Chiral Capillary Zone Electrophoresis Research Articles

Online large volume sample staking preconcentration and separation of enantiomeric GHRH analogs by capillary electrophoresis.

A capillary electrophoresis method is proposed to analyze the four most well-known growth hormone-releasing hormone (GHRH) analogs that are misused by athletes. Dimethyl-β-cyclodextrin used as a chiral selector allowed, for the first time, the separation of those basic peptide analogs, including enantiopeptides (sermorelin and CJC-1293) that differ by the chirality of only one amino acid. To increase the method sensitivity, electrokinetic preconcentration methods have been investigated. The large volume sample stacking with polarity switching (PS-LVSS) method with an injected sample volume corresponding to 80% of the capillary one was found superior to the sweeping in terms of signal enhancement factor (SEF). Acid and organic solvent addition to the sample (0.1mM phosphoric acid with 30% methanol) led to a twofold signal improvement, when compared to water as a matrix. We increased capillary dimensions to provide a signal enhancement through the injection of a larger sample volume. Finally, using a combination of the optimized PS-LVSS preconcentration with the chiral capillary zone electrophoresis (CZE), the GHRH analogs were separated and limits of detection between 75 and 200ng/mL were reached. This method was successfully applied to urine after a desalting step. An optimized C18 SPE was used for that purpose in order to provide low sample conductivity (<130µS/cm) and preserve the efficiency of LVSS preconcentration. SEF of 640 was obtained with desalted urine spiked with sermorelin by comparison to the CZE (without preconcentration) method.

Determination of the chiral status of different novel psychoactive substance classes by capillary electrophoresis and β-cyclodextrin derivatives.

Besides the abuse of well‐known illicit drugs, consumers discovered new synthetic compounds with similar effects but minor alterations in their chemical structure. Originally, these so‐called novel psychoactive substances (NPS) have been created to circumvent law of prosecution because of illicit drug abuse. During the past decade, such compounds came up in generations, the most popular compound was a synthetic cathinone derivative named mephedrone. Cathinones are structurally related to amphetamines; to date, more than 120 completely new derivatives have been synthesized and are traded via the Internet. Cathinones possess a chiral center; however, only little is known about the pharmacology of their enantiomers. However, NPS comprise further chiral compound classes such as amphetamine derivatives, ketamines, 2‐(aminopropyl)benzofurans, and phenidines. In continuation of our project, a cheap and easy‐to‐perform chiral capillary zone electrophoresis method for enantioseparation of cathinones presented previously was extended to the aforementioned compound classes. Enantioresolution was achieved by simply adding native β‐cyclodextrin, acetyl‐β‐cyclodextrin, 2‐hydroxypropyl‐β‐cyclodextrin, or carboxymethyl‐β‐cyclodextrin as chiral selector additives to the background electrolyte. Fifty‐one chiral NPS served as analytes mainly purchased from online vendors via the Internet. Using 10 mM of the aforementioned β‐cyclodextrins in a 10 mM sodium phosphate buffer (pH 2.5), overall, 50 of 51 NPS were resolved. However, chiral separation ability of the selectors differed depending on the analyte. Additionally, simultaneous enantioseparations, the determination of enantiomeric migration orders of selected analytes, and a repeatability study were performed successfully. It was proven that all separated NPS were traded as racemic mixtures.

Chiral separation of cathinone derivatives using β-cyclodextrin-assisted capillary electrophoresis-Comparison of four different β-cyclodextrin derivatives used as chiral selectors.

In the past decade, more than 100 different cathinone derivatives slopped over entire Europe due to their enormous popularity. Generally, these novel psychoactive substances are easily available via the internet. This fact leads to various social problems, since cathinones are substances with consciousness‐changing effects and are mainly misused for recreational matters by their consumers. Cathinones possess a chiral center including two enantiomeric forms with potentially different pharmacological behavior. This fact makes analytical method development regarding their chiral separation indispensable. In this study, a chiral capillary zone electrophoresis method for the enantioseparation of 61 cathinone and pyrovalerone derivatives was developed by means of four different β‐cyclodextrin derivatives. As chiral selectors, native β‐cyclodextrin as well as three of its derivatives namely acetyl‐β‐cyclodextrin, 2‐hydroxypropyl‐β‐cyclodextrin, and carboxymethyl‐β‐cyclodextrin were used. The cathinone and pyrovalerone derivatives were either purchased in internet stores or seized by police. As a result, overall 58 of 61 studied substances were partially or baseline separated by at least one of the four chiral selectors using 10 mM of β‐cyclodextrin derivative in a 10 mM sodium phosphate buffer (pH 2.5). Furthermore, the method was found to be suitable for simultaneous enantioseparations, for enantiomeric purity checks and to differentiate between positional isomers. Moreover, an intra‐ and an interday validation was performed successfully for each chiral selector to prove the robustness of the method.

Chiral capillary zone electrophoresis in enantioseparation and analysis of cinacalcet impurities: Use of Quality by Design principles in method development

A capillary electrophoresis method for the simultaneous determination of the enantiomeric purity and of impurities of the chiral calcimimetic drug cinacalcet hydrochloride has been developed following Quality by Design principles. The scouting phase was aimed to select the separation operative mode and to identify a suitable chiral selector. Among the tested cyclodextrins, (2-carboxyethyl)-β-cyclodextrin and (2-hydroxypropyl)-γ-cyclodextrin (HPγCyD) showed good chiral resolving capabilities. The selected separation system was solvent-modified capillary zone electrophoresis with the addition of HPγCyD and methanol. Voltage, buffer pH, methanol concentration and HPγCyD concentration were investigated as critical method parameters by a multivariate strategy. Critical method attributes were represented by enantioresolution and analysis time. A Box-Behnken Design allowed the contour plots to be drawn and quadratic and interaction effects to be highlighted. The Method Operable Design Region (MODR) was identified by applying Monte-Carlo simulations and corresponded to the multidimensional zone where both the critical method attributes fulfilled the requirements with a desired probability π≥90%. The working conditions, with the MODR limits, corresponded to the following: capillary length, 48.5cm; temperature, 18°C; voltage, 26kV (26–27kV); background electrolyte, 150mM phosphate buffer pH 2.70 (2.60–2.80), 3.1mM (3.0–3.5mM) HPγCyD; 2.00% (0.00–8.40%) v/v methanol. Robustness testing was carried out by a Plackett-Burman matrix and finally a method control strategy was defined. The complete separation of the analytes was obtained in about 10min. The method was validated following the International Council for Harmonisation guidelines and was applied for the analysis of a real sample of cinacalcet hydrochloride tablets.

Enantioselective column coupled electrophoresis employing large bore capillaries hyphenated with tandem mass spectrometry for ultra‐trace determination of chiral compounds in complex real samples

A new multidimensional analytical approach for the ultra-trace determination of target chiral compounds in unpretreated complex real samples was developed in this work. The proposed analytical system provided high orthogonality due to on-line combination of three different methods (separation mechanisms), i.e. (1) isotachophoresis (ITP), (2) chiral capillary zone electrophoresis (chiral CZE), and (3) triple quadrupole mass spectrometry (QqQ MS). The ITP step, performed in a large bore capillary (800 μm), was utilized for the effective sample pretreatment (preconcentration and matrix clean-up) in a large injection volume (1-10 μL) enabling to obtain as low as ca. 80 pg/mL limits of detection for the target enantiomers in urine matrices. In the chiral CZE step, the different chiral selectors (neutral, ionizable, and permanently charged cyclodextrins) and buffer systems were tested in terms of enantioselectivity and influence on the MS detection response. The performance parameters of the optimized ITP - chiral CZE-QqQ MS method were evaluated according to the FDA guidance for bioanalytical method validation. Successful validation and application (enantioselective monitoring of renally eliminated pheniramine and its metabolite in human urine) highlighted great potential of this chiral approach in advanced enantioselective biomedical applications.

Evaluation of enantiomeric purity of magnesium-l-aspartate dihydrate

Magnesium supplementation in form of organic magnesium salts is a very popular practice. We examined the enantiomeric purity of “Magnesium aspartate dihydrate” monographed in the European Pharmacopeia. A chiral capillary zone electrophoresis using (2-hydroxypropyl)-β-cyclodextrin coupled to laser induced fluorescence detection and a HPLC-fluorescence method with chiral derivatization using o-phthaldialdehyde and N-acetyl-l-cysteine as an orthogonal method were developed and validated. Two batch samples of this substance and three drug products containing the salt were analyzed by means of both methods. The concentration of the d-enantiomer of aspartic acid ranged from 0.03 to 0.12%. Simulations of the synthesis revealed that the d-aspartic acid content is elevated if the dissolution of l-aspartic acid was performed at acidic pH values.

Enantioselective separation of mirtazapine and its metabolites by capillary electrophoresis with acetonitrile field-amplified sample stacking and its application.

A simple, rapid and sensitive chiral capillary zone electrophoresis coupled with acetonitrile-field-amplified sample stacking method was developed that allows the simultaneous enantioselective separation of the mirtazapine, N-demethylmirtazapine, 8-hydroxymirtazapine and mirtazapine-N-oxide. The separation was achieved on an uncoated 40.2 cm × 75 μM fused silica capillary with an applied voltage of 16 kV. The electrophoretic analyses were carried out in 6.25 mM borate–25 mM phosphate solution at pH 2.8 containing 5.5 mg/mL carboxymethyl-β-cyclodextrin. The detection wavelength was 200 nm. Under these optimized conditions, satisfactory chiral separations of four pair enantiomers were achieved in less than 7 min in vitro. After one step clean-up liquid-liquid extraction using 96-well format, sample was introduced capillary zone electrophoresis with acetonitrile-field-amplified sample stacking to enhance the sensitivity of enantiomers. The method was validated with respect to specificity, linearity, lower limit of quantitation, accuracy, precision, extraction recovery and stability. The lower limit of quantification was 0.5 ng/mL with linear response over the 0.5–50 ng/mL concentration range for each mirtazapine, N-demethylmirtazapine and 8-hydroxymirtazapine enantiomer. The developed and validated method has been successfully applied to the enantioselective pharmacokinetic studies in 12 healthy volunteers after oral administration of rac- mirtazapine.

Chiral separation of cathinone derivatives used as recreational drugs by cyclodextrin‐modified capillary electrophoresis

In recent years, cathinone derivatives have entered the global drug market and caused serious social problems in many European countries. Modification of the basic structure of cathinone leads to a multitude of derivatives, including the most popular representative mephedrone. All those substances contain a stereogenic center and therefore two isoforms exist. As it is the case with many chiral active pharmaceutical ingredients, even the pharmacological effect of the enantiomers of those psychoactive compounds may differ. During this research, an easy-to-prepare chiral capillary zone electrophoresis method for the enantioseparation of a set of 19 cathinone derivatives was developed. Testing different types of cyclodextrin (CD), including native-β-CD, carboxymethyl-β-CD, 2-hydroxypropyl-β-CD, sulfated-β-CD, and native γ-CD, best results were obtained with the negatively charged sulfated-β-CD. The effect of the CD concentration, the temperature, and the addition of ACN to the BGE on the enantioseparation is shown by three model compounds. Under optimal conditions, using 20 mg/mL sulfated-β-CD in 50 mM ammonium acetate buffer pH= 4.5 containing 10% v/v ACN at a cassette temperature of 40°C and with an applied voltage of 20 kV, all derivatives except methedrone were resolved in their enantiomers within 20 min.

Dynamic high‐resolution computer simulation of electrophoretic enantiomer separations with neutral cyclodextrins as chiral selectors

GENTRANS, a comprehensive one-dimensional dynamic simulator for electrophoretic separations and transport, was extended for handling electrokinetic chiral separations with a neutral ligand. The code can be employed to study the 1:1 interaction of monovalent weak and strong acids and bases with a single monovalent weak or strong acid or base additive, including a neutral cyclodextrin, under real experimental conditions. It is a tool to investigate the dynamics of chiral separations and to provide insight into the buffer systems used in chiral capillary zone electrophoresis (CZE) and chiral isotachophoresis. Analyte stacking across conductivity and buffer additive gradients, changes of additive concentration, buffer component concentration, pH, and conductivity across migrating sample zones and peaks, and the formation and migration of system peaks can thereby be investigated in a hitherto inaccessible way. For model systems with charged weak bases and neutral modified β-cyclodextrins at acidic pH, for which complexation constants, ionic mobilities, and mobilities of selector-analyte complexes have been determined by CZE, simulated and experimentally determined electropherograms and isotachopherograms are shown to be in good agreement. Simulation data reveal that CZE separations of cationic enantiomers performed in phosphate buffers at low pH occur behind a fast cationic migrating system peak that has a small impact on the buffer composition under which enantiomeric separation takes place.

2D separations on a 1D chip: gradient elution moving boundary electrophoresis—chiral capillary zone electrophoresis

A new method is described for two-dimensional (2D) separations using a microfluidic chip normally employed for single dimension electrophoresis. The method employs a combination of gradient elution moving boundary electrophoresis (GEMBE) and chiral capillary zone electrophoresis (CZE). The simplicity of the first dimension GEMBE method enables its implementation in the injection channel of a conventional electrophoresis chip, simplifying the design and operation of the device. The method was used for high resolution 2D chiral separations of a mixture of amino acids considered as possible signatures of extant or extinct life for solar system exploration. The enantiomers of aspartic acid, glutamic acid, serine, alanine, and valine were all resolved as well as glycine (achiral) and several unidentified impurities, giving an estimated peak capacity of 35 for the region between valine and glycine. The results highlight the need for high peak capacity separations for chiral amino acid analysis if accurate enantiomeric ratios are to be determined.

Role of chemical structure in stereoselective recognition of β-blockers by cyclodextrins in capillary zone electrophoresis

Most of the β-blocking drugs for treating diseases of the cardiovascular system are chiral aryloxy–propanolamine derivatives. Tipically, the S(−) enantiomers are more active than the R(+) enantiomers. Only some of them (for example timolol) are used as single enantiomers, the others are employed as racemates. For the determination of the enantiomeric purity of timolol European Pharmacopoeia prescribes an HPLC method using chiral stationary phase. However, the use of chiral capillary zone electrophoresis for the determination of the enantiomeric purity is of pharmaceutical interest. This study describes the application of various cyclodextrin derivatives, hydroxypropyl-β-cyclodextrin, randomly methylated β-cyclodextrin, sulphated β-cyclodextrin and sulphated α-cyclodextrin for the stereoselective analyses of β-blockers. Baseline separation was obtained for bopindolol, carvedilol, mepindolol, pindolol and alprenolol, while only partial separation was observed for sotalol, propranolol, oxprenolol, atenolol, bisoprolol, bupranolol, and metoprolol. The uneven molecular recognition of the enantiomers of the β-blockers, especially of the optical isomers of labetalol and nadolol, showed the importance of the chemical nature of the separators and the analytes.

Assessment of the stereoselective metabolism of methaqualone in man by capillary electrophoresis.

Methaqualone (MQ) and its hydroxylated metabolites are quinazoline derivatives that exhibit atropisomerism. As a continuation of our previous work with these compounds (Electrophoresis 2001, 22, 3270-3280), chiral capillary zone electrophoresis with hydroxypropyl-beta-cyclodextrin as buffer additive and multiwavelength absorbance detection is shown to be an effective tool to provide insight into the stereoselectivity of the MQ metabolism. The five major monohydroxy MQ metabolites formed during biotransformation do not show enantiomerization at temperatures up to 85 degrees C. Enzymatic and acidic hydrolysis of urines that were collected after concomitant administration of 250 mg of MQ and 25 mg diphenhydramine (DH) chloride are both shown to provide stereoselective metabolic patterns with 4'-hydroxymethaqualone, the major urinary metabolite, being excreted almost exclusively as a single enantiomer. A stereoselectivity in the formation of 2'-hydroxymethaqualone and 2-hydroxymethaqualone was also observed in vitro using human liver microsomes and preparations containing the cytochrome P450 enzyme (CYP) CYP3A4 only. The presence of DH during incubation with human liver microsomes did not reveal a difference in the metabolic pattern obtained. Furthermore, CYP2D6 and CYP2C19 do not significantly contribute to the metabolism of MQ. This was independently observed in vitro and via analysis of urines of individuals that are either efficient metabolizer phenotypes or poor metabolizer phenotypes for the two polymorphic enzymes. Although interindividual differences in the monitored metabolic patterns were noted, no marked difference could be related to a CYP2D6 or CYP2C19 polymorphism.

An experimental design methodology applied to the enantioseparation of a non-steroidal anti-inflammatory drug candidate

An experimental design methodology has been applied to the enantioseparation of a new synthesized aryl propionic acid of pharmaceutical interest, namely 2-[(4′-benzoyloxy-2′-hydroxy)phenyl-propionic acid] (DF-1770y) by chiral capillary zone electrophoresis (CCZE). The chiral separation of the studied compound has been achieved employing vancomycin as the chiral selector. The partial filling-counter current method has been used in order to avoid the presence of the absorbing chiral selector in the path length of the detector and to increase the method sensitivity. A central composite design has been employed to optimize the experimental conditions for a fast separation of the enantiomers of the new synthesized aryl propionic acid. Critical parameters such as chiral selector concentration, pH and temperature have been studied to evaluate how they affected responses such as resolution and migration times. The desirability function approach has been employed in order to find the best compromise between the different experimental responses. The proposed CCZE method provided the baseline enantioseparation of the investigated drug. A Britton-Robinson buffer at pH 6.4 supplemented with 7 mM of vancomycin at 22 °C and −20 kV were the optimum experimental conditions allowing to achieve the highest enantioresolution of DF-1770y in less than 8.5 min.

Chiral capillary electrophoresis as predictor for separation of drug enantiomers in continuous flow zone electrophoresis

Separation of the enantiomers of chlorpheniramine and methadone in acidic buffers containing carboxymethyl-β-cyclodextrin (CMCD) as chiral selector was investigated by capillary zone electrophoresis. For a range of pH and CMCD concentrations, the mobility difference and resolution of the enantiomers were determined. Then, conditions known to provide well resolved enantiomers and optimized chiral separation were applied to chiral continuous flow electrophoresis. In that approach, a thin film of fluid flowing between two parallel plates is employed as carrier for electrophoresis. The electrolytes and the sample are continuously admitted at one end of the electrophoresis chamber and are fractionated by an array of outlet tubes at the other. The number of pure enantiomeric fractions obtained by chiral continuous flow electrophoresis was found to be directly dependent on the enantiomeric mobility difference. For racemic chlorpheniramine separated in a betaine–acetic acid buffer at a total throughput of 5 mg/h, complete enantiomeric separation is shown to require a mobility difference of about 3·10 −9 m 2/V s. Furthermore, compared to the previous investigations with hydroxypropyl-β-cyclodextrin, CMCD was found to permit improved fractionation of methadone enantiomers. With a total racemic drug throughput of about 15 mg/h, continuous flow zone electrophoresis processing with CMCD as chiral selector is shown to have the potential of providing pure enantiomers on a mg/h scale. The results indicate that chiral capillary zone electrophoresis data can be employed as predictor for preparative scale chiral separations based upon continuous flow zone electrophoresis.

Tensioactive Compounds from the Aquatic Plant Ranunculus fluitans L. (Ranunculaceae)

In the search for the cause for the formation of persistent foam in the Rhine River below the Rhine Fall at Schaffhausen, an investigation of the tensioactive principles from the aquatic plant Ranunculus fluitans L. (Ranunculaceae) was carried out. Two new (see 1 and 2) and four known bisdesmosidic triterpene saponins (see 4 – 6) were isolated along with the two known diacylglycerol galactosides 7 and 8. The saponin structures were established by the identification of the aglycon and sugar moieties by HPLC and chiral capillary zone electrophoresis (CZE), ion-spray LC/MS and extensive 1- and 2D homo- and heteronuclear NMR spectroscopy. The structures of the new oleanane-type saponins were identified as 3-O-[β-D-glucopyranosyl-(1→3)-α-L-arabinopyranosyl]-28-O-[α-L-rhamnopyranosyl-(1→4)-β-D-glucopyranosyl-(1→6)-β-D-glucopyranosyl]hederagenin (1) and 3-O-[β-D-glucopyranosyl-(1→3)-β-D-glucopyranosyl]oleanolic acid [α-L-rhamnopyranosyl-(1→4)-β-D-glucopyranosyl-(1→6)-β-D-glucopyranosyl] ester (2). LC/MS Studies of tensioactive fractions revealed the presence of additional glycoglycerolipids.

Major flavonoids from Arabidopsis thaliana leaves.

The three major flavonoids isolated from Arabidopsis thaliana plants grown in the greenhouse were identified by means of spectroscopic analysis (UV, NMR, MS) and chiral capillary zone electrophoresis as the novel kaempferol 3-O-beta-[beta-D-glucopyranosyl(1-->6)D-glucopyranoside]-7-O-alpha-L- rhamnopyranoside (1), kaempferol 3-O-beta-D-glucopyranoside-7-O-alpha-L-rhamnopyranoside (2), and kaempferol 3-O-alpha-L-rhamnopyranoside-7-O-alpha-L-rhamnopyranoside (3). Comprehensive NMR studies including selective 1D and gradient-enhanced 2D techniques were applied in order to achieve full signal assignment and definitive proof of linkage for compound 1.

Characterization of the stereoselective metabolism of thiopental and its metabolite pentobarbital via analysis of their enantiomers in human plasma by capillary electrophoresis

Using capillary zone electrophoresis (CZE) with a 75 m M phosphate buffer at pH 8.5 containing 5 m M hydroxypropyl-γ-cyclodextrin (OHP-γ-CD) as chiral selector, the separation of the enantiomers of thiopental and its oxybarbiturate metabolite, pentobarbital, is reported. Enantiomer assignment was performed via preparation of enantiomerically enriched fractions using chiral recycling isotachophoresis (rITP) processing of racemic barbiturates and analysis of rITP fractions by chiral CZE and circular dichroism spectroscopy. Thiopental and pentobarbital enantiomers in plasma were extracted at low pH using dichloromethane and extracts were reconstituted in acetonitrile or 10-fold diluted, achiral running buffer. The stereoselectivity of the thiopental and pentobarbital metabolism was assessed via analysis of 12 plasma samples that stemmed from patients undergoing prolonged or having completed long-term racemic thiopental infusion. The data obtained revealed a modest stereoselectivity with R-(+)-thiopental/ S-(−)-thiopental and R-(+)-pentobarbital/ S-(−)-pentobarbital plasma ratios being <1 ( P <0.05 compared to data obtained with racemic controls) and >1 ( P<0.001), respectively. The total S-(−)-thiopental plasma concentration was found to be on average about 24% higher compared to the concentration of R-(+)-thiopental, whereas the total R-(+)-pentobarbital plasma level was observed to be on average 29% higher compared to the S-(−)-pentobarbital concentration.

Enantiomeric separation of methadone by cyclodextrin-based capillary and recycling isotachophoresis.

The separation of methadone enantiomers by cationic capillary isotachophoresis (CITP) and recycling isotachophoresis (RITP) having (2-hydroxypropyl)-beta-cyclodextrin (OHP-beta-CD) as chiral selector in the leading electrolyte is described. Sodium acetate/acetic acid (pH between 4 and 5) served as leading electrolyte (catholyte) and acetic acid as terminator (anolyte). Complete separation of the enantiomers was obtained by CITP in a 50 microm internal diameter (ID) fused-silica capillary and in a 500 microm ID Teflon capillary. In the first approach, enantiomeric separation could be monitored via UV absorbance detection at low wavelength. With the second instrumental setup, an additional conductivity sensor permitted the visualization of the enantiomeric separation and the characterization of the buffer system employed. A 10 mM sodium acetate/acetic acid leading buffer of pH 4.3, containing 5 mM OHP-beta-CD, was found to provide best enantiomeric separation and was thus chosen for RITP. With RITP processing of a few mg of racemic methadone, partial separation of methadone enantiomers was obtained. R-(-)-methadone and S-(+)-methadone were found to be significantly (up to about 80%) enriched at the front and back side, respectively, of the isotachophoretic zone. The enantiomeric composition of methadone in the collected fractions was assessed by chiral capillary zone electrophoresis (CZE) and circular dichroism spectroscopy. CZE was found to represent a simple and efficient method for the determination of the enantiomeric excess, whereas the latter technology was noted to be the superior approach for properly characterizing fractions that contain similar amounts of the two enantiomers. Furthermore, chiral RITP and analysis of the collected fractions by circular dichroism spectroscopy is shown to be potentially useful for identification of single enantiomers in absence of pure chiral standards.

Use of heptakis(2,6-di-O-methyl)-β-cyclodextrin in on-line capillary zone electrophoresis-mass spectrometry for the chiral separation of ropivacaine

The on-line coupling of chiral capillary zone electrophoresis (CZE) with mass spectrometry (MS) is described for the chiral separation of the basic drug ropivacaine using a coupled capillary system with the possibility of voltage switching. With this set-up, the introduction into the MS of the chiral selector heptakis(2,6-di-O-methyl)-β-cyclodextrin (DM-β-CD) that has a detrimental effect on MS performance is avoided. In combination with MS detection, this coupled capillary set-up can be regarded as universally applicable for all CZE separations where the use of buffer additives that have negative influence on the MS is necessary.