Study On Applications Of Microchip Electrophoresis With On-Line Preconcentration Techniques In Food And Environmental Analysis

Microchip electrophoresis (MCE) has attracted the worldwide interest since its advent. As one of the most important applications of micro total analysis systems (μ-TAS), MCE is increasingly being viewed as a successful alternative to capillary electrophoresis (CE).In addition to several superior characteristics obtained in CE, MCE offers significant benefits such as easier miniaturization of the analytical instrumentation, reduced sample and reagent consumption due to an extremely reduced injection length of a sample, rapid operation because of shorter separation channel and higher electric field strength compared to CE. However, due to the low sample injection volume and short separation channel of MCE, it may have an inadequate detection limit for the detection of low-abundance analytes in food and environmental samples. One way of improving the sensitivity is to integrate on-line preconcentration methods. A single step of on-line preconcentration method in MCE may not meet high sensitivity requirement for low-abundance analytes. Thus, multiple-concentration methods combining two or more on-line preconcentration techniques are highly desired to obtain higher signal enhancement for MCE.In chapter I, the development status, on-line preconcentration method, separation mode, and applications for MCE were introduced comprehensively. The research significance and features of this paper were also illustrated in this chapter.In charpter II, an on-line preconcentration strategy combining field-amplified stacking and reversed-field stacking was developed for efficient and sensitive analysis of amino acids and vitamin B3 including lysine (Lys), taurine (Tau), and niacinamide (NA) by microchip electrophoresis with LIF detection. In this technique, the addition of a reversed polarity step termed reversed-field stacking could enhance the preconcentration effect of field-amplified stacking and push most of the sample matrix out of the separation channel, thus greatly improving the sensitivity enhancement by 1-2 orders of magnitude over those classical MCE-LIF methods. The related mechanism as well as important parameters governing preconcentration and separation have been investigated in order to obtain strongest sensitivity amplification and maximum resolution. Under optimal conditions, all analytes were successfully focused and completely separated within 4 min. The limits of detection for Lys, Tau, and NA were 0.25,0.50, and 0.20 nM (S/N = 3), respectively, and enhancement factors of 165-,285-, and 236-fold were obtained for Lys, Tau, and NA as compared to using no concentration step. Other validation parameters such as linearity and precision were considered as satisfactory. The proposed method also gave accurate and reliable results in the analysis of these functional ingredients in eight functional drink samples.In charpter III, an on-chip multiple-concentration method combining field-amplified sample stacking (FASS) and reversed-field stacking (RFS) in microchip micellar electrokinetic chromatography (MCMEKC) was developed for the simultaneous analysis of three antibiotics (kanamycin, vancomycin, and gentamycin) using poly (styrene sulfonic acid) sodium salt (PSS) as the pseudostationary phase. Results indicated that the polymeric surfactant PSS provided high stability, unique selectivity, and high efficiency for the separation of these antibiotics as compared to SDS micelles, and the multiple-preconcentration strategy could greatly improve the sensitivity enhancement over those classical CE-LIF methods for antibiotics detection. The stacking and separation mechanism as well as important parameters governing preconcentration and separation have been investigated in order to obtain maximum resolution and sensitivity. Under optimal conditions, three antibiotics were successfully focused and completely separated within< 3 min. The limits of detection for kanamycin, vancomycin, and gentamycin were 0.25,0.20, and 0.80 μg/L (S/N = 3), respectively, and the detection sensitivities were improved 259-,296-, and 308-fold, respectively. The method also gave accurate and reliable results in the analysis of these antibiotics in river water samples.In charpter IV, a microchip electrophoresis method based on an on-line multiple-preconcentration technique was developed for highly efficient analysis of acrylamide in food products for the first time. The related mechanism as well as important parameters governing separation and preconcentraton have been investigated in order to obtain maximum resolution and sensitivity. The best separation was achieved using a 100 mM borate solution at pH 9.3 as running buffer, and a sensitivity enhancement factor of 432 was obtained using this concentration method under optimal conditions. The detection limit of acrylamide was 1 ng/mL, which was comparable to those previously reported CE methods with on-line preconcentration techniques. Other parameters including linear calibration curves over the range studied (0.002 and 0.1 μg/mL), intraday precisions (up to 3.4% and 2.6% for peak height and migration time, respectively), and interday precisions (up to 9.5% and 6.9% for peak height and migration time, respectively) were established and considered satisfactory. The proposed method also gave satisfactory and reliable results in the analysis of acrylamide in potato chips and French fries. In summary, these results testify to the good performance of the proposed method for the quantification of acrylamide in food samples.