Investigation And Applications Of Bias-free Electrokinetic Injection System In Capillary Electrophoresis

Injection system is one of the most important parts of capillary electrophoresis. Usually, internal standard addition and mathematical methods are used to correct the injection results. Additionally, various kinds of non-bias injection device are playing a more and more important role in eliminating the composition bias of the electrokinetic injection for capillary and chip electrophoresis. These methods can minimize the bias to some degree. However, the selection of internal standard and mathematical methods are very limited in practice, partially due to the fact that those methods required too many specific conditions and make the experiments too complicated and time-consuming. The methods with improved injection assembly reported generally involve multi-step procedures with low successful rate and high cost and impact the EOF. Therefore, new protocols to develop the non-bias injection device that can eliminate the sampling discrimination for electrokinetic capillary injection efficiently and effectively are in demand.Based on the study of the bridge electric field injection (BEFI), equal outside potential injection (EOPI) and compensatory pendulum injection (CPI) , novel electroosmotic pump injection (EPI) and Teflon union fracture injection (TUI) were developed here by which the injection tip of capillary was isolated from the local electric field. Using the electroosmotic flow (EOF) as the pump, the sample zone was introduced into the capillary. For convenient determine the bias, bias degree (BD) and standard deviation of bias (SDB) are defined here. Factors relating to bias elimination were examined, such as length of capillary, injection voltage and conductivity of sample, and optimal conditions were obtained. These two sampling methods were evaluated for their performance in CE and the feasibility of bias elimination. Applications of EPI and TUI in real sample, injection for capillary electrochromatography (CEC) and chip were also performed. For eliminating the reverse bias, grounded injection electrode was used in EPI and TUI.According to the results, the EPI and TUI can eliminate the bias effectively, they also adaptable for the reverse EOF system and ions with different mobilities. With the grounded injection electrode, the reverse bias due to capacitance effect in single electric field EPI and TUI was avoided. These two injection methods can apply in CEC, analysis of real sample and"spotting"in chip.The EPI and TUI developed in this study avoided several shortcoming in methods reported. The two-capillary system and on-column fracture can not affect the current, EOF, reproducibility of sampling amount, migration time, shape of peak and column efficiency significantly. These two injection methods were proven to be successful by meeting the following criteria: a) simple construction step, b) high efficiency, c) low cost, d) high reproducibility and broad applications, e) long-term stability. All of these merits warrant that this coating is superior to many other no-bias injections.