Study On Capillary Electrophoresis Coupled With Contactless Conductivtity Detection

Capillary electrophoresis (CE) is a highly efficient and powerful instrumental technique in the area of liquid-phase separation which has attained great acceptance since 1980s. Because of its short analysis time, speed and automatization of separations, low consumption of reagents and great simplicity, CE has been applied widely to analyze a great variety of substancs ranging from small inorganic ion to large bio-macromolecules, such as medicine, environmental pollution and so on. A large amount of detectors coulpled to capillary electrophoresis has been created including UV/Vis, Chemiluminescence, Mass spectrometry, Electrochemical and fluorescence detection. Among them, contactless conductivity detection (C4D) is preferred since it is universal and sensitive. Compared with conductivity detection, the electrode of C4D is not contact with the solution directly, so it can solve the problem of electrode pollution.In this paper, using contactless conductivity detector coupled to capillary electrophoresis technology, a new method to determine the β2-agonists, metal ions and sulfonamides was established. The next four parts of the paper has made the detailed introduction to the key related technology and its application.In charpter Ⅰ, the course of CE and C4D technology history, separation models, a wide range of detection methodologies, the application of C4D, as well as on-line preconcentration method were described comprehensively.In charpter Ⅱ, an on-line preconcentration method of field-enhanced sample injection (FESI) was implemented in the determination of four β2-agonists-terbutaline (TER), procaterol (PRO), formoterol (FOR) and bambuterol (BAM) by capillary electrophoresis coupled with capacitively coupled contactless conductivity detection (CE-C4D). Under optimized conditions the background electrolyte (BGE) was 5 mM Tris(hydroxymethyl)aminomethane (Tris) and 10 mM citric acid (Cit) at a pH of 3.2 while the sample dilution solution was obtained by methanol. The detection limits (defined as S/N=3) of this mehod were found to be 0.02 mg/L for TER, PRO, FOR, BAM, which were much lower than that of the conventional CE-C4D method without preconcentration procedure, the enhancenment factors were greatly improved to be 30-40-fold. The linearity ranges of four β2-agonists were 0.1～15 mg/L, with good linear correlation coefficients (r2>0.9900). In order to evaluate the application potential of the developed method, real sample from pig feed was analyzed with recoveries of 91.4% to 106.2%.In charpter Ⅲ, a simple method based CE-C4D was developed and optimized for the determination of K+, Na+, Mg2+, Sr2+, Ca2+ in samples of mineral waters. The parameters of the separation electrolyte solution, such as pH and concentration of L-histidine, were optimized. Best results were performed in background electrolyte (BGE) composed of 12 mM L-histidine (His),3 Mm HIBA and 0.4 mM 18-crown-6, adjusted to pH 3.6 with acetic acid. Under these conditions, complete separation between all metal cations was achieved in less than 6 min. The LOD values for the optimized procedure ranged 0.02 mg/L to 0.2 mg/L. The repeatability of migration times and peak areas was better than 2.3% and 5.1%, respectively. The methodology was evaluated and validated for the cations and it was found to be reliable for determing metal cations in six different brands of mineral water samples.In charpter IV, a method was validated and optimized to determine sulfonamides (sulfamethazine, sulfadimethoxine, sulfamethoxazole) by CE-C4D. A suitable electrolyte consists of 15 mM Tris(hydroxymethyl)aminomethane (Tris) and acetic acid at pH 8.0. The composition of the background electrolyte provides excellent separation of three sulfonamides within 9 min with limits of detection (S/N=3) of 0.005～0.02 mg/L. the repeatability of the migration times and peak area were less than 2.1% and 3.5%(n=5), respectively. With a simplified sample pretreatment protaocol, fast determination of sulfonamides in milk samples was successfully performed with standard addition recoveries of 93.9%～108.6%.