Thin-layer adsorption chromatography with mixed mobile phases. 4. Extension of Ościk's equation to heterogeneous adsorbents

In this paper the equation for thin-layer adsorption chromatography with multicomponent mobile phases, proposed by O?cik in 1965 is extended to energetically heterogeneous solid surfaces. Other forms of this equation, more convenient in practical applications, are presented. Model calculations are made for TLC with binary mobile phases according to the modified form of O?cik's equation. Finally, this equation is compared with that of Snyder.     

Thin-layer adsorption chromatography with mixed mobile phases. 1. Characterization of chromatographic systems showing energetic heterogeneity of adsorbent surfaces with regard to admolecules of solvents and solutes

Thin-layer adsorption chromatography with a multicomponent mobile phase is discussed. A new equation for predicting R_M-values in TLC with mixed mobile phases using the R_M-ValUeS obtained for pure solvents is proposed. This equation takes into account effects of energetic heterogeneity of the adsorbent surface with regard to adsorbed molecules of solvents and solutes. Experimental verification of this equation is presented for R_M-data obtained by TLC using a binary mobile phase.     

Retention in liquid chromatography with multicomponent mobile phases: Relationship with binary systems

Summary Using the concept of an effective concentration a method is proposed for predicting retention in liquid chromatography with multicomponent mobile phases based on experiments with corresponding binary ones. The method is verified for normal and reversed-phase systems with ternary mobile phases and agrees closely with experimental data.     

Thin-layer adsorption chromatography with mixed mobile phases. 2. Effects of solute-solvent interactions and energetic heterogeneity of surfaces with regard to admolecules in TLC

In the Part 1 of this series a new equation for determining the R_m values in TLC with mixed mobile phases was proposed and examined by using the parameter m, which is a measure of energetic heterogeneity of the adsorbent surface with regard to the adsorbing molecules (admolecules). The numerical values of m, evaluated for 13 chromatographic systems, have been compared with that of the O?cik's parameter A, which characterizes solute-solvent interactions.     

Adsorption TLC with binary mobile phases

Summary An equation describing R_M values in TLC with a binary mobile phase has been derived and examined by using TLC data. Two different methods have been proposed to determine the chromatographic parameters characterizing energetic heterogeneity of the adsorption system and solute-solvent interactions. These methods differ in the estimation of the mole fractions of solvents in the surface phase. In method I an analytical equation for evaluating these mole fractions is assumeda priori. Method II utilized the excess adsorption isotherm measured for the mobile phae-adsorbent system.     

Adsorption model for retention in normal-phase liquid chromatography with ternary mobile phases

The review gives a link between the theory of adsorption from multicomponent solutions and liquid chromatography. The article surveys the methods developed to describe the retention in normal-phase chromatography with ternary mobile phases with emphasis on the results of the authors. In the model used the driving force for the separation is the difference in adsorption of a solute and all solvents onto the solid surface. The general equation generates a series of simple linear relationships to predict the retention factor in ternary mobile phase for which certain parameters remain fixed. Theoretical concepts are tested by comparison with experimental data. The correlations between parameters characterizing retention in ternary, binary and pure solvents are discussed.     

Correlation between excess adsorption data measured for solvent mixture/adsorbent systems and RM values obtained for different solutes chromatographed in binary mobile phases

This paper concerns the application of excess adsorption isotherms, measured for solvent mixture/adsorbent systems, to the characterization of TLC data. For this purpose the excess adsorption isotherms for three liquid mixtures: cyclohexane/ benzene, benzene/acetone, and carbon tetrachloride/ethyl acetate on silica gel at 20°C have been measured. These mixtures have been used as binary mobile phases in TLC measurements. It has been shown for a given solute in binary mobile phase that the quantity R_M is a simple function of the excess adsorption. Parameters of this function have been used to characterize chromatographic systems with binary mobile phases.     

Adsorption-driven retention in normal-phase chromatography with ternary mobile phases

The model for retention in chromatographic systems using ternary mobile phases is considered. The driving force for the separation is assumed to be only a difference in adsorptive properties of a solute and all solvents. The effects of mobile phase composition are discussed. A series of very simple dependences between parameters characterizing retention in ternary and binary solvents is presented. The linear relationship is proposed to predict the capacity factor in the ternary mobile phase, for which the ratio of mole fractions of two less-polar solvents remains fixed. Theoretical concepts are verified by comparing the calculated values with experimental data measured in the entire concentration region.     

Adsorption interaction parameter of polyethers in ternary mobile phases: The critical adsorption line

It is shown that in LC of polymers, the interaction parameter in ternary mobile phases can be described by a plane, which is determined by the dependencies in binary mobile phases. Instead of a critical adsorption point, critical conditions are observed along a straight line of composition between the two critical points in binary mobile phases. Consequently, a separation of block copolymers under critical conditions for one block by an adsorption mechanism for the other block can be achieved in ternary mobile phases of different compositions, which allows an adjustment of the retention of the adsorbing block.     

Thin-layer chromatography with high-boiling mobile phase. part 2: Effect of temperature on retention characteristics in TLC with high-boiling mobile phases

A study has been undertaken on the effect of temperature on retention characteristics in thin-layer chromatography (TLC) with low-volatility mobile phases (MP). It is shown that temperature variations in TLC in melts bring about variations in both the relative retention values and, in some cases, in the order of migration of the chromatographic zones across the layer. The variation in the capacity factor k' with temperature agrees well with Martin's equation. To explain the temperature dependence of R_f one must, in general, take into account the variations with temperature in both the partition coefficient and the phase ratio. To describe the variation in R_f with temperature in TLC with low-volatile MP one can use an approximate equation in which In R_f is a linear function of 1/T. The experiments indicate that temperature is a major factor in TLC in melts.     

Thin-layer chromatography with high-boiling mobile phases.1. Investigation of the flow of the high-boiling mobile phases

This paper considers some aspects of a new TLC technique using a molten mobile phase which is solid under ambient conditions. The flow of high-boiling mobile phase at elevated temperature in thin-layer chromatography has been investigated and it is shown that the equation Z_f² = kt is not applicable to migration of the high boiling mobile phase front. The flow stability of the high-boiling mobile phase is noted. It is suggested on the basis of studies of concentration profiles of the solidified mobile phases by scanning photometers that the shape of the mobile phase concentration profile be taken into account in calculation of R_f Values.     

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.     

Computerized optimization of gradient elution conditions with ternary solvent mobile phases in RPLC

Summary In this work, an optimization procedure for gradient RPLC separation, using ternary mobile phases, is described. This procedure requires eight preliminary experiments in gradient elution mode to predict the retention surface for each solute over the whole triangular space. This is followed by computerized calculations to determine the best ternary gradient elution profile with respect to both selectivity and analysis time. The efficiency of this procedure from the point of view of rapidity and of accuracy, is illustrated for the specific separation of twelve phenyl urea herbicides.     

磷酸钛离子交换薄层色谱分离无机离子(英文)

The chromatographic behavior of 30 inorganic cations has been studied on thin layers of titanium phosphate ion-exchanger using several aqueous,organic and mixed mobile phases.The separation of one ion from several other ions and also ternary and binary separations have been developed.Some important analytical separations are reported.The effect of pH of the mobile phase on retention factor(Rf)values of the cations in the presence of complex-forming anion along with the separation power of the ion-exchanger were studied.This ion-exchanger exhibits high sorption capacity and varying selectivity towards metal ions and makes it a suitable stationary phase in thin layer chromatography.     

A refined physico-chemical model of solute retention in reversed-phase high-performance liquid chromatography with ternary mobile phases

Summary In our previous publication we have introduced a new model of solute retention in RP-HPLC systems with ternary mobile phases of the B+AB₁+AB₂ type (B: acetonitrile or tetrahydrofuran; AB₁: methanol; AB₂: water). That model proposed no stoichiometric differentiation between acetonitrile and tetrahydrofuran, alternatively present in the solvent system; moreover, it made some very rough assumptions only as to the intermolecular interactions among the mobile phase constituents.This paper introduces a significant refinement to the already established retention model, which is based on the simple quantitative relationships between acetonitrile and tetrahydrofuran, and the remaining components of the ternary liquid system. The refined model is tested with same experimental data.     

Retention prediction in ternary solvent reversed-phase liquid chromatography systems based on the variation of retention with binary mobile phase composition

An extension of the treatment adopted in a recent paper [P. Nikitas, A. Pappa-Louisi, P. Agrafiotou, J. Chromatogr. A 946 (2002) 33] was used to derive expressions describing the variation of solute retention k with composition in ternary reversed phase liquid chromatography, RP-LC, solvent systems. The equation of the partition model obtained in this way for a ternary mobile phase was identical to that previously derived using the solubility parameter concept. This equation as well as two new expressions of In k versus organic modifiers content were tested in a variety of ternary solvent systems in order to examine the possibility of predicting retention behavior of solutes under ternary solvent mixture elution conditions from known retention characteristics in binary mobile phases. It was demonstrated the superiority of both new equations derived in this paper to that previously proposed and applied to date in ternary solvent mixtures.     

The chromatographic quantification of hydrophobicity using micellar mobile phases

Summary In micellar liquid chromatography (MLC), the hydrophobicity of a compound is the predominant factor in its retention and interaction with micelles. A non-linear empirical model can describe the dependence between the retention factor (logk) in MLC and the logarithm of partition coefficients octanol-water (logP). An algorithm based on such a model has been used to makelogP predictions. Retention data for series of neutral compounds eluted with different mobile phases and alkyl-bonded stationary phases have been used to test the predictive ability of the algorithm. The results of this approach are compared with those obtained from automatic computational software packages.     

Packed column supercritical fluid chromatography with light-scattering detection. II. Retention behaviour of squalane and glucose with mixed mobile phases

Summary Evaporative light scattering detectors can be used to detect organic substances without chromophoric groups in packed column supercritical fluid chromatography (SFC). A detector of this type has been used to detect squalane and glucose after SFC with various packed columns and binary mobile phases. In this study, the amount of organic modifier in carbon dioxide/modifier mixtures was varied. The results give further insight into the mechanisms that influence retention behaviour in packed column separations with super- and subcritical mobile phases. Squalane is an ideal non-polar test solute which shows long retention times on non-polar columns while its elution can be accelerated by non-polar modifiers in carbon dioxide. Glucose is an extremely polar solute containing hydroxyl groups. Elution of this sugar can be improved with polar modifiers. Column packings with polar end groups lead to high capacity ratios and long retention times for glucose. Most columns used in this study contained silica-based packing materials. For purposes of comparison, a polymeric packing (HEMA RP-18) was also employed.     

Evaluation of ternary mobile phases for reversed-phase liquid chromatography: Effect of composition on retention mechanism

The effect of varying mobile phase composition across a ternary space between two binary compositions is examined, on four different reversed-phase stationary phases. Examined stationary phases included endcapped C8 and C18, as well as a phenyl phase and a C18 phase with an embedded polar group (EPG). Mobile phases consisting of 50% water and various fractions of methanol and acetonitrile were evaluated. Retention thermodynamics are assessed via use of the van’t Hoff relationship, and retention mechanism is characterized via LSER analysis, as mobile phase composition was varied from 50/50/0 water/methanol/acetonitrile to 50/0/50 water/methanol acetonitrile. As expected, as the fraction of acetonitrile increases in the mobile phase, retention decreases. In most cases, the driving force for this decrease in retention is a reduction of the enthalpic contribution to retention. The entropic contribution to retention actually increases with acetonitrile content, but not enough to overcome the reduction in the enthalpic contribution. In a similar fashion, as methanol is replaced with acetonitrile, the v, e, and a LSER system constants change to favor elution, while the s and c constants change to favor retention. The b system constant did not show a monotonic change with mobile phase composition. Overall changes in retention across the mobile phase composition range varied, based on the identity of the stationary phase and the composition of the mobile phase.     

Theory of retention in reversed phase liquid chromatography with ternary mobile phases

The partition model of retention is developed for reversed phase liquid chromatography with multicomponent mobile phases. Simple equations for the retention and selectivity in ternary mobile phases are derived. For the systems in which the ratio of volume fractions of organic modifiers remains fixed, new linear dependences for retention factor and selectivity are proposed. These equations are successfully used to describe experimental data found in the literature. An influence of the nature of organic solvents and proportion in which they are mixed on retention and selectivity is discussed.