Electrokinetic Chromatography Research Articles

Online preconcentration and determination of five alkaloids in Yangxinshi tablet by large-volume sample stacking and micelle to solvent stacking in cyclodextrin-modified electrokinetic chromatography.

The two-step preconcentration technique consisting of large-volume sample stacking (LVSS) and micelle to solvent stacking (MSS) in cyclodextrin-modified electrokinetic chromatography (CDEKC) was developed for the analysis of five cationic alkaloids in complex Chinese herbal prescriptions. Relevant parameters affecting separation and stacking performance were optimized separately. Under the optimal LVSS-MSS-CDEKC conditions, less analysis time and organic solvent were required, and the enhancement factors of analytes ranged from 12 to 15 compared with the normal CDEKC separation mode. Further, all validation results demonstrated good applicability and multiple alkaloids (epiberberine, dehydrocorydaline, jatrorrhizine, coptisine and berberine) in Yangxinshi tablet (YXST) have been simultaneously determined. This approach presents powerful potential for the determination of multiple components in complex preparations of Chinese medicine.

Multi-criteria decision analysis: technique for order of preference by similarity to ideal solution for selecting greener analytical method in the determination of mifepristone in environmental water samples

This work proposes the use of multi-criteria decision analysis (MCDA) to select a more environmentally friendly analytical procedure. TOPSIS, which stands for Technique for Order of Preference by Similarity to Ideal Solution, is an example of a MCDA method that may be used to rank or select best alternative based on various criteria. Thirteen analytical procedures were used in this study as TOPSIS input choices for mifepristone determination in water samples. The input data, which consisted of these choices, was described using assessment criteria based on 12 principles of green analytical chemistry (GAC). Based on the objective mean weighting (MW), the weights for each criterion were assigned equally. The most preferred analytical method according to the ranking was solid phase extraction with micellar electrokinetic chromatography (SPE-MEKC), while solid phase extraction combined with ultra-high performance liquid chromatography tandem mass spectrometry (SPE-UHPLC-MS/MS) was ranked last. TOPSIS ranking results were also compared to the green metrics NEMI, Eco-Scale, GAPI, AGREE, and AGREEprep that were used to assess the greenness of thirteen analytical methods for mifepristone determination. The results demonstrated that only the AGREE metric tool correlated with TOPSIS; however, there was no correlation with other metric tools. The analysis results suggest that TOPSIS is a very useful tool for ranking or selecting the analytical procedure in terms of its greenness and that it can be easily integrated with other green metrics tools for method greenness assessment.

Simultaneous separation and determination of seven biphenyl cyclooctene lignans in Schisandra chinensis and its preparations by micellar electrokinetic chromatography with dual organic solvent system.

Gomisin is a natural dibenzo cyclooctene lignan, which is mainly derived from the family Magnoliaceae. It has anti-inflammatory, antioxidant, anti-tumor, anti-aging, and hypoglycemic effects. Gomisins play important roles as medicines, nutraceuticals, food additives, and cosmetics. The objective of this study is to establish a micellar electrokinetic chromatography (MEKC) method for simultaneous separation and determination of seven biphenyl cyclooctene lignans (Gomisin D, E, G, H, J, N, and O) in Schisandra chinensis and its preparations. The method was optimized by studying the effects of the main parameters on the separation. The method has been validated and successfully applied to the determination of seven Gomisins in S.chinensis and its preparations. In the separation system, the running buffer was composed of 20 mM Na2HPO4, 8.0 mM sodium dodecyl sulfate (SDS), 11% (v/v) methanol, and 6.0% (v/v) ethanol. A diode array detector was used with a detection wavelength of 230 nm, a separation voltage of 17 kV, and an operating temperature of 25°C. Under this condition, the seven analytes were separated at baseline within 20 min, and a good linear relationship was obtained with correlation coefficient ranging from 0.9919 to 0.9992. The limit of detection (LOD, S/N = 3) and the limit of quantification (LOQ, S/N = 10) ranged from 0.8 to 0.9μg/mL and from 2.6 to 3.0μg/mL, respectively. The recovery rate was between 99.1% and 102.5%. The experimental results indicated that this method is suitable for the separation and determination of seven Schisandra biphenyl cyclooctene lignan compounds in real samples. At the same time, it provides an effective reference for the quality control of S.chinensis and its preparations.

Nanoconfined Electrokinetic Chromatography (NEC): Gradient Separation and Sensing of Short DNA Fragments at the Single-Molecule Level.

Glass nanopipets have been demonstrated to be a powerful tool for the sensing and discrimination of biomolecules, such as DNA strands with different lengths or configurations. Despite progress made in nanopipet-based sensors, it remains challenging to develop effective strategies that separate and sense in one operation. In this study, we demonstrate an agarose gel-filled nanopipet that enables hyphenated length-dependent separation and electrochemical sensing of short DNA fragments based on the electrokinetic flow of DNA molecules in the nanoconfined channel at the tip of the nanopipet. This nanoconfined electrokinetic chromatography (NEC) method is used to distinguish the mixture of DNA strands without labels, and the ionic current signals measured in real time show that the mixed DNA strands pass through the tip hole in order according to the molecular weight. With NEC, gradient separation and electrochemical measurement of biomolecules can be achieved simultaneously at the single-molecule level, which is further applied for programmable gene delivery into single living cells. Overall, NEC provides a multipurpose platform integrating separation, sensing, single-cell delivery, and manipulation, which may bring new insights into advanced bioapplication.

Combination of large-volume sample stacking with polarity switching and micelle electrokinetic chromatography for the analysis of anion compounds in Yangxinshi tablets.

Yangxinshi tablet (YXST) is a traditional Chinese medicine preparation characterized by its high efficacy and safety for the treatment of cardiovascular diseases. Anionic compounds have been revealed as potential active components. However, there is currently limited research regarding its quality control. We aimed to establish a strategy for the simultaneous separation and determination of five key anionic compounds in YXST. A sensitive and efficient analytical method was developed and applied for the simultaneous separation and determination of five key compounds in YXST using large-volume sample stacking with polarity switching and micelle electrokinetic chromatography (LVSS-PS-MEKC) coupled with diode array detection. Crucial parameters, including sample volume, applied voltage, composition and pH of the running buffer, concentration of organic modifier, and switching time of the polarity, were systematically evaluated and optimized using a single variable method to enhance separation performance. Furthermore, the impact of cyclodextrin and sodium dodecyl sulfate as electrolyte modifiers was also investigated. Under the optimal conditions, baseline separation of the five compounds (daidzein, puerarin, glycyrrhiztinic acid, chlorogenic acid, and salvianolic acid B) was achieved within 20 min. In comparison to the conventional MEKC mode, the constructed LVSS-PS-MEKC method exhibited a more than sixfold increase in the enrichment factor. The method was validated in terms of linearity, precision, accuracy, 24 h stability, and recovery and successfully applied to analyze YXST samples. A sensitive strategy was developed for the simultaneous separation and determination of five key anionic components in YXST, offering a robust and efficient strategy for pharmaceutical analysis.

Purines recognition and quantitative analysis by surface-enhanced Raman spectroscopy

The common quantification methods of purines, including high-performance liquid chromatography, micellar electrokinetic chromatography, reverse phase ion pair chromatography, and capillary zone electrophoresis, have been used for the analysis of purines. These conventional techniques are limited by long operation times, large sample volumes, requirements for pretreatment and separation processes, or sophisticated, bulky and expensive equipment. Here, we have developed a simple method to prepare a probe for the quantitative analysis of purines using the surface-enhanced Raman scattering (SERS) method. The SERS probe is a rough Ag wire obtained with simple electrochemical treatment, which is optimized to reach the maximum SERS signal enhancement. The Raman enhancement factor (EF) of Ag wire after roughening can reach ∼106. Under optimized conditions, the rough Ag wire is capable of recognizing four purine bases (namely, guanine, adenine, hypoxanthine, and xanthine) in the range of 10−5 to 10−1 mg/mL with a linear relationship between SERS intensity of signature peak and purine concentration. The recovery rate of each purine base is higher than 80% in the mixture of four purines. The overall method was successfully applied to the monitoring of the level of purines in marketplace beer beverages. The novel wire-based SERS sensor used with portable Raman spectroscopy is prospective in diet safety and personalized point-of-care medical detection.

Separation and determination of phenolic compounds using novel deep eutectic solvent-in-water microemulsion electrokinetic chromatography

BackgroundMicroemulsion electrokinetic chromatography (MEEKC) is a mode of capillary electrophoresis with a wide range of applications in which microemulsion is utilized as background electrolyte to achieve the separation of analytes. Microemulsions are composed of oil droplets, aqueous buffer, surfactant, and co-surfactant. Currently, conventional organic reagents act as the most commonly used oil phase in microemulsions, which are unfriendly to the environment. Recently, deep eutectic solvent (DES) has become a new type of eco-friendly solvent due to its non-toxicity. Therefore, it is of great value to establish a new MEEKC method by replacing conventional organic reagents as the oil phase with DES. ResultsThe novel DES/W MEEKC method was established for phenolic compounds in Senecio scandens samples. Single-factor experiments and response surface methodology were performed to systematically optimize the crucial parameters for the method, including the type and content of the oil phase, surfactant content, concentration of borax buffer, and pH of the background solution.Under the optimized conditions, satisfactory regression curves were established for all standard analytes with correlation coefficients ≥0.9990. The method featured high sensitivity and favorable accuracy, with the instrumental detection limit in the range of 0.22–1.04 μg/mL, and intraday and interday precision for migration time expressed as relative standard deviations of 0.18–0.82% and 1.25–2.50%, respectively. The DES/W MEEKC method was successfully applied to Senecio scandens with good recoveries of 87.72–106.99%. In conclusion, the newly established DES/W MEEKC method is highly efficient, green and environmentally friendly. SignificanceDES is considered a green and efficient solvent. The DES/W MEEKC method is highly efficient and environmentally friendly. Actually, the method provides a novel and effective analytical tool for the simultaneous separation and determination of multiple phenolic compounds, especially in complex plant matrices. In the future, the DES/W MEEKC method still has the prospect of being widely used in the separation of other complex phytochemicals.

Abstract TP162: Polyamine Levels Are Elevated After Intracerebral Hemorrhage

Introduction: Intracerebral hemorrhage (ICH) has high morbidity and mortality without available targets for intervention. Polyamines are metabolites implicated in neurological diseases such as traumatic brain injury, Alzheimer’s Disease, and ischemic stroke. No studies have evaluated polyamines as they relate to ICH occurrence or outcomes. In this pilot study, we sought preliminary data on whether polyamines could be potential novel targets to improve outcomes after ICH. Methods: We analyzed plasma samples from 7 ICH cases and 10 control participants from the Genetics and Environmental Risk Factors for Stroke (GERFHS) IV study for polyamine measurements using Capillary Electrophoresis with Laser Induced Fluorescence Detection with the modality of Micellar Electrokinetic Chromatography. Plasma samples were deproteinized and derivatized with Fluorescein Isothiocyanate. Samples were spiked with standard solutions and compared with standard curves developed per each polyamine. We report median age and sex of the cohort. Peak spermine, spermidine and putrescine levels were compared using a student’s t-test. Results: In this pilot study of participants enrolled into GERFHS IV (median age 67 vs 61, cases vs controls respectively, 50% female) all three unacetylated polyamine levels were higher in cases. Although sample size is modest, there was a trend towards increased spermidine levels with higher mRS at 90 days (r 2 = 0.3342) (Figure 1). Conclusions: For the first time, we have shown that polyamines are elevated after ICH, and that higher polyamine levels may be associated with worse outcomes. This preliminary data supports further evaluation of polyamines as potential targets to improve outcomes after ICH in a larger cohort.

Rapid indirect separation of glutamine enantiomers by micellar electrokinetic chromatography. Analysis of dietary supplements.

Glutamine is the most abundant free proteinogenic α-amino acid. It is naturally produced in the organism and acts as a precursor for the synthesis of different biologically important molecules (such as proteins or nucleotides). However, under stressful conditions, the organism is unable to produce it in enough amounts to function properly. Thus, glutamine (Gln)-based supplements have become increasingly popular over the last decade. Since legal regulations establish that amino acid-based dietary supplements must contain only the L-enantiomer and not the racemate, adequate chiral methodologies are required to achieve their quality control. In this work, an analytical methodology based on the use of micellar electrokinetic chromatography is proposed for the rapid enantiomeric determination of DL-Gln in dietary supplements. Using (+)-1-(9-fluorenyl)-ethyl chloroformate as a derivatizing agent and ammonium perfluorooctanoate as separation medium, the Gln diastereoisomers formed under optimal conditions were separated in 8min with a resolution of 2.8. The analytical characteristics of the method were evaluated in terms of linearity, precision, accuracy, and limits of detection/quantitation, and they were found appropriate for the analysis of L-Gln-based dietary supplements.

Analysis of Mass Transfer Kinetics at Lipid Bilayer Membranes of Liposome by Means of Electrokinetic Chromatography and Moment Theory

Analysis of Mass Transfer Kinetics at Lipid Bilayer Membranes of Liposome by Means of Electrokinetic Chromatography and Moment Theory

Rapid enantiomeric separation of indacaterol by electrokinetic chromatography

The first chiral methodology enabling the separation of indacaterol enantiomers was developed in this work by cyclodextrin-electrokinetic chromatography. Indacaterol (IND) is a chiral drug marketed as a pure enantiomer. Then, the separation and quantification of each enantiomer is of great importance for the quality control of pharmaceutical formulations. After selecting the most suitable chiral selector and background electrolyte, two Box-Behnken designs were achieved to optimize the electrophoretic conditions using two different approaches to shorten analysis times: i) decreasing the capillary length, or ii) performing a short-end injection. Indacaterol enantiomers were separated in less than 5 min with a resolution value of 3.6 under the optimal separation conditions: 0.7% (m/v) carboxymethyl-α-cyclodextrin in 50 mM sodium formate buffer (pH 4.0) and using a short-end injection. Then, the analytical characteristics of the method were evaluated and LODs of 0.05 mg/L for S-IND and 0.04 mg/L for R-IND were achieved. Also, the method allowed the detection of a 0.1% enantiomeric impurity (S-IND) in the R-IND-based pharmaceutical formulations. The developed method was applied to the analysis of two pharmaceutical formulations. Percentages of 97 ± 3% and 103 ± 6% of R-IND with respect to the labeled amounts were found.

Chiral separation of propranolol by electrokinetic chromatography using nanodiamonds and human serum albumin as a pseudo-stationary phase in river water.

Propranolol is currently considered as an emerging contaminant in water bodies. In this study, R- and S-propranolol were determined in river samples by electrokinetic chromatography (EKC) using nanodiamonds (NDs) and human serum albumin (HSA) as a pseudo-stationary phase in order to achieve enantioseparation. Previously, river samples were preconcentrated using a column filled with Amberlite® IR-120 and Dowex® 50WX8 resins. The setting up of influential factors such as temperature, voltage, pH, and HSA and NDs concentration is accurately described along this manuscript. A multivariate study and optimization was carried out to obtain the enantioseparation of propranolol (Rs = 2.91), which was reached under the following experimental conditions: voltage of 16 kV, temperature of 16°C, phosphate buffer pH 9.5, NDs of 0.20%, and HSA of 15 μmol l-1 . The recoveries of analytes under optimal conditions were higher than 98%. The limits of detection were 0.85 μg l-1 for R- and S-propranolol. The method was applied to real samples, and the obtained results in three different water sources studied were 1.02, 0.59, and 0.30 μg l-1 for the R-enantiomer and 0.99, 0.54, and 0.28 μg l-1 for the S-enantiomer. The accuracy of the proposed methodology (including bias and precision) has allowed us to propose it as a successful tool for the control of water quality.

Ability of biomimetic chromatography and physicochemical systems to predict the skin permeation of neutral compounds. A comparison study

Five in vitro physicochemical systems have been evaluated in terms of its ability to emulate the skin permeation of neutral compounds: the permeation in two different PAMPA membranes, the classical octanol-water partition coefficient, and two biomimetic chromatography systems, one based in cerasome electrokinetic chromatography and another based in reversed-phase liquid chromatography measurements.The coefficients of the solvation parameter model equation of the mentioned systems have been compared to the ones of the skin permeation process through different comparison parameters. Moreover, a method to predict whether a physicochemical system is able to emulate satisfactorily a biological one, just by the analysis of the equation coefficients has been developed. Results reveal that the two PAMPA systems are a good choice to emulate directly the skin permeation of neutral compounds. Instead, the other three systems need a volume correction term to provide a satisfactory emulation. However, after the correction, all the evaluated systems show a similar ability to emulate well skin permeation, as predicted.

Capillary electrokinetic chromatography for chiral separation of potential SARS-CoV-2 3CL protease inhibitors.

In this work, a capillary electrophoresis method was developed as a quality control tool to determine the enantiomeric purity of a series of five chiral compounds evaluated as potential severe acute respiratory syndrome coronavirus 2 3CL protease inhibitors. The first cyclodextrin tested, that is, highly sulfated-β-cyclodextrin, at 6% (m/v) in a 25mM phosphate buffer, using a capillary dynamically coated with polyethylene oxide, at an applied voltage of 15kV and a temperature of 25°C, was found to successfully separate the five derivatives. The limits of detection and quantification were calculated together with the greenness score of the method in order to evaluate the method in terms of analytical and environmental performance. In addition, it is noteworthy that simultaneously high-performance liquid chromatography separation of the enantiomers of the same compounds with two different columns, the amylose tris(3,5-dimethylphenylcarbamate)-coated and the cellulose tris(3,5-dichlorophenylcarbamate)-immobilized on silica stationary phases, was studied. Neither the former stationary phase nor the latter was able to separate all derivatives in a mobile phase consisting of n-heptane/propan-2-ol 80/20 (v/v).

Capillary electrophoresis separations with deep eutectic solvents as greener separation media: A proof-of-concept study

Capillary electrophoresis (CE) has conventionally been classified into aqueous and non-aqueous categories based on the types of buffer solvents employed. Traditionally, non-aqueous CE has always been associated with the use of organic solvents, which are considered hazardous to health and environmentally detrimental. In this work, we introduce deep eutectic solvents (DESs) as CE separation media for the first time, presenting a novel and environmentally friendly approach to CE separations. The DES employed consists of proline and urea (Proline:Urea, PU), both of which are naturally occurring compounds that are readily available, cost-effective, and environmentally benign. Various fundamental aspects of the DES-type CE media were investigated, including thermal property, viscosity, electroconductivity, Joule heating effect, and compatibility with detectors. A simulated complex mixture of ten naphthalene-based compounds with varied charges and sizes was separated using the DES-based medium in capillary zone electrophoresis (CZE) mode. Moreover, we also established a DES-based micellar electrokinetic chromatography (MEKC) system utilizing Tween-20 as the surfactant. Six structurally similar naphthalene derivatives (isomers) that couldn't be resolved by CZE were effectively separated due to their strong hydrophobic interaction with Tween-20 micelles within the DES medium. Given that DESs are “designer” solvents with highly tunable properties and environmentally friendly characteristics, this study demonstrates the potential of employing DESs as an alternative to organic solvents for greener CE separations.

Determination of vitamins K1 and K3 in green tea and in pharmaceutical supplements by capillary micellar electrokinetic chromatography

A method based on capillary micellar electrokinetic chromatography (MEKC) was developed for vitamin K1 and K3 determination. Experimental and instrumental parameters optimized for electrophoretic separation with better peak efficiency were: borate buffer at 0.05 mol L−1, pH 8.5, cetyltrimethylammonium bromide (CTAB) at 0.05 mol L−1, acetonitrile 20 % v/v, 25 °C and a negative potential difference of 30 kV. Sample introduction was made by hydrodynamic at 50 mbar for 15 s. Migration times for vitamins K1 and K3 were (5.2 ± 0.1) and (3.4 ± 0.1) min respectively. Limits of detection and quantification were on the order of 10−5 g L−1 and 10−4 g L−1. For vitamin K1, the precision was between 2 and 7 % for the peak area. Recoveries were 101 ± 2 % and 103 ± 2 % for green tea and vitamin supplement samples, respectively. For vitamin K3, recoveries were 99 ± 3 % for vitamin supplement. Comparative tests were performed with the reference method based on liquid chromatography with agreement of results. The uncertainty and the contribution of the relevant sources was carefully evaluated. The method was found adequate to enable reliable and sensitive measurements of different forms of vitamin K with low consumption of solvents and less generation of waste.

On-line concentration and separation of multiple derivatized monosaccharides from edible fruit with cyclodextrin-encapsulated sweeping by micellar electrokinetic chromatography

An on-line enrichment and separation of multiple derivatized monosaccharides with cyclodextrin-encapsulated sweeping (CDES) by micellar electrokinetic chromatography (MEKC) was presented. Five monosaccharides (L-(−)-Mannose, D-(+)-Glucose, D-(−)-Ribose, D-(+)-Xylose, and L-(+)-Rhamnose) were derivatized with 1-phenyl-3-methyl-5-pyrazolone, subsequently concentrated and separated by MEKC. The optimized conditions were as follows: 50 mM phosphoric acid (PA), 100 mM sodium dodecyl sulfate (SDS), and 30 % (v/v) methanol in background solution; 140 s injection of sample solution containing 50 mM CD and 100 mM PA, followed by 90 s injection of 40 mM SDS solution. Under the optimized conditions, the correlation coefficients ≥ 0.9953, and the limits of detection ranged from 4.2 to 7.4 ng/mL. Relative standard deviation values ranged from 0.24–4.23 %, and sensitivity enrichment factors were in the range of 53–82 compared with typical injection (50 mbar, 3 s). The CDES-MEKC method was successfully applied to Jujube with good recoveries of 84.22–104.33 %. The method provides new ideas for the on-line enrichment and detection of trace monosaccharides and even other target analytes in foods with complex matrices.

Analytical Methods and Regulative Viewpoint of Antimicrobial Preservatives in Cosmetics

Cosmetics need to be resistant to microbial contamination to protect consumer health and increase shelf life, much like any other product containing water, organic and inorganic components. The aims of anti-microbiological activity are to protect consumers from potentially harmful bacteria and to preserve products subject to degradation. Chemical, physical, or physicochemical methods are used to ensure this. Organic acid preservatives, alcohols, formaldehyde releasers, halogenated preservatives, isothiazolinones, quaternary ammonium salts and chlorhexidine are among the preservatives included in the legislation. Indeed, high quantitiesare more successful from a preservation standpoint, nevertheless they are toxic to consumers, whereas low amounts can lead to microbial resistance. Accordingly, the criteria of several international legislation and validation methods for introducing microbiologically safe items to the market have become essential. Although there are many approaches based on gas chromatography (GC) as per literature, the most common methods for the determination of preservatives are based on liquid chromatography (LC). Both of these procedures, as well as capillary electrophoresis (CE) and micellar electro kinetic chromatography (MEKC), have been frequently utilized in the cosmetics industry to determine preservative levels. Analytical approaches have been primarily focused on parabens, whereas the number of available methods to investigate other preservatives is limited. There is a tendency toward the usage of miniature extraction processes where new and improved sample preparation and extraction techniques including matrix solid-phase dispersion, solid-phase extraction, pressurized liquid extraction/supercritical fluid extraction and microextraction-based method have been introduced with high levels of efficiency and extraction capacities. Considering the significance and relevance of preservatives in cosmetics, this study highlights the most recent state-of-the-art information on their safety and regulatory concerns. Given the rising influence on consumer health, sample preparation and analytical methods forpreservative detection were also investigated which have been proposed by the international scientific literature.
 Keywords: Preservatives, Cosmetics, Analytical Techniques, Derivatization, Extraction

A novel cation-selective exhaustive injection and sweeping micellar electrokinetic chromatography method for the simultaneous determination of second-generation triazoles in human plasma

In this study, we introduce the first capillary electrophoresis method that combines cation-selective exhaustive injection and sweeping micellar electrokinetic chromatography (CSEI-sweeping-MEKC) for the simultaneous and sensitive quantification of voriconazole (VRC), posaconazole (PSC), and isavuconazole (ISV) levels in human plasma. The sensitivity was remarkably improved, with a 5374-fold enhancement compared to the traditional MEKC method. We systematically optimized key parameters affecting sensitivity, resolution, and efficiency. The separation buffer included 100 mM NaH2PO4, 13 % acetonitrile, and 13 % tetrahydrofuran. This was followed by a high-conductivity buffer zone (1 psi, 50 s) of 100 mM NaH2PO4, an extended electrokinetic sample injection (10 kV, 600 s), and analyte sweeping with 100 mM sodium dodecyl sulfate micelles at −20 kV. Under these optimized conditions, the method allowed for an analytical run in 10 min and was validated for linearity (r ≥ 0.9997), precision (%RSD ≤ 8.8 %), and accuracy (%RE ≤ 2.20 %), delivering satisfactory results. The limit of detection was 2.55 ng/mL for ISV, 0.89 ng/mL for PSC, and 1.04 ng/mL for VRC. This method was successfully applied to analyze plasma samples from patients undergoing triazole antifungal treatment, demonstrating its feasibility for clinical testing.

Study on the interactions between RS-licarbazepine and carboxyethylated cyclodextrins by electrokinetic chromatography and nuclear magnetic resonance

The interactions taking place in the enantiomeric separation of the antiepileptic drug licarbazepine by Electrokinetic Chromatography (EKC) using two carboxyethylated cyclodextrins (CE-CDs) (CE-β-CD and CE-γ-CD) as chiral selectors were investigated in this work to intend to explain the reversal in the enantiomer migration order observed depending on the CD. As these CDs were mixtures of isomers, only apparent and estimated association constants for enantiomer-CD complexes could be calculated based on EKC experiments, which agreed with the enantiomer migration order observed for CE-β-CD but not for CE-γ-CD. Additional experiments were carried out using NMR to study the stoichiometry of the complexes formed, their association constants and their structure. The construction of the corresponding Job plots, from 1H NMR titrations and intermolecular NOE interactions (between some of licarbazepine’s aromatic protons and the internal hydrogens of both CDs), permitted to conclude in the formation of 1:1 inclusion complex in both cases. Also, Scott plots for both systems were obtained showing a linear behavior for CE-β-CD while a non-linear behavior was observed for CE-γ-CD. As a result, only the apparent association constant for licarbazepine-CE-β-CD complexes was calculated (0.309 mM−1) (no significant differences between licarbazepine enantiomers were found in all NMR experiments). The structure of the complexes originated by licarbazepine and both CE-CDs was investigated. Insertion complexes were formed in each case, although some structural differences were noticed as the licarbazepine-CE-γ-CD complex would be less tight than that with CE-β-CD. Molecular dynamics (MD) simulations corroborated the structures derived from NMR results.