| 1. PrefaceCapillary electrophoresis (CE) is a kind of liquid phase separation technology with a high-voltage power supply providing electric field and a capillary tube as the separation channel; analytes could be separated through the capillary on the base of several characteristics (charges, molecular sizes, polarity, affinity, etc.). It has the characteristics of high speed and efficiency, minimal consumption of sample and solvent, etc. Nowdays, CE has been successfully used to separate inorganic ions, organic acids, carbohydrates, proteins and so on. Moreover, it has great potential in analytical chemistry, medicinal chemistry, food chemistry, environmental chemistry, biological chemistry, molecular biology and clinical chemistry, etc. In this part, the history of CE development has been retrieved, and the basic principle, the separation modes, the instrumental system of CE, and in particular the method of micellar electrokinetic capillary chromatography with capacitively coupled contactless conductivity detection and amperometric detection (MECC-C4D/AD). In this thesis, CE has been mainly applied for the study on the fast diagnosis of phenylketonuria, as well as the determination of aldehydes in food and sulfonamides in animal tissues, this method would find wide application in the fields of disease diagnosis and food analysis.2. Determination of unconjugated aromatic acids in urine by capillary electrophoresis with dual electrochemical detection--potential application in fast diagnosis of phenylketonuriaThe urinary metabolic marker compounds, namely phenylpyruvic acid (PPA), 2-hydroxyphenylacetic acid (oOPAA),4-hydroxyphenylacetic acid (pOPAA), phenyllactic acid (PLA) and phenylacetic acid (PAA) of phenylketonuric individuals were detected by a novel method of micellar electrokinetic capillary chromatography with capacitively coupled contactless conductivity detection and amperometric detection (MECC-C4D/AD). Electrophoretic runs were performed in a 35 mmol/L SDS/60 mmol/L H3BO3-Na2B4O7 running buffer (pH 8.2) at a separation voltage of 16 kV, and five marker compounds and the major coexisting compound uric acid (UA) could be well separated within 23 min. Highly linear response was obtained for five marker compounds over three orders of magnitude with detection limits ranging from 6.4×10-2 to 6.6μg/mL (S/N=3). The proposed method has been used to detect the marker compounds simultaneously in urine samples with the advantages of obtaining more information about target analytes and avoiding redundant measurements and high assay cost. Urinary patterns in phenylketonuric babies were distinct and easily distinguished from those of healthy newborns. PPA, as the primary abnormal metabolite of phenylalanine, has been determined in all urine samples of PKU patients, and the content of PPA in PKU patients without dietotherapy were higher than those with dietotherapy; however, PPA was not found in all urine samples of healthy babies as its content was below the LOD of the proposed method. Therefore, PPA and other four aromatic acids (usually several, ten, or even more times higher than the normal levels) could be taken as the initial diagnosis proof of PKU. Besides, the assay results showed that the abnormal metabolism of phenylalanine could be maintained at a stable level with a long-time low-phenylalanine diet. The proposed MECC-C4D/AD method could find potential clinical application in early noninvasive diagnosis of phenylketonuria (PKU), with the character of minimal consumption of sample and without sample derivatization.3. A novel miniaturized electrophoretic method for determining formaldehyde and acetaldehyde in food with amperometric detectionA novel miniaturized capillary electrophoresis with amperometric detection (mini-CE-AD) method has been developed for fast determination of formaldehyde (FA) and acetaldehyde (AA) in several food products without preconcentration. Because FA and AA usually exist as uncharged molecules with zero electrophoretic mobility, plus the fact that these two compounds lack of chromophore for sensitive ultraviolet (UV) detection, effective and sensitive determination of FA and AA in real samples is often a challenging task. In this work, an electroactive compound 2-thiobarbituric acid (TBA) was selected as the ideal derivatization reagent to facilitate the electrochemical determination of FA and AA. Under the optimum conditions, FA-TBA and AA-TBA adducts can be well separated by mini-CE-AD with low detection limit of 9.10×10-2μg/mL (13.2 fg) for FA (S/N=3). The proposed method should find a wide range of analytical applications in food products as an alternative to conventional and microchip CE approaches.4. Multi-residue analysis of sulfonamides in animal tissues by capillary zone electrophoresis with amperometric detectionThe objective of this study was to adapt and improve previously published analysis methods aimed at the simultaneous determination of sulfonamide residues in edible animal tissues by capillary zone electrophoresis with amperometric detection (CZE-AD). The effects of several factors such as the acidity and concentration of running buffer, the separation voltage, the applied potential and the injection time on CZE-AD were investigated. Complete separation of six sulfonamides was achieved within 17 min by using 40 mmol/L Na2B4O7-25 mmol/L KH2PO4 (pH 6.2) at an applied voltage of 18 kV. Excellent linearity was obtained over two orders of magnitude with the improved detection limits (S/N=3) ranged from 4.4×10-3 to 0.17μg/mL for all six sulfonamides in comparison with previous reports. A solvent extraction, centrifuge, evaporation procedure was used to extract sulfonamides from animal tissues, sample clean-up and pre-concentration of sulfonamides prior to CZE-AD analysis. Good recoveries from 81.2% to 92.3% were achieved. Results obtained in this work indicated that the proposed CZE-AD method was sensitive, rapid and simple for the simultaneous determination of sulfonamides in edible animal tissues. Therefore, the new faster and easy handling procedure provides an additional powerful tool that can be employed for the analysis of sulfonamide residues in foodstuff. |
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