气液色谱中串联柱、多相柱与均相柱的保留体积的热力学讨论

本文测定了一些溶质在一些二元固定液串联柱、多相柱与均相柱的比保留体积,应用三元体系的Flory-Huggins公式以及两种不同溶剂的Flory-Huggins型相互作用参数数据,揭示了溶质在这些柱中比保留体积异同的热力学原因.     

反相液相色谱中计量置换线性参数logI的热力学特征

依据液相色谱中溶质计量置换保留模型及线性参数 log I(与 1mol溶质对固定相的亲和势大小有关的常数 ) ,通过作图得知非极性和极性小分子溶质及生物大分子的 log I与绝对温度的倒数 1/T,以及小分子溶质的log I与其在正辛醇 -水中分配系数的对数 log Po/ w呈线性关系 ,从两方面进一步证明了 log I具有热力学平衡常数的性质。基于小分子溶质、生物大分子的 log I和分配系数大小的差别 ,对两者在反相液相色谱中的保留对柱长的依赖关系给予了定量的说明     

MECC保留值与logP的相关性

研究了不同有机改性剂下胶束电动毛细管色谱 (MECC)中电中性化合物的保留值与其正辛醇 水分配系数 (logP)间的相关性。结果表明 :溶质在MECC中的保留值 (logk′)与logP的相关性决定于MECC体系在分配行为上与正辛醇 水体系的相似性 ,用logk′w 代替logk′并不能改善相关性 ;溶质的受质子碱性是影响相关性的最主要的溶质性质 ;使用有机改性剂可以调节溶质在MECC体系中的分配行为接近于正辛醇 水体系 ,THF是调节溶质受质子碱性的影响的最佳有机改性剂 ;要使MECC体系在溶质分配行为上全面接近于正辛醇 水体系 ,同时加入两种作用相互补充的有机改性剂可能是更好的方法     

反相液相色谱中计量置换线性参数logI的热力学特征

 依据液相色谱中溶质计量置换保留模型及线性参数logI(与1mol溶质对固定相的亲和势大小有关的常数),通过作图得知非极性和极性小分子溶质及生物大分子的logI与绝对温度的倒数1/T,以及小分子溶质的logI与其在正辛醇-水中分配系数的对数logPo/w呈线性关系,从两方面进一步证明了logI具有热力学平衡常数的性质。基于小分子溶质、生物大分子的logI和分配系数大小的差别,对两者在反相液相色谱中的保留对柱长的依赖关系给予了定量的说明。     

色谱柱分离过程的驰豫理论--溶质非平衡线性分配流出曲线的特征

假设溶质在两相间非平衡线性分配,根据色谱柱分离过程驰豫理论的基本模型,得到了反映各输运参量与流出曲线间关系的卷积形式表达式。采用统计矩的方法加以研制,说明了在柱效较低、流动相线速较快时可能出现的峰分裂现象。研究结果也表明,在线性色谱的情况下,两相间非平衡传质是影响峰形对称性的最重要原因。     

醋酸水流动相体系中硅胶键合相上生物大分子保留行为的研究

 提出了以醋酸 水作为流动相的体系中 ,在ODS柱上分离生物大分子的反相高效液相色谱 (RPLC)方法。实验结果表明 ,醋酸 水的洗脱能力强于甲醇 水 三氟醋酸体系 ,在一定程度上克服了色谱分离中一些蛋白质的不可逆吸附且具有便于冷冻干燥的优点。用参数Z(1mol溶剂化溶质被溶剂化固定相吸附时从两者接触表面释放出置换剂的摩尔总数 ) ,logI(与 1mol溶质对固定相亲和势有关的常数 )和 j(与 1mol溶剂对固定相亲和势有关的常数 )对 9种蛋白质在此流动相体系中的保留进行了表征。     

磺酸甜菜碱型两性离子亲水作用色谱固定相的制备及色谱性能评价

以丙烯酸二甲氨基乙酯(DMAEA)和1,3-丙磺酸内酯为原料,合成了含磺酸甜菜碱型两性离子的N,N-二甲基-N-丙烯酰氧乙基-N-丙基磺酸铵(DMAEAPS)功能单体,通过原子转移自由基聚合(ATRP)技术将其接枝到硅胶表面,制备了磺酸甜菜碱型两性离子色谱固定相(Sil-DMAEAPS)。研究了该固定相对安息香、维生素B6、芸香叶苷、对香豆酸和咖啡酸5种极性溶质的亲水作用色谱分离性能。结果表明,在典型的亲水作用色谱条件下,极性溶质的保留主要由静电作用和亲水作用控制;而在典型的反相色谱条件下,极性溶质则表现出反相柱的分离特征。与ZIC-HILIC商品柱进行对比,自制色谱柱对5种极性溶质表现出不同的分离选择性。将自制色谱柱用于芦丁片中芸香叶苷含量的测定,操作方法简单,为极性样品的分离提供了新方法。     

逆流溶质出峰顺序的预测

 根据逆流保留方程可知,溶质的出峰顺序主要取决于其在互不混溶的两液相间分配系数的大小顺序。以饱和及不饱和脂肪酸乙酯、2,4 二硝基苯胺基脂肪醇和对硝基苯基葡萄糖甙等结构较为简单、极性差别较大的溶质系列为研究对象,应用修正的通用基团活度系数(UNIFAC)(Dortmund)模型,通过相平衡计算,预测了它们在含水或不含水的溶剂体系中分配系数的变化趋势,并与前人的工作进行了对比。结果表明,由该方法预测出的相似结构溶质分配系数的顺序基本上与实验值相同,其中对饱和脂肪酸乙酯在己烷 乙腈(体积比为1∶1)体系中分配系数的预测最好。     

胶束反相高效液相色谱最佳化研究

本文介绍以YWG-C_(18)为固定相,十二烷基硫酸钠(SDS)胶束溶液为移动相,探讨了SDS浓度和柱温对胶束反相高效液相色谱分离最佳化的影响。测定了胶束体系中苯胺的热力学函数ΔH~0值及SDS的临界胶束浓度(C.M.C.),还讨论了非极性和极性溶质的保留机理。     

手性化合物的毛细管胶束电动色谱分离研究

以4种不同的N-长链烷酰-L-氨基酸胶束为手性选择剂,对3种不同性质的手性化合物(α-氯代丙酰替苯胺,2-氨基-3-对硝基苯基-1,2-丙二醇和华法林)的毛细管胶束电动色谱分离进行研究.结果表明,手性表面活性剂中不同的氨基酸残基和烷基链的长度对分离影响较大;随手性表面活性剂浓度增加,溶质保留时间增大,分离度增加,不同溶质的最佳分离浓度在100～150mmol/L之间;pH对电中性手性化合物分离影响不大,但对酸性或碱性手性化合物的分离影响较大.在选定的条件下,3种样品均在20min内完全分离,分离柱效达1×10⁵理论板数/m.     

Application of linear solvation energy relationships to polymeric pseudostationary phases in micellar electrokinetic chromatography

Polymerized sodium 11-acrylamidoundecanoate (poly(Na 11-AAU)) was used as a pseudostationary phase (PSP) for micellar electrokinetic chromatography to separate uncharged compounds. The polymer PSP showed signifcantly different solute migration behaviors from conventional micelles including sodium dodecyl sulfate and poly (sodium 10-undecylenate), giving high separation efficiencies (>200000 theoretical plates/m). Linear solvation energy relationships were used to evaluate and characterize the chemical interactions that influence the retention behavior in the poly (Na 11-AAU) micellar system. It was found that the solute volume and solute hydrogen bond basicity mainly influenced the retention. The characteristic feature of the poly (Na 11-AAU) micellar system is that the micelle has a significantly higher capacity for dipole-dipole and dipole-induced dipole interactions as well as a slightly higher capacity for electron pair interactions than the aqueous phase. Due to its unique selectivity, the poly(Na 11-AAU) micellar system would become an attractive new option for selectivity optimization on methods development.     

Application of micellar electrokinetic chromatography to pharmaceutical analysis

Electrokinetic chromatography is a new type of analytical separation method which belongs to the group of high performance capillary electrophoretic techniques but whose separation principle is based on that of chromatography. The solute distributes itself between a carrier and the surrounding medium. The carrier, which corresponds to the stationary phase in conventional chromatography, can be transported by electrophoresis with a different velocity from the surrounding medium. The separation is achieved by the differential solute distribution and the differential migration of the carrier. The charged molecules or charged molecular aggregates are employed as the carrier. Various kinds of carriers are available for electrokinetic chromatography along with different partition mechanisms. Among them, micellar electrokinetic chromatography, which employs an ionic micelle as a carrier, has become the most popular method because of its unique and attractive characteristics as well as the separating capability of electrically neutral or nonionic solutes in comparison with capillary zone electrophoresis. The present paper describes the principle, separation characteristics and its application to the analysis of pharmaceuticals.     

Spectral curve deconvolution in micellar systems with H-point curve isolation and H-point standard addition methods

A method for spectral curve deconvolution is described, evaluated and applied to micellar systems. The technique is based on combination of H-point curve isolation method (HPCIM) and H-point standard addition method (HPSAM). HPCIM is used for extracting the spectrum of solute in micellar pseudophase and HPSAM is used for calculation of equilibrium concentrations of solute in aqueous phase for each sample. The outputs of procedure are spectrum of dye molecules in micellar pseudophase free from contribution of the dye in the aqueous phase, and partition coefficients of considered solutes between micelle and water phase. The effects of noise and extent of solute partitioning on the reliability of the method are evaluated using model data. The applications of the method to the study of interaction of two different solutes, m-cresol purple (m-CP) and Azure C with Brij-35 and 2-amino-cyclopentene-1-dithiocarboxylic acid (ACDA) with cetyltrimethylamonium bromide (CTAB) micellar systems are presented.     

Micellar electrokinetic chromatography in coated capillaries: Determination of micelle–aqueous partition coefficients

A micellar electrokinetic chromatography method is presented for the determination of the partition coefficient for the distribution of nonpolar and moderately polar solutes between the micelle and the aqueous phases in aqueous micellar solutions. In comparison with the literature the method is, theoretically and experimentally, the most straightforward for this application. An equation is derived for the determination of the partition coefficient in a coated fused silica capillary, with neglible electroosmotic flow, from simple measurements of the migration times of solutes and a marker for micelle migration. The advantages and limitations of this method are discussed. The method is tested by using sodium dodecylsulfate (SDS) surfactant and naphthalene, benzene, toluene, and phenol solutes. Micellar electrokinetic chromatography in coated columns isideally suited for the separation of hydrophobic solutes in aqueous samples.     

Adsorption of octadecyltrimethylammonium chloride and adsolubilization on to cellulosic fibers

The coadsorption of different organic solutes on cellulosic fibers treated with octadecyltrimethylammonium chloride (ODTMA) has been studied. In the absence of ODTMA cellulosic fibers had little tendency to retain organic compounds. The enhanced solute incorporation was ascribed to the adsolubilization of these compounds on the aggregated domains of the adsorbed surfactant molecules at the solid/liquid interface. The specific shape of solute coadsorption isotherms indicated that the adsolubilization process may be regarded as a partition phenomenon between the aqueous bulk phase and the adsorbed surfactant aggregates. The decrease in solute uptake at the cellulose/water interface above the CMC of ODTMA was ascribed to micelle formation in the bulk solution and to the ensuing micellar solubilization of organic solutes. Preliminary experiments performed using vertical fixed bed columns showed that modified cellulosic fibers can be conveniently used as substrate for treating organic pollutants.     

Application of a chemical equilibrium model to thermodynamic functions of transfer of alcohols from water to aqueous surfactants

In ternary aqueous solutions, hydrophobic solutes such as alcohols tend to aggregate with surfactants to form mixed micelles. These systems can be studied by meas of the functions of transfer of hydrophobic solutes from water to aqueous solutions of surfactant. These thermodynamic functions often go through extrema in the critical micellar concentration (CMC) region of the surfactant. A simple model based on interactions between surfactant and hydrophobic solute monomers, on the distribution of the hydrophobic solute between water and the micelles and on the shift in the CMC induced by the hydrophobic solute, can simulate the magnitude and trends of the transfer functions using parameters which are mostly derived from the binary systems. In order to check the model more quantitatively, volumes and heat capacities of transfer of alcohols from water to aqueous solutions of a nonionic surfactant, octyldimethylamine oxide, were measured. A quantitative agreement was achieved with three adjustable parameters. Good fits are also obtained for the transfers to the ionic surfactants, octylamine hydrobromide and sodium dodecylsulfate. When the equilibrium displacement contribution is small, the distribution constants and the partial molar properties of the alcohols in the micellar phase agree well with the parameters obtained with similar models.     

Study of Partitioning and Solubilization of Some New Chalcones Between Aqueous and Micellar Phases

The partitioning behavior of four newly synthesized chalcones between aqueous and micellar phases of ionic surfactants (SDS and CTAB) was investigated using ultraviolet-visible spectroscopy. The simple absorption spectra were recorded to study the interaction between these drugs and surfactants (in the concentration range below critical micelle concentration to above critical micelle concentration). The absorption data is also used to determine the number of additive molecules incorporated per micelle of the surfactant. The partition coefficient (K_x) of additives between bulk water phase and the micellar phase was determined in the range of 5.52 × 10⁺⁴ to 5.06 × 10⁺⁵ at 298 K by differential spectroscopic method. The corresponding standard free energy of partition ΔG°_p obtained was in the range of ?27.05 kJmol^?1 to ?32.54 kJmol^?1. The relative solubility of additives between aqueous and micellar phases in different micellar concentrations was also estimated. The results showed that the chalcones are preferably soluble in cationic surfactant micelles.     

An extended description of the effect of detergent monomers on migration in micellar electrokinetic chromatography

Three equilibria determine the interaction of a neutral analyte with the detergent in micellar electrokinetic chromatography and therefore its migration: (i) that of the free analyte in the aqueous phase with the micelle, (ii) its association with free detergent monomers in the aqueous phase, and (iii) the partition of the associate of analyte and monomer between the aqueous solution and the micelle. For the first equilibrium, non-stoichiometric partitioning between two phases is preferred in the present work over the assumption of complex formation between one molecule of the analyte with one micelle. The second equilibrium is described by the formation of a 1:1 associate of the analyte and monomer. In this paper, thirdly an additional equilibrium is introduced, namely, the distribution of the analyte-monomer associate between the aqueous and the micelle phase; it is expressed by the according partition coefficient. The three equilibrium constants are interrelated. Mobility data for a lipophilic fluorescent compound and a series of n-alkylphenones (differing in chain length) were measured as a function of the SDS concentration below and above the critical micellar concentration. Curve fitting enabled the derivation of the equilibrium constants. It was found that the association constants of the analytes with the detergent monomers are between 2 and 75 M(-1). Interestingly, the partition coefficient of the analyte-monomer associate between the aqueous and micellar phase is by a factor of 5-200 larger than that of the free analyte.     

Tautomerization equilibria in aqueous micellar solutions: a spectrophotometric and factor-analytical study

The keto-enol equilibria of benzoylacetone (BZA) as a model for 1,3-dicarbonyl compounds are studied in aqueous acid and cationic micellar solution. Evolving factor analysis (EFA), multivariate curve resolution-alternating least-squares (MCR-ALS), and rank annihilation factor analysis (RAFA) are used for complete resolving of measured spectrophotometric data. The acidity constants of the enolic, KaE, and ketonic, KaK, forms of BZA and also the tautomerization constant, Kt, and its related thermodynamic parameters have been determined by using EFA and MCR-ALS methods and spectral variation of BZA solutions in various pHs and temperatures. The concentration and spectral profiles of all species were calculated without any assumption about chemical models. The spectral variation of BZA solutions as a function of cationic micelle concentration sufficiently beyond its critical micelle concentration is analyzed according to the partition model for distribution between water and micellar pseudo-phase and RAFA. The outputs of using RAFA on measured rank deficient data are the spectrum of enolic form in the micellar pseudo-phase, free from contribution of the enolic form in the aqueous phase, the partition coefficient of enolic form, KdE, between the micelle and water phases, and the tautomerization constant in the micellar pseudo-phase, Ktm.