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The Ościk’s equation based on the theory of conformal solutions was used to describe the chromatographic process in RP-HPLC. Theoretically calculated values of the logarithms of retention factors (log k ) were compared with experimental values for a group of aromatic substances, i.e. alkylbenzenes, PAHs, and polar benzene derivatives. Studies were conducted using two columns: RP-18 and RP-4, as well as water-methanol and water-acetonitrile mixtures as mobile phases. The applicability of Everett’s equation to describe the composition of surface phase was also verified. For this purpose, the excess methanol adsorption isotherm on LiChrospher RP-18e, was experimentally determined. [ABSTRACT FROM AUTHOR]

• Expanding the potentials of CEC to the analysis of various aromatic compounds. • Introducing carboxyethyl acrylate-based precursor monolith. • Grafting anthracenyl ligands to the carboxy precursor monolith. • The anthracenyl monolith exhibited both π-π and hydrophobic interactions. • Anthracenyl monolith selectivity was superior to that of octadecyl monolith. In this research report, the post polymerization functionalization (PPF) of a carboxyethyl acrylate (CEA)-co-ethylene glycol dimethacrylate (EDMA) [poly-CEA-co-EDMA)] precursor monolith with 2-aminoanthracene was carried out in the presence of an organic solvent soluble carbodiimide, namely N,N´ -dicyclohexylcarbodiimide (DCC), yielding the so-called anthracenyl-poly-CEA-co-EDMA monolith. This novel monolith proved to be an excellent monolithic stationary for reversed-phase capillary electrochromatography (RP-CEC) with hydrophobic and π-π interactions of a wide range of nonpolar solutes including those bearing aryl functional groups in their structures such as polycyclic aromatic hydrocarbons (PAHs), toluene derivatives and aniline derivatives as well as solutes carrying in their structures electron withdrawing substituents such as dinitrophenyl-amino acids (DNP-AAs) and di-DNP-AAs. The retention behaviors of the just mentioned solutes obtained on the anthracenyl-poly-CEA-co-EDMA monolithic column were compared to those obtained on octadecyl-poly-CEA-co-EDMA monolithic column prepared from the same carboxy-precursor monolith. The results demonstrated the superiority of anthracenyl column over the octadecyl column for the separation and enhanced selectivity for aromatic solutes since it provides not only hydrophobic interactions but also π-π interactions with aromatic nonpolar solutes. [ABSTRACT FROM AUTHOR]

Two approaches for incorporating carbon nanotubes into monolithic columns for HPLC are described in this report. They pertain to the investigation of carbon nanotubes either (i) as entities to modulate solute retention on monolithic columns bearing well defined retentive ligands or (ii) as entities that constitute the stationary phase responsible for solute retention and separation. Approach (i) involved the incorporation of carbon nanotubes into octadecyl monolithic columns while approach (ii) concerns the preparation and evaluation of an ideal monolithic support and coating it with carbon nanotubes to yield a real "carbon nanotube stationary phase" for the HPLC separation of a wide range of solutes. First, an octadecyl monolithic column based on the in situ polymerization of octadecyl acrylate and trimethylolpropane trimethacrylate was optimized for use in HPLC separations of small and large solutes (e.g., proteins). To further modulate the retention and separation of proteins, small amounts of carbon nanotubes were incorporated into the octadecyl monolith column. In approach (ii), an inert, relatively polar monolith based on the in situ polymerization of glyceryl monomethacrylate (GMM) and ethylene glycol dimethacrylate (EDMA) proved to be the most suitable support for the preparation of "carbon nanotube stationary phase". This carbon nanotube "coated" monolith proved useful in the HPLC separation of a wide range of small solutes including enantiomers. In approach (ii), a more homogeneous incorporation of carbon nanotubes into the diol monolithic columns (i.e., GMM/EDMA) was achieved when hydroxyl functionalized carbon nanotubes were incorporated into the GMM/EDMA monolithic support. In addition, high power sonication for a short time enhanced further the homogeneity of the monolith incorporated with nanotubes. In all cases, nonpolar and π interactions were responsible for solute retention on the monolith incorporated carbon nanotubes. [ABSTRACT FROM AUTHOR]

Abstract: We have studied the energetics of solvation of benzene (C6H6), nitrobenzene (C6H5NO2) and aniline (C6H5NH2) in the mixtures of water with oxygen-containing H-bond acceptors — acetone (Me2CO), 1,4-dioxane (DO) and dimethylsulfoxide (DMSO). The enthalpies of solution determined calorimetrically at 298K have been used to study the pair interaction between aromatic solutes and their groups with H-bond acceptors in water and with water in pure aprotic non-aqueous solvents. The general trends occurring for enthalpies of solute transfer and enthalpies of pair interactions are discussed. [Copyright &y& Elsevier]

Retention factors (log kw) in pure water were calculated for a homologous series of alkylbenzenes, PAHs, and aromatic monosubstituted derivatives for column C18, C8, and C4, using the numerical method based on the linear form of the Ościk's equation, which were correlated with the log kw values determined by the linear extrapolation method from the log k dependence on methanol volume fraction in binary eluent. The chromatographic parameters (log kw), being the hydrophobicity measure, were compared with the experimental partition coefficients in n-octanol/water system (log P). The author examined the contribution of the substituents (-CH2-, -OH, -Cl, -NO2, and -CHO) in the substance retention in pure water for columns of different hydrocarbon chain length of the bonded phase. Moreover, the transfer thermodynamics of the particular functional groups from water to the stationary phase, as well as the influence of the kind of the stationary phase on the thermodynamics of this process were studied. For this purpose the standard free enthalpy (ΔGo) of the functional groups transfer from water to the stationary phase and from the gas to stationary one was calculated. [ABSTRACT FROM AUTHOR]

A numerical method based on the linear form of the Ościk equation was used for calculation of the logarithms of the retention factors of alkylbenzenes, PAHs, and several polar monosubstituted benzenes of a RPLC system with pure water as mobile phase. The author used a system consisting of a column packed with LiChrospher RP-18e and mobile phases containing methanol and acetonitrile as organic modifier of the mobile phase. Also, the influence of the kind of the organic modifier of the mobile phase as well as the range of its concentration on the calculated log kw values was studied. Moreover, the correlations between the log kw values determined by various methods and the partition coefficients in the n-octanol/water system (log P) have been presented. The log kw values calculated by the numerical method do not practically depend on the concentration range of the organic modifier and show the best linear correlations with the experimental log P values, number of carbon atoms in alkylbenzenes (nC), and the log kw values determined by linear extrapolation from log k dependence on the volumetric fraction of methanol. [ABSTRACT FROM AUTHOR]