Dual selector system
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We introduce an easy but highly descriptive model of separation efficiency of dual-selector systems in capillary electrophoresis. The model expresses effective mobilities of analytes in dual-selector mixtures as a function of mixture composition and total concentration. The effective mobility follows the pattern familiar from single-selector systems, while complexation constant and mobility of the complex are replaced by the same but "overall" parameters and a total concentration of the mixture takes the role of a selector concentration. The overall parameters can be either calculated from the individual ones (an arbitrary mixture) or measured directly (a particular mixture). We inspected two model dual-selector systems consisting of heptakis(2,6-di-O-methyl)-β-CD and β-CD and of heptakis(2,6-di-O-methyl)-β-CD and 6-O-α-maltosyl-β-CD, and ibuprofen and flurbiprofen as model analytes (pH 8.2, non-enantioselective separation). Adopting any optimization strategy typically used in single-selector systems and finding an optimal mixture composition and total concentration is perhaps the prime benefit of the model. We demonstrate this approach on the selectivity parameter and show that the model is precise enough to be used in analytical practice. It also results that an electromigration order (reversal) of analytes can exhibit a rather curious dependency on the mixture composition and concentration. Last, the model can be used for better understanding of separation principles in dual-selector systems in general.
The CE method employing an indirect UV detection for the enantioseparation of 1,3-dimethylamylamine (DMAA), widely used in various preworkout and dietary supplements labeled as a constituent of geranium extract has been developed. The dual-selector system consisting of negatively charged sulfated α-CD (1.1% w/v) and sulfated β-CD (0.2% w/v) in 5 mM phosphate/Tris buffer (pH 3.0) containing the addition of 10 mM benzyltriethylammonium chloride (BTEAC) as the chromophoric additive was used for the enantiomeric separation of DMAA stereoisomers with the LODs in the range of 7.82-9.24 μg/mL. The method was partly validated and applied for the determination of the stereoisomeric composition of DMAA in commercial dietary supplements to verify the potential natural origin of DMAA.
- MeSH
- aminy chemie izolace a purifikace MeSH
- beta-cyklodextriny chemie MeSH
- elektroforéza kapilární přístrojové vybavení metody MeSH
- limita detekce MeSH
- potravní doplňky analýza MeSH
- pufry MeSH
- stereoizomerie MeSH
- ultrafialové záření MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
The aim of this study was to focus on the reduction of chiral selector concentration, sulfated-β-cyclodextrin, in an attempt decrease the running costs associated with separating cetirizine enantiomers by capillary electrophoresis. The decrease in the concentration of chiral selector was achieved by adding D-glucose to the background electrolyte, which consisted of sodium borate. Optimal separation of cetirizine enantiomers was obtained in the electrolyte containing 500 mmol L-1 borate pH 9.5 with 1.0 mg mL-1 sulfated-β-cyclodextrin, and 1000 mmol L-1D-glucose. This means a 15-fold reduction in the concentration of sulfated-β-cyclodextrin. The mechanism of the separation in this electrolyte was investigated using direct injection mass spectrometry. The electrolyte of borate, D-glucose, and sulfated-β-cyclodextrin forms a dual selector system, in which one selector is represented by the sulfated-β-cyclodextrin and the second selector is represented by the D-glucose-borate complexes.
- Publikační typ
- časopisecké články MeSH
Novel capillary electrophoresis methods using CDs as chiral selectors were developed and validated for the chiral separation of lansoprazole and rabeprazole, two proton pump inhibitors. Fourteen different neutral and anionic CDs were screened at pH 4 and 7 in the preliminary analysis. Sulfobutyl-ether-β-CD with a degree of substitution of 6.5 and 10 at neutral pH proved to be the most suitable chiral selector for both compounds. Various dual CD systems were also compared, and the possible mechanisms of enantiomer separation were investigated. A dual selector system containing sulfobutyl-ether-β-CD degree of substitution 6.5 and native γ-CD proved to be the most adequate system for the separations. Method optimization was carried out using an experimental design approach, performing an initial fractional factorial screening design, followed by a central composite design to establish the optimal analytical conditions. The optimized methods (25 mM phosphate buffer, pH 7, 10 mM sulfobutyl-ether-β-CD/20 mM γ-CD, +20 kV voltage; 17°C temperature; 50 mbar/3 s injection, detection at 210 nm for lansoprazole; 25 mM phosphate buffer, pH 7, 15 mM sulfobutyl-ether-β-CD/30 mM γ-CD, +20 kV voltage; 18°C temperature; 50 mbar/3 s injection, detection at 210 nm for rabeprazole) provided baseline separation for lansoprazole (Rs = 2.91) and rabeprazole (Rs = 2.53) enantiomers with favorable migration order (in both cases the S-enantiomers migrates first). The optimized methods were validated according to current guidelines and proved to be reliable, linear, precise, and accurate for the determination of 0.15% distomer as chiral impurity in dexlansoprazole and dexrabeprazole samples.
- MeSH
- cyklodextriny chemie MeSH
- elektroforéza kapilární metody MeSH
- lanzoprazol analýza chemie izolace a purifikace MeSH
- limita detekce MeSH
- lineární modely MeSH
- Rabeprazol analýza chemie izolace a purifikace MeSH
- reprodukovatelnost výsledků MeSH
- stereoizomerie MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Interactions among analyte forms that undergo simultaneous dissociation/protonation and complexation with multiple selectors take the shape of a highly interconnected multi-equilibrium scheme. This makes it difficult to express the effective mobility of the analyte in these systems, which are often encountered in electrophoretical separations, unless a generalized model is introduced. In the first part of this series, we presented the theory of electromigration of a multivalent weakly acidic/basic/amphoteric analyte undergoing complexation with a mixture of an arbitrary number of selectors. In this work we demonstrate the validity of this concept experimentally. The theory leads to three useful perspectives, each of which is closely related to the one originally formulated for simpler systems. If pH, IS and the selector mixture composition are all kept constant, the system is treated as if only a single analyte form interacted with a single selector. If the pH changes at constant IS and mixture composition, the already well-established models of a weakly acidic/basic analyte interacting with a single selector can be employed. Varying the mixture composition at constant IS and pH leads to a situation where virtually a single analyte form interacts with a mixture of selectors. We show how to switch between the three perspectives in practice and confirm that they can be employed interchangeably according to the specific needs by measurements performed in single- and dual-selector systems at a pH where the analyte is fully dissociated, partly dissociated or fully protonated. Weak monoprotic analyte (R-flurbiprofen) and two selectors (native β-cyclodextrin and monovalent positively charged 6-monodeoxy-6-monoamino-β-cyclodextrin) serve as a model system.
