Optimisation of selectivity in the separation of aromatic amino acid enantiomers using sulfated ß‐cyclodextrin and dextran sulfate as pseudostationary phases

Zakaria, Philip; Macka, Mirek; Haddad, Paul R.

doi:10.1002/elps.200305743

Cited by 14 publications

(12 citation statements)

References 27 publications

(26 reference statements)

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“…Unfortunately, while distribution constants are often reported with enantioseparation studies, mobility data are rare. Nevertheless, some published data can be found where measured limit mobilities considerably differ in such systems 49–52. On the other hand, also similar overall limit mobilities were reported in some multi‐CS systems 49, 51, 53, 54.…”

Section: Resultssupporting

confidence: 67%

Enhanced selectivity in CZE multi‐chiral selector enantioseparation systems: Proposed separation mechanism

et al. 2010

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It has been reported many times that the commercial mixtures of chiral selectors (CS), namely highly sulfated beta-CDs (HS-beta-CDs), provide remarkable enantioselectivity in CZE when compared with single-isomer CDs, even single-isomer HS-beta-CDs. This enhanced enantioselectivity of multi-CS enantioseparative CZE is discussed in the light of multi-CS model that we have introduced earlier. It is proposed on a theoretical basis and verified experimentally that the two enantiomers of a chiral analyte under interaction with a mixture of CSs are very likely to differ in their limit mobilities, which is opposite to single-CS systems where the two limit mobilities are likely to be the same. Thus while the enantioseparation is usually controlled by different distribution constants between the two enantiomers and CS used in single-CS systems, an additional, electrophoretic, enantioselective mechanism resulting from different limit mobilities may play a significant role in multi-CS systems. This additional mechanism generally makes the multi-CS systems more selective than the single-CS systems. The possible inequality of limit mobilities is also significant for optimization of separation conditions using mixtures of CSs. A practical example supporting our considerations is shown on enantioseparation of lorazepam in the presence of a commercial mixture of HS-beta-CDs and a single-isomer HS-beta-CD, heptakis(6-O-sulfo)-beta-CD.

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Section: Resultssupporting

confidence: 67%

Enhanced selectivity in CZE multi‐chiral selector enantioseparation systems: Proposed separation mechanism

et al. 2010

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“…Among articles dealing with the determination of interaction constants of various analytes with charged CDs, methanol seems to be the most popular EOF marker . The other often used neutral markers are: mesityl oxide (MO) , DMSO , thiourea (TU) , nitromethane (NM) , ethanol , and acetone . Muzikar et al used water‐gap next to MO to determine EOF mobility and Cai and Vigh used the method of Williams and Vigh mentioned above.…”

Section: Introductionmentioning

confidence: 99%

Determination of effective mobilities of EOF markers in BGE containing sulfated β‐cyclodextrin by a two‐detector method

et al. 2013

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A neutral marker of the EOF can gain a nonzero effective mobility because of its possible interaction with a charged complexing agent, such as a chiral selector in CE. We determined effective mobilities of four compounds often used as EOF markers (dimethyl sulfoxide, mesityl oxide, nitromethane, and thiourea) in the BGE-containing sulfated β-CD (60 g/L). All the compounds studied were measurably mobilized by their interaction with the selector. The highest effective mobility (-3.0·10(-9) m(2) s(-1) V(-1)) was observed for thiourea and the lowest (-1.5·10(-9) m(2) s(-1) V(-1)) for dimethyl sulfoxide and nitromethane. The mobilities were determined by a new two-detector pressure mobilization method (2d method), which we propose, and the results were confirmed by standard CE measurements. In the 2d method, one marker zone is situated in the BGE containing the charged selector, while the second marker zone is surrounded with a selector-free BGE, which prevents its complexation. The initial distance between the two marker zones equals the capillary length from the inlet to the first detector. After a brief voltage application, the final distance between the marker zones is determined based on known capillary length from the first to the second detector. The difference between these two distances determines the effective mobility.

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“…Both literature [19,36,38] and Eq. (5) show that pH largely impacts the separation: ] will be a peak-shaped curve rising from the points of extreme pH, with the maximum being dependent on samples species.…”

Section: Eluent Ph and Buffer Reagentmentioning

confidence: 98%

Chiral ion‐exchange capillary electrochromatography of arylglycine amides with dextran sulfate as a pseudostationary phase

Chen

Han

et al. 2005

Electrophoresis

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A low-cost tunable chiral ion-exchange capillary electrochromatographic method has been developed for the separation of arylglycine amide racemic mixtures with dextran sulfate (DS) as an anionic and chiral pseudostationary phase and Tris-tartrate as a buffer system. The concentrations of DS and Tris had opposite influences on retention and resolution and could serve as ideal factors to finely tune the running speed and chiral resolution. Tartrate and pH largely impact the separation but pH should be confined within 3.0-5.5, only suitable for coarse tuning, while tartrate was preserved as the key buffering reagent, normally maintained at 40 mmol/L. With a working system composed of 0.1-1.0% DS, 20-60 mmol/L Tris, and 40 mmol/L tartrate at pH 3.50-4.50, the enantioresolution of arylglycine amides was shown to be dependent on their chemical structure: The chiral resolution increased when the hydrogen at the alpha-amino group or at the p-position of phenyl ring was replaced by other larger group(s) but the resolution decreased when the group at the o- or m-site on the phenyl ring was enlarged. Further, the electronegative substitute of -Cl had larger resolution increment than methyl or methoxy at the position p- of phenyl ring but much lower increment at position m-. It is possible to well explain the resolution variation phenomenon by considering the group resistance and the variation of hydrogen-bonds formed inside the amino amides and between the solutes and DS. The amido group was shown irreplaceable to have chiral resolution with DS alone as an ionic and chiral pseudostationary phase.

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Optimisation of selectivity in the separation of aromatic amino acid enantiomers using sulfated ß‐cyclodextrin and dextran sulfate as pseudostationary phases

Cited by 14 publications

References 27 publications

Enhanced selectivity in CZE multi‐chiral selector enantioseparation systems: Proposed separation mechanism

Enhanced selectivity in CZE multi‐chiral selector enantioseparation systems: Proposed separation mechanism

Determination of effective mobilities of EOF markers in BGE containing sulfated β‐cyclodextrin by a two‐detector method

Chiral ion‐exchange capillary electrochromatography of arylglycine amides with dextran sulfate as a pseudostationary phase

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