A linear relationship between partition ratio and composition of a binary mobile phase in reversed-phase liquid chromatography using chemically bonded stationary phases

A simple linear relationship which enables the effect of the composition of a binary mobile phase on the retention of a solute to be assessed in reverse phase liquid chromatography using a bonded stationary phase has been derived. The equations have been tested using published experimental data.     

HPLC with chemically bonded stationary phases. 1. ω-hydroxyalkyl silicas

Grignard and trichlorosilane coupling methods have been applied to the synthesis of surface-modified silicas carrying alkyl chains of varying length, terminally substituted by a hydroxyl group. The new phases have been characterized chromatographically using aromatic hydrocarbons, substituted anilines and metal acetylacetonates.     

高效硅胶化学键合固定相的研究进展

对高效液相色谱用硅胶作为基质的化学键合固定相的研究进展进行了全面的评述。介绍了硅胶基质填料的物理化学性质及前处理过程,详细阐述了化学键合固定相的键合反应机制和种类,概括了化学键合固定相在高效液相色谱中的应用,并对我国的硅胶基质填料研究和应用前景进行了展望。     

Synthesis of a nonpolar,chemically bonded stationary phase with low residual hydroxyl group content

Summary A microporous silica support, LiChrosorb Si-100, has been silanized with octyldimethylchlorosilane and octylmethyldichlorosilane. The repeatability of the silanization procedure was within about 2%. In general, these nonpolar modified silicas still contain too many residual hydroxyl groups, causing bifunctional behaviour of the adsorbent. A partial condensation of surface silanol groups at a drying temperature >200°C, prior to the chemical modification, decreases the residual hydroxyl group content. With respect to this residual polarity, monochlorosilanes appear to be effective. The concentration of bonded octyl chains remains virtually constant up to a drying temperature of 400°C. Owing to silanization, the specific surface decreases by 15–20%, whereas the pore volume decreases by 25%.     

Retention process in reversed phase TLC systems with polar bonded stationary phases

The retention of a solute in RP chromatography is a very complex process which depends on many factors. Therefore, the study of the influence of a mobile phase modifier concentration on the retention in different reversed phase chromatographic systems is very important for understanding the rules governing retention and mechanisms of substance separation in a chromatographic process. Composition changes and the nature of mobile phases enable tuning of the separated analytes' retention over a wide range of retention parameters and optimization of the chromatographic process as well. Optimization of the chromatographic process can be achieved by several different methods; one of them is the so-called interpretative strategy. The key approach adopted in this strategy is the implementation of adequate retention models that couple the retention of solute with the composition of a mixed mobile phase. The use of chemically bonded stationary phases composed of partially non-bonded silica matrix and organic ligands bonded to its surface in everyday chromatography practice leads to questions of the correct definition of the retention model and the dominant retention mechanism in such chromatographic systems. The retention model for an accurate prediction of retention factor as a function of modifier concentration and the heterogeneity of the adsorbent surface should be taken into consideration. In this work the influence of mobile-phase composition on the retention of sixteen model substances such as phenols, quinolines, and anilines used as test analytes in different RP-TLC systems with CN-, NH2-, and Diol-silica polar bonded stationary phases has been studied. The aim of this study is to compare the performance of three valuable retention models assumed as the partition, adsorption/partition, and adsorption mechanism of retention. All the models were verified for different RP-TLC systems by three statistical criteria. The results of investigations presented in this work demonstrate that the best agreement between the experimental and calculated Rf values was obtained by the use of new-generation retention models, which assume heterogeneity of adsorbent surface. The results reported here show that heterogeneity of the adsorbent surface may be important in analysis of the elution process in liquid chromatography. Consideration of the goodness of fit for the experimental data to the examined retention models is in conformity with the adsorption mechanism of retention on all polar bonded stationary phases in most eluent systems for most investigated compounds.     

Comprehensive evaluation of lipophilicity of biogenic amines and related compounds using different chemically bonded phases and various descriptors

The retention behavior for a series of biogenic amines and related sympathomimetic drugs has been investigated in reversed-phase thin-layer chromatography using RP-2, RP-8, RP-18W, and Diol stationary phase and mixtures of phosphate buffer (pH = 7.10) and methanol in different proportions as mobile phases. Several methodologies like arithmetic mean of experimental retention values, extrapolation to zero methanol concentration procedure and principal component analysis were applied to retention data values (R(M)) in order to determine relevant parameters (mean of R(M) - mR(M), R(M0), and scores corresponding to the first principal component - PC1/R(M) respectively) encoding information on the lipophilic behavior of compounds. High similarities in lipophilicity behavior of investigated amines were highlighted by mR(M) and PC1/R(M) lipophilicity indices for all of the studied stationary phases. The experimental results were compared with some computed lipophilicity parameters expressed as distribution coefficients at working pH (logD), partition coefficients (logP(N), logP(I), and diff(logP(N-I))) concerning both neutral and fully protonated species and difference between both species, and also with various lipophilicity values (logP) generated by different commonly used software. Significant correlations were observed between the experimental lipophilicity indices mR(M) respectively PC1/R(M) and diff(logP(N-I) ) values in all cases.     

Chemically-bonded stationary phases for thin-layer chromatography of metal ions

Summary A numer of bonded stationary phases were investigated for the separation of Cd²⁺, Cu²⁺, Fe³⁺, Mn²⁺, Ni²⁺, Pb²⁺, and Zn²⁺ by thin-layer chromatography. The effect of structure, surface loading, type of silica gel and mobile phase concentration was considered.     

葫芦脲在色谱固定相中的研究进展

葫芦脲是超分子化学中继冠醚、环糊精、杯芳烃之后发展起来的又一类新型高度对称的桶状大环主体分子,是一种由多个甘脲单元组成的大环穴状配体,被誉为"第四代超分子化合物"。由于其具有特殊的分离选择性和稳定性,在超分子化学和色谱的交叉领域备受关注。本文从葫芦脲的结构特征出发,侧重概述了葫芦脲同系物及其衍生物在色谱固定相中的研究现状和进展。     

Effect of chemically bonded stationary phases and mobile phase composition on beta-blockers retention in RP-HPLC

The effects of stationary and mobile phase on retention of 18 beta-adrenolytic drugs (beta-blockers) have been studied. Four 'deactivated surface' stationary phases (polar-embedded or end-capped) were examined. Special attention was drawn to the cholesterolic (SG-CHOL) and alkylamide (SG-AP) stationary phases, and their application for analysis of the compounds. The retention of analyzed substances was also examined in terms of mobile phase composition. Sixteen different configurations of mobile phases were prepared, all based on methanol and acetonitrile with ammonium acetate and ammonium formate. The difference in retention between ammonium formate and acetate water solutions, and peak shape changes related to the addition of triethylamine (TEA), were investigated. Principal component analysis was used to find the similarities between stationary phases. Polar-embedded phases synthesized on the same sorbent possess very similar properties. All phases based on silica gel compared with the monolithic column also showed similarities in retention of beta-blockers. The addition of TEA to the mobile phase did not influence strongly the retention, and analysis of asymmetry factors showed only a little peak broadening for a few compounds on the monolithic column.     

Novel method for the preparation of chemically bonded phases and studies of their chromatographic performance

Summary This paper describes a novel process for the production of chemically bonded phases using fluidised bed technology. Hitherto fluidisation of particles with the size range below 50 μm was considered impossible. In this study, particles with sizes as small as 7 μm have been successfully fluidised and subsequently reacted to produce bonded phases. The operating parameters of the fluidised bed system have been studied and their effect on the chromatographic properties of the products have been investigated. Advantages of the process are thein situ removal of fines, high batch to batch repeatability andin situ chemical post-treatments (end-capping). Studies of the chromatographic performance of the fluidised bed products show them to possess markedly superior retention characteristics and good peak shapes. Comparisons were made with various C₈ and C₁₈ commercially available bonded phases and on bonded phases prepared by conventional method. Mass loading effects were also investigated for preparative HPLC use.     

The allyl bonded stationary phase. II. Conversions to new phases for gas chromatography

Summary The presence of the double bond on the allyl moiety has been utilized as a site for addition reactions which could produce new stationary phases. Bromination and hydrobromination reactions have been employed to prove the feasibility of making modifications to the allyl bonded phase. Both retention volumes and thermodynamic parameters for the solutes studied change upon conversion to one of the brominated phases. Sample size studies are consistent with a bonded phase adsorption mechanism. FTIR spectra also confirm the modifications which have occurred on the allyl bonded material.     

Influence of solvent strength in possible optimization of adsorption thin-layer chromatography

Considerations of TLC process optimization have been based on the thermodynamic theory of adsorption from multicomponent solvents using experimental and theoretical R_{M1, 2} = f (Φ₁) relationships. It was found that a relationship exists between the A_z parameter (log k where k is the partition coefficient of the substance chromatographed) of the above theory and pK_a values of substances as well as the solubility parameter δ of the mobile phase components. Analysis of the A_z values of substances shows that a slight variation therein is associated with lower selectivity of chromatographic separation.     

Cholesteric bonded stationary phases for high-performance liquid chromatography: a comparative study of the chromatographic behavior

The properties of four cholesteric bonded stationary phases differing in the nature of the spacer and the end-capping were assessed using simple chromatographic tests based on the retention of nonpolar compounds and of planar or nonplanar probe solutes. All cholesteric columns showed a hydrophobicity close to that of conventional octadecyldimethylsilyl (ODS) materials. Non-end-capped cholesteric bonded phases showed greater selectivity than ODS ones and both end-capped cholesteric bonded phases exhibit behavior intermediate between that of the non-end-capped original material and that of the ODS bonded phase.