Simultaneous Chiral Separation Research Articles

Modelling the simultaneous chiral separation of a group of drugs by electrokinetic chromatography using mixtures of cyclodextrins

Two mixtures of neutral cyclodextrins (CDs) were used in Electrokinetic Chromatography (EKC) to model and optimize the simultaneous enantiomeric separation of a group of seven drugs. Heptakis(2,6-di-O-methyl)-β-CD (DM-β-CD) combined with methyl-γ-CD (M-γ-CD) or with carboxyethyl-γ-CD (CE-γ-CD) was employed in a 25 mM formate buffer at pH 3.0 to have the drugs studied positively charged. Dubsky's model was applied to calculate the enantiomer effective electrophoretic mobilities for each combination of CDs at different averaged molar fractions and total CDs concentrations. The most adequate averaged molar fraction and total CDs concentration in terms of the simultaneous enantiomeric separation of the drug mixture were predicted by the model and results were experimentally corroborated. The model also foresaw interesting effects, derived from the combination of DM-β-CD with M-γ-CD or with CE-γ-CD, on the individual chiral separation of some of the drugs studied. The observed reversal of the migration order for some compounds when changing the total CDs concentration was also predicted and the model showed its potential even at concentrations out of the experimental range of CD concentrations experimentally employed. The use of an averaged molar fraction of 0.8 for DM-β-CD at a total CDs concentration of 40 mM in the DM-β-CD/CE-γ-CD system predicted by the model enabled the simultaneous enantiomeric separation of six of the drugs studied (except verapamil) with resolutions ranging from 0.6 to 4.0.

Fast enantiomeric separation of amino acids using liquid chromatography/mass spectrometry on a chiral crown ether stationary phase

Fast enantiomeric separation of amino acids was studied by liquid chromatography/mass spectrometry (LC/MS) on a chiral crown ether stationary phase. A chiral crown ether bonded silica column (3mm internal diameter (i.d.), 5cm long) packed with 3μm particles was employed instead of a 15cm column packed with 5μm particles used in our previous study. In addition, the extra-column variance, becoming more serious for smaller columns, was reduced by replacing 0.127mm i.d. post-column tubes with shorter, smaller-diameter (0.0635mm i.d.) tubes. The results demonstrated the benefits of using shorter columns packed with smaller particles and the reduction of the extra-column band broadening for fast enantiomeric separation. Finally, the enantiomeric separation of 18 pairs of proteinogenic amino acids was achieved within 2min with a resolution (Rs) > 1.5 for each pair using an isocratic mobile phase of acetonitrile/water/trifluoroacetic acid (ACN/W/TFA)= 96/4/0.5, and a flow rate 1.2mL/min at 30°C. This is the highest throughput method for simultaneous chiral separation of all proteinogenic amino acids except proline to date.

Enantioselective analysis in complex matrices using capillary electrophoresis-mass spectrometry: A case study of the botanical drug Corydalis Rhizoma

Enantioselective analysis is critically important in the pharmaceutical and agricultural industries. However, most of the methods reported were developed for the analysis of pure racemates acquired from chemical synthesis or purification. Direct analysis of chiral enantiomers in complex matrices has rarely been reported. This work demonstrated capillary electrophoresis-mass spectrometry (CE-MS) for the enantioselective analysis of botanical drugs for the first time, using a widely used botanical drug, Corydalis Rhizoma, as an example. The method was used for the simultaneous enantioselective analysis of dl-tetrahydropalmatine and (RS)-tetrahydroberberine (canadine) in Corydalis Rhizoma extract. Using (2-hydroxypropyl)-β-cyclodextrin as the chiral selector, a partial filling technique was used to avoid signal suppression and contamination of the MS detector. Post column organic modifier was used to assist with ionization in the flow through microvial CE-MS interface, therefore, organic solvents was not used in the background electrolyte. The completely aqueous background electrolyte contributed to better chiral separations. The CE-MS method established here can directly determine the analytes in their complex matrix without any pre-purification steps, while also offering high sensitivity and low operational costs (including sample, chiral selector and solvent). In the method validation process, good linearity (r > 0.993), sensitivity and accuracy (recoveries within 89.1–110.0%) were demonstrated. The CE-MS technique was shown to be able to provide good selectivity for the simultaneous chiral separation of multiple pairs of enantiomers in complex matrices.

Simultaneous chiral separation of tramadol and methadone in tablets, human urine, and plasma by capillary electrophoresis using maltodextrin as the chiral selector

The stereoselective analysis and separation of racemic drugs play an important role in pharmaceutical industry to eliminate the unwanted isomer and find the right therapeutic control for the patient. Present study suggests a maltodextrin-modified capillary electrophoresis method for a single-run chiral separation of two closely similar opiate pain relief drugs: tramadol (TRA) and methadone (MET). The best separation method possible for the both enantiomers was achieved on an uncoated fused-silica capillary at 25°C using 100 mM phosphate buffer (pH8.0) containing 20% (wv-1 ) maltodextrin with dextrose equivalent of 4-7 and an applied voltage of 16kV. Under optimal conditions, the baseline resolution of TRA and MET enantiomers was obtained in less than 12minutes. The relative standard deviations (n=3) of 20μgmL-1 TRA and MET were 2.28% and 3.77%, respectively. The detection limits were found to be 2μgmL-1 for TRA and 1.5μgmL-1 for MET. This method was successfully applied to the measurement of drugs concentration in their tablets, urine, and plasma samples.

Simultaneous chiral analysis of amphetamine-type stimulants and ephedrine by capillary electrophoresis coupled to time-of-flight mass spectrometry.

This study focused on the chiral characteristics of methamphetamine seizures in Shanghai for inferring the synthetic pathways of drugs. Capillary electrophoresis coupled to time-of-flight mass spectrometry was used for simultaneous chiral separation of amphetamine-type stimulants and ephedrine, including S(+)-amphetamine/R(-)-amphetamine, S(+)-methamphetamine/R(-)-methamphetamine, (±)-MDA (3,4-methylenedioxyamphetamine), (±)-MDMA (3,4-methylenedioxymethamphetamine), (±)-MDEA (3,4-methylenedioxy-N-ethylamphetamine), d,l-N-ethylamphetamine, methylephedrine/methylpseudoephedrine, and 1S,2R(+)-ephedrine/(-)-ephedrine. The running buffer was 50-mM ammonium formate (pH2.2 was adjusted by 1-M formic acid) containing 0.26% highly sulfated γ-cyclodextrin as the chiral selector. All enantiomers were well resolved within 40minutes by capillary electrophoresis at 20kV in an uncoated fused-silica capillary (50-μm I.D.×375-μm O.D.×90-cm length) and detected by micro time-of-flight mass spectrometry. Twenty seized methamphetamine samples were determined by the established method. They were classified into two groups through their chiral characteristics.

Development of a modified partial filling method in capillary electrophoresis using two chiral plugs for the simultaneous enantioseparation of chiral drugs: Comparison with mixed chiral selector capillary electrophoresis

In this study, a chiral CE method was developed based on the partial filling technique with two chiral plugs for the simultaneous enantioseparation of some racemic drugs, including baclofen, carvedilol, cetirizine, chlorpheniramine, citalopram, fluoxetine, hydroxyzine, propranolol, tramadol, trihexyphenidyl. This method of capillary filling involves the application of two adjacent chiral plugs containing the same BGE, but with different chiral selectors in the plugs for the enantioseparation of a mixture of drugs which cannot be separated with single or mixed chiral selectors. By using this method, each plug can separate the enantiomers independently (same as a single chiral selector modified CE) and the possible interactions between the chiral selectors would be inhibited. The best results were obtained using a fused silica capillary (60cm×50μm id (50cm effective length)) with phosphate buffer (100mM, pH 3.0) containing 10mM hydroxypropyl-α/β-cyclodextrin and 10% (w/v) maltodextrin and detected by UV at 214nm. The influence of the length and order of the chiral plugs on the enantioresolution was also studied and optimized. The proposed method was compared with a mixed chiral selector-CE system with a combination of hydroxypropyl-α-cyclodextrin/hydroxypropyl-β-cyclodextrin and maltodextrin in the BGE. According to the results, the modified partial filling method is a simple and efficient method for the simultaneous chiral separation and offers appropriate migration times and resolutions compared to the results obtained from mixed chiral selector CE.

Enantioselective fractionation of fluoroquinolones in the aqueous environment using chiral liquid chromatography coupled with tandem mass spectrometry

This paper aims to examine the multiresidue enantiomeric profiling of (fluoro)quinolones and their metabolites in solid and liquid environmental matrices using chiral HPLC-MS/MS method and a CHIRALCEL® OZ-RH column. Simultaneous chiral separation was obtained for chiral ofloxacin and its main metabolites ofloxacin-N-oxide and desmethyl-ofloxacin; moxifloxacin; the prodrug prulifloxacin and its active compound ulifloxacin; flumequine; nadifloxacin and R-(+)-besifloxacin. Achiral antibiotics (ciprofloxacin, norfloxacin and nalidixic acid) were also included in the method to enable the analysis of all targeted quinolones within one analytical run. Satisfactory enantiomeric resolution (Rs ≥ 1) was obtained for five out of eight chiral drugs enabling quantitative analysis. The overall performance of the method was satisfactory with a method precision <20%, relative recoveries >70% for most of the analytes and method detection limits (MDL) at low ng L−1 levels (0.1 < MDL (ng L−1)< 6.4, 0.1 < MDL (ng L−1)< 6.6 and 0.1 < MDL (ng L−1)< 7.0 in influent, effluent and river waters for 83% compounds, 0.01 < MDL (ng g−1)< 4.9 in solids for 91% compounds). Enantiomeric profiling from a week-long monitoring campaign in the UK showed that (±)-ofloxacin was found to be racemic in upstream waters but it was enriched with S-(−)-enantiomer in wastewater and in receiving waters. This could be due to the fact that ofloxacin can be used both as a racemate and as a S-(−)-enantiomer. Its consumption was further confirmed by the chiral signature of the investigated ofloxacin metabolites. As a result, alterations in the enantiomeric composition of antibiotics could influence not only their activity and toxicity in the environment, but also could induce changes in the microbial communities constantly exposed to them.

Simultaneous chiral separation of three triazole pesticide enantiomers with submicron C18 bonded silica stationary phase by pressurized capillary electrochromatography

A monodispersed C18 silica stationary phase with particle size of 420 nm was prepared by modified St ber method.The column packed with submicron C18 bonded silica was successfully used for simultaneous enantioseparation of three chiral triazole pesticides by pressurized capillary electrochromatography (pCEC).Some effects on separation were investigated, and the optimized conditions were as follows:mobile phase of acetonitrile and 20 mmol/L phosphate buffer (pH=6.8) containing 20 mmol/L (2-hydroxypropyl)-γ-cyclodextrin (HP-γ-CD)(45:55, v/v), flow rate of 0.04 mL/min and applied voltage of-9.4 kV, the detection wavelength at 220 nm.The resolutions of adjacent peaks of uniconazole, diniconazole and propiconazole enantiomers were 4.20, 12.9, 4.41, 4.09 and 1.70 in 12 min, respectively, with the column efficiency up to 310000 plates/m.This study provides an alternative way for the simultaneous separation of chiral triazole pesticides with high efficiency.

Indirect chiral separation of 8 novel amphetamine derivatives as potential new psychoactive compounds by GC–MS and HPLC

Amphetamine and its derivatives gained high popularity on the illegal drug market. In the last few years, a lot of new psychoactive compounds structurally related to amphetamine, such as 4-fluoroamphetamine and 4-fluoromethamphetamine swamped the drug market. They were designed to circumvent prohibition of amphetamine and N-methylamphetamine and are distributed via the Internet. Often, a halogen atom is introduced into the phenyl ring of amphetamine to turn the illegal amphetamine legal. Since amphetamines possess a chiral centre, two enantiomers are available, which might differ in activity. Since most of them are partially not commercially available to date, synthesis and characterisation of amphetamine derivatives might help authorities to identify these substances of abuse.The aim of this study was to investigate self-synthesized amphetamines concerning their identity and their enantiomeric status either by GC–MS or by HPLC. For GC–MS, derivatization with (R)-(+)-α-methoxy-α-trifluoromethylphenylacetic acid (MTPA) or (1R)-(−)-menthylchloroformate prior to analysis on a HP-5MS column was done. For chiral separation by HPLC a LiChrospher 100 RP-18e column and sulfated beta-cyclodextrin added to the mobile phase as chiral selector were used. Enantioseparation was accomplished successfully by both methods. Furthermore, simultaneous chiral separation of three positions isomers, namely 2-fluoroamphetamine, 3-fluoroamphetamine and 4-fluoroamphetamine, was shown successfully by HPLC.

Simultaneous Chiral Separation of Flavanone, Naringenin, and Hesperetin Enantiomers by RP-UHPLC-DAD.

A rapid and effective RP-UHPLC-DAD method for enantioseparation of three flavanones, i.e., flavanone, naringenin, and hesperetin, was developed and validated. Chromatographic separation of the analytes was performed using a Chiralpak AD-3R analytical column under reverse phase conditions with methanol as the mobile phase. The method was validated in the concentration range of 0.2 to 50 µg/mL for enantiomers of flavanone and 0.5 to 50 µg/mL for enantiomers of naringenin and hesperetin. The limits of quantification were between 0.03 to 0.5 µg/mL. Intraday and interday precision were below 14% and accuracy varied from 0.04 to 8.17%.

Simultaneous Chiral Separation of Four H1-Antihistamines by Capillary Zone Electrophoresis Using a Dual Cyclodextrin System

Capillary zone electrophoresis employing a dual cyclodextrin (CD) system, consisting of anionic sulfobutylether-β-CD and native β-CD, was developed for the simultaneous chiral separation of four H1-antihistamine racemates (brompheniramine, chlorpheniramine, cetirizine and promethazine). A cost-effective screening using different native and derivatized, neutral and ionized CDs as chiral selectors was performed to find suitable derivatives for the dual CD system. Under the optimized conditions consisting of 25 mM phosphate background electrolyte at pH 7.0, a combination of 15 mM SBE-β-CD and 10 mM β-CD as chiral selectors, +25 kV applied voltage and 20 °C system temperature, the baseline chiral separation of all racemates was accomplished in less than 8 min. The method proved to be suitable for routine analysis, since it provided satisfactory results during sensitivity, linearity and repeatability studies.

Enantioseparation of Penconazole, Myclobutanil and Triadimefon by Cyclodextrin-Modified Micellar Electrokinetic Chromatography

Simultaneous enantioseparation of three chiral triazole fungicides i.e. penconazole, myclobutanil and triadimefon bycyclodextrin-modified micellar electrokinetic chromatography (CD-MEKC) under acidic condition was investigated withdifferent HP--CD concentrations as chiral selector. The three triazole fungicides have an asymmetrically substitutedcarbon atom respectively, and they all contain two enantiomers. In order to achieve the best enantioresolution of thesetriazole fungicides, the HP--CD concentration range was optimized from 0 to 40 mM in 10 mM increment. The resultsindicate that separation of enantiomers was not achieved with concentration range of HP--CD from 0 to 20 mM.Simultaneous enantioseparation was successfully achived at 30 mM and 40 mM HP--CD concentration in 25 mMphosphate buffer (pH 3.0) solution that containing 50 mM SDS, 10% methanol and 5% acetonitrile. However,enantioresolution decreased for myclobutanil and triadimefon enantiomers with HP--CD concentration greater than 30mM. In addition, an increase in the concentration of HP--CD caused a significant increase in the analysis time. In light ofthese aspects, the optimal concentration for HP--CD was decided to be 30 mM for the simultaneous chiral separation ofthe three triazole fungicides with resolutions (Rs) between enantiomers for penconazole, Rs = 0.81; myclobutanil, Rs = 1.14;triadimefon, Rs = 2.09; peak efficiencies (N) greater than 108 000 for all stereoisomers and analysis time of less than 15min.

Simultaneous chiral separation and determination of carvedilol and 5′-hydroxyphenyl carvedilol enantiomers from human urine by high performance liquid chromatography coupled with fluorescent detection

Abstract A sensitive and specific high performance liquid chromatography coupled with fluorescent detection (HPLC-FL) and tandem mass spectrometry detection (HPLC-MS/MS) methods for separation and determination of carvedilol (CAR) enantiomers and 5′-hydroxyphenyl carvedilol (5′-HCAR) enantiomers has been developed and validated. The analysed compounds were extracted from human urine by solid phase extraction. Good enantioseparation of the studied enantiomers was achieved on CHIRALCEL® OD-RH column using 0.05% trifluoroacetic acid and 0.05% diethylamine in water and acetonitrile in a gradient elution. The mass spectrometric data were acquired using the multiple reaction monitoring mode by positive electrospray ionisation. The method was validated over the concentration range from 25.0 ng mL−1 to 200 ng mL−1 for the analysed compounds. The limit of quantification varied from 14.2 ng mL−1 to 24.2 ng mL−1. Both the repeatability and inter-day precisions were below 10.0%, and the accuracy varied from −13.2% to 3.77%. The extraction recoveries ranged from 79.2% to 108%. The present paper reports the method for the simultaneous determination of CAR enantiomers and their metabolite enantiomers (5′-HCAR) in human urine samples. This newly developed method was successfully used to analyse the aforementioned analytes in human urine samples obtained from patients suffering from cardiovascular disease.

Chiral HPLC Separation of Rosiglitazone and its Main Metabolites and Studies on Their Racemization

Rosiglitazone (RSG) is marketed as a racemic mixture although the antidiabetic activity is essentially related to the (S)-enantiomer. The chiral center has an adjacent carbonyl group; therefore, the (R)-enantiomer could be transformed to the (S)-enantiomer or vice versa by keto-enolic tautomerism. The literature indicates that this racemization is slow enough to allow the evaluation of the properties of the isolated enantiomers. However, there is no information about the enantioselective kinetic disposition and metabolism of RSG. Additionally, there are no studies on the racemization of its metabolites. Considering these facts, a chiral HPLC method was developed and used for the first time to study the racemization of RSG and its main metabolites. Different conditions, including those used to evaluate the in vitro enantioselective metabolism, were employed. The simultaneous chiral separation of RSG and metabolites was achieved on a Chiralcel OJ-H column by employing methanol/ethanol (90:10, v/v) as mobile phase. The racemization studies showed that the half-life of RSG decreased more than 30 times when the temperature increased from 4 to 37 °C. It was also observed that the half-life of RSG changed from approximately 20 h at pH 3.5 to approximately 2 h at pH 7.4. The same profile was observed for its metabolites. Organic solvents and UV light did not present influence on the racemization process. In addition, a Complete Factorial Design was conducted to evaluate the influence of some parameters that can be changed during an in vitro metabolism study. The results obtained showed that the racemization occurs under in vitro metabolism conditions.

Normal phase LC coupled with direct analysis in real time MS for the chiral analysis of 4‐(methylnitrosamino)‐1‐(3‐pyridyl)‐1‐butanol and jasmonic acid

Normal phase chiral LC (NPLC) has been proved to be powerful and efficient for chiral separation. However, the combination of NPLC with ESI or atmospheric pressure chemical ionization MS is restricted by the poor ionization efficiency and thermal fragmentations of analytes to some extent. Direct analysis in real time MS (DART-MS) is an ambient ionization technique that shows high ionization efficiency of the analytes in the normal phase mobile phase. In this work, we coupled chiral NPLC to DART-MS for the chiral qualitative and quantitative analysis of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol and jasmonic acid enantiomers. Satisfactory results for the enantiomers of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol operating in the positive mode were obtained in terms of linearity (2.5-250 μg/mL, R(2) , 0.999-1.000) and repeatability (25 μg/mL, RSDs, 4.7-5.6%). Moreover, chiral NPLC-DART-MS resulted in the simultaneous chiral separation and detection of jasmonic acid enantiomers, which are very difficult to be analyzed by NPLC-ESI-MS and NPLC-APCI-MS. Compared with the coupled techniques of NPLC-ESI-MS and NPLC-APCI-MS, NPLC-DART-MS showed advantages in increasing the ionization efficiency and reducing the in-source thermal fragmentation of analytes.

Simultaneous chiral separation of methylamphetamine and common precursors using gas chromatography/mass spectrometry

Methylamphetamine, ephedrine, and pseudoephedrine were derivatized using trifluoroacetic anhydride and enantiomers of each were analyzed using gas chromatography coupled to mass spectrometry (GC/MS) fitted with a γ-cyclodextrin (Chiraldex™ G-PN) chiral column. A temperature-programmed method was developed and optimized and the results compared with those obtained using a previously published isothermal GC method applied to GC/MS analysis. Trifluoroacetylated 3-(trifluoromethyl)phenethylamine hydrochloride was used as an internal standard, and mass fragmentation patterns are proposed for all derivatives analyzed. Qualitative validation of the optimized chromatographic conditions was completed in accordance with the guidelines published by the United Nations Office on Drugs and Crime (UNODC). Under conditions of repeatability and reproducibility, the method gave relative retention times with a relative standard deviation of less than 0.02% for all six analytes of interest. This surpasses the UNODC's acceptance criteria of 2% for validation of qualitative precision. Ephedrine and pseudoephedrine are common precursors in the clandestine manufacture of methylamphetamine. Seizures of illicit methylamphetamine therefore often contain mixtures of these optically active compounds. The simultaneous enantioseparation of these compounds to produce a profile would provide valuable information to law enforcement agencies regarding the provenance of a methylamphetamine seizure.

Dual CD system in capillary electrophoresis for direct separation of the four stereoisomers of agonist and antagonist melatoninergic ligands

In this study, baseline separation of the stereoisomers of six tetrahydronaphthalenic derivatives (agonists and antagonists for the melatonin (N-acetyl-5-methoxytryptamin) binding sites) was successfully achieved using CE and CDs as chiral selectors. The method for the simultaneous chiral separation of the four stereoisomers uses a capillary dynamically coated with polyethylene oxide and a dual CD system. Optimisation was performed first upon the constituents of the CD system, by varying neutral and anionic CD type, size and concentration, at first in mono-CD systems and subsequently in dual neutral/anionic CD systems. Once these characteristics of the dual CD system were established, operational parameters such as voltage and temperature were then optimised. Under the optimal conditions (i.e. 1.5% w/v of highly S-beta-CD and 10 mM of gamma-CD in 25 mM phosphate buffer (pH 2.5) as the BGE, separation voltage 20 kV and a temperature of 25 degrees C), complete resolution of the six molecules was accomplished. Preliminary results for repeatability and the migration order of the optimised method are described.

Simultaneous Chiral Separation of Geometry Isomers and Enantiomers of Nateglinide by Capillary Electrophoresis with Mixture of CD Derivations as Chiral Selector

A capillary electrophoresis (CE) method for the simultaneous separation of geometry isomers and enantiomers of nateglinide was built. Several different dyclodextrin (CD) derivatives were tested for the chiral separation of nateglinide, and it was proved that ionic CDs [i.e., carboxymethy-β-CD (CM-β-CD) and sulphonic-β-CD (S-β-CD)] could show better chiral selectivity for both geometry isomers and enantiomers than the neutral CDs. The separation of geometry of both isomers and enantiomers of nateglinide was obtained by CE in a 75-µm i.d. × 60 cm (effective length 45 cm) fused-silica capillary at 11 kV voltage, while 30 mM phosphate (pH = 8.38) acted as running buffer and a mixture of 40 mM S-β-CD + 21 mM CM-β-CD served as chiral selector. The detective wavelength was set at 254 nm.

Simultaneous chiral separation and determination of ephedrine alkaloids by MEKC‐ESI‐MS using polymeric surfactant I: Method development

In this work, simultaneous separation of eight stereoisomers of ephedrine and related compounds ((+/-)-ephedrine, (+/-)-pseudoephedrine, (+/-)-norephedrine and (+/-)-N-methylephedrine) was accomplished using a polymeric chiral surfactant, i.e. polysodium N-undecenoxycarbonyl-L-leucinate (poly-L-SUCL) by chiral (C)MEKC-ESI-MS. The conditions of CMEKC were first investigated. The baseline separation of all eight stereoisomers of ephedrine and related compounds was achieved under optimum CMEKC conditions (35 mM poly-L-SUCL, 15 mM NH(4)OAc, pH 6.0, 30% v/v ACN, 30 kV and 20 degrees C) in less than 30 min. Next, a central composite design for response surface modeling has been described to evaluate the electrospray chamber parameters and the sheath liquid conditions. Optimum mass abundance of stereoisomers of ephedrine and related compounds was observed using the spray chamber parameters, namely 250 degrees C drying gas temperature and 8 L/min drying gas flow rate at a nebulizer pressure of 4 psi. Furthermore, the experimental design indicates that the optimum mass abundance of the stereoisomers of ephedrine and related compounds can be obtained using a sheath liquid containing 80:20 v/v methanol-water, 5 mM NH(4)OAc at pH 8.5 delivered at 5 microL/min. Finally, compared to MEKC-UV, the use of poly-L-SUCL in MEKC-MS provided significantly higher sensitivity for stereoisomers of ephedrine and related compounds.

Simultaneous chiral separation of ephedrine alkaloids by MEKC‐ESI‐MS using polymeric surfactant II: Application in dietary supplements

Chiral MEKC-MS method was utilized for separation, identification, and quantitation of ten enantiomers of ephedrine and related compounds. Enantioselective separations of all ephedrine alkaloids were accomplished through a combination of polysodium N-undecenoxycarbonyl-L-leucinate (poly-L-SUCL) with 30% v/v ACN. Interestingly, the more hydrophilic stereoisomers were eluted later than the hydrophobic ones indicating that hydrogen bonding interactions are much stronger than hydrophobic interactions in the presence of ACN in chiral MEKC. The method was validated in terms of linearity, LOD, LOQ, precision and robustness. The method was finally used in the analysis of three standard reference materials (SRMs). Results of (-)-ephedrine ranged from 12.49 to 0.24 mg/g, for (+)-pseudoephedrine from 4.04 to 0.019 mg/g, for (-)-norephedrine from 0.36 to 0.0031 mg/g, for (+)-norpseudoephedrine from 0.68 to 0.0052 mg/g, for (-)-methylephedrine from 1.18 to 0.0092 mg/g and for (+)-methylpseudoephedrine from 0.086 to 0.00037 mg/g in the SRMs.