Determination Of Amino Acids And Phenols By Capillary Electrophoresis And Arsenic, Lead, Chromium And Cadmium In Xanthan Gum By Atomic Absorption Spectrometry

In this thesis, the determination of amino acids and phenols by capillaryelectrophoresis was reported with enhanced sensitivity. The trace of As, Cd, Cr and Pdin Xanthan gum was determinated by Atomic Absorption Spectrometry. Details arelisted below.1. Determination of amino acids by capillary electrophoresis with differentialresonant contactless conductivity detectorA capacitively coupled contactless conductive detector （C⁴D） is a type universal iondetector that has found extensive applications in capillary electrophoresis （CE）. Inseparation of amino acids by CE, high concentration of acetic acid （>1mol/L） was usedcommonly as the running buffer, in which most of amino acids are presented in cations.The high background conductivity in the running buffer is disadvantage in C⁴Ddetermination due to large temperature draft and unmeet solution impedance. Toincrease the sensitivity of C⁴D, the equivalent circuit parameters of C⁴D in CEconditions used in this work were measured by an impedance analysis method. Theinfluence of solution conductivity and capillary dimension on impedance parameterswas investigated. Under the experimental conditions used,8699.9%of the totalimpedance of a C⁴D is composed by its imaginary part from the capillary wall capacitor.With increasing inner diameter of capillary and solution conductivity in detection zone,the wall capacitance increases, which results in the increase in the response signal ofC⁴D. But the wall capacitance is only0.5-12%of the predicted value according to acylinder capacitor model. In this work, a series combination of a C⁴D and a piezoelectric quartz crystal （PQC） resonator was employed. At the resonant frequencyof the combination, the response current in the resonant C⁴D （RC⁴D） was increasedsignificantly because the capacitive impedance of C⁴D from capillary wall is eliminatedby an inductive impedance from the PQC resonator. The application of an end-to-enddifferential C⁴D system in CE was demonstrated in the determination of ten amino acids.The running buffer consisted of2mol/L acetic acid and0.1%hydroxyethylcellulose（pH2.1）. The limit of detection for amino acids is in the range of0.1-0.4M. Under ourexperimental conditions, the sensitivity of DRC⁴D enhances by a factor of15-29ascompared with C⁴D.2. Enhancement sensitivity for phenols determination by capillary electrophoresiswith large volume sample preconcentrationThe sensitivity for phenols determination by capillary electrophoresis was enhancedby an on-line large volume sample preconcentration technique. Simultaneousdetermination of phenol,2-chlorophenol,4-chloro-3-methylphenol,2,4-dichlorophenol,2,4-dinitrophenol,4-nitrophenol, pentachlorophenol and2,4,6-trichlorophenol with UVdetection was reported. It was shown that the sensitivity for the eight phenolsdetermination with large volume sample injection was enhanced by factors of52-86and6-17in compared with that in hydrostatical and electrokinetical sample injectionapproaches, respectively. Under the experimental conditions used, the detection limit forthe eight phenols is in the range of0.004-0.02mg/L.3. Determination trace of Arsenic, Lead, Chromium and Cadmium in Xanthangum by microwave digestion-graphite furnace atomic absorption spectrometryA new method using microwave digestion technique was developed for thedetermination of As,Cd, Cr and Pb in Xanthan gum by graphite furnace atomicabsorption spectrometry （GFAAS）. The effect of dry ashing and microwave digestiontechnique was studied. Digestion solvents and microwave digestion conditions werediscussed for sample preparation by microwave digestion technique, The study showthat HNO3+H2O2was suitable for the digestion of Xanthan gum samples.The optimum condition of determination by GFAAS was studied in the presence of（NH₄）₃PO₄+Pd（NO₃）₂matrix modifier,which can effectly eliminate the matrix effect.Under optimized conditions,the detection limits of As, Pb, Cr and Cd are18,2.78、0.74、0.084μg/L,respectively, the RSD of determinationwas lower than10%, Therecoveries were in the range of84-108%. The method is simple, sensitive, rapid andsuitable for the simultaneous determination of As, Pb, Cr and Cd in Xanthan gum.4. Determination of chromium speciation in Xanthan gum by cloud pointextraction-graphite furnace atomic absorption spectrometryBy using dry ashing method for sample treatment, a cloud point extraction （CPE）was applied for simultanous preconcentration and separation of chromium （Ⅵ） inXanthan gum using sodium diethyl-dithiocarbamate trihydrate （DDTC） as chelatingagent and nonionic surfactantoctyl phenoxypolyethoxyethanol （TritonX-114） as theextractant. The separation of DDTC chelates of Cr（Ⅵ） was determinated byGFAAS.The main factors affecting the CPE, such as pH, concentrations of DDTC andTriton X-114, reaction temperature and time, buffer amount were studied. Underoptimized conditions,an enrichment factor of5is obtained in the CPE. The linear rangeof the calibration curve for Cr（Ⅵ） was0.4-40μg/L with the correlation coefficients （r）of0.9994，and the detection limit of0.012μg/L, The relative standard deviations wereless than5%. The recoveries of the method were89～107%. The method hasadvantages such as simple, safe with lower toxicity， higher efficiency andsensitive,rapid and broad test range. It was applied to the determination of chromiumspeciation in Xanthan gum samples.