Studies of Separation and On-line Concentration of s-Triazine Herbicides and Phenothiazines in Capillary Electrophoresis

Environmental pollutants and pharmaceutical compounds were selected for studying the enhancement of detection sensitivity. In this dissertation, on-line concentration of small molecules on capillary electrophoresis studied is consisting of three parts:

In the first part, we focus on the stacking of environmental pollutants, such as methylthio-s-triazines herbicides, in normal stacking mode using sodium dodecyl sulfate (SDS) as an anionic surfactant and borate electrolyte at pH 9.0. The sample matrix used for concentration of neutral analytes is 30 mM borate electrolyte, and the optimal electrophoretic system for separation consists of 20 mM SDS and 20 mM borate buffer at pH 9.0. Interestingly, two maxima were observed in the plot of absorbance versus SDS concentration in the range 10-150 mM. Stacking efficiency of each individual analyte depends on its binding constant to SDS micelles, terbutryn can afford about 1000-fold enhancement under an optimal electrophoretic system. With this stacking mode, the sample solution can be injected up to 180 s, and the limits of detection (S/N=3) of terbutryn, prometryn, ametryn and simetryn determined to be 61, 25, 11 and 2 ng / mL, respectively.

In the second part, we focus on the stacking of s-triazines herbicides using sweeping technique. The separation buffer consisting of anionic surfactant and phosphate electrolyte at pH 5.6 was used. The injection time of 480 sec can be achieved for baseline separation of four s-triazines. The concentrations of phosphate buffer at 50 mM was used as the sample matrix, while separation buffer consists of 50 mM phosphate electrolyte and 50 mM SDS containing 20 % methanol at pH 5.6, sample matrix and separation buffer were optimized. With this sweeping mode, the sample solution can be injected up to 480 s, and the limits of detection (S/N=3) of terbutryn, prometryn, ametryn and simetryn determined to be 3.0, 2.0, 1.5 and 1.2 ng / mL, respectively, with UV detection.

In the third part, the enantioseparation and stacking of phenothiazine enantiomers based on the pH junction-sweeping mechanism were investigated. Phenothiazine samples were dissolved in water at neutral pH, whereas phosphate buffer at pH 3.0 containing different type of cyclodextrins (CDs), such as randomly sulfated β-CD (S-β-CD), β-CD HP-β-CD, DM-β-CD and γ-CD, was used as separation buffer. γ-CD shows the best enantioresolution for four phenothiazines, including promethazine, ethopropazine, trimeprazine and thioridazine. Effective enantioseparation and stacking of phenothiazine enantiomers could be achieved with the injection time of 1800 sec, when multi-cyclodextrins, such as S-β-CD / β-CD / γ-CD was employed. Due to extremely large injection volume (a filling of 98.9 % effective length), the signal of thioridazine (5a) could be greatly enhanced.