Relationship between resolution and analysis time in chiral subcritical fluid chromatography

Stringham, Rodger W.

doi:10.1002/(sici)1520-636x(1996)8:3<249::aid-chir4>3.0.co;2-c

Cited by 15 publications

(5 citation statements)

References 24 publications

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“…In other cases, resolution is decreased, as in the case of dansylated leucine with trifluoroacetic acid. A confounding factor with these comparisons, however, is that retention has not been normalized to correct for its effect on resolution . Regardless, the large changes in resolution obtained here indicate that additives may be used effectively to enhance chiral selectivity.…”

Section: Resultsmentioning

confidence: 93%

Effect of Mobile Phase Additives in Packed-Column Subcritical and Supercritical Fluid Chromatography

1997

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The effect of mobile phase additives is investigated for a variety of compounds under subcritical and supercritical conditions using packed columns. Retention of hydrogen bond donor/acceptor analytes was found to be more dependent on the presence of mobile phase additives than weak hydrogen bond acceptor analytes. The temperature and pressure of the mobile phase are major factors in the extent of this dependence. Consequently, selectivity between homologous compounds is dependent on both the additive used and the state of the mobile phase. Efficiency is nearly always improved by the presence of mobile phase additives, more so under supercritical conditions than under subcritical conditions. These observations suggest that surface molar excesses of mobile phase additives play a large part in the resulting character of the supercritical chromatographic system.

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Section: Resultsmentioning

confidence: 93%

Effect of Mobile Phase Additives in Packed-Column Subcritical and Supercritical Fluid Chromatography

1997

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“…From the resolution expression a maximum resolution may be defined. As capacity factor approaches infinity This expression has value in determining the potential success of a chiral separation and is also valuable as a term of comparison that is independent of retention variables. For any given chiral column, maximum resolution will be defined by an efficiency term, 1 / 4 N 1/2 , and by a selectivity term, [(α − 1)/α].…”

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confidence: 99%

“Entropically Driven” Chiral Separations in Supercritical Fluid Chromatography. Confirmation of Isoelution Temperature and Reversal of Elution Order

Stringham

Blackwell

1996

Anal. Chem.

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Chiral separations depend upon column efficiency and chiral selectivity. Supercritical fluid chromatography (SFC) has been shown to have pronounced advantages in chiral separations due to its enhanced column efficiency at normal flow rates. Examination of factors affecting selectivity in SFC is crucial to systematic chiral method development. Selectivity is a compromise between differences in enantiomeric binding enthalpy and disruptive entropic effects. Increased temperature will decrease the effect of differences in enantiomer binding enthalpy, eventually decreasing selectivity to a point where the enantiomers coelute. Extension of this thermodynamic theory predicts that further increases in temperature lead to selectivity values of less than 1.0, and elution order of the enantiomers reverses. In this region separations are said to be "entropically driven", and selectivity increases (decreases from 1.0) with temperature. Performing separations in this region is attractive because column efficiency is also expected to increase with temperature. Such entropically driven separations have been observed only in gas chromatography. Most data used to support the application of this theory in SFC have been generated at subcritical temperatures, while theory purports to predict behavior above the critical temperature (T(c)). This approach ignores the effects of traversing the critical temperature in SFC, which is known to have a variety of unpredictable consequences. Work presented here shows the effect of temperatures above T(c) on chromatographic behavior. Contrary to theory, capacity factors increase near T(c) and column efficiency declines. Use of pressures well above the critical pressure lessens these effects. In accordance with theory, selectivity does decrease with temperature through T(c) and isoelution temperatures and two instances of elution order reversal are observed here for the first time in SFC.

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“…This problem is made more difficult by the lack of systematic approaches to chiral chromatographic method development. For any given chiral separation, maximum resolution is defined by an efficiency term, 1 / 4 N 1/2 , and by a selectivity term, (α − 1)/α. Attempts to increase chiral resolution must focus on column efficiency and selectivity.…”

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Effect of Various Modifiers on Selectivity in Packed-Column Subcritical and Supercritical Fluid Chromatography

et al. 1996

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A number of common mobile phase modifiers were characterized by chromatographing monofunctional probe solutes on a cyano-bonded stationary phase under subcritical and supercritical conditions. Solvatochromic analysis techniques were used to characterize the relative selectivity, efficiency, and eluotropic strengths of the various modified mobile phases. Analysis of the combined results suggests that modifier choice may be made in a rational manner to either enhance or mask a particular type of molecular interaction. This control is necessary for challenging applications such as chiral separations. The relative effects of each modifier property change depending on whether the chromatographic system is subcritical or supercritical, thus making knowledge of the phase equilibria associated with the mobile phase essential.

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Relationship between resolution and analysis time in chiral subcritical fluid chromatography

Cited by 15 publications

References 24 publications

Effect of Mobile Phase Additives in Packed-Column Subcritical and Supercritical Fluid Chromatography

Effect of Mobile Phase Additives in Packed-Column Subcritical and Supercritical Fluid Chromatography

“Entropically Driven” Chiral Separations in Supercritical Fluid Chromatography. Confirmation of Isoelution Temperature and Reversal of Elution Order

Effect of Various Modifiers on Selectivity in Packed-Column Subcritical and Supercritical Fluid Chromatography

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