Study On Application Of Capillary Electrophoresis With Amperometric Detection In Food And Cosmetic Analysis

1. PrefaceCapillary electrophoresis (CE) is a liquid phase separation technology which is developing rapidly. It has the characteristics of high efficiency, high speed, ultra-small sample volume, minimal consumption of solvent and ease of clearing up the contaminants. CE has been used to separate inorganic ions, organic acids, carbohydrates, DNA, proteins, and even the whole cell.It has great potential to be applied in analytical chemistry, biological chemistry, food chemistry, environmental chemistry, medicine and so on. In this part, the history of CE development has been retrieved, and the principle, the separation modes, the instrumental system, the technological characteristics of CE, and especially the method of capillary electrophoresis-amperometric detection (CE-AD) have been introduced. According to the research area of this thesis, the application of CE in food and cosmetic analysis has been reviewed.In this thesis,CE-AD has been used in the determination of melamine residue in milk products, the determination of preservatives in foods, as well as the simultaneous determination of preservatives and antioxidants in cosmetics.2. Residue analysis of melamine in milk products by micellar electrokinetic capillary chromatography with amperometric detectionA high-performance micellar electrokinetic capillary chromatography with amperometric detection (MECC-AD) method for the fast determination of melamine (MM), occasionally used to increase the apparent protein content of milk products, has been developed. Method development involved optimization of the working electrode, the running buffer system and acidity, the concentration of sodium dodecyl sulfate (SDS), the separation voltage, the applied potential and the sample injection time.Under the optimum conditions, MM can be well separated from its co-existing interferences in real-world samples within 9 min at the separation voltage of 20 kV in an 8 mmol/L SDS-20 mmol/L H3BO3-Na2B4O7 running buffer (pH 7.4).Satisfactory recovery (83.3%-105.5%), repeatability of the peak current (3.2%) and migration time (3.8%), and limit of detection (2.1×10-6 g/mL) for the method were achieved. This proposed procedure has been successfully used for the determination of MM in milk products.3. Sensitive determination of parabens in soy sauces by capillary zone electrophoresis with amperometric detectionA high performance capillary zone electrophoresis with amperometric detection (CZE-AD) method has been developed for the separation and sensitive determination of the preservatives methylparaben (MP), ethylparaben (EP), propylparaben (PP) and butylparaben (BP) in soy sauce samples.Under the optimum conditions, four preservatives can be well separated within 16 min at the separation voltage of 16 kV in an 80 mmol/L borax running buffer (pH 9.94), and adequate extraction was obtained with ethanol for the determination of the above four parabens.Satisfactory recovery (95.0%-102.0%), repeatability of the peak current (≤2.4%) and migration time (≤0.5%) of analytes, as well as detection limits (5.7×10-8g/mL-4.4×10-8 g/mL) for the method were achieved. This proposed procedure has been successfully used for the analysis of soy sauce samples.4. Indirect amperometric detection with capillary electrophoresis for determination of preservatives in foodA method based on indirect amperometric detection with capillary electrophoresis has been employed for the separation and determination of three preservatives, including potassium sorbate, sodium benzoate, and sodium propionate, in soft drinks, soy sauce and oyster sauce. Several important factors including the type of electroactive additive, running buffer acidity, working electrode potential and etc, were evaluated to acquire optimum analysis conditions. Under the selected optimum conditions, the analytes could be well separated. Good linear relationship was established between the peak current and the concentration of each analyte with detection limits (S/N=3)ranging from 3.33×10-6 g/mL to 7.50×10-6g/mL. This method has been successfully used in the analysis of preservatives in foods. 5. Simultaneous determination of phenolic additives in cosmetics by micellar electrokinetic capillary chromatography with amperometric detectionA micellar electrokinetic capillary chromatography with amperometric detection (MECC-AD) method has been developed for the simultaneous determination of eight phenolic additives, including propyl gallate (PG), tert-butylhydroquinone (TBHQ), butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), methylparaben (MP), ethylparaben (EP), propylparaben (PP) and butylparaben (BP), in cosmetic products.Method development involved optimization of the working electrode, the pH value of running buffer, the concentration of sodium dodecyl sulfate (SDS), the separation voltage, and the sample injection time. Under the optimum conditions, all analytes can be well separated within 26 min at the separation voltage of 18 kV in a 9 mmol/L sodium dodecyl sulfate (SDS)-60 mmol/L borate running buffer (pH 8.0). A 300μm diameter carbon disk electrode generated good response at+900 mV (vs. SCE) for all analytes.Linearity of the present method was over three orders of magnitude of analyte concentration with detection limits (S/N=3)ranging from 1.1×10-7 g/mL to 1.2×10-6 g/mL for all analytes. This proposed method has been successfully applied to the simultaneous determination of the above additives in commercial cosmetics, and the assay results were satisfactory.