Development Of Fully Automated Quantitative Capillary Electrophoresis And Its Application In The Detection Of Preservatives In Cosmetics

From the mid-to late eighties of the last century, CE began to develop rapidly. As a powerful analytical separation technique characterized by high efficiency, high resolution and low consumption of solvent and sample, CE has established itself as a widely utilized technique for separation and analysis in many fields including environmental, pharmaceutical, biotechnology and food safety. However, in practice, CE is still much lower in popularity than HPLC, especially in quantitative analysis. The major factor for the reluctant adaptation of CE is probably attributable to its “dip-in” sample injection method, which has inherent defects, consequently resulting in poor accuracy and low precision. Problem in accuracy and precision is probably the major reason why CE remains lower in popularity in the scope of utilization than HPLC. Herein, we report our development in a fully automatic quantitative capillary electrophoresis(qCE) system which consists of a lab-made auto-sampler equipped with a 10 nL rotary type injector and a lab-made thermostat with cooling capacity. The accuracy and precision were greatly improved compared with conventional capillary electrophoresis(CE).In chapter 1, we briefly introduced the background and application of CE. The overview of injection technology of traditional CE also provided, with the description of problems and difficulties in current injection technology. Then, we also summarized the development and advantages of sample injection by nano-injector. In addition, we compared conventional CE with automated quantitative capillary electrophoresis(qCE) in system structure.In chapter 2, we constructed the automated qCE system and introduced core modules, such as auto sampler, thermostat, electrical decoupler, et al.. The 10 nL volume accuracy was guaranteed by the carefully designed nano-injector with an accurate internal loop. And an electrical “decoupler” was made in-lab to isolate the injector from the electrical field. A thermostat was designed and constructed with cooling capacity to remove Joule heat in CE. These significantly improved the reliability and stability of the automated qCE system.In chapter 3,we evaluated the performance of the system, such as the repeatability of qualitative and quantitative, column efficiency, resolution. The system repeatability in terms of RSD lower than 1% for migration time and peak area was achieved with DMSO and benzoic acid as test samples. The separation efficiency of qCE system was studied and its loss ratio of plates was compared with traditional CE system with three nucleosides, 5-fluoro-2’–deoxyuridine, adenosine, uridine as samples. In addition, other influences on separation efficiency and plates were also discussed in the chapter.In chapter 4, the system was used to separate six nucleosides successfully, which demonstrated the stability and reliability of automated qCE system. The optimum separation conditions was discussed, which were 30 mM borate(pH9.40) buffer as background electrolyte with-15 kV operating voltage, 40 cm effective lengths of capillary and 1 μL/min for syringe pump. The RSDs of six nucleosides were lower than 0.6% for migration time and 3% for peak area with thermostat. Although there exist some sacrifices in the separation efficiency in this qCE system, it still holds considerable promise to be applied in quantitative analyses, such as pharmaceutical QC/QA.Chapter 5 focused on the application of fully automated quantitative micellar electrokinetic capillary chromatography(qMEKC) in determining the content of benzoic acid, MP, EP, PP, BP in real samples. Establishment of experimental conditions for these five preservatives: the type of buffer, SDS concentration, buffer pH value and the electrophoresis voltage were studied. The optimum experimental conditions for the CE separation: Voltage:-20 kV; Temperature: 15℃; Buffer: 15 mM sodium borate+100 mM SDS(pH 9.3); pressurized flow velocity by syringe pump: 1 μL/min. Under this condition, baseline separation of five kinds of preservatives was achieved. The effectiveness of the system was demonstrated by the quantitative analysis of benzoic acid, MP, EP, PP, BP in real samples, such as Body Cream and Exfoliating Gel.In chapter 6,we summarized the whole project and and looked into the future perspective of this novel technology and its potential applications. The fully automated quantitative capillary electrophoresis(qCE) can be used to analysis real samples and the results are precise and reliable. In addition, the established research method for detecting preservatives in cosmetics with fully automated quantitative micellar electrokinetic capillary chromatography(qMEKC) provides a new solution for determining the content of limited preservatives in cosmetics.