Detection Of Trace Nutrients, Illegal Additives And Pesticide Residues By Highly Sensitive Capillary Electrophoresis

With the improved living standards, there is a growing concern of food safety and food quality. The quick and accurate determination of nutrient and deleterious substances in food has become one of the important issues in the field of food analysis. However, the food analysis is still faced with some questions, such as complex sample matrix, cumbersome sample preparation, low content of the measured component and low instrument sensitivity. Therefore, it is necessary to develop a high efficiency and high sensitivity method for food analysis. Capillary electrophoresis (CE) is a liquid phase separation technique with the advantages of high resolution, high efficiency, short analysis time, simplicity, low sample and solvent consumption. However, poor sensitivity is considered to be one of the major limitations of CE.Therefore, this dissertation focused on develops sensitive capillary electrophoresis methods for the determination of nutrient and deleterious substances in food. Some original studies were carried out as follows:1. Developed an approach to determine melamine in liquid milk, yoghourt, whole milk powder, fish feed, and fish at residue levels using capillary zone electrophoresis with diode array detection for the first time.2. Established an approach of transient isotachophoresis under the strong counter-electroosmotic flow in open system for the rapid and sensitive analysis of reduced and oxidized glutathione without extreme pH conditions, modifying capillary or commercial CE instrument. The method cans determine reduced and oxidized glutathione in tomato and human serum.3. Proposed a novel method combining constant pressure-assisted head-column field-amplified sample injection with laser induced fluorescence for enhancing the sensitivity of capillary electrophoresis. The trace organophosphorus pesticides in grape-steeped-water were determined using the proposed method.This dissertation consists of five chapters.ChapterⅠ:The review of the application of capillary electrophoresis in determining food additives. Edible and inedible food additives, such as colorants, preservatives, antioxidants, sweeteners, Sudan, melamine and clenbuterol, are all reviewed in this chapter.ChapterⅡ:This chapter describes an approach to determine melamine in liquid milk, yoghourt, whole milk powder, fish feed, and fish at residue levels using capillary zone electrophoresis with diode array detection for the first time. By investigating the variables of extraction, separation and detection in detail, the entire analytical procedures including sample preparation could be completed within 30 min. The limit of detection for MEL was found to be 0.01μg/mL. The proposed method was successfully applied for the analysis of melamine in dairy products, fish feed, and fish with the total recoveries ranging from 93 to 104%.ChapterⅢ:This chapter describes an automatic rapid approach for in-capillary derivatization of reduced glutathione (GSH) and the oxidized glutathione (GSSG) using DTAF as fluorescent.reagent. The derivatives was separated by capillary electrophoresis modified withβ-CD. Under the optimal conditions, the limits of detection were found to be 0.28 ng/mL and 4.59 ng/mL for GSH and GSSG, respectively.ChapterⅣ:In this chapter, an approach of transient isotachophoresis under the strong counter- electroosmotic flow in open system is presented for the rapid and sensitive preconcentrating the GSH and GSSG without modifying the capillary and the commercial CE instrument. Under the optimum conditions, the sensitivity enhancement factors were of 320 for GSH and 280 for GSSG. In addition, the detection limit of 23.4 and 18.0 ng/mL for GSH and GSSG was achieved respectively. The method's applicability was demonstrated by determining GSH and GSSG in tomato and human serum.ChapterⅤ:In this chapter, a novel method combining constant pressure-assisted head-column field-amplified sample injection with laser induced fluorescence was developed for enhancing the sensitivity of capillary electrophoresis. By investigating the variables of the presented approach in detail, on-line preconcentration, derivatization and separation could be automatic operated in one run and required no modification of current CE commercial instrument. Moreover, the sensitivity enhancement factor of 520 and 800 together with the detection limits of 16.32 and 6.34 pg/mL were achieved for model compounds:glufosinate and aminomethylphosphonic acid, demonstrating the high detection sensitivity of the presented method.