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Application of Crosslinked Carboxymethyl Konjac Glucomannan to Trace Elements Analysis and Elemental Speciation

Author: ShenMin
Tutor: ChenHao
School: Huazhong Agricultural University
Course: Pesticides
Keywords: Crosslinked carboxymethyl konjac glucomannan solid phase extraction metal ions speciation AAS
CLC: O651
Type: Master's thesis
Year: 2008
Downloads: 9
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Abstract


Sensitive, rapid, reproducible, simple and accurate analytical methods are required for the determination of trace elements in geological, biological and environmental samples. The direct determination of extremely low concentrations of trace elements by modern atomic spectroscopic methods, such as atomic absorption spectrometry （AAS） and inductively coupled plasma optical emission spectrometry （ICP-OES） is often difficult. The limitations are associated not only with the insufficient sensitivity of these techniques but also with matrix interference. For this reason, the separation and preconcentration of trace elements is often required. Solid phase extraction （SPE） technique has become increasingly popular in trace elements separation/preconcentration with modern atomic spectroscopic methods. And the choice of solid-phase adsorbents is decisive factor that affects analytical sensitivity and selectivity. So, it has still been a heated research field to find new and effective adsorbents nowadays.Recently, the adsorption behaviors of natural polymers which are abundant and biodegradable resources like chitosan, starch and cyclodextrin, have been widely reported for separation of metal ions. However, few reports have been published on the investigation of the adsorption capability of konjac glucomannan（KGM） for metal ions. KGM is a linear random copolymer ofβ-1,4-linked D-glucose and D-mannose in a molar ratio of 1.6:1 with a low degree of acetyl groups. It is a water-soluble polysaccharide of high molecular weight, which is a disadvantage in application. Crosslinked carboxymethyl konjac glucomannan （CCMKGM） is prepared through reaction of monochloroacetic acid （MCA）, konjac glucomannan （KGM） and epichlorohydrin, it has reported as a adsorption properties for metal ions. However, it rarely is regarded as solid phase adsorbent to separate and preconcentrate the metal ions.The aim of this dissertation is to systematically study the adsorption characteristics of some metal ions on CCMKGM, and apply it to the separation/preconcentration and speciation analysis of trace elements. The major contents are described as follows:（1） A novel solid phase extraction technique has been developed for the determination of trace lead, cadmium and copper in environmental water samples based on separation and preconcentration with a microcolumn packed with crosslinked carboxymethyl konjac glucomannan （CCMKGM） prior to its determination by graphite furnace atomic absorption spectrometry. Various influencing factors on the separation and preconcentration of lead, cadmium and copper, such as the acidity of the aqueous solution, sample flow rate and volume, eluent concentration and volume, have been investigated systematically, and the optimized operation conditions were established. The analytes could be quantitatively retained by CCMKGM in the pH range of 5.0-7.0, then eluted completely with 1.0 mL 0.5 mol/L HCl. The detection limits（3σ） for analyte ions were 0.038μg/L for Pb（Ⅱ）, 0.0005μg/L for Cd（Ⅱ） and 0.014μg/L for Cu（Ⅱ） with an enrichment factor of 50, and the relative standard deviations were 3.5 % for Pb（Ⅱ）, 9.2 % for Cd（Ⅱ） and 4.7 % for Cu（Ⅱ） (cPb（Ⅱ） = cCu（Ⅱ） = 1.0μg/L; cCd（Ⅱ） = 0.1μg/L, n = 11). The proposed method was successfully applied to the determination of trace lead, cadmium and copper in environmental water samples （local tap water and Lake water）. In order to validate the method, the developed method was applied to the determination of lead, cadmium and copper in environmental water reference materials and the results obtained were in good agreement with the certified value.（2） A novel solid phase extraction technique has been developed for the speciation of trace dissolved Fe（Ⅱ） and Fe（Ⅲ） in environmental water samples with a micro-column packed with crosslinked carboxymethyl konjac glucomannan （CCMKGM） prior to its determination by flame atomic absorption spectrometry. Various influencing factors on the separation and preconcentration of Fe（Ⅱ） and Fe（Ⅲ）, such as the acidity of the aqueous solution, sample flow rate and volume, eluent concentration and volume, have been investigated systematically, and the optimized operation conditions were established. At pH 3.0-7.0 Fe（Ⅲ） was retained on the micro-column, eluted with 2 mL 0.05 mol/L HCl in order to eliminate the Fe（Ⅱ）, then eluted with 2 mL 5.0 mol/L HCl and determined by FAAS. Total Fe was determined after the oxidation of Fe（Ⅱ） to Fe（Ⅲ） by 50μL H2O2. The adsorption capacity of CCMKGM for Fe（Ⅲ） was found to be 151.5 mg/g. The detection limit （3σ） for Fe（Ⅲ） was 0.78μg L-1 and the relative standard deviation （R.S.D.） was 3.5 % （n = 11, C = 20μg/L） with an enrichment factor of 50. The proposed method was successfully applied to the determination of trace Fe（Ⅱ） and Fe（Ⅲ） in environmental water samples （local tap water and South Lake water）. In order to validate the method, the developed method was applied to the determination of total iron in environmental water reference materials and the result obtained was in good agreement with the certified value.（3） CCMKGM was prepared and its static adsorption properties for metal ions （Cr（Ⅲ）, Fe（Ⅲ）, Pb（Ⅱ）, Cd（Ⅱ） and Cu（Ⅱ）） such as capacities, kinetics and isotherm were investigated. The structure of adsorption products was characterized by FTIR, RAMAN, XRD, TG and SEM. The adsorption rapidly reached equilibrium within 30 min （Cd（II）: 180 min） and adsorption followed second-order kinetic equation. The adsorptions of five metal ions are well followed as the Langmuir and Freundlich adsorption isotherm at the same time. The maximum adsorption capacity of CCMKGM were 153.8 mg/g for Cr（Ⅲ）, 151.5 mg/g for Fe（Ⅲ）, 196.1 mg/g for Pb（Ⅱ）, 196.1 mg/g for Cd（Ⅱ） and 61.3 mg/g for Cu（Ⅱ）. The adsorption is a spontaneous endothermic process of increased entropy. The FTIR and RAMAN analysis indicates that the adsorption was realized via coordination of -COOH and -OH groups in CCMKGM to the metal ions. WAXD results indicate Pb（Ⅱ） and Cd（Ⅱ） adsorption onto both the amorphous and crystal of CCMKGM.（4） A novel method based on ion chromatography has been developed for the separation and preconcentration of trace oxalate using chitosan （CTS） as adsorbent. The effects of preconcentration time, dosage of chitosan and co-existing ions have been investigated. It was found that the adsorption rate of chitosan for oxalate was near 100 % at pH 3.0. Under the optimum conditions, the adsorbed oxalate can be quantitatively eluted by 5.0 mL of 0.1 mol/L NaOH and the desorption rate was 96 %. The detection limit （S/N = 3） for the oxalate was 4.3μg/L with relative standard deviation （R.S.D） of 7 %（c = 0.05μg/mL, n = 6）. The adsorption equilibrium was well described by Langmuir isotherm model, and the maximum adsorption capacity of oxalate on CTS was 194.0 mg/g. The proposed method was applied to the determination of trace oxalate in water samples with satisfactory results.

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