Effect of Ionic Liquid on Retention of Solutes on C_(18) Column Based on Linear Solvation Energy Relationships

Several chromatography systems with ionic liquids and a mixture of water with the modifier as mobile phase were characterized via the linear solvation energy relationships(LSER) model. The effects of the ionic liquids and modifier(methanol) concentrations on the retention of 10 solutes(caffeine,pyridine,aniline,phenol,methylparaben,acetopenone,m-cresol,p-cresol,o-cresol,and benzene) were discussed. The LSER model demonstrated high potential to predict retention factors with high squared correlation coeffici...     

Study of the Effect of Mobile Phase Additives on Retention in Reversed Phase HPLC Using Linear Solvation Energy Relationships

Linear solvation energy relationships (LSERs) were used to delineate which specific intermolecular interactions are responsible for changes in retention for a variety of well characterized analytes when acidic and basic additives were used in reversed phase HPLC. The effects of trifluoroacetic acid, triethylamine and a combination of trifluoroacetic acid and triethylamine on the LSERs were compared to those observed in the absence of additives. These effects were examined using four different mobile phase modifiers and five different stationary phases. Trifluoroacetic acid alone and in combination with triethylamine produced LSER regression coefficients nearly identical to those obtained with no additive present in the mobile phase. Triethylamine alone produced different LSER regression coefficients from the other systems unless the mobile phase contained trifluoroethanol as the mobile phase modifier, or the stationary phase consisted of a polymeric support.     

对-叔丁基-杯[4]芳烃键合硅胶及其它硅胶基质键合固定相的色谱保留性质

利用线性溶剂化能相关,在相同色谱条件下,研究了对-叔丁基-杯[4]芳烃键合硅胶固定相与其它硅胶基质键合固定相的反相色谱行为。结果表明,对-叔丁基-杯[4]芳烃键合硅胶固定相和其它固定相在保留机理上有很大不同。控制溶质保留的两个主要因素不是溶质的体积和氢键受体碱性,而是溶质的过剩摩尔折光率和氢键给体酸性。r系数值较大说明π-π作用对溶质的保留贡献较为明显,说明该新固定相对高极化率溶质如稠环芳烃具有较高的选择性。     

用线性溶剂化能相关(LSERs)方法评价聚合物包覆钛胶固定相并与相关固定相比较

利用线性溶剂化能相关(LSERs)方法对聚(乙基苯乙烯-二乙烯基苯)包覆钛胶固定相(ES-DVB-TiO₂)的保留行为进行评价,并与聚丁二烯涂覆钛胶固定相(PBD-TiO₂),键合硅胶固定相(ODS)和树脂固定相(PR-1)作了比较,计算出各变最对logk'的百分方差数,发现V₂、Σα₂^H,和Σβ₂^H对logk'有较大的贡献,与聚合物固定相PRP-1近似,因此它们有相似的保留机理,即吸附机理大于分配机理.     

Retention mechanism of a cholesterol-coated C18 stationary phase: van't Hoff and Linear Solvation Energy Relationships (LSER) approaches

This study examines the effect of temperature on the dynamic cholesterol coating of a C18 stationary phase and the effect of this coating on the retention mechanism. In general, an increase in temperature results in a decrease in the mass of cholesterol coated on the stationary phase. Typically, an increase in temperature from 25°C to 55°C results in a nearly 60% reduction in the mass of cholesterol loaded. The inclusion of temperature, along with loading solvent composition and cholesterol concentration in the loading solvent, allows for loading a targeted amount of cholesterol on the stationary phase over an order-of-magnitude range. In addition to loading studies, the retention mechanism of small non-ionizable solutes was examined on cholesterol-coated stationary phases. A van't Hoff analysis was performed to assess retention thermodynamics, while a LSER approach was used to examine retention mechanism. With 50/50 water/organic mobile phases, the addition of cholesterol results in an increase in the entropic contribution to retention, with a decrease in the enthalpic contribution. The opposite trend is seen with 40/60 water/organic mobile phases. LSER system constants are also affected by a cholesterol coating on the stationary phase, with some changing to favor elution and others changing to favor retention.     

Linear Solvation Energy Relationships in the Determination of Specificity and Selectivity of Stationary Phases

The retention of fifty structurally different compounds has been studied using linear solvation energy relationships. Investigations were performed with the use of six various stationary phases with two mobile phases (50/50 % v/v methanol/water and 50/50 % v/v acetonitrile/water). Packing materials were home-made and functionalized with octadecyl, alkylamide, cholesterol, alkyl-phosphate and phenyl molecules. This is the first attempt to compare all of these stationary phases synthesized on the same silica gel batch. Therefore, all of them may be compared in more complex and believable way, than it was performed earlier in former investigations. The phase properties (based on Abraham model) were used to the classification of stationary phases according to their interaction properties. The hydrophilic system properties s, a, b indicate stronger interactions between solute and mobile phase for most of the columns. Both e and v cause greater retention as a consequence of preferable interactions with stationary phase by electron pairs and cavity formation as well as hydrophobic bonds. However, alkyl-phosphate phase has different retention properties, as it was expressed by positive sign of s coefficient. It may be concluded that most important parameters influencing the retention of compounds are volume and hydrogen bond acceptor basicity. The LSER coefficients showed also the dependency on the type of organic modifier used as a mobile phase component.

     

Linear Solvation Energy Relationships in the Determination of Specificity and Selectivity of Stationary Phases

The retention of fifty structurally different compounds has been studied using linear solvation energy relationships. Investigations were performed with the use of six various stationary phases with two mobile phases (50/50?% v/v methanol/water and 50/50?% v/v acetonitrile/water). Packing materials were home-made and functionalized with octadecyl, alkylamide, cholesterol, alkyl-phosphate and phenyl molecules. This is the first attempt to compare all of these stationary phases synthesized on the same silica gel batch. Therefore, all of them may be compared in more complex and believable way, than it was performed earlier in former investigations. The phase properties (based on Abraham model) were used to the classification of stationary phases according to their interaction properties. The hydrophilic system properties s, a, b indicate stronger interactions between solute and mobile phase for most of the columns. Both e and v cause greater retention as a consequence of preferable interactions with stationary phase by electron pairs and cavity formation as well as hydrophobic bonds. However, alkyl-phosphate phase has different retention properties, as it was expressed by positive sign of s coefficient. It may be concluded that most important parameters influencing the retention of compounds are volume and hydrogen bond acceptor basicity. The LSER coefficients showed also the dependency on the type of organic modifier used as a mobile phase component.     

Reversed-Phase Liquid Chromatography with Mixed Eluents: Partition Model of Retention for Ionogenic Solutes

Abstract

Basing on the pure partition model of solute retention new theoretical equations for ionogenic solutes are discussed. These equations define dependence of the capacity ratio on the mobile phase composition, which is characteristic for the reversed-phase liquid chromatography.     

Retention of Ionized Solutes in Reversed-Phase High Performance Liquid Chromatography

Abstract

The mechanism of retention in reversed-phase high performance liquid chromatography is affected by both solute-eluent interactions and the nature of the stationary phase. The hydrophobic expulsion of ionized solutes plays a major role in affecting solute behavior in the water-rich range of hydroorganic eluents. In the water-lean range of eluent composition, there is little hydrophobic expulsion, and specific interactions between the solute and surface can be observed. The nature of the surface affects the retention of a variety of ionized species, both large cations and anions. Octadecylsilane (ODS) bonded phases can exhibit two different binding sites: one exhibiting a weak interaction and the second a strong specific interaction with a solute. Styrenedivinylbenzene polymeric surfaces exhibit the potential for weak dispersion interactions, and in addition pi-bonding interactions with a solute. A variety of solutes have been injected in a water: methanol eluent system in order to assess solute-surface effects on reversed-phase supports.     

阴离子型胶束液相色谱的溶质保留行为

以SDS阴离子表面活性剂作流动相,酸性、中性及两性药物为受试药物,运用三相平衡理论考察影响阴离子型胶束液相色谱（AMLC）溶质保留行为的几个因素。保留由溶质与胶束相及修饰后固定相的综合作用决定。有机调节剂正丙醇的加入改变了溶质从水相到固定相或到胶束相的平衡,保留取决于溶质疏水性和静电性间的平衡。此外对羟基苯甲酸酯类同系物的亲脂性与3种细菌最小抑菌浓度具有显著相关性,提示其抑菌机理主要取决于药物与生物膜的亲和性。     

溶质在动态改性氧化锆液相色谱柱上的保留行为

分别采用硬脂酸、环糊精和十二烷基磺酸钠动态改性自制的ZrO2微球,研究了流动相中甲醇和改性剂浓度对苯酚及苯甲酸的衍生物、苯胺衍生物及芳香烃类化合物的色谱保留行为的影响。中性及碱性化合物的保留时间较短,色谱峰对称;酸性化合物保留时间较长,色谱峰拖尾较严重。改性氧化锆表现出反相色谱性能。     

Factors Influencing the Isothermal Retention Indices of 51 Solutes on 12 Stationary Phases of Different Polarity: Applicability of the Solvation Parameter Model

Isothermal retention indices (I) at 333–413 K on 12 stationary phases (SPs) covering a wide polarity range of a variety of volatile solutes belonging to 7 one-heteroatom chemical function series and 10 non-series solutes have been determined. The I values were computed with a method (LQG method) which does not require the determination of holdup times of the chromatographic column. I values of some compounds never before studied are reported. The influence on the retention indices of the column temperature, methylene number, and polarity of both the stationary phase and the solute has been studied. The solvation parameter model (SPM) as a function of I has been used for predicting I values, and for unraveling the influence of the polarity of stationary phase and solute on the retention indices. Seeley et al.’s formulation of the SPM has been used for quantifying the influence of polar and non-polar interactions on the I, and for checking the agreement between calculated and experimental values. According to our results, the I values obtained by the modified SPM can be considered equal to the experimental I values at the 99 % confidence level.

     

Solvatochromic Linear Solvation Energy Relationships (LSER) for Solubility of Gases in Various Solvents by Target Factor Analysis

A linear solvation free energy relationship has been conducted to study the effects of solvent and solute properties on the free energy of solvation of inert gases and normal alkanes in different solvents. Factor analysis combined with target factor analysis was used to identify and quantify the factors controlling the variation of free energies of solvation, without the need to postulate any priori hypothetical method. Factor analysis of the solvation data revealed that there are two factors affecting the solubility of both types of gases in non‐polar as well as polar solvents. Target testing of the solvent parameters indicated that the Hildebrand solubility parameter of solvents is the major factor controlling the solubility of gases. Moreover, it was found that the coefficient of the Hildebrand solubility parameter in the linear solvation free energy equations has linear correlation with energy of vaporization and Lennard‐Jones force parameter of inert gases and number of carbon atoms and energy of vaporization of normal alkanes.     

Hybrid Solvation Model with First Solvation Shell for Calculation of Solvation Free Energy

We present a hybrid solvation model with first solvation shell to calculate solvation free energies. This hybrid model combines the quantum mechanics and molecular mechanics methods with the analytical expression based on the Born solvation model to calculate solvation free energies. Based on calculated free energies of solvation and reaction profiles in gas phase, we set up a unified scheme to predict reaction profiles in solution. The predicted solvation free energies and reaction barriers are compared with experimental results for twenty bimolecular nucleophilic substitution reactions. These comparisons show that our hybrid solvation model can predict reliable solvation free energies and reaction barriers for chemical reactions of small molecules in aqueous solution.     

Quantitative Structure-Retention Relationship Studies with Biopartitioning Micellar Chromatography Systems by Amended Linear Solvation Energy Relationships in Consideration of Electronic Factor

Linear solvation energy relationship (LSER) amended by the introduction of a molecular electronic factor was employed to establish quantitative structure-retention relationship of biopartitioning micellar chromatography (BMC) system. The chromatographic indices, log k, were determined by LC on a C18 column for sixty-five structurally diverse compounds, including neutral (32), acidic (19) and basic (14) compounds. Two micellar mobile phases composed of 0.04 mol L^?1 polyoxyethylene (23) lauryl ether (Brij35) were adjusted by phosphate buffer to pH 7.4 and pH 6.5, respectively. When the mean net charge per molecule (δ) was introduced into LSER as the sixth variable, the LSER regression coefficients and predictive capability were significantly improved. However, the δ coefficients of the amended LSER were quite different for acidic and basic compounds, indicating that the molecular electronic factor had a markedly different impact on the retention of acidic and basic compounds in the studied BMC system. This may attribute to the extra interaction for ionized compounds with the free silanol groups in the stationary phase. The comparison of calculated and experimental retention indices suggested that the amended LSER could reproduce adequately the retention of the structurally diverse solutes investigated in BMC.     

Prediction of Retention Time of Solutes under Linear Gradient Elution Conditions in RP-HPLC

A model for prediding retention time of solutes undeir linear gradient elulioa conditions has been established. In this model,the theorelkal expressions under different eluflon modes were derived and tested with the retention behaviors of p-hydroxy-benzaldehyde, vanilUn, biphenyl, phenanthrene in gradient elution. With halting into account the dwell time of the instrumeatal system, the theoretically predicted retention times agreewell with those experimentally determined.     

反相液相色谱中溶质保留参数间的定量关系研究

 比较了Snyder经验公式中的K0w 与S和溶质计量置换保留模型 (SDM R)中溶质保留参数Z(1mol溶剂化溶质被溶剂化固定相吸附时 ,在其接触表面处释放出溶剂或置换剂的总摩尔数 )与lgI(与 1mol溶质对固定相的亲和势有关的常数 )之间的定量关系。SDM R中的两个参数间不仅对同系物溶质可以有很好的线性关系 ,而且对非同系物溶质也有很好的线性关系。其线性关系的好坏主要取决于这两个参数数值范围的大小 ,与文献中报告的线性关系取决于是否单因素影响溶质的保留和完全由统计学规律决定的结论不同。     

反相高效液相色谱中流动相线性梯度洗脱条件下溶质保留时间预测的新方法

 在计算溶质的梯度保留时间时 ,根据流动相在色谱柱内的分布规律 ,对溶质在色谱柱内的迁移距离和流动相梯度同时进行校正 ,从而建立了一种预测溶质线性梯度洗脱条件下保留时间的新方法。该方法在不同的仪器系统中 ,对于弱保留和强保留溶质在不同线性梯度洗脱条件下保留时间的预测 ,都具有良好的准确度。以 15种氨基酸和 8种苯的同系物为例 ,该方法对于弱保留溶质保留时间的预测 ,相对平均误差分别为 3 70 %和 4 90 % ,远小于文献方法得到的结果 (2 3 6 1%和 31 16 % ) ;对于强保留溶质保留时间的预测 ,相对平均误差分别为 0 2 1%和6 0 1% ,略小于文献 。