Hydrophilic interaction liquid chromatography for separation and quantification of selected room-temperature ionic liquids.
ABSTRACT Hydrophilic interaction liquid chromatography (HILIC) is an alternative technique to ion pairing-reversed-phase liquid chromatography (IP-RPLC) and classical RPLC for separation of alkylimidazolium room-temperature ionic liquids (RTILs). Particularly, HILIC offers better retention and selectivity for short-chains RTILs imidazolium compounds. HILIC mechanisms were investigated by studying the influence of organic modifier content and salt concentration in the mobile phase. HILIC method was validated by quantifying 1-butyl-3-methylimidazolium cation (BMIM) degradation under gamma radiation at 2.5MGy. Development of separative reproducible analytical methods, including for low concentration, applicable to RTILs are today mandatory to improve RTILs chemistry.
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ABSTRACT: An effort has been made to investigate the chromatographic behavior and to understand the basic mechanisms in HILIC-based separation of water-soluble vitamins with highly varied properties on a diol column. The water content of the mobile phase is of utmost importance because it directly affects the type and extent of interactions of the solutes with the stationary phase and with the buffered mobile phase. A mixed-mode partitioning-surface adsorption mechanism enables most precise description of their chromatographic retention and separation. The point at which surface adsorption becomes apparent, however, depends on the properties of the solutes on the given stationary phase, and on the presence of buffer salt ions. Adjustment of mobile phase pH and use of different buffer salts can be used to modify electrostatic interactions among the solutes, active silanols, and counter-ions. The role of hydrogen bonding was clarified by substitution of ACN by solvents with moderate to strong hydrogen bonding potential. Analytes which are neutral at the working pH start to interact with the stationary phase when the ACN content is increased to 80%. Negatively charged analytes are adsorbed on the stationary phase when the ACN content is approximately 86%, because augmentation of the counter-ions weakens electrostatic repulsion by the active silanol groups. On the other hand, the electrostatic attraction of thiamine contributes significantly to its retention even when using mobile phases with high water content. KeywordsColumn liquid chromatography-Hydrophilic interaction liquid chromatography-Diol column-Chromatographic behavior-Retention models-Water-soluble vitaminsChromatographia 01/2010; 71(9):751-759. · 1.44 Impact Factor
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ABSTRACT: Four novel β-cyclodextrin (β-CD) derivatives functionalized by ionic liquids, in which the substituents and cyclodextrin cavity are linked by a CH2NC group, were successfully prepared, and the corresponding chiral stationary phases (CSPs) based on silica gel, namely mono-6-deoxy-6-(p-N,N,N-trimethylaminobenzimide)-β-CD nitrate CSP (4a), mono-6-deoxy-6-(p-N,N,N-trimethylaminobenzimide)-β-CD tosylate CSP (4b), mono-6-deoxy-6-(p-N-methylimidazolemethylbenzimide)-β-CD nitrate CSP (4c) and mono-6-deoxy-6-(p-N-methylimidazolemethylbenzimide)-β-CD tosylate CSP (4d), were applied in high-performance liquid chromatography (HPLC). A large number of analytes including chiral 1-phenyl-2-nitroethanol derivatives, aromatic alcohols and ferrocene derivatives were investigated to evaluate the separation performance of the four CSPs, and excellent enantioseparations were obtained for most of the analytes. For 1-phenyl-2-nitroethanol derivatives and aromatic alcohols, the cationic substituent with smaller volume on β-CD derivative was beneficial for the enantioseparation of most compounds. Furthermore, the anion structures on these CSPs play an important role in the separation of solutes. The analytes with smaller molecular volume were more effectively separated on CSP 4b with the tosylate anion by offering hydrogen-bonding and π-π interactions, while the nitrate anions on CSPs 4a and 4c were more favorable for the separation of the compounds with larger volumes due to the weaker steric bulk. The enantiomeric separation results of ferrocene derivatives further showed good separation capability of CSPs 4b and 4c. The cooperation of cationic and anionic substituents on β-CD derivatives is essential for the separation of these chiral compounds.Analytica chimica acta 03/2014; 819:122-9. · 4.31 Impact Factor
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ABSTRACT: Zwitterionic hydrophilic interaction chromatography (ZIC-HILIC) was used to study the retention of selected organoarsenicals. The retention behavior of nine organic arsenic species on ZIC-HILIC was investigated to elucidate which is the driving force for their separation, hydrophilic partitioning or adsorption driven by hydrogen bonds with surface H-donor/acceptor groups of the stationary phase. For this, the retention factor of the compounds k was correlated with log P(O/W) and with the calculated strength of hydrogen bonding of the analytes. By examining aliphatic and phenylic compounds separately, improved correlation was received. This indicates that both phenomena contribute to the separation of these arsenic species on ZIC-HILIC. The results obtained evidence that considerable electrostatic interactions also occur on ZIC-HILIC. Retention behavior of arsenic species was investigated by varying the separation conditions, which shows that the composition of the eluent has a strong influence on the retention behavior. It is highly dependent on water/acetonitrile ratio, pH value and salt additives. Dissociation degree and polarity of arsenic species, which are varying with pH, regulate the distribution of arsenic species between stationary and mobile phases in HILIC. Increase in the ammonium acetate concentration leads to shortened or to prolonged retention depending on the structure of the arsenic species.Journal of Separation Science 03/2010; 33(6-7):817-25. · 2.59 Impact Factor