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<p>Three chiral selectors (diketogulonic acid, benzoxycarbonylglycylproline and ketopinic acid) have been introduced for enantioseparation of pharmacologically active amines in non-aqueous capillary electrophoresis. The use of organic solvents, instead of aqueous buffers in the background electrolyte facilitated ion-pair formation between the analytes and the chiral selectors. The enantioresolution was strongly affected by the choice of selector and organic solvent but also depended on the other electrolytes. The most important parameter for the enantioresolution, apart from the choice of chiral selector, was the direction and magnitude of the electro-osmosis. Thus, covalently coated capillaries were used to suppress and to reverse this flow. Furthermore, the alkali metal hydroxide added to the background electrolyte had a great influence on the electro-osmosis. Exchanging LiOH for NaOH, was found to decrease the electro-osmotic flow. Interestingly, the flow was altered from cathodic to anodic, with KOH, RbOH or CsOH added to the ethanolic BGE. The occurrence of a reversed electro-osmosis had a great positive effect on the enantioresolution. An appropriate choice of solvent and electrolytes promoted also fast chiral separations, e.g., the enantiomers of isoprenaline were resolved within one minute. </p><p>The capillary electrophoresis systems developed within this work were applied for enantiomeric purity determinations of different pharmaceutical forms of drug products. A detection limit of 0.033 % was achieved for <i>1S,2R</i>-ephedrine, the enantiomeric impurity in Efedrin®, when diketogulonic acid was used as the selector. </p><p>By using the pre-concentration technique, transient isotachophoresis, the peak efficiency was enhanced for the enantiomers of timolol. This facilitated the introduction of a higher concentration of the sample into the capillary electrophoretic system containing ketopinic acid as the selector, and lowered the detection limit from 2.5 % to 0.2 % for the enantiomeric impurity <i>R</i>-timolol compared with injection without transient isotachophoresis.</p><p>The volatility of the non-aqueous media in capillary electrophoresis facilitated the hyphenation to mass spectrometry. The partial filling technique ensured that the selector did not contaminate the mass spectrometer, and the separated enantiomers of e.g., pronethalol were detected in the selector-free zone. </p>

Three chiral selectors (diketogulonic acid, benzoxycarbonylglycylproline and ketopinic acid) have been introduced for enantioseparation of pharmacologically active amines in non-aqueous capillary electrophoresis. The use of organic solvents, instead of aqueous buffers in the background electrolyte facilitated ion-pair formation between the analytes and the chiral selectors. The enantioresolution was strongly affected by the choice of selector and organic solvent but also depended on the other electrolytes. The most important parameter for the enantioresolution, apart from the choice of chiral selector, was the direction and magnitude of the electro-osmosis. Thus, covalently coated capillaries were used to suppress and to reverse this flow. Furthermore, the alkali metal hydroxide added to the background electrolyte had a great influence on the electro-osmosis. Exchanging LiOH for NaOH, was found to decrease the electro-osmotic flow. Interestingly, the flow was altered from cathodic to anodic, with KOH, RbOH or CsOH added to the ethanolic BGE. The occurrence of a reversed electro-osmosis had a great positive effect on the enantioresolution. An appropriate choice of solvent and electrolytes promoted also fast chiral separations, e.g., the enantiomers of isoprenaline were resolved within one minute. The capillary electrophoresis systems developed within this work were applied for enantiomeric purity determinations of different pharmaceutical forms of drug products. A detection limit of 0.033 % was achieved for 1S,2R-ephedrine, the enantiomeric impurity in Efedrin®, when diketogulonic acid was used as the selector. By using the pre-concentration technique, transient isotachophoresis, the peak efficiency was enhanced for the enantiomers of timolol. This facilitated the introduction of a higher concentration of the sample into the capillary electrophoretic system containing ketopinic acid as the selector, and lowered the detection limit from 2.5 % to 0.2 % for the enantiomeric impurity R-timolol compared with injection without transient isotachophoresis. The volatility of the non-aqueous media in capillary electrophoresis facilitated the hyphenation to mass spectrometry. The partial filling technique ensured that the selector did not contaminate the mass spectrometer, and the separated enantiomers of e.g., pronethalol were detected in the selector-free zone.

Dans cette thèse, on a étudié l’évolution de l’interface par électro-osmose entre deux couches de fluides dans un canal microfluidique. Les applications de ce problème concernent le mélange et le transport, sans contact avec des actionneurs, de fluides en micro-canal. De nombreuses questions restent toutefois posées lorsque le champ est oscillant en temps, notamment vis à vis de la stabilité de l'interface entre les deux fluides. Une analyse de stabilité linéaire basée sur une perturbation à l’interface a été réalisée pour un film mince d'électrolyte sous des champs électriques continus (constants) et alternatifs (dépendant du temps). Une analyse asymptotique avec une hypothèse de grande longueur d’onde des équations d'Orr-Sommerfeld a été appliquée afin de déterminer les seuils de stabilité paramétriques d'un film mince aqueux. L’accent a été mis sur les effets de la tension de surface, de la pression de disjonction pour l'interaction gaz-liquide-substrat, de l'amplitude et de la fréquence du champ électrique appliqué, ainsi que du potentiel zêta du substrat et de la surface libre. Une analyse comparative des profils de vitesse de l’état de base avec et sans contraintes de Maxwell à l’interface, a montré que les gradients de vitesse étaient importants à l'interface liquide-liquide avec les contraintes de Maxwell. De tels gradients sont essentiels à l'instabilité interfaciale sous l’action d’un champ électrique périodique car ils peuvent atténuer ou amplifier les ondes à l’interface. Parallèlement, un dispositif expérimental a été conçu et monté afin de caractériser l’écoulement électroosmotique dans un micro-canal rectangulaire. Avec l'aide d'une analyse PTV (« Particle Tracking Velocimetry »), les distributions de vitesse ont été obtenues et comparées aux prédictions théoriques. Cette comparaison a permis d’estimer le potentiel zêta du PDMS utilisé, valeur conforme à la valeur indiquée dans la littérature. / Since the past decade, use of electro-osmotic flow (EOF) as an alternative flow mechanism in microdevices is becoming more popular due to its less bulky and low maintenance system design. However, one of the biggest shortcomings for its usage in mainstream applications is that it requires the concerned liquid to be electrically conductive. One idea can be to use the flow of conductive fluids to transport non-conductive liquids passively via interfacial shear transfer. Such an idea can has numerous applications in a wide range of fields like bio-chemical processing (e.g. lab-on-a-chip reactors, mixers, etc.), to oil extraction from porous rock formations. One of the significant characteristics of micro-scale flows is high surface to volume ratio, which significantly highlights the role of multi-phase interfaces in such dynamics. The presence of a fluid-fluid interface in an EOF necessitates the characterization of the parameters responsible for hydrodynamic instability of such systems. The present work focuses on the role of steady and time-dependent electric stress (Maxwell stress), capillary force and disjoining pressure on fluid-fluid interfacial instability. A linear stability analysis of interfacial perturbation was performed for a thin film of electrolyte under DC and AC electric fields. Through long wave asymptotic analysis of the Orr-Sommerfeld equations, parametric stability thresholds of a thin aqueous film explored. Further, a set of experiments were performed in order to characterize the EOF in a rectangular microchannel. With the help of a Particle Tracking Velocimetry analysis, velocity distributions were obtained which agreed well to the theoretical values. This was further used to estimate PDMS zeta potential, which was found to be within the reported values in the existing literature. Liquid-liquid interfacial deformation was also explored under a time-periodic EOF and a wide range of the magnitudes of capillary force, and diffusive and convective transport.

Since the past decade, use of electro-osmotic flow (EOF) as an alternative flow mechanism in microdevices is becoming more popular due to its less bulky and low maintenance system design. However, one of the biggest shortcomings for its usage in mainstream applications is that it requires the concerned liquid to be electrically conductive. One idea can be to use the flow of conductive fluids to transport non-conductive liquids passively via interfacial shear transfer. Such an idea can has numerous applications in a wide range of fields like bio-chemical processing (e.g. lab-on-a-chip reactors, mixers, etc.), to oil extraction from porous rock formations. One of the significant characteristics of micro-scale flows is high surface to volume ratio, which significantly highlights the role of multi-phase interfaces in such dynamics. The presence of a fluid-fluid interface in an EOF necessitates the characterization of the parameters responsible for hydrodynamic instability of such systems. The present work focuses on the role of steady and time-dependent electric stress (Maxwell stress), capillary force and disjoining pressure on fluid-fluid interfacial instability. A linear stability analysis of interfacial perturbation was performed for a thin film of electrolyte under DC and AC electric fields. Through long wave asymptotic analysis of the Orr-Sommerfeld equations, parametric stability thresholds of a thin aqueous film explored. Further, a set of experiments were performed in order to characterize the EOF in a rectangular microchannel. With the help of a Particle Tracking Velocimetry analysis, velocity distributions were obtained which agreed well to the theoretical values. This was further used to estimate PDMS zeta potential, which was found to be within the reported values in the existing literature. Liquid-liquid interfacial deformation was also explored under a time-periodic EOF and a wide range of the magnitudes of capillary force, and diffusive and convective transport.