Further development and applications of capillary electrophoresis with capacitively coupled contactless conductivity detection and sequential injection analysis in analytical chemistry

摘要

This dissertation is based on the further development and applications of capillary electrophoresis (CE) with capacitively coupled contactless conductivity detection (C4D), i. e. sequential injection analysis (SIA) applications when coupled with CE-C4D, or determination and quantification of various ions that are not or barely UV absorbed. ududA purpose made CE-C4D system was used for determination of the DNA fragments of different length, using additives to modify the medium and to sieve charged anions according to their size. We determined DNA mass ladder and PCR products from various sources. Feasibility of the C4D method and its practical application in the separation of DNA fragments was studied and as far as we are concerned has not been implemented for the routine analysis yet. CE-C4D method demonstrated separation with much shorter analysis time than the standard gel-electrophoresis used in conventional approach. No derivatization or sample preparations were necessary.ududFurther on, we investigated employment of an automated system with a sequential injection analysis (SIA) manifold based on a syringe pump and multiport valve coupled with CE-C4D. Hydrodynamic pumping was introduced for electrophoretic separation of most commonly used artificial sweeteners. Compounds were determined in their anionic form at a high pH. Without any surfactant or modifier to reverse the electroosmotic flow, higher separation efficiency was noticed. The conditions were optimized either for better detection limits or for shorter analysis time. In addition, band broadening was observed due to pressure caused by hydrodynamic pumping. Therefore, the requirement of the narrow capillary of 10 µm for sensitive detection was necessary. The best compromise for differences between analysis time and separation efficiency was found. This coupled system setup approved to complete all operation steps to perform complex measurements with possibility to change any of the parameters during the measurements, among which sampling, separation, detection, data acquisition and polarity of the high-voltage. ududSIA-CE-C4D composition was afterwards engaged with an array of 16 contactless conductivity detectors aligned on the capillary for real time monitoring of the entire electrophoretic separation. For better control of pressurization, some modifications were implemented, demonstrating the developments of the peaks throughout the whole capillary.ududDual capacitively coupled contactless conductivity detector was implemented. Both channels were brought into line in a bridge mode where one acts as a reference with subtracted signal. As a result, the electronic zero setting of the baseline, caused by conductivity change of the background buffer, was not necessary as in previous versions of the cell. All the differences in buffer content are consequently considered. ududAt the end, study on the effect of buffer concentration on the sensitivity was taken into consideration. Narrow capillaries employed, resulted in high signal-to-noise ratio when higher buffer concentration are used. Several fundamental aspects of the axial capacitively contactless conductivity detection were investigated in order to explain this uncertain effect. The performance, behavior and the cell geometry of a new detector design are reported but some evidence of the solution for this problem is still missing.ud