Evaluation of sulfated maltodextrin as a novel anionic chiral selector for the enantioseparation of basic chiral drugs by capillary electrophoresis.

www.electrophoresis-journal.com

Page 1

Electrophoresis

Evaluation of sulfated maltodextrin as a novel anionic chiral selector for the enantioseparation of basic chiral drugs by capillary electrophoresis Hadi Tabani, Mojtaba Mahyari, Ali Sahragard, Ali Reza Fakhari, Ahmad Shaabani Department of Pure Chemistry, Faculty of Chemistry, Shahid Beheshti University, G. C., P.O. Box 19396-4716, Evin, Tehran, Iran

Keywords: Anionic chiral selector/ Capillary electrophoresis/ Enantioseparation/ Sulfatedmaltodextrin. Correspondence: Prof. Ali Reza Fakhari, Department of Pure Chemistry, Faculty of Chemistry, Shahid Beheshti University, G. C., P.O. Box 19396-4716, Evin, Tehran, Iran. Tel & Fax: +98 (21) 22431661 E-mail: [email protected] (A.R. Fakhari) Abbreviations:

BGE,

background

electrolyte;

DE,

dextrose

equivalent;

EOF,

electroosmotic flow, FT-IR, Fourier transform infrared; MD, maltodextrin; XPS, X-ray photoelectron spectroscopy

Received: 26-Jul-2014; Revised: 02-Sep-2014; Accepted: 19-Sep-2014 This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1002/elps.201400370. This article is protected by copyright. All rights reserved.


Page 2

Electrophoresis

Abstract Introducing a new class of chiral selectors is an interesting work and this issue is still one of the hot topics in separation science and chirality. In this study, for the first time, sulfatedmaltodextrin (MD) was synthesized as a new anionic chiral selector and then it was successfully applied for the enantioseparation of five basic drugs (amlodipine, hydroxyzine, fluoxetine, tolterodine, and tramadol) as model chiral compounds using capillary electrophoresis (CE). This chiral selector has two recognition sites: a helical structure and a sulfated group which contribute to three corresponding driving forces; inclusion complexation, electrostatic interaction and hydrogen binding. Under the optimized condition (buffer solution: 50 mM phosphate (pH 3.0) and 2% (w/v) sulfated-MD; applied voltage: 18 kV; temperature: 20C), baseline enantioseparation was observed for all mentioned chiral drugs. When instead of sulfated-MD neutral MD was used under the same condition, no enantioseparation was observed which means the resolution power of sulfated-MD is higher than MD due to the electrostatic interaction between sulfated groups and protonated chiral drugs. Also, the counter current mobility of negatively charged MD (sulfated-MD) allows more interactions between the chiral selector and chiral drugs and this in turn, results in a successful resolution for the enantiomers. Furthermore, a higher concentration of neutral MD (~five times) is necessary to achieve the equivalent resolution comparing with the negatively charged MD.

This article is protected by copyright. All rights reserved.


Page 3

Electrophoresis

1 Introduction The separation of enantiomers has received a great deal of attention, specifically in pharmaceutical industry. Since chiral drugs are commonly administered as racemic mixtures, and each enantiomer often exhibits different pharmacological effects, it is of great interest to develop new analytical methods for chiral analysis. A broad range of enantioselective analysis methods has been developed applying different methodologies. Chromatographic methods such as gas chromatography (GC) [1, 2], high-performance liquid chromatography (HPLC)

[3-5],

supercritical

fluid

chromatography

(SFC)

[6-8],

and

thin-layer

chromatography (TLC) [9, 10] have been developed using different chiral separation principles. Capillary electrophoresis (CE) [11-13] has shown its capability to be a powerful alternative to the chromatographic methods. Typically enantiomeric separation by CE is achieved using a bare capillary tube (without any special column), with high resolutions and relatively fast runs. On the other hand, an extremely small amount of sample and media are required for the CE technique [14-16]. Separating enantiomers by CE is typically accomplished by exploiting stereospecific interactions between chiral analytes and chiral selector that has been introduced into the background electrolyte. The separation of two enantiomers can take place if there is a difference in the binding or the stability constant (K) of each enantiomer with the chiral selector as well as a difference between the mobility of free analyte and its complex [17]. Maltodextrins (MDs) are complex malto-oligo and polysaccharide mixtures obtained from partial acidic and/or enzymatic hydrolysis of starch [18]. They are characterized by their dextrose equivalent (DE), which is the equivalent for the degree of malto-oligo saccharides polymerization. D’Hulst and Verbeke first introduced MDs to the CE enantiomer separation in 1992 [19]. They further investigated the enantiomer separation of three coumarinic



Page 4

Electrophoresis

anticoagulant drugs and two chlorinated derivatives employing MD with DE 2 [20]. An extensive study of the chiral selector MD with DE 2 was also performed [21]. The effect of various parameters such as pH of BGE, concentration of the BGE, etc. on the enantioseparation was evaluated by the same group [22]. Soini et al. used a range of MDs (Dextrin 10, Dextrin 15 and Dextrin 20) to separate four acidic drugs and three basic drugs [23]. High molecular mass dextrins (ca. 3700 to >10 000) were employed by Nishi et al. for the enantiomer separations of more than 40 drugs, including both acidic and basic drugs [24]. Different interactions between the chiral solutes and the helical structure of MD emerge as the basis of their enantioselectivity [25]. The change in conformation from a flexible coil to a helix in the presence of chiral analytes and buffer salts play an important role in selective interactions leading to enantioresolution [22, 26]. The helical structure has a hydrophobic inside, much like the cavity of CDs, but MDs represent a considerably more flexible entity than CDs, leading to less restriction toward a steric approach of an interacting solute [23]. The formation of a helical structure supported by additional interactions, such as hydrogen bonds and dipole-dipole interactions is assumed to be responsible for chiral recognition [2731]. Although neutral chiral selectors such as cyclodextrin (CD) and MD are the ones most frequently used, several reports have demonstrated the advantages of negatively charged chiral selectors such as sulfated-CDs [32], dextran sulfate [33], and heparin [34]. Tait et al. explained that the use of a negatively charged chiral selector effectively increases the “separation window”, as the maximum opportunity for separation may exist when the analyte and chiral selector migrate in opposite directions [35]. It has been established that charged chiral selectors can display superior enantioselectivity in comparison with the neutral ones in most cases [36]. This may be due to the fact that charged chiral selectors can offer not only an inclusion complexation interaction, but also strong electrostatic interactions. Also, based



Page 5

Electrophoresis

on Wren and Rowe equation, apparent mobility difference between the two enantiomers will be greatest when the mobility of the analyte-chiral selector complex is in the opposite direction to that of the analyte itself. This suggests that chiral selectors which carry a charge opposite to that on the analyte will be useful [37]. Furthermore, neutral chiral compounds can be resolved by CE using charged chiral selectors. Consequently, in this work, we decided to evaluate sulfated-MD as a novel anionic chiral selector for the enantiomeric separation of five basic chiral drugs (amlodipine (AML), hydroxyzine (HCZ), fluoxetine (FLU), tolterodine (TOL), and tramadol (TRA)) as model chiral compounds (Fig. 1). The main parameters affecting the resolution such as pH of the background electrolyte (BGE), the chiral selector concentration, cartridge temperature, and the applied voltage were optimized. Finally, MD as a neutral chiral selector was employed for the enantioseparation of these chiral model drugs and the results were compared with the obtained resolutions from sulfated-MD.

2 Experimental 2.1 Materials and chemicals AML, FLU, TOL and HCZ drugs were obtained from Tofigh Daru Company (Tehran, Iran) and were used without further purification. Pure trans-TRA was purchased from Grünenthal (Stolberg, Germany). Hydrochloric acid, sodium hydroxide, chloroform, methanol, chlorosulfonic acid, phosphoric acid, Na2HPO4, and NaH2PO4.2H2O salts were purchased from Merck (Darmstadt, Germany). MD with DE (4-7) was purchased from Fluka (Buchs, Switzerland). All solutions were prepared using HPLC grade water which was obtained from a Milli-Q system (Millipore Milford, MA, USA). To prevent capillary



Page 6

Electrophoresis

blockage, all buffers and sample solutions were filtered through 0.45 µm filter membranes (Millipore, Bedford, MA, USA). 2.2 Apparatus X-ray photoelectron spectroscopy (XPS) analysis was performed using a VG multilab 2000 spectrometer (Thermo VG scientific) in an ultra high vacuum medium. The elemental analysis (CHNS) was performed on a Thermo Finnigan Flash EA112 elemental analyzer (Okehampton, UK). The Fourier transform infrared (FT-IR) measurements were carried out using a Bomem MB-Series FT-IR spectrometer in the form of KBr pellets. A digital pH meter, WTW Metrohm 827 Ion analyzer (Herisau, Switzerland), equipped with a combined glass calomel electrode was used for pH adjustments at 25±1 °C temperature. All CE experiments were carried out using a Lumex Capel 105 (Lumex Ltd., St. Petersburg, Russia) equipped with a UV detector. The electrophoretic experiments were performed in an uncoated fused-silica capillary (Lumex Ltd., St. Petersburg, Russia) 60 cm × 50 m I.D. (50 cm effective length). The CE system was operated in the conventional mode with the anode at the injector end of the capillary (normal polarity). Prior to use, the capillary was conditioned for 5 min with 0.5 M HCl, 5 min with water, 5 min with 0.5 M NaOH and 5 min with water. Additionally, the capillary was washed for 2 min with 0.5 M NaOH, 2 min with water and 2 min with the BGE before each run with positive pressure applied at the injection end. Acquisition of the electropherograms was computer-controlled by a Chrom & Spec software version 1.5. The analytes were injected at the anodic end by applying a pressure of 60 mbar for 5 seconds. 2.3 Preparation of sulfated-MD Chlorosulfonic acid (1.00 g, 9 mmol) was added dropwise to a magnetically stirred mixture of MD (1.00 g) in CHCl3 (20 mL), at 0oC during 2 h. When the addition of chlorosulfonic acid was completed, the mixture was evaporated for 2 h until HCl was



Page 7

Electrophoresis

removed from the reaction vessel. Then, the mixture was filtered and washed with methanol (10 mL) and dried at room temperature to obtain sulfated-MD in the form of a white powder. Sulfur content in sulfated-MD samples was found to be 1.9 mmol g-1 by conventional elemental analysis. The number of H+ sites on MD-SO3H determined by an acid–base titration was 1.8 meq g-1 [38,39].

3. Results and discussion 3.1 Characterization of sulfated-MD The synthesized sulfated-MD was characterized via elemental analysis (CHNS), FT-IR and XPS and the resulting figures are shown in the following. One of the most powerful techniques in order to verify the functionalization of MD with sulfonic acid groups, is XPS analysis (Fig. 2). Sulfated-MD has a C (1s) peak at 285.3 eV and an O (1s) peak which is appeared at 532.5 eV. XPS is also well suited for identifying sulfated groups covalently bonded to MD. The peak which was appeared at 168.9 eV is related to S (2p3/2) in SO3- groups on the synthesized sulfated-MD [40,]. In order to confirm the synthesis of sulfated-MD, the atomic percent of carbon, hydrogen, and sulfur were monitored using elemental analysis (CHNS). The atomic percent of these elements in sulfated-MD were found to be: (% found); C (42.16 %), H (6.15 %), and S (6.07 %), which confirms the successful covalent binding of SO3H groups on MD. FT-IR spectra of MD and sulfated-MD are given in Fig. 3A and B, respectively. The spectrum of MD shows bands around 2924 cm-1 (ν C-H, aliphatic) and 3425 cm-1 (ν O-H). The results obtained from Fig. 3B shows that functionalizing MD with sulfated groups has been successfully accomplished. The absorption band at 3458 cm-1 can be attributed to O-H



Page 8

Electrophoresis

stretching vibrations. The bands at 1120 cm-1 and 1005 cm-1 (O=S=O stretching in SO3H) in the FT-IR spectrum indicate that MD possesses sulfated groups. 3.2 Method development and optimization using sulfated-MD as a chiral selector In this work, sulfated-MD as an inexpensive and efficient chiral selector was used for the enantioseparation of five basic drugs (HCZ, AML, FLU, TOL, TRA) as model chiral compounds in CE. Different interaction between enantiomers and the helical structure of the synthesized sulfated-MD emerges as the basis of its enantioselectivity. Changing the conformation from a flexible coil to a helix in the presence of chiral analytes and buffer salts may play an important role in selective interactions. The helical structure of MD mimics the cavity responsible for chiral recognition by cyclodextrins [23]. In addition, the resolving power of sulfated-MD could be considered as a consequence of the electrostatic interactions between the sulfated-MD and the oppositely charged solutes. To obtain the optimum enantioseparation, effective experimental parameters such as the pH value of the BGE, chiral selector concentration, capillary column temperature and applied voltage were optimized. Within the course of optimization, one of the mentioned parameters was varied while the others were kept constant. The BGE pH value is one of the most important parameters in CE analysis due to its effect on the electroosmotic flow (EOF) and ionization state of the analyte. Sulfated-MD is negatively charged over the entire pH range and therefore moves in the opposite direction of the electroosmotic flow. Considering pKa values of the mentioned drugs (Fig. 1), all analytes contain a positively charged moiety (protonated amine groups) under acidic pH condition and consequently move in the opposite direction of the chiral selector. This counter current movement enhances the enantiomeric separation window which in turn, results in remarkably good resolutions. The effect of BGE pH on the migration time and resolution were investigated, using a solution of 50 mM phosphate buffer containing 2% sulfated-MD within



Page 9

Electrophoresis

the pH range of 2.0–5.0 (Table 1). The resolution and migration time of the enantiomers increased with a decrease in pH value, which is due to a decrease in the velocity of EOF. However at pH 2.0, no peak was appeared within 60 min for HCZ and AML. It seems that the electrostatic interaction between these drugs and sulfated-MD is strong enough to prevent them coming out of the capillary column and also EOF is very slow at this pH value. HCZ and AML longer migration time seems quite reasonable because, presumably, these drugs are dication so their electrostatic interaction with sulfated-MD is stronger than that of TOL, FLU and TRA. Therefore, a buffer with a higher pH value, in which the electroosmotic flow is high enough to push the chiral selector- drug complex toward the detector, was selected. In order to obtain a rational resolution and migration time, buffer solution with pH 3.0 was used in the following experiments. The concentration of sulfated-MD is another important parameter affecting the enantiomeric separation. In the range of investigated concentrations, 0.5–3.0% (w/v), migration times and resolution values of the chiral drugs increased with increasing sulfated-MD concentration. The results are shown in Fig.4. The higher MD concentrations introduce more interaction sites for chiral drugs that results in better separation of the enantiomers and their longer migration times. Although the increase of viscosity due to the addition of sulfated-MD leads to a decrease in the velocity of EOF, the observed increase in the migration times can be interpreted mainly by the ionic interactions. Maximum resolution was obtained at 2% (w/v) for AML and HCZ, while for TRA, TOL and FLU maximum resolution was obtained at 2.5% (w/v). The different maximum resolution values can come from their interaction energy and affinity different between the analyte and analyte-chiral selector complex [37]. With a higher concentration of the chiral selector, longer times were required for the enantioseparation of chiral drugs. In addition, the solute peaks were broadened. Therefore, the optimum chiral selector concentration was chosen to be 2% (w/v) for all chiral drugs.



Page 10

Electrophoresis

The cartridge temperature can also affect the EOF and the electrophoretic flow by causing a change in the viscosity of the BGE. Several temperatures in the range of 15-30 °C were examined in order to find the optimum temperature at which a good resolution is obtained in a reasonable migration time. Increasing the temperature from 15 to 30°C, decreases both the migration time and the resolution due to the shorter time which is required for essential interactions. Chiral recognition between enantiomer and chiral selectors is generally resulted from the formation of inclusion complex and this process is greatly influenced by temperature. The chemical interaction between enantiomer and chiral selectors is most likely to be an exothermic process and low temperature generally favors its enantioseparation by improving its enantioselectivities based on Van ’t Hoff equation [41, 42]. Although the best resolutions were achieved at 15°C, the temperature of 20 °C was chosen as the optimum temperature because of its shorter migration times. We also investigated the effect of the applied voltage on the migration time and resolution using a 50 mM phosphate buffer solution (pH 3.0, sulfated-MD 2% (w/v)) in the range of 15– 22 kV. A good separation for the enantiomers was obtained at all voltage levels. Considering suitable resolutions and faster migration times, the voltage of 18 kV was used in the further experiments. 3.3 Comparing the resolution power of neutral MD with sulfated-MD When electrically neutral chiral selectors are used, only ionic chiral drugs can be separated (CE mode), while with charged chiral selectors both neutral and ionic chiral compounds can also be separated. Plus the fact that, charged chiral selectors have higher resolution power than the neutral ones, due to their good interactions with analytes such as electrostatic interaction. Thus, MD as a neutral chiral selector was applied for the enantioseparation of chiral model drugs and the results were compared with the obtained resolutions from sulfated-MD. When



Page 11

Electrophoresis

enantioseparation was applied in the same condition as of sulfated-MD (buffer solution: 50 mM phosphate (pH 3.0, 2% (w/v) MD); applied voltage 18 kV and 20C temperature) no enantioseparation was observed. Increasing the MD concentration up to 10% (w/v), baseline enantioseparation was achieved for HCZ and AML, while partial enantioseparation was obtained for TOL, TRA, and FLU. Figure 5 shows the electropherograms of these chiral drugs in the presence of MD (10% (w/v)) and sulfated-MD (2% (w/v)). Thus, the results showed that sulfated-MD as a charged chiral selector exhibits higher resolution power than MD which is a neutral chiral selector. Also, migration times in the presence of sulfated-MD are longer, confirming stronger interactions between the chiral selector and enantiomers. For example, the migration time of AML in the presence of 2% (w/v) sulfated-MD was 37.4 min while in the presence of 10% (w/v) MD the value of this parameter was 21.8 min (Figure 5). 4 Concluding remarks The present work was designed to evaluate sulfated-MD as a novel anionic chiral selector using CE for its several attributes, good resolution power, characteristic structure (allowing multiple interactions with analytes) and cost-effectiveness. The presence of sulfate groups on MD not only enhances its aqueous solubility but also confers considerable electrophoretic mobility, which is then exploited to achieve better enantiomeric separations. Under acidic conditions, basic drugs are positively charged and thus, intrinsically migrate toward the cathode. On the other hand, sulfated-MD is also charged and migrates towards the anode. These opposite inherent mobilities enhance the differences in enantiomer binding, making sulfated-MD more capable to resolve the enantiomers of these drugs. The enhanced resolving power of sulfated-MD could also be caused by the electrostatic interaction between sulfated-MD and the oppositely charged solutes. The results showed that sulfated-MD as a charged chiral selector has higher resolution power than MD which is a neutral chiral selector. Stronger interactions, as evidenced by longer migration times, were observed



Page 12

Electrophoresis

between sulfated-MD and chiral drugs in comparison with the interactions between the neutral MD and chiral drugs. In future, sulfated-MD will be a new candidate for the chiral separation of basic and neutral analytes due to its electrostatic interaction and also its helical structure. Furthermore, using sulfated-MD as a chiral selector, this method can be considered as an inexpensive alternative for the previous CE methods which are mainly based on sulfated-CDs as chiral selectors.

Acknowledgements Financial support from the Research Affairs of Shahid Beheshti University is gratefully acknowledged.

5 References [1] Nolin, T.D., Frye, R.F., J. Chromatogr. B 2003, 783, 265-271. [2] Juvancz, Z., Markides, K.E., Petersson, P., Johnson, D.F., Bradshaw, J.S., Lee, M.L., J. Chromatogr. A 2002, 982, 119-126. [3] Matarashvili, I., Chankvetadze, L., Fanali, S., Farkas, T., Chankvetadze, B., J. Sep. Sci. 2013, 36, 140-147. [4] Gubitz, G., Schmid, M.G., Biopharm. Drug Dispos. 2001, 22, 291-336. [5] Gasparrini, F., Misiti, D., Villani, C., J. Chromatogr. A 2001, 906, 35-50. [6] Garzotti, M., Hamdan, M., J. Chromatogr. B 2002, 770, 53-61. [7] Toribio, L., Bernal, J.L., delNozal, M.J., Jimenez, J.J., Nieto, E.M., J. Chromatogr.A 2001, 921, 305-313. This article is protected by copyright. All rights reserved.


Page 13

Electrophoresis

[8] Terfloth, G., J. Chromatogr. A 2001, 906, 301-307. [9] Armstrong, D.W., Faulkner, J.R., Han, S.M., J. Chromatogr. A 1988, 452, 323-330. [10] Aboul-Enein, H.Y., El-Awady, M.I., Heard, C.M., Nicholls, P.J., Biomed. Chromatogr. 1999, 13, 531-537. [11] Fakhari, A.R., Tabani, H., Nojavan, S., Abedi, H., Electrophoresis 2012, 33, 506-515. [12] Zakaria, P., Macka, M., Haddad, P.R., J. Chromatogr. A 2004, 1031, 179-186. [13] Lomsadze, K., Vega, E.D., Salgado, A., Crego, A.L., Scriba, G.K.E., Marina, M.L., Chankvetadze, B., Electrophoresis 2012, 33, 1637-1647. [14] Nishi, H., Terabe, S., J. Chromatogr. A 1995, 694, 245-276. [15] Fanali, S., J. Chromatogr. A 1996, 735, 77-121. [16] Nishi, H., J. Chromatogr. A 1997, 792, 327-332. [17] Gratz, S.R., Stalcup, A.M., Anal. Chem. 1998, 70, 5166-5171. [18] Chankvetadze, B., Lindner, W., Scriba, G.K.E., Anal. Chem. 2004, 76, 4256-4260. [19] D'Hulst, A., Verbeke. N., J. Chromatogr. 1992, 608, 275-287. [20] D'Hulst, A., Verbeke. N., Chirality 1994, 6, 225-229. [21] D'Hulst, A., Verbeke. N., J. Chromatogr. A 1996, 735, 283-293. [22] D'Hulst, A., Verbeke N., Electrophoresis 1994, 15, 854-863. [23] Soini, H., Stefansson, M., Riekkola, M.L., Novotny, M., Anal. Chem. 1994, 66, 34773284. [24] Nishi, H., Izumoto, S., Nakamura, K., Nakai, H., Sato, T., Chromatographia 1996, 42, 617-630. [25] Rundle, R.J., Am. Chem. Soc. 1944, 66, 2116-2120. [26] D'Hulst, A., Verbeke, N., Enantiomer 1997, 2, 69-79. [27] Nishi, H., J. Chromatogr. A 1997, 792, 327-332. [28] Mikus, F.F., Hixon, R.M., Rundle, R.E., J. Am. Chem. Soc. 1946, 68, 1115-1123.



Page 14

Electrophoresis

[29] Aoyama, Y., Otsuki, J., Nagai, Y., Kobayashi, K., Toi, H., Tetrahedron Lett. 1992, 33, 3775-3778. [30] Fakhari, A.R., Tabani, H., Behdad, H., Nojavan, S., Taghizadeh, M., Microchemical J. 2013, 106, 186-193. [31] Jane, J.L., Robyt, J.F., Huang, D.H., Carbohydr. Res. 1985, 140, 21-35. [32] Gahm, K., Stalcup, A., Chirality 1996, 8, 316-324. [33] Agyei, N., Gahm, K., Stalcup, A., Anal. Chim. Acta 1995, 307, 185-191. [34] Stalcup, A., Agyei, N., Anal. Chem. 1994, 66, 3054-3059. [35] Tait, R., Thompson, D., Stella, V., Stobaugh, J., Anal. Chem. 1994, 66, 4013-4018. [36] Gübitz, G., Schmid, M.G., Electrophoresis 2000, 21, 4112-4135. [37] Wren, S.A.C., Rowe, R.C., J. Chromatogr. 1992, 603, 235-241 [38] Shabani, A., Maleki, A., Appl. Catal. A 2007, 331, 149-151. [39] Safari, J., Banitaba, S.H., Khalili, S.D., J. Mol. Catal. A: Chem. 2011, 335, 46-50. [40] Chronakis, I.S., Crit. Rev. Food Sci. 1998, 38, 599-637. [41] Fulde, K., Frahm, A.W., J. Chromatogr. A 1999, 858, 33-43. [42] Tong, S., Zhang, H., Shen, M., Ito, Y., Yan J., J. Chromatogr. B, 2014, 962, 44-51.



Page 15

Fig. 1. Chemical structures of basic chiral drugs.


Electrophoresis


Page 16

Fig. 2. XPS spectrum of sulfated-MD.


Electrophoresis


Page 17

Fig. 3. FT-IR spectra of A) MD and B) sulfated-MD.


Electrophoresis


Page 18

Electrophoresis

Fig.4. The effect of sulfated-MD concentration on the resolution of the basic chiral drugs.



Page 19

Electrophoresis

Fig.5. Electropherograms of the basic chiral drugs in the presence of 2% (w/v) sulfated-MD and 10% (w/v) MD. Experimental conditions: capillary column: 60 cm (50 cm effective length) × 50 μm I.D.; detection: 214 nm; applied voltage: 18 kV; injection: 60 mbar × 5s; separation solution: 50 mM phosphate (pH 3.0).



Page 20


Electrophoresis


Page 21

Electrophoresis

Table 1 Analytes

pH 2.0 t1

t2

pH 3.0 Rs

t1

t2

pH 4.0 Rs

t1

t2

pH 5.0 Rs

t1

t2

Rs

HCZ

-

-

-

41.77 42.83 1.84

28.35 28.86 1.53

20.81 21.04 0.88

AML

-

-

-

37.47 38.29 1.81

30.14 30.56 1.60

23.62 23.82 1.06

TRA

30.45 31.30 2.34

22.47 22.9

1.96

16.12 16.47 1.77

12.85 13.06 1.48

TOL

40.48 41.66 1.76

28.28 28.74 1.58

22.46 22.78 1.14

15.83 15.95 1.02

FLU

27.50 28.05 1.86

21.02 21.32 1.57

15.14 15.19 1.09

12.11 12.18 0.76

The effects of BGE pH on the migration times (t1, min) and resolutions (Rs) of chiral drugs enantiomers.


Clarithromycin as a chiral selector for enantioseparation of basic compounds in nonaqueous capillary electrophoresis.

Penicillin G as a novel chiral selector in capillary electrophoresis.

Application of maltodextrin as chiral selector in capillary electrophoresis for quantification of amlodipine enantiomers in commercial tablets.

Study on clarithromycin lactobionate based dual selector systems for the enantioseparation of basic drugs in capillary electrophoresis.

Tetramethylammonium-lactobionate: A novel ionic liquid chiral selector based on saccharides in capillary electrophoresis.

A comprehensive study of the enantioseparation of chiral drugs by cyclodextrin using capillary electrophoresis combined with theoretical approaches.

Octaproline, a conformationally flexible chiral selector in liquid chromatographic enantioseparation.

Quantitative prediction of enantioseparation using β-cyclodextrin derivatives as chiral selectors in capillary electrophoresis.

Molecular modeling study of the recognition mechanism and enantioseparation of 4-hydroxypropranolol by capillary electrophoresis using carboxymethyl-β-cyclodextrin as the chiral selector.

Maltodextrins as chiral selectors in CE: molecular structure effect of basic chiral compounds on the enantioseparation.

Chiral separation by capillary electrophoresis with oligosaccharides.

Evaluation of ionic liquids-coated carbon nanotubes modified chiral separation system with chondroitin sulfate E as chiral selector in capillary electrophoresis.

Enhancement of enantioselectivity in chiral capillary electrophoresis using hydroxypropyl-beta-cyclodextrin as chiral selector under molecular crowding conditions induced by dextran or dextrin.

Establishment and Evaluation of the Novel Tetramethylammonium-L-Hydroxyproline Chiral Ionic Liquid Synergistic System Based on Clindamycin Phosphate for Enantioseparation by Capillary Electrophoresis.

Application of cyclodextrins in chiral capillary electrophoresis.

Chiral separations of basic drugs and quantitation of bupivacaine enantiomers in serum by capillary electrophoresis with modified cyclodextrin buffers.

Cationic permethylated 6-monoamino-6-monodeoxy-β-cyclodextrin as chiral selector of dansylated amino acids in capillary electrophoresis.

Enantio-separation of drugs with multiple chiral centers by chromatography and capillary electrophoresis.

Investigation of chondroitin sulfate D and chondroitin sulfate E as novel chiral selectors in capillary electrophoresis.

Synthesis of novel chiral imidazolium stationary phases and their enantioseparation evaluation by high-performance liquid chromatography.

Enantioseparation performance of novel benzimido-β-cyclodextrins derivatized by ionic liquids as chiral stationary phases.

Chiral separation of four stereoisomers of ketoconazole drugs using capillary electrophoresis.

Enantioseparation of benzofurys and other novel psychoactive compounds by CE and sulfobutylether β-cyclodextrin as chiral selector added to the BGE.

Evaluation of the chiral separation ability of single-isomer cationic β-cyclodextrins in capillary electrophoresis.