| Capillary electrophoresis (CE) is a novel separation and analytical technique. It has the advantages of high efficiency, quickness, sample saving and so on. Micellar electrokinetic capillary chromatography (MEKC) is the most commonly used CE separation mode. It can simultaneously achieve the goal of separation of charged particles, neutrals and strong hydrophobic substances, with a very good application prospects. However, low sensitivity is a shortcoming of CE. Online or/and off-line enrichment technologies are generally needed to improve sensitivity. Sweeping is one of the commonly used enrichment technologies in MEKC with the advantages of simple operation and high enrichment efficiency.Dispersive liquid-liquid microextraction (DLLME) has attracted much attention in recent years. DLLME has a high enrichment factor, high flexibility and can overcome the disadvantages of traditional methods such as complex operation, time-consuming and laborious procedure, high reagent consumption and environment-polluting. In this article, MEKC was combined with DLLME and sweeping to improve the sensitivity of CE. The content is described as the following three chapters:1. An in-situ sweeping-MEKC was established to determine β-amyloid peptide (Aβ1-42) which is regarded as the early diagnostic marker of Alzheimer disease. Electrophoresis was carried out at a constant voltage of5kV in an uncoated fused-silica capillary. The15mmol/L borate buffer containing20mmol/L sodium dodecyl sulfate (SDS) with pH9.3was used as the running buffer. The samples were injected into the capillary by applying a pressure of50mbar for60s. Under the optimal conditions, the detection limit of Aβ1-42was as low as0.08μmol/L. The recoveries of normal addition method in real serum sample analysis were found to be between89.2%and98.5%. The relative standard deviation (RSD) of the determination was less than6%.2. A high-performance method was developed to determine four triazine herbicides in vegetables (metribuzin, hexazinone, cyanazine and prometryn) using sweeping-MEKC coupled with DLLME. In the DLLME experiment, the effort factors such as extractant, dispersant, extraction time, ionic strength and pH values were optimized. The samples were injected into an uncoated fused-silica capillary by applying a pressure of50mbar for30s, and then separated at a constant voltage of15kV. The20mmol/L Tris buffer (Tris:HCl=1:1.2, concentration ratio) containing60mmol/L SDS and10%methanol with pH8.6was used as the running buffer. Under the optimal conditions, the enrichment factors of four herbicides were between253and475. The addition standard recoveries in real sample analysis were between90.0%and103.3%and RSD was less than7%. The detection limits were26.4,23.6,19.4and8.2ng/mL, respectively. Our approach is useful for the rapid detection of herbicides in vegetables and the results are satisfactory.3. For most analytical techniques, most kinds of pesticide residues can be separately determined. In this paper, the four most common different pesticides in Chinese herbal medicines (bifenthrin, carbosuifan, dursban and quintozene) were simultaneously analyzed using QuEChERS-DLLME-sweeping-MEKC. In the QuEChERS pre-treatment, acetonitrile was used as the extractant. Primary secondary amine (PSA) and graphitized carbon black (GCB) were used as the adsorbent. The resultant samples were injected into an uncoated fused-silica capillary by applying a pressure of50mbar for2s, and then separated at a reverse voltage of-23kV. The running buffer was30mmol/L phosphate buffer at pH6.9(NaH2PO4:Na2HPO4=1:1) containing35mmol/L SDS,1.0mol/L urea and30%methanol (V/V). Under the optimal conditions, the detection limits were80.0,62.0,93.0and70.0ng/mL, respectively. The addition standard recoveries were between76.8%and97.4%. The RSD values were smaller than7%. The established method was readily used to determine four different kinds of pesticides in Chinese herbal medicines, i.e. rganochlorine, organophosphorus, carbamate and pyrethroid, with satisfactory results. |
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