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1.
The capillary electrophoretic separation of cationic enantiomers with single-isomer multivalent anionic resolving agents was reexamined with the help of the charged resolving agent migration model. Three general model parameters were identified that influence the shape of the separation selectivity and enantiomer mobility difference curves: parameter b, the binding selectivity (K(RCD)/K(SCD)), parameter s, the size selectivity (mu0(RCD)/mu0(SCD)), and parameter a, the complexation-induced alteration of the analyte's mobility (mu0(RCD)/mu0). In addition to the previously observed discontinuity in separation selectivity that occurs as mu(eff) of the less mobile enantiomer changes from cationic to anionic, a new feature, a separation selectivity maximum was predicted to occur in the resolving agent concentration range where both enantiomers migrate cationically provided that (i) K(RCD)/K(SCD) <1 and mu0(RCD)/mu0(SCD) >1 and (K(RCD)mu0(RCD))/(K(SCD)mu0(SCD)) > 1, or (ii) K(RCD)/K(SCD) >1 and mu0(RCD)/mu0(SCD) <1 and (K(RCD)mu0(RCD))/(K(SCD)mu0(SCD)) <1. This hitherto unseen separation selectivity pattern was experimentally verified during the nonaqueous capillary electrophoretic separation of the enantiomers of four weak base analytes in acidic methanol background electrolytes with octakis(2,3-diacetyl-6-sulfato)-gamma-cyclodextrin (ODAS-gammaCD) as resolving agent. 相似文献
2.
The capillary electrophoretic separation of noncharged enantiomers with single-isomer anionic resolving agents is reexamined here with the help of the charged resolving agent migration model. Two general model parameters have been identified that influence the effective mobility, separation selectivity and mobility difference curves of the enantiomers: parameter b, called binding selectivity (K(RCD)/K(SCD)), and parameter s, called size selectivity (mu(o)RCD/mu(o)SCD). Analysis of the model in terms of these parameters indicates that in addition to the known, previously observed separation selectivity vs. resolving agent concentration patterns, a new pattern, increasing separation selectivity with increasing resolving agent concentration, is also possible provided that (i) K(RCD)/K(SCD)<1 and mu(o)RCD/mu(o)SCD>1 and (K(RCD)mu(o)RCD)/(K(SCD)mu(o)SCD)>1, or (ii) K(RCD)/ K(SCD)>1 and mu(o)SCD/mu(o)SCD<1 and (K(RCD)mu(o)RCD)/(K(SCD)mu(o)SCD)<1. This hitherto unseen separation selectivity pattern was experimentally verified during the capillary electrophoretic separation of the enantiomers of O-isopropyl p-nitrophenyl methylphosphonate with the single-isomer octakis(2,3-diacetyl-6-sulfato)-gamma-cyclodextrin as resolving agent. 相似文献
3.
The newest member of the single-isomer isomer sulfated cyclodextrin family, octakis(2,3-diacetyl-6-sulfato)-gamma-cyclodextrin (ODAS-gamma-CD) was used for the first time as a resolving agent for the nonaqueous capillary electrophoretic separation of the enantiomers of 26 weak base pharmaceuticals in an acidic methanol background electrolyte. The solubility limit of ODAS-gamma-CD at room temperature proved to be 55 mM in this background electrolyte, which afforded good, fast enantiomer separations for most of the basic drugs tested. For all the bases studied, the effective mobilities and separation selectivities were found to follow the predictions of the charged resolving agent migration model of electrophoretic enantiomer separations. The effective mobilities of the weakly binding weak bases remained cationic throughout the entire 0 to 45 mM ODAS-gamma-CD concentration range; separation selectivities increased as the ODAS-gamma-CD concentration was increased. The effective mobilities of the moderately binding weak bases became anionic in the 2.5 to 45 mM ODAS-gamma-CD concentration range; separation selectivities first increased as the effective mobilities approached zero, then decreased again as the ODAS-gamma-CD concentration was increased further. The effective mobilities of the strongly binding weak bases became anionic in the 0 to 2.5 mM ODAS-gamma-CD concentration range; separation selectivities decreased as the ODAS-gamma-CD concentration was increased above 2.5 mM. 相似文献
4.
The dichloride salt of mono-6-deoxy-6-N,N,N',N',N'-pentamethylethylenediammonio-cyclomaltoheptaose (PEMEDA-BCD), the first single-isomer, monosubstituted, permanently dicationic beta-CD has been synthesized, analytically characterized, and used for the capillary electrophoretic separation of the enantiomers of a group of analytes in acidic and basic BGEs. When the concentration of PEMEDA-BCD was changed in the BGEs, the resulting effective mobilities of the analytes and the respective separation selectivities followed the predictions of the ionic strength-corrected charged resolving agent migration model. Good separation selectivities and favorable normalized EOF mobilities allowed for the rapid, efficient separation of the enantiomers of anionic, weak acid and nonionic analytes in the low- and/or high-pH BGEs. 相似文献
5.
The sodium salt of the single-isomer, chiral resolving agent, octakis(2,3-diacetyl-6-sulfo)-gamma-cyclodextrin (ODAS-gammaCD) has been used for the capillary electrophoretic separation of the enantiomers of alkylarylphosphates which carry a phosphorus-based stereogenic center. The effective mobilities and separation selectivities were measured at different ODAS-gammaCD and methanol concentrations to find the conditions under which the minor enantiomers could be adequately quantitated in samples obtained by chemical resolution of the racemic mixtures. This work extends the utility of ODAS-gammaCD to a hitherto unexplored field, the capillary electrophoretic separation of the enantiomers of organophosphorus compounds. 相似文献
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The second member of the single-isomer, sulfated gamma-cyclodextrin family, the sodium salt of octa(6-O-sulfo)-gamma-cyclodextrin (OS) has been synthesized, characterized and used to separate the enantiomers of nonelectrolyte, acidic, basic, and ampholytic analytes by capillary electrophoresis in acidic aqueous background electrolytes. The anionic effective mobilities of the nonelectrolyte and anionic analytes increased with increasing concentration of OS. The effective mobilities of strongly complexing cationic analytes became anionic with very low OS concentrations and passed local anionic effective mobility maxima as the OS concentration, and along with it, the ionic strength, of the background electrolyte increased. The effective mobilities of the weakly binding cationic analytes became only slightly anionic at high OS concentration values and did not show the local anionic effective mobility maxima. For nonelectrolyte analytes, separation selectivities decreased with increasing OS concentration. For cationic analytes, separation selectivities were highest where the effective mobilities of the less mobile enantiomers approached zero. OS proved to be a broadly applicable chiral resolving agent. 相似文献
8.
The sodium salt of heptakis(2-O-methyl-6-O-sulfo)cyclomaltoheptaose (HMS), the second single-isomer, sulfated beta-CD carrying nonidentical substituents at all of the C2, C3, and C6 positions, has been synthesized, analytically characterized, and used for the capillary electrophoretic separation of the enantiomers of a group of 23 weak base analytes in acidic aqueous and methanolic BGEs. HMS interacted strongly with only about half of the analytes studied. The good separation selectivities and favorable normalized EOF mobilities allowed for rapid, efficient separation of the enantiomers of 19 of the 23 weak base analytes in the aqueous BGEs, often with separation selectivity values complimentary to those obtained with other single-isomer sulfated CDs. HMS did not prove to be as good a resolving agent in acidic methanolic BGEs as its counterpart, heptakis(2-O-methyl-3-O-acetyl-6-O-sulfo)cyclomaltoheptaose. 相似文献
9.
A novel approach to continuous, preparative-scale electrophoretic enantiomer separations has been developed based on the observation that stable, equal-but-opposite effective mobilities can be created for the enantiomers of a single-charged analyte by complexing them with a single-isomer, multiply charged resolving agent, provided that the charge of the resolving agent is opposite in sign to that of the uncomplexed analyte enantiomers. When such an analyte-resolving agent system is fed into a continuous, free-flow electrophoretic apparatus, stable, steady-state operating conditions can be established which permit the continuous feeding of the racemic analyte and the collection of pure enantiomers at the opposite sides of the feed stream. This concept is demonstrated via the separation of the enantiomers of terbutaline using heptakis-6-sulfato beta-cyclodextrin as resolving agent, affording production rates as high as 2.8 mg/h in the general-purpose, continuous free-flow electrophoretic system, the Octopus. 相似文献
10.
A rapid, simple method is proposed here for the identification of the experimental conditions that lead to satisfactory preparative-scale isoelectric focusing enantiomer separations in continuous free-flow electrophoretic units. The method first calls for the use of a commercially available, full-column imaging capillary electrophoretic system to find the background electrolyte composition that generates the largest pI difference between the bands of the enantiomers. The method then calls for the finding of the minimum residence time that permits full development of the pH gradient across the separation chamber of the continuous free-flow electrophoretic unit by measuring the pH in the sample-free carrier electrolyte fractions collected during these runs. Finally, the quality of the predicted preparative-scale separation is verified by analyzing the enantiomer-containing collected fractions by capillary electrophoresis using a 14-sulfated, single-isomer cyclodextrin as resolving agent. The pI difference values and production rate values observed in this work agree well with the literature values that were obtained by much more time-consuming methods. 相似文献
11.
The enantiomers of 34 pharmaceutical weak-base analytes were separated by nonaqueous capillary electrophoresis in acidic methanol background electrolytes using the sodium salt of the new, single-isomer chiral resolving agent, octakis(2,3-O-dimethyl-6-O-sulfo)-gamma-cyclodextrin (ODMS). The effective mobilities, separation selectivities and peak resolution values of the weak-base analytes were determined as a function of the ODMS concentration in the 0-40 mM range and were found to follow the theoretical predictions of the charged resolving agent migration model (CHARM model) modified for ionic strength effects. Fast, efficient separations were achieved for both comparatively small and large enantiomers. 相似文献
12.
The enantiomeric separation of some nonsteroidal anti-inflammatory drugs (NSAIDs) was investigated in capillary electrophoresis (CE) using dual systems with mixtures of charged cyclodextrin (CD) derivatives. A significant enhancement of selectivity and resolution could be achieved in the enantioseparation of these analytes in their uncharged form by the simultaneous addition of two oppositely charged CD derivatives to the background electrolyte. The combination of the single-isomer cationic CD, permethyl-6-monoamino-6-monodeoxy-beta-CD (PMMAbetaCD) and the single-isomer polyanionic CD, heptakis-6-sulfato-beta-cyclodextrin (HSbetaCD) in a pH 2.5 phosphoric acid-triethanolamine buffer, was designed and employed for the enantioseparation of profens. The improvement in selectivity and resolution can be attributed to the fact that the two CDs, which lead to independent and enantioselective complexation with the analyte enantiomers, have not only opposite effects on the electrophoretic mobility of these compounds but also opposite affinity patterns towards the enantiomers of these compounds. Binding constants for these enantiomers with each CD were determined using linear regression approach, in order to be able to predict the effect of the concentrations of the two CDs on enantiomeric selectivity and resolution in such dual systems. 相似文献
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Khaldun M. AL Azzam Bahruddin Saad Rohana Adnan Muhammad Idiris Saleh 《Mikrochimica acta》2009,166(3-4):311-317
A fast capillary electrophoretic method is described for the separation and determination of the enantiomers of the novel wake-promoting agent, modafinil. Several parameters affecting the separation were studied, including the type and concentration of chiral selector, buffer pH, buffer concentration, voltage and temperature. Good chiral separation of the racemic mixture was achieved in less than 5 min with resolution factor Rs?=?2.51, using a bare fused-silica capillary and a background electrolyte (BGE) of 25 mM H3PO4?1 M tris solution; pH 8.0; containing 30 mg mL?1 of sulfated-β-cyclodextrin (S-β-CD). The separation was carried out in normal polarity mode at 25 ?C, 18 kV and using hydrostatic injection. Acceptable validation criteria for selectivity, linearity, precision, and accuracy were included. The developed method was successfully applied to the assay of enantiomers of modafinil in pharmaceutical formulations. The computational calculations for the enantiomeric inclusion complexes rationalized the reasons for the different migration times between the modafinil enantiomers. 相似文献
15.
The sodium salt of heptakis(2-O-methyl-3-O-acetyl-6-O-sulfo)cyclomaltoheptaose (HMAS), the first single-isomer, sulfated beta-cyclodextrin carrying nonidentical substituents at all of the C2, C3, and C6 positions, has been synthesized, analytically characterized, and used for the capillary electrophoretic separation of the enantiomers of a group of 24 weak base pharmaceuticals in acidic aqueous and acidic methanolic background electrolytes. HMAS interacted more strongly with most of the analytes studied than heptakis(2,3-di-O-methyl-6-O-sulfo)cyclomaltoheptaose, but less strongly than heptakis(2,3-di-O-acetyl-6-O-sulfo)cyclomaltoheptaose, the respective analogs with identical substituents at the C2 and C3 positions. The good separation selectivities and favorable normalized electroosmotic flow mobilities allowed for rapid, efficient separation of the enantiomers of 19 of the 24 weak base analytes in the aqueous and methanolic background electrolytes. The trends in the effective mobilities and separation selectivities as a function of the HMAS concentration closely followed the predictions of the ionic strength-corrected charged resolving agent migration model. 相似文献
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A method for the enantioseparation of linezolid, the first compound of a truly new class of antibiotics-the oxazolidinones, was developed. The elaborated method of linezolid enantiomers separation was successfully performed using an anionic single-isomer cyclodextrin-heptakis-(2,3-diacetyl-6-sulfato)-beta-cyclodextrin (HDAS-beta-CD) as a resolving agent with the help of the charged resolving agent migration model (CHARM model). The best results were obtained with 27.5mM HDAS-beta-CD dissolved in 50mM borate buffer, pH 9.0, 15 degrees C, normal polarity. The facile strategies for the reversal of the enantiomers elution order are also described. Afterwards, the optimized method was validated in terms of sensitivity, linearity, accuracy and precision. 相似文献
18.
The first single-isomer, 14-sulfated beta-cyclodextrin, the sodium salt of heptakis(2-O-methyl-3,6-di-O-sulfo)-beta-cyclodextrin (HMdiSu) has been used to separate 24 pharmaceutical weak base enantiomers in pH 2.5 background electrolytes using capillary electrophoresis. For the weakly binding bases, the cationic effective mobilities decreased, approached zero, and then increased again. For the strongly binding bases, the cationic effective mobilities decreased, became anionic at very low concentrations of HMdiSu, passed an anionic mobility maximum, then decreased again as the HMdiSu concentration was increased. Viscosity corrections according to Walden's rule did not eliminate these unexpected effective mobility extrema. The mobility extrema were rationalized by extending the charged resolving agent migration model (CHARM model) to include ionic strength effects. 相似文献
19.
A capillary electrophoretic method for the separation of the aminoglutethimide (AGT) enantiomers using methylated-β-cyclodextrin (M-β-CD) as chiral selector is described. Several parameters affecting the separation were studied, including the type and concentration of chiral selector, buffer pH, voltage and temperature. Good chiral separation of the racemic mixture was achieved in less than 9 min with resolution factor Rs = 2.1, using a fused-silica capillary and a background electrolyte (BGE) of tris-phosphate buffer solution (50 mmol L−1, pH 3.0) containing 30 mg mL−1 of M-β-CD. The separation was carried out in normal polarity mode at 25 °C, 16 kV and using hydrostatic injection. Acceptable validation criteria for selectivity, linearity, precision, and accuracy/recovery were included. The proposed method was successfully applied to the assay of AGT enantiomers in pharmaceutical formulations. The computational calculations for the inclusion complexes of the R- and S-AGT-M-β-CD rationalized the reasons for the different migration times between the AGT enantiomers. 相似文献
20.
Enantiomeric separations of six anionic and two neutral racemates were achieved using a fully substituted heptakis(6-hydroxyethylamino-6-deoxy)-beta-cyclodextrin (beta-CD-EA) as a chiral selector. As beta-CD-EA provides a dynamic coating on the capillary wall, reverse-polarity capillary electrophoresis (CE) configuration is applied for separations of anionic and neutral chiral compounds. Chiral separations of various classes of anionic and neutral enantiomers were found to be highly dependent on pH because the degree of protonation of beta-CD-EA can alter the shape of the CD cavity by charge repulsion, altering complexation, aiding selectivity, and leading to better enantiomeric separation. In general, the chiral resolution of anionic enantiomers was enhanced at higher pH. This suggests that carboxylate or phosphate groups on the analyte may interact with the protonated amine groups of cationic CD. The successful enantioseparation was achieved in a pH range of 6.6-7.8 for all six anionic analytes, in the presence of 10 mM beta-CD-EA. 相似文献