Comparison of Methods for Determination of the RM Values of Substances in Thin - Layer Chromatography by Using Binary Mobile Phase

Abstract

Methods of calculating the function R_M= f(?₁) of some aromatic substances from the data of experimental and theoretically calculated parameters have been compared. It has been shown that there is a possibility to calculate this function with high accuracy on the basis of the measured partition coefficients of the substances chromatographed in partition systems consisting of components of the mobile phase as well as parameters obtained theoretically. Thus obtained results were also compared with the functions R_{M 1.2} = f (?₁) obtained experimentally and a high agreement was reached. This in turn contributes to optimization of systems of thin-layer chromatography.     

Purification of a Water-Sensitive Natural Product with an Aprotic CPC Solvent System

Abstract

The partition coefficients of arachidonic acid (AA), prostaglandin (PG) H₂ and PGE₂ in the binary acetonitrile-hexane two-phase solvent system can be favorably modified by addition of diethyl ether. In the ternary two-phase solvent system acetonitrile-hexane-diethyl ether the partition coefficients of AA and the prostaglandins diverge as the ratio of ether to acetonitrile-hexane (1:1) is increased from 0.00 to 0.15 while the partition coefficients of PGH₂ and PGE₂ diverge as the ratio of ether to acetonitrile-hexane (1:1) is increased from 0.15 to 0.30. Isolation by CPC of PGH₂ from the AA bioconversion reaction mixture is described.     

Extended Octanol-Water Partition Coefficient Determination by Dual-Mode Centrifugal Partition Chromatography

Abstract

The range of determination of octanol-water partition coefficients by CPC has been extended by the dual-mode approach. In this mode, the analyte was pumped in the descending mode with water as the mobile phase for a predetermined time. The mode was then switched to ascending with octanol as the mobile phase. Lipophilic materials only moved partially through the system in the descending mode. They rapidly eluted in the ascending mode with good signal-to-noise. The partition coefficient was shown to equal the volume of water pumped in the descending mode divided by the retention volume in the octanol phase ascending. A systematic positive error resulted when the experimentally selected descending volume was too small.     

Gradient Elution Centrifugal Partition Chromatography: Comparison with HPLC Gradients and use of Ternary Diagrams to Build Gradients

Abstract

Just as with HPLC, gradient elution provides to CPC an easy way to fractionate solutes of widely differing polarities and partition coefficients, and to reduce run times. The easiest way to design a gradient for CPC is to refer to ternary diagrams corresponding to the ternary liquid mixtures generally encountered in centrifugal partition chromatography.     

Linear free energy relationship correlations for the solubilising characterisation of room temperature ionic liquids containing 1-hexyloxymethyl-3-methylimidazolium and 1,3-dihexyloxymethylimidazolium cations

Gas-to-room temperature ionic liquid (RTIL) partition coefficients have been compiled from the published literature for solutes dissolved in 1-hexyloxymethyl-3-methylimidazolium bis(trifluoromethylsulphonyl)imide, {[HxomMIm]⁺[(Tf)₂N]^?}, and in 1,3-dihexyloxymethylimidazolium bis(trifluoromethylsulphonyl)imide, {[(Hxom)₂Im]⁺[(Tf)₂N]^?}. These partition coefficients are converted into water-to-RTIL partition coefficients using the corresponding gas-to-water partition coefficients. Both sets of partition coefficients are analysed using the Abraham model with cation-specific and anion-specific equation coefficients. The equation coefficients are reported for the 1-hexyloxymethyl-3-methylimidazolium and 1,3-dihexyloxymethylimidazolium cations. The calculated cation coefficients can be combined with our previously determined nine sets of anion-specific equation coefficients to yield expressions capable of predicting the partition coefficients of solutes in 18 different RTILs.     

Linear free energy relationship (LFER) correlations for the solubilising characterisation of room temperature ionic liquids containing triethylsulphonium and 1-butyl-1-methylpyrrolidinium cations

Gas-to-room temperature ionic liquid (RTIL) partition coefficients have been compiled from the published literature for solutes dissolved in triethylsulphonium bis(trifluoromethylsulphonyl)imide, {[E₃S]⁺[(Tf)₂N]^?}, and in 1-butyl-1-methylpyrrolidinium trifluoromethanesulphonate, {[BMPyr]⁺[Trif]^?}. These partition coefficients were converted into water-to-RTIL partition coefficients using the corresponding gas-to-water partition coefficients. Both sets of partition coefficients were analysed using the Abraham model with cation-specific and anion-specific equation coefficients. Equation coefficients are reported for the triethylsulphonium and 1-butyl-1-methylpyrrolidinium cations. The calculated cation coefficients can be combined with our previously determined eight sets of anion-specific equation coefficients to yield expressions capable of predicting the partition coefficients of solutes in 16 different RTILs.     

Development of Abraham model IL-specific correlations for N-triethyl(octyl)ammonium bis(fluorosulfonyl)imide and 1-butyl-3-methylpyrrolidinium bis(fluorosulfonyl)imide

ABSTRACT

Abraham model correlations are derived for describing gas-to-ionic liquid and water-to-ionic liquid partition coefficients from published experimental data for solutes dissolved in both N-triethyl(octyl)ammonium bis(fluorosulfonyl)imide and 1-butyl-3-methyl-pyrrolidinium bis(fluorosulfonyl)imide. Derived Abraham model correlations describe the observed partition coefficient data to within 0.13 log units. As part of the current study the existing equation coefficients for the N-triethyl(octyl)ammonium cation were updated and reported for the first time were equation coefficients for the bis(trifluorosulfonyl)imide anion.     

Physicochemical studies on the micellization behavior of cetylpyridinium chloride and triton X-100 binary mixtures in aqueous medium

Physicochemistry of micellization of binary mixtures of cetylpyridinium chloride (CPC) and Triton X-100 (TX-100) have been investigated and the data collected have been analyzed and correlated. Tensiometric, conductometric, spectrophotometric, calorimetric and polarographic methods have been employed in the study. Parameters like critical micellar concentration (CMC), counter-ion binding, energetics of micellization, interfacial surfactant adsorption and minimum area of amphiphile head groups at CMC have been determined. The diffusion coefficients of pure and mixed micelles in solution have been determined by the polarographic method. The regular solution theory of Rubingh has been considered to get information on the micellar composition and their mutual interaction (synergistic for the studied system) in solution. The packing of the monomer in micelle has been estimated to witness spherical geometry for CPC and its mixtures with TX-100, whereas the later has been found to be spheroidal. Polarographic measurements have evidenced comparable diffusion coefficients of CPC and TX-100 micelles whereas their mixed micelles have shown lower values with a minimum, at equimolar composition.     

Abraham model correlations for transfer of neutral molecules and ions to sulfolane

Data have been compiled from the published literature on the partition coefficients of solutes and vapors into anhydrous sulfolane. The logarithms of the water-to-sulfolane partition coefficients, log P, and gas-to-sulfolane partition coefficients, log K, were correlated with the Abraham solvation parameter model. The derived correlations described the observed log P and log K values for solutes dissolved in sulfolane to within average standard deviations of 0.14 log units or less. The log P correlation was extended to include the partition of ions by inclusion of a cation-solvent and an anion-solvent term.     

Diffusion and partition coefficients of small organic solvents in molten miscible polymer blends: Correlations with thermodynamic interactions

The transport properties of small organic molecules in molten poly(vinyl chloride) (PVC)/atactic poly(methyl methacrylate) (PMMA) blends and their homopolymers were studied with inverse gas chromatography. The elution profiles resulting from various organic solvents and different experimental conditions were used for measuring diffusion and partition coefficients. With the van Deemter equation and retention volumes at infinite dilution, diffusion coefficients of 10^?7 to 10^?8 cm²/s and partition coefficients of 10–50 were calculated. The dependence of the diffusion and partition coefficients on experimental variables such as the blend concentration, temperature, and solute nature was examined. The presence of PMMA in PVC blends affected the sorption behavior of the PVC matrix up to a certain concentration. Beyond that, it was hard to derive any composition–diffusivity dependence. On the contrary, the diffusion and partition coefficients were greatly influenced by changes in the temperature and by the nature of the solute. For those solutes (e.g., chlorinated hydrocarbons) showing stronger interactions with polymer blends (higher negative values for the Flory–Huggins interaction parameter χ₁₍₂₃₎), higher diffusion and partition coefficients were obtained. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 267–279, 2004     

Direct Measurement of Octanol-Water Partition Coefficients Using Centrifugal Partition Chromatography with a Back-Flushing Technique

Abstract

Octaol-water partitioning coefficients (K_oct) are an accepted parameter in the prediction of biological activity of organic chemicals. Centrifugal Partition Chromatography (CPC), a form of counter current chromatography, is shown to have several distinct advantages in the direct measurement of these partition coefficients. A new CPC technique, back-flushing, is introduced which allows the direct determination of K_oct values that previously were thought to be unobtainable by this method. The theoretical and experimental aspects of this technique are presented. K_oct of six solutes that ranged from 75 to 3091 were determined and compared with literature values. The direct determination of K_oct values greater than 10⁴ may be possible. Both accuracy and ease of automation may make this a highly desirable method by which to measure octanol-water partition coefficients in the future.     

Interaction of Humic Substances with Organic Pollutants and its Influence on the Concentration of these Pollutants from Water

Abstract

The influence of fulvic acids (FAs) and humic acids (HAs) of different origin on liquid-liquid and solid-phase extraction of hydrophobic organic compounds (HOCs) with broadly varying values of octanol-water partition coefficients K_ow has been investigated. It is shown that the solubilization by dissolved FAs and HAs can lead to a significant decrease in recovery of some HOCs even from very dilute (10–20 mg/l) aqueous solutions of these acids. The results of these investigations and an analysis of the relevant literature data, demonstrate that the extent of solubilization of HOCs by humic substances is determined not only by K_ow, but also by the specific structure of the HOCs. The hypothesis of the formation of intramolecular micelles (IMMs) by unaggregated FAs and HAs, and the partition of HOCs between water and the IMMs is put forward to explain the solubilization of HOCs.     

Evaluation of Octanol-Water Partition Coefficients Using Capillary Gas Chromatography With Cold On-Column Injection

Abstract

A general procedure is described for the determination of the octanol-water partition coefficients (log P) of very lipophilic compounds by the shake flask method, employing the analytical technique of capillary gas chromatography with cold on-column injection. The solute and an internal reference with a known log P value are partitioned between the layers of an octanol-water mixture and their relative concentrations are determined by analysis of each phase, using highly standardized chromatographic conditions. The overall method is demonstrated to be convenient, reproducible, and useful for the determination of the partition coefficients of a wide variety of compounds with log P values as high as 5.7.     

Evaluation of the liquid-liquid partition coefficient of bis(acetylacetonato)copper(II): Contribution of specific solute-solvent interaction

Partition coefficients of Cu(acac)₂ were determined in eleven organic solvents-0.10M perchlorate systems. Their magnitude was compared with that of the enol form of Hacac and evaluated by a modified equation based on the regular solution theory. The partition coefficient of the copper (II) chelate has been demonstrated to strongly depend on some specific solute-solvent interactions such as direct coordination to the central metal and hydrogen bonding to the ligand molecules. In the case of chloroform, particularly the specific interaction has been elucidated by an association reaction, for which the equilibrium constant has been determined.     

Assessment of Centrifugal Partition Chromatography for Determination of Octanol-Water Partition Coefficients

Abstract

Centrifugal partition chromatography (CPC) has been assessed as a convenient automated method for the determination of octanol-water partition coefficients (K_OW) over the range of -0.5 to 2.5 log units. The stationary (V_s) and mobile phase (V_m) volumes, which are needed for the calculation of K_ow, are determined in situ by injecting four compounds with known K_ow. V3 and V_m were also determined by independent analytical means to demonstrate that this is a direct measurement of K_ow from fundamental chromatographic principles with no unexplained fitted parameters. Propagation of error shows that a single four-component calibration with duplicate injections of each unknown is sufficient to determine log K_ow with a precision of less than 0.1 log units.     

Abraham Model Correlations for Transfer of Neutral Molecules to Tetrahydrofuran and to 1,4-Dioxane,and for Transfer of Ions to Tetrahydrofuran

Data have been compiled from the published literature for the partition coefficients of solutes and vapors into anhydrous tetrahydrofuran and 1,4-dioxane. The logarithms of the water-to-ether partition coefficients, log₁₀ P, and gas-to-ether partition coefficients, log₁₀ K, were correlated with the Abraham solvation parameter model. The derived correlations described the observed log₁₀ P and log₁₀ K values for both ether solvents to within average standard deviations of 0.16 log₁₀ units or less. The log₁₀ P correlation for tetrahydrofuran was extended to include the partition of ions by inclusion of a cation-solvent and an anion-solvent term.     

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.     

Chromatographic investigations of adsorption of some aromatic compounds on aluminium oxide and silica gel from solutions

Summary Using adsorption TLC R_M values were measured for a number of aromatic compounds on aluminium oxide and silica gels having different specific surface areas, using the following binary mobile phases: benzene+toluene, benzene+carbon tetrachloride and chloroform+carbon tetrachloride. The results are graphically presented and compared with theoretically calculated values. Generally, a good agreement was found between the calculated and measured R_M values. The agreement is valid both when the R_M values were calculated using experimentally (indirectly) determined partition coefficients or when the coefficients are obtained with help of Ocik's equation [cf. Roczn. Chem.34, 745 (1960) and Chromatographia4, 516 (1971)]. One can assume that in the case of systems in which strong intermolecular interactions are absent, the statically determined partition coefficients of the compounds may be used for the calculation of their R_M values.     

Spectroscopic analysis of naphtholazobenzimidazole in organised solution

Micelle–water partition coefficient (K_x ) of naphtholazobenzimidazole dye (NAB) in aqueous solutions of cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulphate (SDS) has been determined spectrophotometerically. Changes in absorption patterns of dye caused by surfactants and solvents were quantified in terms of dye–surfactant ratio (n _D/n _S) and solvent water partition coefficients (P), respectively. Multiple residence sites have been suggested for dye molecules within micelles, based on shifts in azo-hydrazone tautomeric equilibrium. Micelle–water partition coefficients were used to evaluate the influence of dye on critical micelle concentration of CTAB and SDS. At same micelle concentration, M, the relative solubility of NAB was greater in cationic surfactant CTAB than in anionic surfactant SDS.