Studies of Association Effects in Liquid Adsorption Chromatography with Ternary Mobile Phases

Abstract

In this paper a model of chromatographic process, which takes into account molecular association in the mobile phase is discussed. This model is applied to study the association effects in liquid adsorption chromatography with ternary mobile phases. Efects of nature of the eluent and structure of the chromatographed substance on the type of association is also investigated. Association effects in the chromatographic system containing ternary mobile phase can be evaluated by means of equations describing chromatographic process with the binary mobile phases.     

Solvation Effects in Liquid Adsorption Chromatography with Mixed Mobile Phases

JPC – Journal of Planar Chromatography – Modern TLC - Molecular interactions have been evaluated in liquid adsorption chromatography with mixed mobile phases. Two equations based on...     

Determination of Solvation Effects in Liquid Adsorption Chromatography with Mixed Mobile Phases

Abstract

A model of chromatographic process, involving formation of multimolecular solute-solvent solvates in the mobile phase, is discussed. This model leads to an equation describing dependence of the capacity ratio upon mobile phase composition. The TLC data for some solutes chromatographed in n-heptane+chloroform on silica gel are interpreted by means of the above equation.     

Molecular Theory of Liquid Adsorption Chromatography

Abstract

A statistical-mechanical theory, based on a lattice model, has been developed to address the molecular mechanism of retention and selectivity in both normal-phase and reversedphase liquid adsorption chromatography. The model is a natural “competitive-equilibrium” one, where possible contributions from solvent-solvent and solute-solvent interactions, and, hence, from solution nonideality, are not neglected. Homogeneous and heterogeneous adsorbent surfaces, single-solvent and binary mixed-solvent mobile phases, and solute molecules of different size and shape are treated. Practical applications of the theory are presented to demonstrate its utility and significance.

For homogeneous adsorbents and neat solvents, the molecular energetics of retention and selectivity are examined, with special emphasis on the effects of solute size and shape, and, relatedly, the modes of solute adsorption. Separations of geometrical isomers and homologous series in real and simulated chromatographic processes are investigated, confirming predictions of the theory and the important role of solvent-solvent and solute-solvent interactions in reversed-phase systems. The implications of a more general retention equation for microscopically heterogeneous adsorbents are discussed. The dependence of capacity ratio on mobile-phase composition for binary solvents is analyzed in some detail. An often important contribution arising from solution nonideality is predicted theoretically. This is shown to be consistent with experimental results on normal-phase and reversed-phase systems.     

Retention Behavior of some Alkaloids in Thin Layer Chromatography with Bonded Stationary Phases and Binary Mobile Phases

JPC – Journal of Planar Chromatography – Modern TLC - The retention behavior of twenty-four alkaloids has been investigated in normal-phase systems on thin layers of aminopropylsilica...     

Quantitative Determination of Methyl Red Adsorption on Stationary Phases Used in Liquid Chromatography

Abstract

The method described is a modification of the dye adsorption method, first published by Shapiro and Kolthoff. It is reproducible and allows the estimation of the relative amount of the reachable free silanol groups on silica gels and reversed phase materials which are frequently used as stationary phases in liquid chromatography. Results obtained with commercially available thin layer and high performance liquid chromatographic materials, as well as with self-made reversed phase materials, are reported.     

Adsorption of Solvents and Molecular Interactions in LSC with a Ternary Mobile Phase

Abstract

A modification of Jaroniec equation [1] is proposed. Adsorption of all solvents is taken into account. A physical meaning of the slope of the equation is analysed. The effects of solvents adsorption, solvent-solvent and solute-solvent molecular interactions on the retention in LSC with ternary mobile phase are discussed.     

Optical Properties of Binary Mobile Phases as Constituent Objective Functions in Optimizing the Conditions for High-Performance Liquid Chromatography of Hydrophobic Phenol-Like Compounds

The dependence of the absorbance and the UV absorption limits of typical binary mobile phases for high-performance liquid chromatography (HPLC) on the volume fraction of modifiers was analyzed. The applicability of the found relationships to the multiparametric optimization of the mobile-phase composition with a generalized objective function using the Microsoft Excel 2000 spreadsheet program was considered by the example of microcolumn HPLC of hydrophobic phenol-like additives.     

An Extension and new Interpretation of Oscik's Equation Describing Liquid Chromatography with Mixed Mobile Phases

Abstract

An extension of oscik's original approach, which was first proposed for liquid solid chromatography (LSC) with a multicomponent eluent in the normal-phase mode (Przem. Chem. 44, 1965, 129), leads to a new equation describing the dependence of the distribution coefficient upon mobile phase composition. This equation is also derived in terms of the expressions defining classical partitioning (J. Phys. Chem. 87, 1983, 1045). The above derivation provides a new view on the physical meaning of the parameters and indicates that O?ck's equation is more suitable for describing partition effects in reversed-phase liquid chromatography (RPLC).     

Separating Ability of Some Polar Mobile Phases in Reverse Phase High Performance Liquid Chromatography

Abstract

Homologous series of n-alkanes, n-alcohols, ethers, esters, amides and ketones were studied as solutes. Methanol, acetonitrile, ethanol, dioxane, 2-propanol and tetrahydrofuran were mobile phases. Spherisorb ODS columns with light and heavy octadecyl coatings were used. Methanol and acetonitrile were found to be the most selective solvents for reverse phase separation. The polar amides, alcohols, and ketones behaved differently from nonpolar solutes in acetonitrile mobile phases. Results were interpreted with the solvophobic theory.     

Prediction of Retention in Liquid-Solid Chromatography with Ternary Mobile Phases

The method for the prediction of capacity factors in ternary mobile phases is presented. The adsorption mechanism of retention is considered. The simple theoretical equations are proposed for mobile phases for which the ratio of mole fractions of the weaker solvents remains fixed. The relations between parameters characterizing retention in ternary and binary mobile phases are discussed. The theoretical model is verified for numerous solutes and different mobile phases.     

Enhanced Stability of Electrochemical Detection with Surfactant Containing Mobile Phases in Liquid Chromatography and Flow Injection Analysis

Abstract

The use of surfactant containing mobile phases to prevent or reduce the effects of adsorptive fouling of glassy carbon electrodes is reported. Both cationie and antonic surfactants are studied at concentrations above and below the critical micelle concentration. For the oxidative reactions studied here, anionic surfactants have little effect on the fouling problem, likely because of electrostatic attraction of the generated cattonic intermediate to surfactant adsorbed on the electrode surface. Cationic surfactants, however, have the desired effect. Two cationic surfactants, cetyltrimethylammonium chloride and n-decylamine were studied with solutes p-nitrophenol, phenylenediamine and chlorpromazine. With these surfactants present in the mobile phase there was generally no loss of electrochemical response after up to 55 sequential injections. Adsorption of the electroactive specie prior to the electron-transfer process is shown to be a significant cause of poor chromatographic efficiency for some solutes.     

Evaluation of Mobile and Stationary Phases in Reversed-Phase High-Performance Liquid Chromatography of Conjugated Bile Acids

Abstract

The reversed-phase high-performance liquid chromatographic separation of the ten major conjugated bile acids of man using isocratic conditions is described. Each component of the mobile and stationary phases was examined for its ability to influence the separation selectivity. Manipulation of pH, buffer species, organic modifier and different types of packings showed that optimal resolution was obtained with a mobile phase of methanol-0.02M sodium acetate (60:30) adjusted to pH 4.2 with phosphoric acid, on a Supelcosil LC-18-DB column. Advantages of the optimized phase system are the complete baseline separation of compounds within a short period of time, improved peak symmetry and a high rate of reproducibility. This new chromatographic method, coupled with UV detection at 205 nm, is suitable for the simultaneous determination of bile acid conjugates in routine clinical analysis.     

Liquid Crystals as Stationary Phases for High Performance Liquid Chromatography

Abstract

Liquid crystals have not yet been used as stationary phases in High Performance Liquid Chromatography. This is surprising since Gas Chromatography has demonstrated some remarkable separations, many of which are not possible with normal stationary phases, that have been achieved where liquid crystals have been employed as the stationary phase. The objective of the work reported here was to evaluate the chromatographic properties of several cholesteric liquid crystals as stationary phases in HPLC. Included in this study was an investigation of the feasibility of bonding a cholesteric moiety to a solid support for use in HPLC. The columns showed a dramatic increase in capacity factor for steroid molecules as the temperature of the column was increased.     

Analysis of Selected Macrocyclic Antibiotics by HPTLC with Non-Aqueous Binary Mobile Phases

JPC – Journal of Planar Chromatography – Modern TLC - The retention behavior of selected macrocyclic antibiotics (ery-thromycin, troleandomycin, tylosin, vancomycin, rifamycin B, and...     

Substitution-Inert Metal Complex Mobile Phases in Non-Suppressed Cation Chromatography

Substitution-inert metal complexes, [Co(edda)(H₂O)₂]⁺, (Co(edda)(en)]⁺, [Co(edda)(dmen)]⁺, [Co(en)₂-(gly)]²⁺, [Co(en)₂(acac)]²⁺, and [Co(trien)(gly)]²⁺ in their nitrate salt solutions are used as eluents in nonsuppressed cation chromatography (where edda = ethylenediamine-N,N′-diacetic acid, en = ethylenediamine, dmen = N,N′-dime-thylethylenediamine, gly = glycine, acac = acetylacetone, and trien = triethylenetetraamine). It is found that all the mono- and di-valent charged complexes can be used to separate alkali and alkaline earth metal cations, respectively. The separations for monovalent cations are sometimes comparable to those using ultrapure HNO₃ solutions. However, the divalent Ca²⁺ and Sr²⁺ ions cannot be resolved using the metal complex eluents. On the other hand, a selected, direct non-suppressed IC separation of zinc(II) and cadmium(II) ions is demonstrated for the first time using a substitution-inert metal complex eluent and a conductivity detector. Comparisons of these eluents with those reported previously, i. e. HNO₃ and ethylenediammonium salt solution are made and explanations are proposed to account for the different selectivities observed where possible. The future development of this technique is also briefly discussed.     

The Evolution of Chiral Stationary Phases for Liquid Chromatography

The development of effective chiral stationary phases (CSPs) and separation strategies for the liquid chromatographic (LC) resolution of enantiomers has been beneficial to many scientific disciplines. Over the last decade the number and type of CSPs has expanded tremendously. Not only have new classes of chiral selectors been introduced, but also many of the first CSPs have been changed and/or improved. The second or third generation of a CSP often can be different from the original. This can be confusing and intimidating to someone just entering the area of LC enantiomeric separations. Fortunately, all CSPs can be categorized in one or another of a few classes. There are generally one or two columns that can accomplish the majority of separations in each class. In this work we look at the different classes of CSPs and how they have expanded and changed over the last decade.