线性溶剂-能量关系模型法评价纤维素三(3,5-二甲基苯基氨基中酸酯)涂敷手性固定相的作用力及其对手性拆分的影响

利用线性溶剂-能量关系模型(LSER)对分别以氨丙基硅胶(APS)和硅胶(SiO2)为基质的两种纤维素三(3,5-二甲基苯基氨基甲酸酯)(CDMPC)手性固定相(CSP)存在的作用力进行研究.利用33种分析物的LSER描述符号及分析物在固定相上的保留时间进行多元线性回归,通过对回归所得到的系统参数的分析来评价固定相存在的作用力.分析表明:两种固定相在正相条件下存在较弱的π-π作用力,较强的偶极-偶极作用力.而氢键作用力的大小受到基质的影响,以APS为基质的固定相给电子能力较强;而以SiO2为基质的固定相给质子能力较强.     

Comments on the paper “Characterization of stationary phases by a linear solvation energy relationship utilizing supercritical fluid chromatography” by C. R. Mitchell,N. J. Benz,S. Zhang

In a recent paper published by Mitchell et al. in this journal, some results obtained in supercritical fluid chromatography and interpreted with the solvation parameter model to characterize interactions for “novel stationary phases” were surprising to us. Indeed, we had already published results for most of the stationary phases reported, but, except for polar phases, our results were not in agreement with those, despite the use of identical mobile phases in both studies. These data were disturbing because they suggest that supercritical fluid chromatography is always a normal‐phase mode, while we have shown that it is a reversed‐phase mode when working with non‐polar stationary phases. In the process of establishing the reason for the differences between our works, we examined several different factors. This paper deals with practice of linear solvation energy relationships: choice of dead‐volume marker, choice of test‐solutes to adequately probe the possible interactions and appropriate column length for characterization of chromatographic systems with highly eluting mobile phases are discussed. The importance of control experiments to validate retention models and confirm their accordance with the chromatographer's experience is evidenced. Recommendations for good linear solvation energy relationship practice are suggested in order to avoid the publication of results leading to erroneous conclusions.     

Characterisation of stationary phases in subcritical fluid chromatography with the solvation parameter model IV. Aromatic stationary phases

The purpose of the present work was to systematically study the chromatographic behaviour of different aromatic stationary phases in a subcritical fluid mobile phase. We attempted to assess the chemical origin of the differences in retention characteristics between the different columns. Various types of aromatic stationary phases, all commercially available, were investigated. The effect of the nature of the aromatic bonding on interactions between solute and stationary phases and between solute and carbon dioxide-methanol mobile phase was studied by the use of a linear solvation energy relationship (LSER): the solvation parameter model. This study was performed to provide a greater knowledge of the properties of these phases in subcritical fluid chromatography, and to allow a more rapid and efficient choice of aromatic stationary phase in regard of the chemical nature of the solutes to be separated. Charge transfer interactions naturally contribute to the retention on all these stationary phases but are completed by various other types of interactions, depending on the nature of the aromatic group. The solvation vectors were used to compare the different phase properties. In particular, the similarities in the chromatographic behaviour of porous graphitic carbon (PGC), polystyrene-divinylbenzene (PS-DVB) and aromatic-bonded silica stationary phases are evidenced.     

Combined supercritical fluid chromatographic tests to improve the classification of numerous stationary phases used in reversed-phase liquid chromatography

In this paper, we present a combination of a key-solute test based on retention and separation factors of large probe solutes (carotenoid pigments) and a quantitative structure-retention relationship analysis based on the retention factors of small probe solutes (aromatic compounds), both performed in supercritical fluid chromatography, to investigate the different chromatographic behaviour of octadecylsiloxane-bonded stationary phases of all sorts: classical, protected against silanophilic interactions or not, containing polar groups (endcapping groups or embedded groups). The results indicate that the two approaches chosen (carotenoid test and solvation parameter model) are complementary and provide precise information on the chromatographic behaviour of ODS phases. The applicability of the classification to the selection of stationary phases is evidenced with some examples of separations.     

Solvation parameter models for retention on perfluorinated and fluorinated low temperature glassy carbon stationary phases in reversed-phase liquid chromatography

The retention of solutes on two fluorinated low temperature glassy carbon (F-LTGC) stationary phases under reversed-phase liquid chromatographic conditions was studied by employing the solvation parameter model. The two fluorinated glassy carbon stationary phases were produced by slowly heating zirconia particles that were encapsulated with oligo[1,3-dibutadiyne-1,3-(tetrafluoro)phenylene] precursor polymer to two different final temperatures (200 and 400 degrees C). The resulting carbon particles had different amounts of fluorine after thermal processing. The solvation parameter models indicated that different intermolecular interactions are important in describing retention on the two stationary phases. The interactions that are important for describing retention on the 200 degrees C processed F-LTGC stationary phase are hydrogen bond basicity> or =dispersion>hydrogen bond acidity>dipolarity/polarizability. The interactions that describe the retention on the 400 degrees C processed F-LTGC are hydrogen bond basicity>dispersion>excess molar refraction> or =hydrogen bond acidity. The solvation parameter model for the 200 degrees C processed F-LTGC showed similar trends in the relative importance of intermolecular interactions as previously found for octadecyl-polysiloxane stationary phases, while the 400 degrees C processed F-LTGC had similar intermolecular interactions with solutes as found with porous glassy carbon in that pi-pi interactions with the carbon surface contribute more so to the retention.     

Characterisation of stationary phases in subcritical fluid chromatography with the solvation parameter model. III. Polar stationary phases

In this third paper, varied types of polar stationary phases, namely silica gel (SI), cyano (CN)- and amino-propyl (NH2)-bonded silica, propanediol-bonded silica (DIOL), poly(ethylene glycol) (PEG) and poly(vinyl alcohol) (PVA), were investigated in subcritical fluid mobile phase. This study was performed to provide a greater knowledge of the properties of these phases in SFC, and to allow a more rapid and efficient choice of polar stationary phase in regard of the chemical nature of the solutes to be separated. The effect of the nature of the stationary phase on interactions between solute and stationary phases and between solute and carbon dioxide-modifier mobile phases was studied by the use of a linear solvation energy relationship (LSER), the solvation parameter model. The retention behaviour observed with sub/supercritical fluid with carbon dioxide-methanol is close to the one reported in normal-phase liquid chromatography with hexane. The hydrogen bond acidity and basicity, and the polarity/polarizability favour the solute retention when the molar volume of the solute reduces it. As with non-polar phases, the absence of water in the subcritical fluid allows the solute/stationary phase interactions to play a greater part in the retention behaviour. As expected, the DIOL phase and the bare silica display a similar behaviour towards acidic and basic solutes, when interactions with basic compounds are lower with the NH2 phase. On the CN phase, all interactions (hydrogen bonding, dipole-dipole and charge transfer) have a nearly equivalent weight on the retention. The polymeric phases, PEG and PVA, provide the most accurate models, possibly due to their better surface homogeneity.     

Combined supercritical fluid chromatographic methods for the characterization of octadecylsiloxane-bonded stationary phases

In this paper, we present a combination of a key-solute test based on retention and separation factors of large probe solutes (carotenoid pigments) and a quantitative structure-retention relationship analysis based on the retention factors of small probe solutes (aromatic compounds) to investigate the different chromatographic behavior of octadecylsiloxane-bonded stationary phases of all sorts: classical, protected against silanophilic interactions or not, containing polar groups (endcapping groups or embedded groups). Varied chemometric methods are used to enlighten the differences between the 27 phases tested. The results indicate that the two approaches chosen (carotenoid test and solvation parameter model) are complementary and provide precise information on the chromatographic behavior of ODS phases.     

Characterization of stationary phases in subcritical fluid chromatography by the solvation parameter model. I. Alkylsiloxane-bonded stationary phases

Varied types of alkylsiloxane-bonded and fluoroalkylsiloxane-bonded stationary phases, all commercially available, were investigated with subcritical fluid mobile phase. The effect of the alkyl chain length (from C4 to C18) and of the nature of the bonding (fluorodecylsiloxane, phenyl-C18 and polar-embedded-C18) on the chromatographic behaviour was investigated by the use of a linear solvation energy relationship (LSER), the solvation parameter model. A large set of test compounds provides precise and reliable information on the intermolecular interactions responsible for retention on these stationary phases used with a subcritical mobile phase. First of all, the results underline the close properties between subcritical fluid and organic liquid. The use of non aqueous mobile phases reduces the cavity energy and the mobile phase acidity generally encountered with aqueous liquid phases, allowing other interactions to take a part in retention. As expected, an increase in the alkyl chain length favours the dispersive interactions between the solutes and the stationary phases. Changes in basicity and acidity of the stationary phases are also related to the chain length, but, in this case, mobile phase adsorption onto the stationary phase is supposed to explain these behaviours. The addition of a phenyl group at the bottom of the C18 chain, near the silica, does not induce great modifications in the retentive properties. The fluorodecylsiloxane and the polar-embedded alkylsiloxane phases display very different properties, and can be complementary to the classical alkylsiloxane-bonded phases. In particular, the fluorinated phase does not favour the dispersive interactions, in comparison to hydrogenated stationary phases, when the basicity of the polar-embedded phase is obviously greater than the one of classical alkylsiloxane-bonded phases, due to the amide function. Finally, logk-logk curves plotted between the different phases illustrate the effect of the interaction properties on the retention of different classes of compounds.     

Retention properties of novel β-CD bonded stationary phases in reversed-phase HPLC mode

With the given special structures, the CD bonded stationary phases are expected to have complementary retention properties with conventional C18 stationary phase, which will be helpful to enhance the polar selectivity in RP mode separation. In this work, two β-cyclodextrin (β-CD) bonded stationary phases for reversed-phase HPLC, including 1, 12-dodecyldiol linked β-CD stationary phase (CD1) and olio (ethylene glycol) (OEG) linked β-CD stationary phase (CD2), have been synthesized via click chemistry. The resulting materials were characterized with FT-IR and elemental analysis, which proved the successful immobilization of ligands. The similarities and differences in retention characteristics between the CD and C18 stationary phases have been elucidated by using comparative linear solvation energy relationships (LSERs). The force related to solute McGowan volume has no significant difference, while the hydrogen bonding and dipolar interactions between solutes and CD stationary phases are stronger than between solutes and C18, which is attributed to the special structures (CD and triazole groups) of CD stationary phases. Chemical origins are interpreted by comparison between CD1 and CD2. Similar dispersive interactions of CD1 and CD2 are attributed to their similar length of spacer arms. CD2 which contains OEG spacer arm has relative weaker HBD acidity but stronger HBA basicity. CD stationary phases display no serious different methylene selectivity and higher polar selectivity than in the case of C18. Higher acid selectivity and lower basic selectivity are observed on CD2 than on CD1. Distinctive retention properties and good complementary separation selectivity to C18 make the novel CD bonded stationary phases available for more application in RPLC.     

Mobile phase effects on retention on a new butylimidazolium-based high-performance liquid chromatographic stationary phase

A new HPLC stationary phase based on n-butylimidazolium bromide has been characterized by a linear solvation energy relationship (LSER) approach in the binary acetonitrile/water mobile phases. The retention properties of the stationary phase were systematically evaluated in terms of intermolecular interactions between 28 test solutes and the stationary phase. The results and further comparisons with conventional reversed phase system confirm that retention properties are similar to phenyl phases in acetonitrile/water mixtures. The results obtained with acetonitrile/water mixtures are also compared with results obtained using methanol/water mixtures.     

Solute-solvent interactions from gas chromatographic activity coefficients and the solvation parameter model for nitrogen-containing stationary phases

Infinite dilution gas-liquid chromatographic activity coefficients (gamma) and excess thermodynamic molar partial magnitudes [Gibbs energy (G(E)), enthalpy (H(E)), and entropy (S(E))] for 37 solutes of varied polarity on four stationary phases with -NH groups are obtained from partition coefficients taken from literature. Relationships between G(E) and S(E) with the 37 solutes' structure in terms of the molecular connectivity index ((1)chi(v)) are investigated. Correlations of solute-solvent interactions calculated in light of the solvation parameter model for selected solutes and stationary phases are tested. The effect of the solute's structure, expressed as the molecular connectivity index, on the nonpolar (cavity formation and dispersion interaction) [c+l. log L(16)] and the effect of the dipole moment and of the activity coefficient on the dipolarity-polarizability interaction (spi(2)(H)) are studied. The correlation between the nonpolar interaction with the athermal activity coefficient on the nonpolymeric stationary phases is also attempted. In addition, the influence of the stationary phase polarity on the solute-stationary phase interactions for a series of solutes is studied.     

Retention characteristics of a new butylimidazolium-based stationary phase. Part II: anion exchange and partitioning

A surface-confined ionic liquid (SCIL) and a commercial quaternary amine silica-based stationary phase were characterized employing the linear solvation energy relationship (LSER) method in binary methanol/water mobile phases. The retention properties of the stationary phases were evaluated in terms of intermolecular interactions between 28 test solutes and the stationary phases. The comparison reveals a difference in the hydrophobic and hydrogen bond acceptance interaction properties between the two phases. The anion exchange retention mechanism of the SCIL phase was demonstrated using nucleotides. The utility of the SCIL phase in predicting logk _IL/water values by chromatographic methods is also discussed.