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11.
Electroanalytical and chromatographic determination of pentachlorophenol and related molecules in a contaminated soil: a real case example 总被引:1,自引:0,他引:1
L. Codognoto V. G. Zuin D. de Souza J. H. Yariwake S. A. S. Machado L. A. Avaca 《Microchemical Journal》2004,77(2):177-184
Electroanalytical and chromatographic methodologies have been applied for the determination of pentachlorophenol (PCP) and some of its derivatives in real soil samples contaminated by industrial discharge. The analytes were extracted with hexane from soil samples collected at different points of the site and mixed to produce a representative sample. Square wave voltammetry (SWV) experiments were carried out on either a boron-doped diamond (BDD) electrode or a gold ultramicroelectrode (Au-UME) in an analyte composed by the Britton-Robinson (B-R) buffer at pH 5.5 with the direct addition of proper amounts of the extract. The voltammetric responses revealed an irreversible anodic peak at approximately 0.80 V vs. Ag/AgCl with a peak current showing a linear dependence on PCP concentration. This linear relationship yielded a detection limit (DL) of 2×10−8 mol l−1 (or 5.5 μg l−1) for the BDD electrode and 6.9×10−8 mol l−1 (18.4 μg l−1) for the Au-UME, while the independently measured HPLC detection limit was 1.1×10−8 mol l−1 (3.0 μg l−1). The application of electroanalytical and chromatographic methodologies in the analysis of soil extracts revealed, besides the PCP responses, signals for some related molecules such as o-tetrachlorobenzoquinone (o-chloranil), hexachlorobenzene and tetrachlorophenol. Recovering experiments for PCP showed a concentration of 27.5 mg kg−1 for the electroanalytical determinations and 26.8 mg kg−1 for the HPLC analysis, values exceedingly high if considering that the maximum residue limit established for natural waters by the Brazilian Environmental Agency is 10 μg l−1. 相似文献
12.
CHLOROPHYLL BINDING PROTEINS WITH ANTENNA FUNCTION IN HIGHER PLANTS and GREEN ALGAE 总被引:16,自引:0,他引:16
Roberto Bassi Fernanda Rigoni Giorgio M. Giacometti 《Photochemistry and photobiology》1990,52(6):1187-1206
13.
Studies on the complexation of copper(II) by phenolic acids, as ligand models of humic substances were done by potentiometry. The acids under study were: 3,4-dihydroxyhydrocinnamic acid or hydrocaffeic acid (1), 3,4-dihydroxyphenylacetic acid (2) and 3,4-dihydroxybenzoic acid or protocatechuic acid (3). Acidity constants of the ligands and the formation constants of metal-ligand complexes were evaluated by computer programs. The carboxylic group of the phenolic acids has different pKa1 values, being the dissociation constants intrinsically related with the distance between the function and the aromatic nucleus. The results obtained allow concluding that acidity constants of the catechol moiety of the compounds are similar with pKa2 and pKa3 values between 9.47-9.41 and 11.55-11.70. The complexation properties of the three ligands towards copper(II) ion are quite similar, being the species found not different either in nature or stability. Although the model ligands have some structural differences no significant differences were found in their complexation properties towards copper(II). So, it can be postulated that complexation process is intrinsically related with the presence of a catechol group. 相似文献
14.
The quenching of the fluorescence of three anthropogenic fulvic acids (FA) provoked by Cu(II) (pH 6.0), Fe(III) (pH 4.0) and UO22+ (pH 3.5), was analyzed by a non-linear method and by Stern-Volmer plots. The FA samples were extracted from composted sewage sludges (csFA), composted municipal wastes (mwFA) and composted livestock wastes (lsFA). Synchronous-scan fluorescence (SyF) spectra were collected as a function of metal ion concentration. Spectral data were treated by a self-modeling mixture analysis method (SIMPLISMA) to detect the SyF spectral band with the strongest quenching and to calculate the corresponding quenching profile. The analysis of these profiles by a non-linear method allowed the estimation of conditional stability constants (K) and of the percentage of non-complexing fluorophores. The same quantitative information was obtained by the modified Stern-Volmer equation taking into account the existence of fluorophores that do not participate in the complexation. Good agreement was found between the results of the two procedures. The log K calculated by the non-linear method were (standard deviation in parenthesis): csFA, Cu(II), 4.22 (5); Fe(III), 5.0 (1); UO22+, 5.2 (2); mwFA, Cu(II), 4.21 (3); Fe(III), 5.6 (2); UO22+, 4.7 (3); lsFA, Cu(II), 4.51 (8); Fe(III), 5.5 (2); UO22+, 3.6 (2). 相似文献
15.
Maria Fernanda Silva Estela Soledad Cerutti Luis D. Martinez 《Mikrochimica acta》2006,155(3-4):349-364
The purpose of this article is to review and evaluate cloud point extraction of metals and its coupling to different contemporary
instrumental methods of analysis. This review covers a selection of the literature published on this topic over the period
mainly between 1997 and September 2005 (consisting of 50 publications). The current state of the art for CPE concerning metals
and metal chelates is presented with special emphasis on the hyphenation of this interesting extraction/preconcentration approach
mediated by surfactants to spectrophotometry, atomic spectroscopy and separation techniques. We present contemporary CPE developments
concerning metal speciation and determination and their application to different environmental, clinical, geological and food
samples. Strategies for method development as well as future perspectives are also covered. 相似文献
16.
Machado AM Wypych F Drechsel SM Nakagaki S 《Journal of colloid and interface science》2002,254(1):158-164
Two samples of montmorillonite (one of Brazilian origin, BNC1 clay, and the other STX-1, supplied by the Clay Mineral Society Repository (University of Missouri, USA) were allowed to react with biomimetic metalloporphyrins of Fe(III) and Mn(III) in cationic form. The compounds were characterized by several techniques, showing that the metalloporphyrins molecules were adsorbed at the surface of the clay platelet crystals. The catalytic activities of the intercalated complexes for the oxidation of alkane were dependent upon the concentration of the porphyrin immobilized in the clay and factors such as the metal ion species in the porphyrins, choice of solvent, and concentration of the iodosylbenzene oxidant. Good selectivity to cyclohexanol instead of cyclohexanone was observed for the catalytic oxidation of cyclohexane by iodosylbenzene. 相似文献
17.
The mathematical evaluation of the activation
energy, E, of non-isothermal degradation
reactions is usually made using the Ozawa/Flynn–Wall isoconversion principle
and involves the numerical resolution of a set of integrals without closed
form solution, which are solved by polynomial approximation or by numeric
integration. In the present work, the isoconversion principle, originally
described and maintained until now as an algebraic problem, was written as
a set of ordinary differential equations (ODEs). The individual ODEs obtained
are integrated by numeric methods and are used to estimate the activation
energy of simulated examples. A least square error (LSE) objective function
using the introduced ODEs was written to deal with multiple heating rate CaCO3
thermal decomposition TG experiments. 相似文献
18.
Carla M. Bossu Edilene C. Ferreira Fernanda S. Chaves Eveline A. Menezes Ana Rita A. Nogueira 《Microchemical Journal》2006,84(1-2):88-92
A flow injection system was proposed to evaluate the transient product of a colorimetric reaction between hydrolysable tannin and potassium iodate (KIO3) solution. The system optimization was accomplished by using statistical methods based on experimental design. Flow rate of KIO3 solution, sample volume, carrier flow rate, and reaction coil were the selected factors for evaluation. On screening step, complete factorial 24 was used and two levels for each selected factor were studied. For the optimization phase, a centered face composite design 22 + star was employed to evaluate sample volume and flow rate of KIO3 solution, which were the factors identified in the screening phase as having more influence on the absorbance signal. After optimization, the proposed system was compared with batch determination. Some characteristics, such as analytical frequency, reagent consumption and chemical residues generation presented better results by the use of the proposed system if compared with batch method. The system presented good repeatability with standard deviation lower than 3%, for n = 10, linearity (R2 = 0.9974) for tannic acid standard, analytical frequency of 15 injections h− 1 and limit of quantification of 24 mg L− 1 of tannic acid. Good results were obtained when the proposed system was applied to hydrolysable tannin determination in Stryphnodendron barbatimão, Eucalyptus citriodora and Phyllanthus niruri, samples of plants commonly used in popular medicine. 相似文献
19.
Esculetin ( 1 ) and the novel compounds 5-chloroesculetin ( 5 ) and 5-bromoesculetin ( 6 ) were obtained from a light-induced cyclization of trans-caffeic acid ( 3 ) catalyzed by [FeNa(edta)] and/or H2SO4, HCI, or HBr (Scheme 1). The experimental conditions for trans-cis-isomerization of the cinnamic-acid derivative 3 and subsequent non-enzymatic cyclization were described. The photoperiod and the presence of air and iron-chelate catalyst are shown to be important parameters that markedly affect yields. The reactions probably occur by a free-radical mechanism involving a photo-initiated one-electron redox process (Scheme 2). 相似文献
20.
Machado AA 《Talanta》1980,27(12):1099-1101
Details of diagrams recently presented for the regions where approximation formulae give the pH of mono- and diprotic acids with an error of less than 0.02 pH unit are discussed. 相似文献