Linear Solvation Energy Relationship Analysis Research Articles

Effect of pendent group structures on the chemical selectivity and performance of sulfonated copolymers as novel pseudophases in electrokinetic chromatography.

Amphiphilic copolymers of 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS) with dihydrocholesteryl acrylate (pDHCHAt) or tert-octyl acrylamide (ptOAm) as comonomers were synthesized, characterized and used as new polymeric pseudostationary phases in electrokinetic chromatography. High-efficiency separations with theoretical plates around 500,000 to 870,000/m were achieved. Linear solvation energy relationships analysis of 20 solutes was performed to investigate the retention mechanism. Polycyclic aromatic hydrocarbons (PAHs) were separated under 30% v/v acetonitrile. The separation of nine aromatic model solutes by pDHCHAt showed significantly different selectivity from that of sodium dodecyl sulfate. Although only minor difference in selectivity was found for small aromatic compounds on pDHCHAt and poly(AMPS-lauryl acrylate), significantly different retention mechanism was found for PAHs and n-dodecanophenone comparing both copolymers. Significant chemical selectivity difference was found for selected small aromatic compounds on ptOAm and poly(AMPS-stearyl acrylamide).

The characterization of nitrogen-enriched activated carbons by IR, XPS and LSER methods

The aim of this work is to study the efficiency of the nitrogen enrichment by urea of lignites and the induced changes of the adsorptive properties towards volatile organic compounds (VOCs) of the activated carbons derived from these modified precursors. The study is made using infrared and X-ray photoelectrons spectroscopies and the LSER (linear solvation energy relationship) modeling. Four activated lignites derived from the same raw material, original or enriched with nitrogen, are characterized in this way. The effect of the chemical treatment by urea and of the burn-off amount are investigated in term of evolution of the chemistry of the studied materials. The influence of these parameters on the selective behavior of the activated lignites towards two pairs of VOCs is also discussed in terms of molecular interactions using the LSER approach. The results show that the chemical treatment of the raw material is successful, leading to significant enrichment with nitrogen under pyridinic form at the surface of the activated carbons. Moreover, they reveal some selective properties well explained by the LSER analysis and spectroscopic measurements. The selective character of the studied materials is modulated by the duration of the activation step.

The Change in the Properties of Sodium Dodecyl Sulfate Micelles upon Addition of Isomeric and Unsaturated Short-Chain Alcohols Probed by Photophysical Methods

The properties of sodium dodecyl sulfate micelles (SDS) in the presence of 1-propanol, 2-propanol, and 2-propen-1-ol (allyl alcohol) were investigated using electrical conductivity and fluorescence quenching methods. The constants of association of the alcohols to SDS micelles, obtained experimentally and calculated from linear solvation energy relationship analysis, are in the range 1–2 M−1, indicating that these additives behave not only as cosolvents but also as micellar surface active solutes. Larger molecular volume and lower basicity of the alcohol favor partitioning to the micelle. The formation of smaller micelles upon addition of the alcohols is accompanied by an enhancement of solute intermicellar migration and intramicellar quenching rate constants. In particular, the micelle fragmentation–coagulation process of the SDS (0.04 M)/allyl alcohol (1.5 M) system occurs in the time range of 1.5 μs, as indicated by the intermicellar exchange rate constant of the N-dodecylpyridinium ion.

Effect of pendant chain lengths and backbone functionalities on the chemical selectivity of sulfonated amphiphilic copolymers as pseudo-stationary phases in electrokinetic chromatography

Amphiphilic copolymers of AMPS (2-acrylamido-2-methyl-1-propanesulfonic acid) and hydrophobic monomers with various chemical structures were synthesized, characterized and used as novel electrokinetic chromatography polymeric pseudo-stationary phases, showing significant chemical selectivity differences from that of the conventional monomeric pseudo-stationary phase, sodium lauryl sulphate. Copolymers of AMPS and methacrylates with different pendant chain lengths (C 8, C 12 and C 18) were investigated and no significant difference in chemical selectivity was observed among them. However, the spacer bonding chemistry was shown to contribute to significant chemical selectivity difference, e.g. poly(AMPS–lauryl methacrylate) showed different chemical selectivity from poly(AMPS–lauryl methacrylamide). Linear solvation energy relationship analysis of 20 solutes by eight different polymeric pseudo-stationary phases was employed to investigate the solute molecule structural contributions to the retention. Hydrogen-bonding properties (described by system constants b and a) of poly(AMPS–alkyl methacrylamide) were found stronger than these of poly(AMPS–alkyl methacrylate).

Some aspects of chromatographic behavior in capillary electrochromatography

Retention behavior and column efficiency in capillary electrochromatography (CEC) were compared with those in micro-high-performance liquid chromatography (μ-HPLC). Using a unified microcolumn separation apparatus, capacity factors of 27 neutral solutes in pressurized electrochromatography (PEC), CEC and μ-HPLC were investigated and no significant differences were found among these three modes. By linear solvation energy relationship analysis, the same linear equations were obtained in CEC, PEC and μ-HPLC. Systematic investigation of the retention behaviors under mobile phases with four different kinds of organic solvents showed that some of the retention rules in HPLC can be applied in CEC for neutral solutes. Gradient elution of ketones and aldehydes is discussed.

Chemical selectivity in micellar electrokinetic chromatography II. Rationalization of elution patterns in different surfactant systems

Retention behavior in micellar electrokinetic chromatography (MEKC) is investigated using linear solvation energy relationships (LSERs) for two pseudo-stationary phases, one consisting of cationic micelles of tetradecyltrimethylammonium bromide (C 14TAB) and the other of an anionic triblock copolymer, poly(methyl methacrylate-ethyl acrylate-methacrylic acid) (Elvacite 2669). It was found that solutes' migration behaviors in these two MEKC systems are mainly influenced by their si/e ( V/100) and hydrogen bonding acceptor (HBA) strength (β). However, solutes' hydrogen bonding donor (HBD) strength (α) has minor effects on their migration in MEKC. The characteristics of these two systems were compared to three other previously reported anionic micellar systems of sodium dodecyl sulfate (SDS) (anionic hydrocarbon), sodium cholate (SC) (anionic bile salt) and lithium perfluorooctane sulfonate (LiPFOS) (anionic fluorocarbon). It was concluded that hydrogen bonding interactions play a major role in providing different chemical selectivity among these five MEKC systems. Both C 14TAB micelles and the ionic polymer of Elvacite 2669 provide hydrogen bonding acceptor (HBA) sites for solutes, which is similar to SC micelles. In fact, C 14TAB is the strongest HBA, while Elvacite 2669 has HBA strength similar to that of SC micelles. On the other hand, the fluorocarbon micelles of LiPFOS are the strongest hydrogen bond donor (HBD) micelles, followed by the weak HBD SDS micelles. In general, cavity formation has little or no effect on chemical selectivity among hydrocarbon surfactant MEKC systems (i.e., SDS, SC and C 14TAB). Information obtained from the LSER analysis is used to rationalize the elution patterns in MEKC with different types of pseudo-stationary phases.