On-line concentration techniques in capillary electrophoresis and the experimental investigation of electroextraction

Capillary electrophoresis is a great option for analyzing metabolomics compounds since the analytes are often charged. The technique is simple and cost-efficient but it is not the most popular equipment because it lacks high concentration sensitivity. Therefore, on-line concentration techniques have been developed for capillary electrophoresis. The aim of this thesis is to give an introduction to the most common on-line concentration methods in capillary electrophoresis, and to demonstrate a novel on-line concentration technique termed electroextraction. Until now, the research of on-line concentration techniques in capillary electrophoresis is mainly focused on methods based on field amplification, transient isotachophoresis, titration incorporated methods or sweeping, which are presented in the literature section. In a two-phase electroextraction, the electrodes are placed in an aqueous acceptor phase and in an organic donor phase, in which the analytes are dissolved. When the voltage is applied, the conductivity difference in the two phases cause high local field strength on organic phase leading to fast migration of the cationic analytes towards the cathode. As soon as the analytes cross the solvent interface, their migration speed decrease and they are concentrated at the phase boundary. In these experiments, a normal capillary electrophoresis analyzer was used with a hanging aqueous phase droplet at the tip of the capillary inlet. The experimental part was carried out at Leiden University, Division of Analytical BioSciences in the Netherlands. An electroextraction-capillary electrophoresis system was built for the analysis of biological acylcarnitine compounds. After the method parameters were assessed with ultraviolet detection, the method was coupled with mass spectrometric detection, and the selectivity and repeatability were briefly tested. Sensitivity was enhanced with the electroextraction procedure but the extraction factors were not satisfactory yet. Selectivity of electroextraction was discovered when the extraction of acylcarnitines was performed using different solvents. All parameters affecting the electroextraction procedure were not tested, and therefore the instability of the method was not completely understood. Thus, the method should be further investigated and optimized. In fact, all on-line concentration methods ought to be optimized for the target analytes in their existing matrix