| Capillary electrophoresis is the technique of performing electrophoresis in buffer-filled, narrow-bore capillaries, with a high-voltage power supply providing electric field; separation by electrophoresis relies on differences in the speed of migration (migration velocity) of charged species. The application of CE techniques has been greatly developed after mid-1980s. Nowdays, it has been successfully used for the separation of charged species, as well as neutral molecules, biomacromolecule, and has been widely applied in analytical chemistry, biological chemistry, environmental chemistry, and so on. However, the tiny injected sample volume and very small capillary inner diameter bring about difficulties in detection. The method of electrochemical detection is extensively studied and applied in most analytical fields because of the low detection limit, low cost, high sensitive, etc. The goal of this dissertation is to explore the CE-AD applications in pharmaceutical analysis and food analysis etc. The contents of this dissertation are described as follows:Part One IntroductionThe basic theories, the separation mechanism, the separation models, the separation behavior, the trend of development and applications of CE are introduced briefly. The goal and significance of this dissertation are also introduced.Part Two The determination of electroactive analytes with CE-AD2.1 Determination of six active constituents in Prunella vulgaris L. by CE-ADA method of CE-AD has been developed for the determination of six active constitutents in Prunella vulgaris L., namely rutin, umbelliferone, hyperin, p-coumaric acid, rosmarinic acid and caffeic acid. A laboratory-built CE-AD system and a 75 cm length of 25μm i.d. and 360μm o.d. fused silica capillary was used, a 300μm diameter carbon disc electrode was employed as the working electrode and the potential was+950 mV (vs. SCE). The analytes could be well separated at the separation voltage of 16 kV in a 60 mmol/L borate buffer (pH 9.0), the injection time was 8 s. Good linear relationships were established between the concentration and peak current of analytes over 2-3 orders of magnitude, the detection limits ranged from 1.42×10-8 g/mL to 3.75×10-7g/mL. This method has been successfully applied to the determination of active constitutents in Prunella vulgaris L. and the assay results were satisfactory.2.2 Seasonal content variation of some active ingredients in Toona sinensis (A. Juss) Roem leavesA method based on CE-AD has been employed for the separation and determination of epicatechin, scopoletin, quercetin and gallic acid in Toona sinensis (A. Juss) Roem leaves collected in April, June and August, respectively. Seasonal variation of these ingredients in Toona sinensis (A. Juss) Roem leaves was discussed. Several important factors including running buffer acidity, separation voltage, working electrode potential and etc, were evaluated to acquire optimum analysis conditions. A laboratory-built CE-AD system and a 75 cm length of 25μm i.d. and 360μm o.d. fused silica capillary was used, a 300μm diameter carbon disc electrode was employed as the working electrode and the potential was+950 mV (vs. SCE). The analytes could be well separated at the separation voltage of 16 kV in a 40 mmol/L borate buffer (pH 9.0). Good linear relationship was established between the peak current and the concentration of each analyte over 2-3 orders of magnitude with detection limit (S/N=3) ranging from 4.00×10-8 g/mL to 1.73×10-7g/mL. The proposed method has been successfully applied for the evaluation of the seasonal content variation of these four active ingredients in Toona sinensis (A. Juss) Roem leaves with satisfactory results.2.3 Determination of P-agonists in pig feed, pig urine and pig liver using CE-ADThe fast separation capability of a CE-AD system was demonstrated by determining fiveβ-agonists including clenbuterol, metoprolol, ractopamine, isoxsuprine and salbutamol in several real samples. Factors influencing the separation and detection were examined and optimized. Under the optimum conditions, the five P-agonists could be well separated at a separation voltage of 14 kV in a 100 mmoL/L H3BO3-Na2B4O7 running buffer (pH 9.0). Good linear relationship was established between the peak current and the concentration of each analyte over 2-3 orders of magnitude with detection limit (S/N=3) ranging from 3.10×10-7 g/mL to 5.90×10-7 g/mL. This method was successfully used in the analysis of clenbuterol, metoprolol, ractopamine, isoxsuprine and salbutamol in pig feed, pig urine, and pig liver, providing a useful method for monitoring the illegal use ofβ-agonists from growth promotion in food-producing animals.2.4 Study on the effect of cooking on vitamin C and chlorogenic acid in sunflower seeds by CE-ADA simultaneous determination of vitamin C and chlorogenic acid in uncooked sunflower seeds and cooked sunflower seeds by CE-AD was reported. The effects of several important factors such as the acdity and concentration of running buffer, separation voltage, injection time and detection potential were investigated to acquire the optimum conditions. A 300μm diameter carbon disc electrode was used as the working electrode positioned carefully opposite the outlet of capillary at potential of +950 mV (vs SCE). The analytes could be well separated within 15 min in a 75 cm length capillary at a separation voltage of 16 kV in a 40 mmol/L borate buffer (pH=8.7). There is excellent linearity between peak current and concentration of analytes in the concentration range of 5.0×10-7-1.0×10-4 g/mL for vitamin C and chlorogenic acid and the detection limits (S/N=3) is 2.00×10-7 g/mL and 2.25×10-7 g/mL. Relative standard deviations (RSD) of the peak currents were 3.2% (vitamin C) and 3.7% (chlorogenic acid), respectively (n=7). The content of vitamin C and chlorogenic acid in cooked sunflower seeds is about 75.86% and 81.99% of those in uncooked sunflower seeds.2.5 Determination of endocrine-disrupting chemicals (EDCs) in sewage based on miniaturized micellar electrokinetic chromatography (MEKC) with amperometric detectionAn integrated analytical method to monitor five environmental endocrine disrupting chemicals (EDCs):2,4-dichlorophenol (DCP),4-butylphenol (BP), bisphenol A (BPA),17α-ethynylestradiol (EE2) and 4-n-nonylphenol (NP), was developed for. the first time based on miniaturized micellar electrokinetic chromatography (MEKC) with amperometric detection (AD). In order to get the optimum conditions of their separation and detection, several parameters including pH and concentration of running buffer, concentration of micelle, separation voltage and injection time were studied and optimized. Under the optimum conditions, the five EDCs were well separated within 12 min in a 75 cm length of 25μm i.d. and 360μm o.d. fused silica capillary at a separation voltage of 1.15 kV in a 20 mmol/L borate running buffer (pH 7.4) containing 15 mmol/L sodium dodecyl sulfate. A 300μm diameter carbon disk electrode generates good response at+1000 mV (vs. Ag/AgCl) for all analytes. This method was successfully applied for the determination of these five EDCs in sewage sample. Quantitative analysis showed that DCP, BP and BPA existed atμg/L level in the selected sample, while EE2 and NP were not detected.2.6 Determination of six phenolic compounds in cosmetics by CE-ADA CE-AD method to determine some phenolic compounds in cosmetics was described. With a 75 cm length of 25μm i.d. and 360μm o.d. fused-silica capillary and a 300μm carbon disc electrode, well-defined separation of arbutin, phenol, resorcinol, hydroquinone, kojic acid and salicylic acid was achieved in a 40 mmol/L H3BO3-Na2B4O7 running buffer with 10 mmol/L SDS (pH 9.0) at+800 mV (vs. SCE). Good linear relationship was established between the peak current and the concentration of each analyte over 3 orders of magnitude with detection limit (S/N=3) ranging from 4.09×10-8 g/mL to 4.50×10-7 g/mL.Part Three Study on determination of non-electroactive analytes by indirect CE-AD3.1 Simultaneous determination of electroactive and non-electroactive food preservatives by indirect CE-ADA novel CE-AD method was achieved by adding an electroactive additive to the running buffer, so that both electroactive and non-electroactive food preservatives were simultaneously determined. The end-capillary 300μm diameter carbon disc electrode offers favorable signal-to-noise characteristics at potential of+1100 V (vs. SCE). The four electroactive preservatives (methylparaben, ethylparaben, propylparaben and butylparaben) and two non-electroactive preservatives (potassium sorbate and sodium lactate) were well separated in a 75 cm length of 25μm i.d. and 360μm o.d. fused silica capillary at a separation voltage of 16 kV in a 40 mmol/L borate running buffer (pH 8.2) containing 12 mmol/L sodium dodecyl sulfate and 0.018 mmol/L 3,4-dihydroxybenzylamine. The detection limits (S/N=3) rang from 1.06×10-8 g/mL to 2.73×10-6 g/mL. This method has been successfully employed for the determination of both electroactive and non-electroactive preservatives in several food commodities.3.2 Early noninvasive diagnosis of phenylketonuria of infants by indirect capillary electrophoresis with amperometric detectionAn indirect capillary electrophoresis with amperometric detection (CE-AD) has been developed for the simultaneous determination of the mark compounds of phenylketonuria (PKU) in infant urine samples, namely the electroactive phenylpyruvic acid and non-elecroactive phenylacetic acid. Several important parameters including running buffer additive, sodium dodecyl sulfate (SDS) concentration, working electrode potential and etc, were evaluated to acquire optimum analysis conditions. Under the optimum conditions, phenylpyruvic acid and phenylacetic acid could be well separated in 60 mmol/L borate running buffer (pH 7.8) containing 20 mmol/L SDS and 0.018 mmol/L 3,4-dihydroxybenzylamine (DHBA), and the detection limits (S/N=3) were 2.0×10-6 g/mL and 9.2×10-7 g/mL, respectively; and this method is interference free from the coexisting compound uric acid in urine samples. The proposed method has been successfully applied for the simultaneous determination of two PKU mark compounds in infant urine samples after simple preparation, which provided an alternative for the early noninvasive diagnosis of PKU infants.
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