| Herbal medicines are one kind of the most important agricultural products in China. The development of Chinese herbal medicines is the crystallization of the wisdom of the Chinese people for thousands of years. They have made tremendous contributions for human health. At present, in our country, the quality standards of herbal medicines are often limited to the identification of their appearance and character checks, and the analysis of their active ingredients is still uncommon. Therefore, the quality control of herbal medicines has become the bottleneck of their modernization and internationalization. For quantitative analysis of the active ingredient of herbal medicines, commonly used main methods include high performance liquid chromatography, gas chromatography, atomic absorption spectrometry, thin layer chromatography and capillary electrophoresis(CE).CE has been developed as a powerful separation technique due to its high separation efficiency, short analysis time and small sample consumption. It has been widely used in different areas of chemistry and biochemistry. However, because of the short optical path length across the capillary, one of the major limitations of CE is the poor detection sensitivity with the most commonly used ultraviolet detection. Therefore, the improvement of the detection sensitivity of CE has received much attention in recent years. To solve this problem, on-line sample preconcentration or stacking techniques are widely used. On-line preconcentration can be performed easily by adjusting the composition of sample solution and background solution without the need of any modification of current commercial instrument.Micelle to solvent stacking(MSS), as a relatively new on-line preconcentration technique, has attracted much attention because it is not only efficient, rapid, and easy to be operated, but also can be used in different separation modes. Moreover, MSS can be coupled with other on-line preconcentration techniques to achieve better enrichment efficiency. This dissertation is mainly concerned with the following aspects:(1) A novel on-line two-step stacking preconcentration method by sweeping and MSS in CZE was developed for the simultaneous determination of organic anions(vanillic acid, ferulic acid and cinnamic acid) in Chinese herbel medicines. Sophocarpine was used as an internal standard(IS). The main parameters that affect the separation and sensitivity were investigated and optimized. The best separation was achieved in 50 mmol/L ammonium acetate(p H 12.0) containing 50% methanol(v/v) under a votage of-20 k V; micellar solution was the mixture solution containing 12 mmol/L cetyltrimethyl ammonium bromide and 20 mmol/L ammonium acetate; sample matrix was 20 mmol/L ammonium acetate. After injecting a short plug(0.5 psi, 30 s) of micellar solution, the sample was introduced into the capillary at 0.5 psi for 45 s. Under the optimum conditions, the sensitivity enhancement factors obtained by the developed method for the analytes were from 42- to 77-fold. The intra-day(n = 6) and inter-day(n = 5) precisions of the method expressed as the the relative standard deviations(RSDs) were found to be less than 8.2%. The recoveries of the analytes by the method for the analysis of traditional Chinese medicines were in the range from 80.8% to 119.6%.(2) An on-line sample preconcentration method was developed for the determination of strychnine and brucine in traditional Chinese medicines by two-step stacking in capillary zone electrophoresis(CZE) featuring sweeping and MSS. After experimental optimizations, the best separation was achieved in 75 mmol/L phosphate buffer(p H 2.5) with 30% methanol(v/v). After injecting a short plug(0.5 psi, 20 s) of micellar solution, the sample was introduced into the capillary at 0.5 psi for 90 s. Compared with normal CZE injection, 51- and 38-fold improvement in concentration sensitivity was achieved for strychnine and brucine, respectively. The calibration curve was linear over a range of 0.1 ~ 5.0 μg/m L for both strychnine and brucine, with correlation coefficients of 0.9998 and 0.9997, respectively. The limits of detection(LODs)(S/N = 3) for both strychnine and brucine were 0.01 μg/m L. The inter-day(n = 8) and intra-day(n = 5) reproducibility expressed as the RSDs were found to be less than 8.8%. This method was applied to determining both strychnine and brucine in two traditional Chinese medicines, with recoveries ranging from 94.2% to 105.4%. The results indicated that the method is simple, rapid, and can be applied to monitor Strychnos alkaloids in different traditional Chinese medicines.(3) An on-line two-step stacking preconcentration method by sweeping and MSS in CZE was developed and validated for the simultaneous determination of quinolizidine alkaloids(sophocarpine, matrine and oxymatrine) in traditional Chinese medicines. Strychnine was used as an IS. The main parameters that affect the separation and sensitivity were investigated and optimized. Under the optimum conditions, the sensitivity enhancement factors obtained by the developed method for the analytes were from 42- to 52-fold. The method showed a good linearity over the range of 0.1~10.0 mg/m L for sophocarpine, matrine and oxymatrine with the correlation coefficients(r) varying from 0.9992 to 0.9996. The LODs(S/N = 3) were 0.02 ~ 0.03 μg/m L. The intra-day(n = 8) and inter-day(n = 5) precisions of the method expressed as the RSDs were found to be less than 10%. The recoveries of the analytes by the method for the analysis of traditional Chinese medicines were in the range from 87.5% to 109.0% with RSDs(n = 3) less than 9.1%.(4) Two on-line preconcentration techniques named MSS and field-enhanced sample injection(FESI) were combined to determine cationic alkaloids(berberine, palmatine and jatrorrhizine) in urine samples. Sophocarpine was used as an IS. The main parameters that affect the separation and sensitivity were investigated and optimized. The separation was performed under 20 k V, the separation buffer was 75 mmol/L ammonium bicarobonate containing 40% methanol(v/v), micellar solution was 7 mmol/L SDS and 15 mmol/L ammonium acetate, and sample matrix was 40% methonal. MSS was realized by a hydrodynamic injection of micellar solution prior to the electrokinetic injection of sample. The micellar solution was injected by hydrodynamic injection at 0.5 psi for 45, and then the electrokinetic injection of the sample in a low conductivity solution was performed for at 10 k V 45 s. Under the optimum conditions, the sensitivity enhancement factors obtained by the developed method for the analytes were from 314- to 405-fold. The intra-day(n = 6) and inter-day(n = 4) precisions of the method expressed as the RSDs were found to be less than 9.3%. The recoveries of the analytes by the method for the analysis of urine sample were in the range from 85.2% to 105.5%. The method is simple, fast, accurate, and sensitive.(5) A novel stacking method with the combination of FESI and MSS in CZE was developed and applied to the determination of cationic alkaloids(strychnine and brucine) in urine samples. Electrokinetic injection of the sample in a low conductivity solution was performed for 30 s at 10 k V. MSS was realized by a hydrodynamic injection of a small plug of micellar solution prior to the electrokinetic injection of sample. This combined stacking approach, when compared to typical CZE, provided the sensitivity improvements in peak height in the range of(1590 ~ 1638)-fold. The LODs(S/N = 3) in the range of(2.5 ~ 4.0) ng/m L were obtained for strychnine and brucine. The sensitivity of the method was sufficient for the determination of the analytes in urine sample.(6) A new on-line preconcentration technique, MSS in capillary electrophoresis was developed for the determination of three antihistamine drugs(chlorpheniramine, diphenhydramime, and promethazine) in human plasma. Palmatine was used as the IS. The parameters that affect the separation and detection sensitivity were investigated and optimized. Under the optimum conditions, the sensitivity enhancement factors obtained by the develped method for the analytes were from 43- to 111-fold. The method showed a good linearity in the range of(0.6 ~ 60.0) μg/m L for the three antihistamines with the correlation coefficients varying from 0.9971 to 0.9996. LODs(S/N = 3) were(0.1 ~ 0.2) μg/m L. For the precision, RSDs in intra-day(n = 8) and inter-day(n = 5) analysis were found to be less than 9.1%. The recoveries of the analytes for the method were in the range from 89.7% to 108.0%. The method is considered feasible for fast screening of antihistamine drugs in plasma. |
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