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This thesis focuses on instrumental advances in microfluidics-based capillary electrophoresis systems for achieving various goals. Microfluidics systems and purpose-made scientific instruments in general may consist of many different hardware units, often made by different companies. This presents a challenge for system builders who want to efficiently build and use purpose-made instruments for conducting scientific experiments. As this challenge was relevant for all of the projects described in this thesis, it was the first one to be tackled by the development of the software package Instrumentino. The package allows system builders to build a useful graphical user interface (GUI) for their experimental setups, allowing automation of multiple components controlled by separate microcontrollers. A Code could be reused between projects using the same hardware units. Instrumentino was eventually used in all of the projects in this thesis, and while it required a lot of invested time for its development, it saved a lot of time in running experiments afterwards. The first CE systems built for this thesis were for a collaborative project about the use of a C4D cell array for following after separation processes, and comparing them to computer simulations. It was first (using 16 detectors) employed for CZE separations of inorganic anions and cations for the sake of demonstration, and later (using 8 detectors) for investigating CZE and ITP separations in linear polyacrylamide (LPA) coated silica capillaries, exhibiting a very low EOF. Another issue discussed in this thesis is the implementation of concurrent CZE separations for anions and cations in portable systems. Two multi-channel portable CE instruments were built in collaboration with others and two review publications were written on the subject of concurrent determination of anions and cations (also a collaboration). Relying on the experience gained from building the previous systems, a new approach for building electrophoretic separation systems was developed, based on a commercial breadboard system for miniaturized microfluidic parts, offering high design flexibility and small size as in lab-on-chip systems, yet using standard silica capillaries and obtaining comparable results to commercial CE instruments. The applicability of this method was exemplified by the implementation of various electrophoretic experiments using the same building blocks. This approach proved to be very useful and was later employed for all following projects, enabling a quick realization of new designs in a miniaturized way. A third multi-channel portable CE system was developed, offering a thermostated chamber in which separations took place and a new microfluidic design which employed a syringe pump for pressurization, enabling, among other things, a special semi- automatic mode for analyzing volume-limited samples. It was used to determine concentrations of target ions in groundwater and mine water samples in an abandoned mining site in Argentina, as well as the determination of inorganic ions in sediment porewater from Lake Baldegg in Switzerland. In parallel, another desktop system was developed for the semi-automatic analysis of volume-limited samples, employing a micro syringe for sample introduction. Finally, a novel fully automated pre-concentration approach for CE was developed, employing a purpose-made microfluidic trapping block in which a hydrodynamic flow can be applied in a channel alongside an electric field that induces electrophoretic flow of the target ions in the opposite direction. A discontinuity in the target ions’ electrophoretic flow in the channel results in a trapping point for these ions, to which their net flow is directed to from both sides (upstream and downstream). This is achieved by applying the trapping voltage through ion-exchange membranes, which only pass ions of opposite charge than that of the target ions. This trapping block was coupled to a capillary inlet, so that it could be injected and be separated in it, automatically. This approach was found to be applicable also for high conductivity samples (up to 0.1 M), which is unique as most pre-concentration approaches that are based on electrokinetic phenomena are limited to low conductivity samples. Furthermore, the system allows selectively trapping ions with mobilities over a certain level, determined by the relative strengths of the applied hydrodynamic flow and electric field.

Dynamic computer simulation data are compared for the first time with CE data obtained with a laboratory made system comprising an array of 8 contactless conductivity detectors (C(4) Ds). The experimental setup featured a 50 μm id linear polyacrylamide (LPA) coated fused-silica capillary of 70 cm length and a purpose built sequential injection analysis manifold for fluid handling of continuous or discontinuous buffer configurations and sample injection. The LPA coated capillary exhibits a low EOF and the manifold allows the placement of the first detector at about 2.7 cm from the sample inlet. Agreement of simulated electropherograms with experimental data was obtained for the migration and separation of cationic and anionic analyte and system zones in CZE configurations in which EOF and other column properties are constant. For configurations with discontinuous buffer systems, including ITP, experimental data obtained with the array detector revealed that the EOF is not constant. Comparison of simulation and experimental data of ITP systems provided the insight that the EOF can be estimated with an ionic strength dependent model similar to that previously used to describe EOF in fused-silica capillaries dynamically double coated with Polybrene and poly(vinylsulfonate). For the LPA coated capillaries, the electroosmotic mobility was determined to be 17-fold smaller compared to the case with the charged double coating. Simulation and array detection provide means for quickly investigating electrophoretic transport and separation properties. Without realistic input parameters, modeling alone is not providing data that match CE results.

The final publication is available via https://doi.org/10.1016/j.talanta.2018.11.056., A water quality analyzer based on the working principle of capillary electrophoresis (CE) was developed to determine ionic inorganic nitrogen compounds contained in wastewater samples. The instrument provides simultaneous quantification of anions and cations by superimposing hydrodynamic pumping with electrokinetic motion. It features a single separation capillary with contactless conductivity detection and a sequential injection manifold for fluid handling. Dynamic adaption of the system calibration was enabled by the use of a high precision pressure regulator to cover a wide measurement range showing low relative standard deviations (< 2 %) and high measurement accuracy comparable to conventional wastewater analyzers. The prototype is transportable, integrated in a 19 in. rack and connected to a membrane filter system developed for direct sample aspiration in the wastewater process. For operation on site, only a power supply and a network connection for remote control is necessary. Continuous operation was demonstrated over 24 h at the aeration tank of a pilot scale wastewater treatment plant at TU Wien and a good correlation with laboratory results was achieved. At this time, there is no device available, on the market, to analyze all nitrogen species in one assembly with limited hardware complexity and chemical demand. This entails a significant step forward towards automated water quality monitoring with respect to the implementation of new advanced wastewater treatment technologies.