The Application Of Capillary Electrophoresis To Some Pharmaceutical Analysis

Capillary electrophoresis (CE) is increasingly recognized as a highly attractive separation technique because of its high separation efficiencies, short analysis time, small sample requirements and low operation cost. However, the main drawback of CE is the poor concentration sensitivity due to the small injection volumes and a short optical path length in the most commonly used UV detection. One solution to the problems is to apply off-line or on-line sample concentration methods. The on-line concentration techniques have advantages of simplicity and economy because of no requirements of modification in CE instrumentation. Some on-line concentration techniques such as sweeping, anion or cation selective exhaustive injection-sweeping, large volume sample stacking, field-enhanced sample stacking, acid or base pH-mediated stacking and dynamic pH junction-sweeping have enjoyed much success to the analysis of many types of samples. This thesis is mainly concerned with the following aspects:(1) A simple capillary zone electrophoresis method was developed for the determination of chlorogenic acid, caffeic acid and ferulic acid in some Chinese herbal medicines. The influence of the pH and concentration of the running buffer, separation voltage and injection time on separation was investigated. The best separation was achieved on a fused-silica capillary column (50 cm×75μm I. D.) in a running buffer of 150 mmol/L boric acid (pH = 8.7) with injection time of 8s at 0.5 psi and an applied voltage of 23 kV at 25℃. The detection was performed with diode array detection at 320 nm. The calibration curve was linear over a range of 0.01～0.2 mg/mL for ferulic acid, chlorogenic acid and caffeic acid, with correlation coefficients of 0.999, 0.997 and 0.999, respectively. The detection limits(S/N = 3:1)for ferulic acid, chlorogenic acid and caffeic acid were 0.2, 0.4 and 0.2μg/ml, respectively. The average recoveries for ferulic acid, chlorogenic acid and caffeic acid were 96.0～100.4 %. The CZE method has been successfully applied to the analysis of some organic acids in honeysuckle, taraxacum, propolis and gan mao zhi ke ke li.(2) A sensitive and simple on-line sweeping concentration method with photodiode array detection was developed for the determination of anti hypertensive drug nimodipine. The effect of the pH and concentration of the running buffer solution, organic modifier, voltage and injection time on the concentration efficiency was investigated. An untreated fused-silica capillary was used (50 cm, effective length, 40 cm, 75μm i.d.) for the analysis. The background solution (BGS) was 50 mmol/L H₃PO₄ (pH 1.45) and 100 mmol/L SDS containing 20 % acetonitrile with an applied voltage of -20 kV at 25℃. Sample introduction was performed at 0.5 psi for 270 s with diode array detection at 235 nm. In the method validation, the calibration curve was linear over a range of 0.2～15μg/mL for nimodipine with a correlation coefficient of 0.998. The detection limit (S/N = 3:1) of nimodipine was 0.10μg/mL. About 100-fold improvement in concentration sensitivity was achieved in terms of peak height by the sweeping method compared to conventional injection method. The Sweeping-MEKC method has been successfully applied to the analysis of nimodipine in tablet and human serum.(3) A novel method for the determination of aconitum alkaloid in Chinese herbs by capillary electrophoresis field-enhanced sample stacking technology was developed. The effect of the pH and concentration of the running buffer solution, organic modifier, voltage and injection time on the concentration efficiency were investigated. After experimental optimizations, the best separation was achieved in 60 mmol/L borax (pH 8.0) containing 20 % (v/v) acetonitrile, with an applied voltage of 10 kV at 20℃. The detection was performed with diode array detection at 200 nm. The calibration curve was linear over a range of 0.5～10μg/mL for aconitine, hypaconitine, and mesaconitine, with correlation coefficients of 0.992, 0.985 and 0.993, respectively. The detection limits (S/N = 3:1) for aconitine, mesaconitine, and hypaconitine were 0.10, 0.13 and 0.20μg/ml, respectively.