No abstract

No abstract

This work focuses on the separation of standard polystyrenesulfonates (PSS), with molecular masses (Mr) between 16 and 990 x 10(3) in capillaries filled with semidilute (entangled) linear hydrophilic polymers. Contrary to cross-linked chemical gels, which produce permanent networks, solutions of linear polymers lead to dynamic networks. The analytical performances and migration mechanisms are discussed on the basis of experiments performed in solutions of linear polyethyleneoxides and derivatized celluloses of various molecular masses. The influence of the mesh size and of the lifetime of the obstacles of the separating network has been investigated in detail. The mesh size is assimilated to the blob size of the separating polymer and is a decreasing function of its concentration. The lifetime of the obstacles of the network, identified with the reptation time of the polymer chain, characterizes its dynamics. This characteristic time increases with both the molecular weight of the separating polymer and its concentration. Its impact was first examined at fixed blob size. Then, the influence of the blob size was studied while keeping the reptation time of the network constant. By doing so, the existence of interactions between the solute and the separating polymer or between the solute and capillary wall can be more safely assessed. It appears that the reptation time of the mesh has a large influence on the electrophoretic mobility of the PSSs under a threshold value, which is of the order of magnitude of the time taken by the PSS to migrate on the blob size. Also shown are separations using networks made up with mixtures of polyethyleneoxides of the same nature and same mass concentration, but of very different molecular masses. This latter approach allows one to adapt the viscosity of the solution and the dynamics of the network, keeping the blob size constant.

This work focuses on the understanding of the electrophoretic behavior of flexible chains of polystyrenesulfonates (PSSs) in free solution. It deals mainly with the variation of the electrophoretic mobility with (i) the polymerization degree (N) of fully sulfonated PSSs and (ii) the sulfonation rate of randomly sulfonated PSSs. In both cases, the electrophoretic mobility was modeled following a semi-empirical approach which involves parameters retaining a physical meaning. Fully sulfonated PSS oligomers, having a length smaller than or similar to the Debye length, exhibit a particular electrophoretic behavior, in-between that observed for multicharged small molecules and that for polyelectrolytes. The electrophoretic mobility of these oligomers increases strongly with N, which is attributed to a hydrodynamic coupling between monomers. Then the mobility is maximum for an N of about 10, for which the PSS oligomers are still in a rod-like conformation. Afterwards, as N increases and the PSSs are larger than the Debye length, the electrophoretic mobility decreases slowly until it reaches a constant value corresponding to the free-draining behavior. Next, the electrophoretic behavior of long PSS (N about 1,200) differing in their sulfonation rates was investigated. The effective charge rates were determined independently by conductimetric measurements and the mobilities were modeled as a function of the sulfonation rate. The PSS behavior observed was compared to the one previously reported for classical polyelectrolytes having hydrophilic backbones, such as copolymers of poly(acryamide-coacrylic acid). A specific behavior has been pointed out for these partially sulfonated PSSs, which is attributed to the hydrophobicity of their backbone. Finally, it is shown that separations of PSSs of different sulfonation rates can be obtained with electrolytes containing an anionic surfactant or methanol.

A great interest has been drawn these last years towards ionic liquids in analytical chemistry, especially for separation methods. Recent synthesis of chiral ILs opened the way of the evaluation of new potential selectors for enantiomeric separations. This work focused on the evaluation of two chiral ILs (ethyl- and phenylcholine of bis(trifluoromethylsulfonyl)imide) by CE. Particular selectivities are awaited by exploiting unique ion-ion or ion-dipole interactions and by tailoring the nature of the cation and the anion. To evaluate such phenomena, a study was carried out with anti-inflammatory drugs 2-arylpropionic acids as model compounds. The results show that these chiral ILs did not present direct enantioselectivity with regard to these model analytes. The influence of chiral ILs in the electrolytes was then studied in the presence of classical chiral selectors (di- or trimethyl-beta-cyclodextrin). Although no general trend could be established, an increase in separation selectivity and resolution was observed in some cases, suggesting synergistic effects. The complementary determination of apparent inclusion constant values of these IL cations in the used cyclodextrins by affinity CE provided support to the understanding of the phenomena involved.

In order to accurately evaluate the performances of any electrolyte medium, a clear concept of selectivity in capillary electrophoresis and related electroseparation techniques is proposed. Selectivity is defined as the ratio of the affinity factors of both analytes for a separating agent (phase, pseudophase, or complexing agent present in the background electrolyte). When in the presence of a complexing agent and if only 1:1 complexation occurs, selectivity corresponds to the ratio of the apparent binding constants and is independent of the concentration of the complexing agent. This concept is illustrated through the separations of neutral and anionic enantiomers in the presence of a cationic cyclodextrin, the mono(6-amino-6-deoxy)-β-cyclodextrin, as a chiral complexing agent. The values obtained for different pairs of enantiomers are discussed with regard to the functional groups that distinguish them. When the analytes have the same mobilities in free solution and in their complexed form, then the resolution equation developed in micellar electrokinetic chromatography may be applied and optimum conditions (affinity factors, chiral agent concentration) can be predicted.

A new online coupling of CIEF with ESI-MS has been developed in glycerol-water media. This improved protocol provides: (i) the electric continuity during the whole analysis by a discontinuous filling of the capillary with 60:40 (cm/cm) catholyte/proteins-ampholyte mixture; (ii) the use of an anticonvective medium, i.e. 30:70 glycerol/water, v/v, compatible with MS detection and as an aid to hydrophobic protein solubilization and (iii) the use of unmodified bare fused-silica capillaries, as the glycerol/water medium strongly reduces EOF. Focusing was performed in positive polarity and cathodic mobilization was achieved by both voltage and pressure application. The setup was optimized with respect to analysis time, sensitivity and precision on pI determination. The optimized anolyte and catholyte were composed of 50 mM formic acid/1 mM glutamic acid (pH 2.35) and 100 mM NH(3)/1 mM lysine (pH 10.6), respectively. The effects of ampholyte concentration, focusing time and ESI parameters were presented for model proteins and discussed. This new integrated protocol should be an easy and effective additional tool in the field of proteome analysis, providing a means for the characterization of a large number of hydrophilic and hydrophobic proteins.

No abstract