The Electrokinetic Flow Analysis System And Its Application In Pesticide Residues Analysis

The electrokinetic flow analysis(EFA) system based on sequential injection analysis(SIA),multicommutation analysis,electroosmotic pump delivery and chromatographic separation of monolithic column possesses the advantages of simpleness,convenience,controllability and multifunction.It has been successfully applied in on-line sample pretreatment and analysis.The main aim of the thesis is to entend the application of EFA system.A 4.6 mm i.d.C₈-silica monolithic column and a 2.0 mm i.d.quartz sand monolithic microcolumn were prepared by one-step polymerization.The separation of electrochromatography(EC) with the quartz sand monolithic microcolumn was studied combining with the EFA system.An on-line hollow fiber liquid-liquid-liquid microextraction(HF-LLLME) -EFA system was established for the pretreatment of carbamate pesticide residues.In addition,a method for the determination of free amino acids(AAs) was proposed using capillary electrophoresis(CE) and indirect UV(in-UV) detection.1.A method for one-step polymerization of C₈-silica monolithic column was established with tetramethoxyl silane and octyltrimethoxysilane.Capillary electrochromatography(CEC) possesses its advantages of high separation efficiency and fast analysis velocity,but it also has its shortcomings of poor detection sensitivity, low sample loadability and troublesome preparation due to its small inner diameter. To obtain the optimal preparation,the influence of the reactant concentrations, reaction acidity and polymerization temperature on the structure of monolithic column was investigated.The obtained preparation conditions are as follows:0.31 mL tetramethoxyl silane,0.345 mL octyltrimethoxysilane,0.080 g urea,0.33 mL 0.20mol/L HAc and 0.32 mL ethanol.The silica monolithic column was prepared by the hydrolyzation of tetraethoxysilane and octyltrimethoxysilane in acidic condition and the polycondensation in basic condition.The morphology of the silica gel was like cross network with smooth cylinder skeletons and macropores of micron dimension,which made the column high permeability and low backpressure.The mechanical strength of the silica gel was strong enough and the silica gel solid phase was able to be adopted in organic solvents.Octyl function group distributed in the column,resulting in free of chemically modified proceduce for stationary phase and improvement of reproducibility.The scanning electromicrograph displayed that the microcolumn possessed high permeability and could be employed for chromatographic separation.2.A technique for preparation of C₈-quartz sand monolithic microcolumn by one-step polycondensation was proposed.The heating effect increased acutely with the accretion of diameter of separation column diameter to millimeter dimension, which resulted in serious diffuseness of separation zone.Based on the preparation of C₈-silica monolithic column mentioned,10 cm length and 2.0 mm i.d. electrochromatographic microcolumn filled with 120-150 order quartz sand was prepared,which can be named as quartz sand monolithic microcolumn,which was used to improve the sample loadability and the detection sensitivity.The heating effect was also restricted by packing fine quartz sand into the silica gel,because the electric current in the quartz sand monolithic microcolumn was much lower than that of the normal monolithic microcolumn under the same electric field strength.On the other hand,the shrinkage associated with the polymerization was eliminated practically by packing fine quartz sand into the fused silica tube,and the microcolumn and the wall of fused silica tube could be contacted tightly.Based on the transportation of the EFA and separation of EC,a separation system with the microcolumn and on-line UV detection was assembled.The analytical system was of safety,convenience and automatization.Electroosmotic flow (EOF) or EOF combined with pressure flow was used to drive mobile phase in EC of the microcolumn.A routine spectrophotometer was used to determine the analytes separated by the EC minrocolumn.Separation parameters that affected the column efficiency were explored,such as concentration of organic solvent in mobile phase, buffer pH,electric field strength and flow rate of elctroosmotic pump.The column efficiency could achieve 6052 plates/m under the condition as following:65% acetonitrile(v/v) containingl mmol/L Tris buffer solution(pH 8.0) as mobile phase, 175V/cm electric field strength and 0.2 mL/min pump flow rate.The separation for EC with C₈-quartz sand monolithic microcolumn is being studied.3.An analysis method for the preconcentration of carbamate pesticide residues and clean-up of matrix in vegetable samples was proposed by using EFA with HF-LLLME.A program written in C language of personal computer was used to control the performance of electroosmotic pump and three-way solenoid valves in the HF-LLLME system.A simple,sensitive and inexpensive HF-LLLME unit was designed and assembled.The effect of organic solvent immobilized on the hollow fiber on the stability of liquid membrane was studied.A long-term stability of 156 h and high enrichment factor were obtained with the dodecanol phase of low toxicity. The LLLME conditions are investigated,including organic solvents,flow rate of sample loading,extraction times and sample volume etc.The enrichment factor of carbaryl which was used as a converted concentration for total carbamate pesticides achieved 300.The limit of detection(LOD) of the method was 1.0 ng/mL,much lower than the maximum residue limits(MRLs) of vegetable samples established by European Union(EU).The real samples were then spiked with 0.070 and 0.70μg mL^-1 carbaryl respectively,and the recoveries of carbaryl were in the range of 89.2-108%(n=3).The method was simple,convenient,sensitive,manageable and environmental friendly.The on-line HF- LLLME-EFA system was used to determined the total phenolic compounds.Under the optimized conditions,the total phenolic compounds in 1 mL wastewater was analyzed and the enrichment factor and LOD were 53 and 3μg/L, respectively,much lower than the maximum allowed level in industrial wastewater; When the total phenolic compounds in 6 mL surface water was determined,the analytical time was 49 min and the enrichment factor and LOD were 300 and 0.6μg/L,respectively,lower than the maximum allowed level in surface water.The real samples were then spiked with 0.25 and 0.50 mg/L phenol respectively,and the recoveries of phenol ranged from 86.6%to 96.4%with the relative standard deviation (RSD) of 3.8%(n=3).In the last chapter of this dissertation,a fast,convenient and sensitive method of CE-in-UV was proposed for the determination of 16 AAs in tobacco and tea samples. A background electrolyte(BGE) with a suitable mobility closing to those of the AAs should be selected to reduce the electric dispersion of the analyte peaks in CZE-in-UV. An isolated cell was able to prevent PAB from the electrode reaction and the baseline unstability.To increase the separation velocity,the EOF modifier was added into the BGE butter solution to obtain a reversed EOF.The separation conditions of AAs were investigated,such as different BGE,BGE concentration,buffer pH and EOF modifiers.Under the selected separation conditions,14 amino acid peaks could be separated on baseline.The detection limits of the AAs achieved 1.7μmol/L.The recoveries of the AAs in tobacco(spiked with 0.1 mmol/L and 0.4 mmol/L, respectively) and tea((spiked with 0.2 mmol/L and 0.4 mmol/L,respectively)) samples were in the range of 83.6-109%and 89.6-106%,respectively.The RSD of the peak height for 14 AAs was less than 6.0%,obtained by 5 individual separations.