Advances in capillary electrophoresis using microfluidics

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.