Study of the enantioseparation of imazaquin and enantioselective degradation in field soils by CZE

A fast, simple, and sensitive CE method was developed to study the separation and degradation of imazaquin enantiomers in field soils. The parameters pH and concentration of the buffer electrolyte, type and concentration of the chiral selectors, applied voltage, and temperature of the CE system were investigated. Sodium hydrogen phosphate (50 mM) at pH 10.1 containing 30 mM hydroxypropyl-beta-CD (HP-beta-CD) was found to be the suitable BGE. The reliable determination for imazaquin enantiomers was obtained at 20 kV applied voltage, 15 degrees C separation system, and detection at 214 nm. Under the optimal conditions, the LODs (S/N = 3) were 0.0097 and 0.0098 mg/kg; linearity ranged from 0.019 to 1.24 and 0.020 to 1.26 mg/kg for the first-eluting peak of imazaquin (imazaquin-I) and the second-eluting peak of imazaquin (imazaquin-II) in soil, respectively. The precision in terms of the percentage of RSD (%RSD) calculated from peak area was not greater than 5%. With the suitable characteristics of the present method, it was applied to the study of enantioselective degradation in field soil. According to the calculated values of the enantiomer ratio (ER) and the rate constant of degradation (k), the results suggested that the degradation rate of the two enantiomers were slightly different, and that the pH of the soil had a strong influence on the rate of degradation.     

CE coupling with end-column electrochemiluminescence detection for chiral separation of disopyramide

CE with electrochemiluminescence (ECL) detection technique was successfully applied for the chiral separation of a kind of class IA antiarrhythmic racemic drug. To the best of our knowledge, this is the first report of ECL detection used in chiral CE. To get better detection sensitivity and good enantioresolution at the same time, the conditions of capillary inlet and outlet buffer were systematically optimized. Unlike the traditional chiral separation method, the buffers we used in the capillary inlet and outlet differed from each other in terms of buffer pH, ionic strength, type of BGE as well as buffer composition. Under the optimum conditions, baseline enantioseparation and highly sensitive detection of the enantiomers were achieved. Wide linear relationship of each enantiomer was achieved in the range of 5 x 10(-7) to 2 x 10(-5) mol/L with relative coefficients of 0.996 and 0.997, respectively. The detection limits were estimated to be 8 x 10(-8) and 1.0 x 10(-7) mol/L (S/N = 3) for the enantiomers, respectively. In addition, a successful application of this new method to the chiral separation of the racemic drug in spiked plasma samples confirmed the validity and applicability of the chiral CE-ECL method.     

Chiral separation and quantitation of cetirizine and hydroxyzine by maltodextrin-mediated CE in human plasma: effect of zwitterionic property of cetirizine on enantioseparation

In the present study, a very simple CE method for chiral separation and quantitation of zwitterionic cetirizine (CTZ), as the main metabolite of hydroxyzine (HZ), and HZ has been developed. In addition, the effect of zwitterionic property of CTZ on enantioseparation was investigated. Maltodextrin, a linear polysaccharide, as a chiral selector was used and several parameters affecting the separation such as pH of BGE, concentration of chiral selector and applied voltage were studied. The best BGE conditions for CTZ and HZ enantiomers were optimized as 75 mM sodium phosphate solution at pH of 2.0, containing 5% w/v maltodextrin. Results showed that, compared to HZ, pH of BGE was an effective parameter in enantioseparation of CTZ due to the zwitterionic property of CTZ. The linear range of the method was over 30-1200 ng/mL for all enantiomers of CTZ and HZ. The quantification and detection limits (S/N=3) of all enantiomers were 30 and 10 ng/mL, respectively. The method was used to quantitative enantioseparation of CTZ and HZ in spiked human plasma.     

Coupling of acetonitrile deproteinization and salting-out extraction with acetonitrile stacking in chiral capillary electrophoresis for the determination of warfarin enantiomers

Concurrent sample clean-up and enhancement in detection sensitivity for chiral capillary electrophoresis was demonstrated based on the coupling of salting-out extraction with acetonitrile stacking and the use of dimethyl-beta-cyclodextrin as the chiral selector for the sensitive and enantioselective separation of warfarin enantiomers in urine samples. By optimizing the pH of salting-out extraction, warfarin enantiomers can be efficiently extracted from the aqueous sample solution into a smaller volume organic solvent (acetonitrile) phase. The pressure injection of the enriched acetonitrile phase (containing ca. 1% NaCl) into the CE capillary at 10% capillary volume resulted in additional concentration of the warfarin enantiomers. The limit of detection for both warfarin enantiomers was as low as 1.5 ng/mL in urine sample. Our results show that the novel strategy offers improved sensitivity compared to conventional CE analysis, reaching a combined enrichment factor higher than 1000. Calibration curves of warfarin enantiomers in urine samples were found to be linear between 10 and 1000 ng/mL, and intra- and inter-day precision (N=9) for both warfarin enantiomers in terms of migration time and peak area were found to be within the range of 0.1-0.8% and 1.0-6.7%, respectively. The recovery of warfarin enantiomers from urine was ca. 90%.     

Separation of aminoalkanephosphonic acid enantiomers by indirect UV detection capillary electrophoresis with application of cyclodextrins

Indirect UV detection capillary electrophoresis (CE) was used for the separation of aminoalkanephosphonic acid (AP) enantiomers by applying commercially available cyclodextrins as chiral discriminators. The results show that the separation of the enantiomers depends on pH of the background electrolyte, the molar ratio of cyclodextrin to aminophosphonic acid, and on the type of the applied chiral selector. Optimization of process conditions allowed enantiomeric baseline separation or partial separation of 12 out of 14 alpha-aminophosphonic acids studied. This type of CE might therefore be successfully used for routine determination of enantiomeric purity of aminophosphonic acids.     

直链淀粉-三[(S)-1-苯乙基氨基甲酸酯]手性固定相拆分布地奈德对映体及其制剂含量的测定

22R-布地奈德的药物活性比22S-布地奈德的强2~3倍,开发布地奈德对映体拆分和定量分析方法,可为其药物研发及质量控制提供重要依据。目前,主要以反相C₁₈固定相对布地奈德对映体进行拆分,而采用手性固定相对其进行拆分少有报道。通过考察固定相、流动相和柱温对布地奈德对映体拆分的影响,建立了基于直链淀粉-三[(S)-1-苯乙基氨基甲酸酯]手性固定相快速拆分和检测布地奈德对映体的高效液相色谱方法,其色谱条件如下:色谱柱为Chiralpak AS-RH色谱柱(150 mm×4.6 mm, 5.0 μm),流动相为乙腈-水(45∶55, v/v),柱温40 ℃,流速1.0 mL/min,二极管阵列检测器(DAD),检测波长246 nm,进样量10 μL。在该色谱条件下,布地奈德的两个对映体得到较好拆分,22R-布地奈德和22S-布地奈德的保留时间分别6.40 min和7.77 min,分离度为4.64; 22R-布地奈德和22S-布地奈德分别在各自范围内线性关系良好,相关系数(R²)均为0.9999,检出限分别为0.05 μg/mL和0.07 μg/mL,定量限分别为0.16 μg/mL和0.20 μg/mL; 4个添加水平的样品加标回收率为102.63%~104.17%,相对标准偏差(RSD)为0.08%~0.57%(n=6)。将该方法应用于1批次4个吸入用布地奈德混悬液实际样品进行检测,22R-布地奈德和22S-布地奈德的含量分别为283.15~284.63 μg/mL和259.86~261.51 μg/mL。该方法操作简便,分析时间短,重复性好,准确度高,可用于布地奈德对映体的拆分及其制剂的质量控制。     

Enatiomeric analysis of simendan by CE with beta-CD as chiral selector compared with CMPA-HPLC

The chiral separation of simendan enantiomers using capillary electrophoresis was studied with beta-cyclodextrin (beta-CD) as chiral selector. The influences of the concentration and pH of borate buffer solution, beta-CD concentration and methanol content in the background electrolyte were investigated. These factors were compared with those in an HPLC with beta-CD as chiral mobile phase additive (CMPA-HPLC). The quantification properties of the developed CE method were examined. A baseline separation of simendan enantiomers was achieved in the background electrolyte of 20 mmol/L borate buffer (pH 11.0) containing 12 mmol/L beta-CD-methanol (50:50 in volume ratio). The CE method is comparable with CMPA-HPLC in chiral resolution, although the optimal pH in CE (11.0) is much higher than that (6.0) in CMPA-HPLC. This chiral CE method is applicable to the quantitative ananlysis and enantiomeric excess value determination of L-simendan.     

Chiral capillary electrophoresis-mass spectrometry of tetrahydroisoquinoline-derived neurotoxins: observation of complex stereoisomerism

Previous studies have shown that certain 1,2,3,4-tetrahydroisoquinoline derivatives (TIQs) are neurotoxins inducing Parkinsonism. Further, individual enantiomers of these toxins such as (R/S)-N-methylsalsolinol ((R/S)-NMSal) possess distinct neurotoxicological properties. In this work, a chiral capillary electrophoresis (CE) method with electrospray ionization-tandem mass spectrometric (ESI-MS/MS) detection was developed for the quantification of TIQ enantiomers. Enantioseparation was achieved with sulfated β-cyclodextrin (sulfated β-CD) as chiral selector. To avoid any potential contamination of MS ionization source by the non-volatile chiral selector, partial filling technique was deployed in the CE separation. TIQ derivatives, including (R/S)-6,7-dihydroxy-1-methy-TIQ (salsolinol, Sal), (R/S)-1-benzyl-TIQ (BTIQ), and (R/S)-NMSal, were base-line resolved with resolution values (R) ranging from 3 (for Sal) to 4.5 (for BTIQ), which were much better than those reported previously by HPLC methods. ESI-MS/MS detection of the resolved TIQ enantiomers was specific and sensitive (LOD=1.2 μM for Sal enantiomers). The proposed chiral CE-MS/MS method was used to study in vitro formation of (R/S)-NMSal. It was found that NMSal was formed from the incubation of epinine (a dopamine metabolite) with acetaldehyde (a metabolite of alcohol). More interestingly, four isomers of NMSal were separated and detected in the incubation solution. They were identified as (R)-e.e-NMSal, (R)-e.a-NMSal, (S)-e.e-NMSal, and (S)-e.a-NMSal. This was the first lab evidence that this Parkinsonian neurotoxin exists in multiple isomeric forms.     

毛细管电泳-安培检测法分离分析手性药物索他洛尔

采用毛细管电泳-柱端喷壁式安培检测技术,建立了痕量手性药物索他洛尔的分离检测新方法。以1.5%(w/V)羧甲基-β-环糊精为手性选择试剂,借助于环糊精-客体包合物的拆分原理,索他洛尔对映异构体在优化的分离条件:50mmol/LTris-H3PO4缓冲液(pH5.5),分离电压21kV,进样条件18kV/10s,工作电位1150mV(vs.Ag/AgCl),可实现基线分离,线性范围为5～500μg/L;异构体Ⅰ和Ⅱ的检出限(S/N=3)分别为2.0和1.9μg/L。本方法用于模拟血清样品分析,结果令人满意。     

毛细管电泳在手性化合物分离分析中的研究进展

手性化合物的对映异构体往往表现出不同的生理活性,因此建立手性化合物的有效分离分析方法具有重要意义。毛细管电泳（CE）是一种分离效率高、分析速度快、样品用量少、分离模式灵活多样的分离分析方法,在手性化合物的分离和检测领域应用广泛。该文主要综述了2017~2019年CE在手性分离分析方面的最新进展,并对其未来的发展趋势进行了展望。     

Application of capillary electrophoresis with field-amplified sample injection for the detection of new adrenoreceptor antagonist enantiomers in plasma in the low ng/mL concentration range

Throughout the separation of chiral basic drugs by capillary electrophoresis (CE) with neutral hydroxypropyl-beta-cyclodextrin (HP-beta-CD) as chiral selector, the sensitivity of detection has been improved by using field-amplified sample injection (FASI). In the present work, this on-line stacking method has been used to detect low ng/mL levels of cationic enantiomers of a new adrenoreceptor antagonist in plasma. A systematic study of the parameters affecting on-line concentration of these enantiomers (nature of the preinjection plug, composition of sample solvent, injection times of water and sample plugs) has been performed enabling the detection sensitivity of antagonist enantiomers to be improved by 180 times compared with usual hydrodynamic injection. The quantification of each adrenoreceptor antagonist enantiomer in plasma samples was then performed in the 2-100 ng/mL (or 8-400 nM) concentration range after a solid-phase extraction step. Using this FASI-CE-UV procedure, the limit of quantification (LOQ) for each enantiomer was in the low ng/mL concentration range (3 ng/mL or 10 nM).     

Enantiomeric separation of some common controlled stimulants by capillary electrophoresis with contactless conductivity detection

CE methods with capacitively coupled contactless conductivity detection (C⁴D) were developed for the enantiomeric separation of the following stimulants: amphetamine (AP), methamphetamine (MA), ephedrine (EP), pseudoephedrine (PE), norephedrine (NE) and norpseudoephedrine (NPE). Acetic acid (pH 2.5 and 2.8) was found to be the optimal background electrolyte for the CE‐C⁴D system. The chiral selectors, carboxymethyl‐β‐cyclodextrin (CMBCD), heptakis(2,6‐di‐O‐methyl)‐β‐cyclodextrin (DMBCD) and chiral crown ether (+)‐(18‐crown‐6)‐2,3,11,12‐tetracarboxylic acid (18C6H₄), were investigated for their enantioseparation properties in the BGE. The use of either a single or a combination of two chiral selectors was chosen to obtain optimal condition of enantiomeric selectivity. Enantiomeric separation of AP and MA was achieved using the single chiral selector CMBCD and (hydroxypropyl)methyl cellulose (HPMC) as the modifier. A combination of the two chiral selectors, CMBCD and DMBCD and HPMC as the modifier, was required for enantiomeric separation of EP and PE. In addition, a combination of DMBCD and 18C6H₄ was successfully applied for the enantiomeric separation of NE and NPE. The detection limits of the enantiomers were found to be in the range of 2.3–5.7 μmol/L. Good precisions of migration time and peak area were obtained. The developed CE‐C⁴D method was successfully applied to urine samples of athletes for the identification of enantiomers of the detected stimulants.     

Direct injection analysis of ketoprofen enantiomers in plasma using column-switching high-performance liquid chromatography system

A high-performance liquid chromatography system was developed for the stereoselective determination of ketoprofen enantiomers in human plasma following direct sample injection. The system comprised of a pretreatment column and a chiral separation column connected in a series via a switching valve. When a 200 microliter portion of human plasma containing a therapeutic level of ketoprofen was directly applied to the system, ketoprofen was adsorbed in the pretreatment column, while plasma proteins were excluded. After the elution of proteins from the pretreatment column, the valve was switched and ketoprofen was desorbed and transferred to the chiral separation column where the enantiomers were separated and determined by ultraviolet-absorption. The mobile phase conditions for the pretreatment and chiral separation were optimized, which enabled rapid and complete recovery followed by satisfactory separation of the enantiomers. The calibration line for each enantiomer showed good linearity in the range of 0.25-5 micrograms/ml with a detection limit of 0.02 micrograms/ml (signal to noise ratio (S/N) greater than 3), which was sufficient for practical demands. The precision test indicated that the coefficient of variation for five repeated determinations of (-) ketoprofen was 5.4% at 0.1 microgram/ml and 1.4% at 1 microgram/ml.     

Liquid-phase microextraction combined with capillary electrophoresis,a promising tool for the determination of chiral drugs in biological matrices

A disposable device for liquid-phase microextraction (LPME) based on porous polypropylene hollow fibres has recently been introduced. In the present paper, LPME was combined with capillary electrophoresis (CE) and the combination was for the first time evaluated for chiral determination of drugs in biological matrices. The chiral antidepressant drug mianserin was selected as model compound. The mianserin enantiomers were extracted from 0.5 ml of plasma added internal standard and made alkaline with 0.25 ml of 2 M NaOH. The unionised analytes were extracted into di-n-hexyl ether impregnated in the pores of the hollow fibre, and into an acidic solution inside the hollow fibre. This resulted in a three-phase system where the extracts were aqueous, and hence directly compatible with the CE system. Efficient sample clean-up was seen and the extraction recovery was 80% for both enantiomers. Discrimination between the enantiomers in the extraction system was not observed. The limit of quantitation (S/N= 10; 12.5 ng/ml for both enantiomers) and the limit of detection (S/N=3; 4 ng/ml for both enantiomers) were below the therapeutic range for mianserin. The method was validated and successfully applied to determine R- and S-mianserin in plasma samples from seven patients treated with mianserin, indicating that LPME-CE is a promising combination for analysis of racemic drugs present in low concentrations in biological matrices.     

Fast and simultaneous detection of heavy metals using a simple and reliable microchip-electrochemistry route: An alternative approach to food analysis

This paper reports, for the first, the fast and simultaneous detection of prominent heavy metals, including: lead, cadmium and copper using microchip CE with electrochemical detection. The direct amperometric detection mode for microchip CE was successfully applied to these heavy metal ions. The influences of separation voltage, detection potential, as well as the concentration and pH value of the running buffer on the response of the detector were carefully assayed and optimized. The results clearly show that reliable analysis for lead, cadmium, and copper by the degree of electrophoretic separation occurs in less than 3min using a MES buffer (pH 7.0, 25mM) and l-histidine, with 1.2kV separation voltage and -0.8V detection potential. The detection limits for Pb(2+), Cd(2+), and Cu(2+) were 1.74, 0.73 and 0.13microM (S/N=3). The %R.S.D. of each peak current was <6% and migration times <2% for prolonged operation. To demonstrate the potential and future role of microchip CE, analytical possibilities and a new route in the raw sample analysis were presented. The results obtained allow the proposed microchip CE-ED acts as an alternative approach for metal analysis in foods.     

Efficient applications of capillary electrophoresis-tandem mass spectrometry to the analysis of adrenoreceptor antagonist enantiomers using a partial filling technique

Throughout the separation of chiral basic drugs by capillary electrophoresis (CE) with neutral hydroxypropyl-beta-cyclodextrin (HP-beta-CD) as chiral selector, the sensitivity of detection can be improved by using tandem mass spectrometric (MS-MS) detection with a partial filling technique rather than with UV spectrometric detection. Prior to sample injection. the capillary was partly filled with HP-beta-CD dissolved in volatile ammonium formate buffer (pH 4, ionic strength 50 mM). The effects of modifying the HP-beta-CD concentration in the selector zone and the length of the separation zone on the enantioresolution and the signal-to-noise ratio of the pseudo-molecular MH+ ion were investigated. For a given selector zone length, as the concentration of the neutral cyclodextrin increases, the resolution between enantiomers becomes higher (the opposite of the behavior of the signal-to-noise ratio) and then reaches an optimum value. The decrease of the selector zone length lowered the resolution between the enantiomers but increased peak efficiencies and signal-to-noise ratio values. Accordingly, partial capillary filling at 80% (v/v) and 10 mM concentration of HP-beta-CD was selected as a suitable compromise between resolution and sensitivity of MS detection. Limits of detection for each adrenoreceptor antagonist enantiomer were 5 ng/ml (0.02 microM) in CE-MS-MS instead of 150 ng/ml (0.60 microM) in CE-UV, which enhances sensitivity by a factor of 30.     

黄烷酮对映体的高效液相色谱手性拆分及含量测定

采用环糊精为手性固定相,建立了黄烷酮对映体的高效液相色谱(HPLC)手性拆分方法。考察了流动相组成、流动相比例、流速及柱温对黄烷酮对映体拆分的影响。结果表明,以CD-CSP2手性色谱柱分离,采用乙腈-水(体积比30∶70)为流动相,在流速为1.0mL/min,温度30℃,检测波长254nm下,黄烷酮对映体能达到基线分离,且具有较好的重复性和稳定性,可用于对映体的拆分及质量控制。且R-黄烷酮与固定相的作用弱于S-黄烷酮,在色谱柱中首先被洗脱。以面积归一化法计算可知黄烷酮样品中,R-黄烷酮含量为53.94%,S-黄烷酮含量为46.06%。     

Chiral separation of the β2‐sympathomimetic fenoterol by HPLC and capillary zone electrophoresis for pharmacokinetic studies

The development of methods for the separation of the enantiomers of fenoterol by chiral HPLC and capillary zone electrophoresis (CZE) is described. For the HPLC separation precolumn fluorescence derivatization with naphthyl isocyanate was applied. The resulting urea derivatives were resolved on a cellulose tris(3,5‐dimethylphenylcarbamate)‐coated silica gel column employing a column switching procedure. Detection was carried out fluorimetrically with a detection limit in the low ng/mL range. The method was adapted to the determination of fenoterol enantiomers in rat heart perfusates using liquid–liquid extraction. As an alternative a CE method was used for the direct separation of fenoterol enantiomers comparing different cyclodextrin derivatives as chiral selectors. Copyright © 2010 John Wiley & Sons, Ltd.     

Chiral Separation of Ofloxacin Enantiomers by Microchip Capillary Electrophoresis with Capacitively Coupled Contactless Conductivity Detection

We describe a chiral separation method for ofloxacin enantiomers, levofloxacin and dextrofloxacin by microchip capillary electrophoresis with capacitively coupled contactless conductivity detection. The running buffer included 1 mmol L^?1 MES and 1 mmol L^?1 Tris (pH 8.0) with a separation voltage of 1.5 kV and an injection time of 10s. Under these conditions, the enantiomers were completely separated within 1 min. The linear calibration curves were A = 5.76 c — 0.00587 for levofloxacin and A = 5.41 c — 0.00551 for dextrofloxacin, in which the linear concentration of the components all ranged from 0.05 to 0.15 mg mL^?1 (regression coefficients were both 0.9996). The limits of detection (S/N = 3) were, respectively, 18 and 21 μg mL^?1. The relative standard deviations of migration time were both 2.0% (n = 6). The relative standard deviations of peak area were 3.4% (n = 6) for levofloxacin and 4.0% (n = 6) for dextrofloxacin. The effects of some factors on resolutions, such as separation voltage and injection time, concentration of running buffers, were studied. The method was simple, rapid, high‐efficient. Furthermore, the method could be applied to the chiral separation of the product containing these enantiomers, such as Ofloxacin Eye Drops.     

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

Various chiral selectors have been utilized successfully in capillary electrophoresis (CE); however, the number of polysaccharides used as chiral selectors is still small and the mechanism of enantiorecognition has not been fully elucidated. Chondroitin sulfate D (CSD) and chondroitin sulfate E (CSE), belonging to the group of glycosaminoglycans, are linear, sulfated polysaccharides with large mass. In this paper, they were investigated for the first time for their potential as chiral selectors by CE. The effect of buffer composition and pH, chiral selector concentration, and applied voltage were systematically examined and optimized. A variety of drug enantiomers were resolved in the buffer pH range of 2.8–3.4 using 20 mM Tris/H₃PO₄ buffer with 5.0 % CSD or CSE and 20 kV applied voltage. A central composite design was used to validate the optimized separation parameters and satisfactory uniformity was obtained. As observed, CSE allowed satisfactory separation of the enantiomers of amlodipine, laudanosine, nefopam, sulconazole, and tryptophan methyl ester, as well as partial resolution of citalopram, duloxetine, and propranolol under the optimized conditions. CSD allowed partial or nearly baseline separation of amlodipine, laudanosine, nefopam, and sulconazole. The results indicated that CSE has a better enantiorecognition capability than CSD toward the tested drugs.