydrochloride, pH 2.0) and opera-
3
4
tion voltage of 20 kV. Fig 5B demonstrates the Rs values of the ten analytes at each CD concen-
tration. An increase in Rs for most drug enantiomers was observed from 3.0 mM to 5.0 mM
β-CD concentration due to an increase of the interactions between β-CD and analytes. How-
ever, when the concentration of CD became larger than 5 mM, the Rs of these enantiomers
decreased obviously. It seemed that the analytes were probably fully complexed at CD concen-
tration of 5 mM, and a further increase in concentration had negative effects on Rs.
In summary, the optimal BGE for the separation of the analytes was 25 mM Tris-H PO
3
4
and 5 mM β-CD at pH 2.5 (sibutramine hchloride, pH 2.0) at a voltage of 20 kV. Under such
separation conditions, all the analytes (except for venlafaxine) were baseline separated (Fig
6
B). For zopiclone, chlorphenamine maleate, brompheniramine maleate, dioxopromethazine
hydrochloride, carvedilol, homatropine hydrobromide, homatropine methylbromide, venla-
faxine, sibutramine hydrochloride and terbutaline sulfate, the separation resolutions (averaged
over three runs) were: 4.49, 1.68, 1.88, 1.57, 2.52, 2.33, 3.24, 1.48, 1.63, 3.90, respectively. The
electrochromatograms obtained under optimized separation conditions are shown in Fig 6B.
To test the run-to-run reproducibility, six consecutive separations of two pairs of the drug
enantiomers (zopiclone and homatropine methylbromide) were performed. The RSDs of the
retention time was lower than 2.5% for two drug enantiomers. The reproducibility of the three
PLOS ONE | DOI:10.1371/journal.pone.0146292 January 15, 2016
7 / 11

β-CD-GNPs Modified Column and Its Application on Enantioseparation
S
Fig 5. Effect of pH (A) and β-CD concentration (B) on R of the 10 chiral analytes (1) zopiclone, (2)
chlorphenamine maleate, (3) brompheniramine maleate, (4) dioxopromethazine hydrochloride, (5)
carvedilol, (6) homatropine hydrobromide, (7) homatropine methylbromide, (8) venlafaxine, (9)
sibutramine hydrochloride and (10) terbutaline sulfate.
doi:10.1371/journal.pone.0146292.g005
freshly prepared chiral OT-CEC columns was also investigated in terms of retention time with
zopiclone as model solute. The RSD of the retention time was lower than 4.3%, indicating good
column to column reproducibility of three chiral column. In addition, these capillaries
appeared to be stable for up to one month when not in use and stored in distilled H O.
2
BGE (A): 5 mM β-CD, 25 mM Tris-H PO , 20 kV; BGE (B): pH 2.5 (sibutramine hydro-
3
4
chloride, pH 2.0), 25 mM Tris-H PO , 20 kV.
3
4
Discussion of separation mechanism
As mentioned above, when only OT-CEC column was utilized in the enantioseparation of the
ten chiral drugs, no resolution was observed. However, OT-CEC column accompanying with a
BGE containing β-CD could enantioseparate the ten chiral drugs very well. Fig 6(A) shows the
electrophorogram of separation of the ten drug enantiomers when β-CD was used as chiral
addictive by capillary zone electrophoresis. Under our opitimized separation conditons, nine
pairs of drug enantiomers were partially enantioseparated, with the Rs values of 0.78, 1.16,
1
.30, 1.28, 1.12, 1.21, 0.76, 0.92, 1.10 for zopiclone, chlorphenamine maleate, brompheniramine
maleate, dioxopromethazine hydrochloride, carvedilol, homatropine hydrobromide, venlafax-
ine, sibutramine hydrochloride and terbutaline sulfate, respectively. Only homatropine
PLOS ONE | DOI:10.1371/journal.pone.0146292 January 15, 2016
8 / 11

β-CD-GNPs Modified Column and Its Application on Enantioseparation
Fig 6. Typical electropherograms of the 10 chiral analytes on (A) bare capillary and (B) etched
capillary. BGE: 20 kV, (A) 10 mM β-CD, pH 2.5, 30 mM Tris-H
3 4
PO , (B) 5 mM β-CD, pH 2.5 (sibutramine
hydrochloride, pH 2.0), 25 mM Tris-H PO . (the numbers of the drugs are the same as in Fig 5).
3 4
doi:10.1371/journal.pone.0146292.g006
methylbromide was baseline resolved with Rs of 1.97. Compared with Fig 6(A) and seen in Fig
(B), it can be seen obviously that when an OT-CEC column was utilized, the resolution of all
6
the 10 chiral drugs was improved greatly from partial separation to complete separation, indi-
cating that the CD on the OT-CEC column had a greater contribution in enantioseparation of
the 10 chiral drugs. It was thus clear that there was a synergistic effect between β-CD in BGE
and on the OT-CEC column for the enantioseparation. Fig 7 illustrates the enantioseparation
mechanism by OT-CEC column. The analyte enantiomers could interact with the CD on the
chiral column. If the R-enantiomer had a greater affinity with the CD on the column, the
migration time of the R-enantiomer should be longer than the S-enantiomer. At the same time,
if the R-enantiomer had a greater affinity with the CD in the BGE, the electrophoretic mobility
of the R-enantiomer should be smaller due to its smaller mass charge ratio, resulting in a longer
migration time of R-enantiomer. Therefore, the synergistic effect occurred and improved the
separation efficiency.
Conclusions
In this paper, we described the development of a novel chiral OT-CEC column, which was pre-
pared by the chemically immobilized β-CD-GNPs on prederivatised MPTMS capillary. Suc-
cessful enantioseparation of ten racemic drugs was achieved on the CEC column by combining
the use β-CD as BGE additive. Comparing to the results obtained in capillary electrophoresis
with a comparable amount of β-CD as chiral selector alone, we got the enhancement of enan-
tioseparation of ten drug enantiomers by using β-CD modified OT-CEC column in capillary
electrochromatography. The study demonstrated that there was a synergistic effect between
β-CD in BGE and on the OT-CEC column for the enantioseparation.
PLOS ONE | DOI:10.1371/journal.pone.0146292 January 15, 2016
9 / 11

β-CD-GNPs Modified Column and Its Application on Enantioseparation
Fig 7. Illustration of chiral separation of positively charged analytes on β-CD-GNPs modified
capillary.
doi:10.1371/journal.pone.0146292.g007
Acknowledgments
This work was supported by the National Natural Science Foundation of China
(
No.81473178).
Author Contributions
Conceived and designed the experiments: LLF. Performed the experiments: LLF. Analyzed the
data: LLF JY. Contributed reagents/materials/analysis tools: ZJ XJG. Wrote the paper: LLF JY
XJG.
References
1.
Ammazzalorso A, A Moroso R, Bettoni G, Chiarini M, Filippis BD, Fantacuzzi M, et al. Enantiomeric
separation of gemfi brozil chiral analogues by capillary electrophoresis with heptakis(2,3,6-tri-O-
methyl)-β-cyclodextrin as chiral selector. Journal Chromatogr A. 2005; 1088:110–120.
2.
3.
4.
Mišl’anová C, Hutta M. Role of biological matrices during the analysis of chiral drugs by liquid chroma-
tography. Journal Chromatogr B. 2003; 797: 91–109.
Gübitz G, Schmid MG. Chiral separation by capillary electromigration techniques. J Chromatogr A.
2008; 1204: 140–156. doi: 10.1016/j.chroma.2008.07.071 PMID: 18706565
Wille K, De Brabander HF, DeWulf E, Van Caeter P, Janssen CR, Vanhaecke L. Coupled chro-
matographic and mass-spectrometric techniques for the analysis of emerging pollutants in the aquatic
environment. Trac-Trend Anal Chem. 2012; 35: 87–108.
5.
6.
7.
8.
9.
Mathys K, Brenneisen R. Determination of (S)-(-)-cathinone and its metabolites (R,S)-(-)-norephedrine
and (R,R)-(-)-norpseudoephedrine in urine by high-performance liquid chromatography with photodi-
ode-array detection. J Chromatogr. A. 1992; 593: 79–85.
LeBelle MJ, Savard C, Dawson BA, Black DB, Katyal LK, Zrcek F, et al. Chiral identification and deter-
mination of ephedrine, pseudoephedrine, methamphetamine and metecathinone by gas chromatogra-
phy and nuclear magnetic resonance. Forensic Sci. Int. 1995; 71: 215–223. PMID: 7713461
Davis BA, Durden DA, Boulton AA. Plasma concentrations of p-and m-hydroxyphenylacetic acid and
phenylacetic acid in humans: Gas chromatographic-high-resolution mass spectrometric analysis. J.
Chromatogr. B. 2008; 875: 102–107.
Zhao M, Cui Y, Yu J, Xu S, Guo X. Combined use of hydroxypropyl-β-cyc lodextrin and ionic liquids for
the simultaneous enantioseparation of four azole antifungals by CE and a study of the synergistic
effect. J Sep Sci. 2014; 37: 151–157. doi: 10.1002/jssc.201300831 PMID: 24170554
Yu J, Liang X, Wang Z, Guo X, Sun T, Guo X. Separation of Folinic Acid Diastereomers in Capillary
Electrophoresis Using a New Cationic β-Cyclodextrin Derivative. Plos one. 2015; doi: 10.1371/journal.
pone.0120216
PLOS ONE | DOI:10.1371/journal.pone.0146292 January 15, 2016
10 / 11

β-CD-GNPs Modified Column and Its Application on Enantioseparation
10. Scriba GKE. Cyclodextrins in capillary electrophoresis enantioseparations recent developments and
applications. J Pharm Biomed Anal. 2008; 27: 373–399.
11. Mangelings D, Heyden YV. Enantioselective capillary electrochromatography: Recent developments
and new trends. Electrophoresis. 2011; 32: 2583–2601. doi: 10.1002/elps.201100009 PMID:
21910129
1
2. Aturki ZG. Schmid M, Chankvetadze B, Fanali S. Enantiomeric separation of new cathinone derivatives
designer drugs by capillary electrochromatography using a chiral stationary phase, based on amylose
tris(5-chloro-2-methylpheny lcarbamate). Electrophoresis. 2014; 35: 3242–3249. doi: 10.1002/elps.
201400085 PMID: 24854346
1
1
1
3. Xue Y, Gu X, Wang Y, Yan C. Recent advances on capillary columns, detectors, and two-dimensional
separations in capillary electrochromatography. Electrophoresis. 2015; 36: 124–134. doi: 10.1002/
elps.201400312 PMID: 25223262
4. Cheong WJ, Ali F, Kim YS, Lee JW. Comprehensive overview of recent preparation and application
trends of various open tubular capillary columns in separation science. J Chromatogr. A. 2013; 1308:
1
–24. doi: 10.1016/j.chroma.2013.07.107 PMID: 23948434
5. Liu Z, Otsuka K, Terabe S, Motokawa M, Tanaka N. Physically adsorbed chiral stationary phase of avi-
din on monolithic silica column for capillary electrochromatography and capillary liquid chromatogra-
phy. Electrophoresis. 2003; 24: 3917–3934.
16. Kapnissi-Christodoulou CP, Zhu XF, Warner IM. Analytical separations in open-tubular capillary elec-
trochromatography. Electrophoresis. 2003; 24: 3917–3934. PMID: 14661227
1
7. Matyska MT, Pesek JJ, Boysen RI, Hearn MTW. Electrochromatographic characterization of etched
chemically-modified capillaries with small synthetic peptides. J Chromatogr. A. 2001; 924: 211–221.
PMID: 11521867
1
1
2
2
2
8. Yang L, Guihen E, Holmes JD. Loughran M, O’Sullivan GP, Glennon JD. Gold Nanoparticle-Modified
Etched Capillaries for Open-Tubular Capillary Electrochromatography. Anal. Chem. 2005; 77: 1840–
1846. PMID: 15762594
9. Li M, Tarawally M, Liu X, Liu XL, Guo LP, Yang L, et al. Application of cyclodextrin-modifi ed gold nano-
particles in enantioselective monolith capillary electrochromatography. Talanta. 2013; 109: 1–6. doi:
10.1016/j.talanta.2013.03.035 PMID: 23618133
0. Liang RP, Liu CM, Meng XY, Wang JW, Qiu JD. A novel open-tubular capillary electrochromatography
using β-cyclodextrin functionalized graphene oxide-magnetic nanocomposites as tunable stationary
phase. J Chromatogr. A. 2012; 1266: 95–102. doi: 10.1016/j.chroma.2012.09.101 PMID: 23107120
1. O’Mahony T, Owens VP, Murrihy JP, Guihen E, Holmes JD, Glennon JD. A lkylthiol gold nanoparticles
in open-tubular capillary electrochromatography. J Chromatogr. A. 2003; 1004: 181–193 PMID:
12929973
2. Liu FK, Hsu YT, Wu CH. Open tubular capillary electrochromatography using capillaries coated with
films of alkanethiol-self-assembled gold nanoparticle layers. J Chromatogr. A. 2005; 1083: 205–214.
PMID: 16078709
23. Yang L, Guihen E, Glennon JD. Alkylthiol gold nanoparticles in sol-gel-based open tubular capillary
electrochromatography. J. Sep. Sci. 2005; 28: 757–766 PMID: 15938184
24. Wf Haiss, Thanh NTK, Aveyard J, Fernig DG. Determination of Size and Concentration of Gold Nano-
particles from UV-Vis Spectra. Anal. Chem. 2007; 79: 4215–4221. PMID: 17458937
PLOS ONE | DOI:10.1371/journal.pone.0146292 January 15, 2016
11 / 11