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691.
Camila Bitencourt Mendes Emiliane Pereira Laignier Maisa Ribeiro Pereira Lima Brigagão Pedro Orival Luccas César Ricardo Teixeira Tarley 《Chemical Papers》2010,64(3):285-293
A new method for saccharin determination in liquid sweetener products was developed. The method is based on the precipitation
reaction of Ag(I) ions with saccharin in aqueous medium (pH 3.0), using a flow injection analysis system with merging zones,
the suspension was stabilized with 5 g L−1 Triton X-100. All experimental parameters influencing the flow injection system were optimized by means of chemometric approaches.
The linear analytical curve was built from 2.4 g L−1 up to 9.64 g L−1 (r = 0.9968) with a quantification limit of 2.40 g L−1. The precision assessed as relative standard deviation (n = 10) was found to be 1.75 % for the saccharin concentration of 7.20 g L−1. Based on interference studies performed with the substances commonly found in liquid sweeteners, such as sodium cyclamate,
methylparaben, sodium aspartame, and benzoic and citric acids, at the analyte to interferent mole ratio of up to 1: 10, no
interference with the saccharin determination was observed. The presence of chloride ions interferes with the method, but
a preceding liquid-liquid saccharin extraction with ethyl acetate was successfully employed to overcome this drawback. Accuracy
of the method in sweetener products was evaluated by a comparison with the HPLC method. 相似文献
692.
Bruno S. Souza Ana Paula D. Moreira Ana Maria R. F. Teixeira 《Journal of Thermal Analysis and Calorimetry》2009,97(2):637-642
Thermogravimetry has been widely used for the characterization of several biomasses but the most useful information given
by this technique has been normally concerned to the relative amounts of humidity, hemi-cellulose, cellulose and lignin present
in the biomass. TG-FTIR has been used to yield qualitative data about the pyrolysis products, in an exploratory way, by some
authors. In the present paper, this technique was employed to reach comparative data about the products of pyrolysis of biomasses
that are potentially available at economic bases for the production of biofuels. Agricultural residues such as coconut shell,
sugarcane bagasse, corn stalks and peanut shell were chosen to be investigated. For all samples, the thermogravimetric curves
showed a mass loss between 35 and 400 °C changed up to 73%, while that the loss between 400 and 800 °C changed up to 26%.
TG-FTIR indicated tendencies in the rate of the formation of important species during the pyrolysis process of the four biomasses
studied. The interpretation of the spectra allowed the proposition of characteristic absorbance ratios and the comparison
of these values allowed inferences about the relative abundances of components formed in the pyrolysis of the biomasses. As
an example of the possible inferences reached, among the species formed in the pyrolysis condensate, called bio-oil, the formation
of carboxylic acids has to be specially considered due to their corrosivity. Thus, the data produced indicated that a bio-oil
derived from peanut shell should be a little less acidic while the one derived from sugarcane bagasse should be showed more
acidic among the biomasses studied. 相似文献
693.
Determination of the chemical oxygen demand (COD) using a copper electrode: a clean alternative method 总被引:1,自引:0,他引:1
Claudineia R. Silva Cleone D. C. Conceição Viviane G. Bonifácio Orlando Fatibello Filho Marcos F. S. Teixeira 《Journal of Solid State Electrochemistry》2009,13(5):665-669
A clean alternative method for the determination of chemical oxygen demand (COD) was developed using a copper electrode as
an electrocatalytic sensor. The measuring principle is based on oxidation current of organic compounds in the wastewater.
The effects of important experimental conditions, such as electrolytic solution concentration and potential scan rate, on
analytical performance have been investigated. Analytical linear range of 53.0–2,801.4 mg l−1 COD with detection limit of 20.3 mg l−1 COD was achieved. The procedure was successfully applied to the COD determination in wastewater from soft industries. The
results obtained using the proposed method were in good agreement with those obtained using the conventional (i.e., dichromate)
COD method. In this fashion, the COD value of a sample can be determined in a simple, rapid, accurate manner, and the end
products do not contain toxic metals. 相似文献
694.
Vívian Aparecida Ricardo Teixeira Ernesto Clóvis Augusto Ribeiro Ossamu Hojo Fernando Luis Fertonani Marisa Spirandeli Crespi 《Journal of Thermal Analysis and Calorimetry》2009,97(2):653-656
Bagasse samples from four different sugarcane were directly collected as the residues of milling in a processing plant. The
samples were dried at 105 °C, compressed to small granules and then their TG/DTA and DSC curves in synthetic air were recorded.
Similar thermogravimetric curves were obtained for the different samples and they exhibited four mass loss steps. However,
the analysis of the exotherm DSC peaks showed that the oxidation of the organic matter resulted different enthalpy values
(ΔH/kJ g−1). 相似文献
695.
An amperometric dipyrone sensor based on a polymeric nickel-salen (salen = N,N´-ethylenebis(salicydeneiminato)) film coated platinum electrode was developed. The sensor was constructed by electropolymerization of nickel-salen complex at a platinum electrode in acetonitrile/tetrabuthylamonium perchlorate by cyclic voltammetry. After cycling the modified electrode in a 0.50 mol L-1 KCl solution, the estimated surface concentration was found to be equal to 1.29 x 10-9 mol cm-2. This is a typical behavior of an electrode surface immobilized with a redox couple that can usually be considered as a reversible single-electron reduction/oxidation of the nickel(II)/nickel(III) couple. A plot of the anodic current versus the dipyrone concentration for chronoamperometry (potential fixed = +0.50 V) at the sensor was linear in the 4.7 x 10-6 to 1.1 x 10-4 mol L-1 concentration range and the concentration limit was 1.2 x 10-6 mol L-1. The proposed electrode is useful for the quality control and routine analysis of dipyrone in pharmaceutical formulations. 相似文献
696.
R.A.P.O. d'Amorim M.I. Teixeira S.O. Souza J.M. Sasaki L.V.E. Caldas 《Journal of luminescence》2012,132(2):266-269
The possibility of using different materials for thermoluminescent dosimetry agglutinating their powder with Teflon® (a polymer) has been studied in recent years. In this paper the thermoluminescent properties of spodumene-Teflon® composites were studied exposing them to different doses of a 60Co radiation source, in comparison to the thermoluminescent properties of crystalline powder and of Teflon. The thermoluminescent emission curve of pure Teflon® pellets showed two peaks at 200 and 250 °C at doses above 1 kGy, which may influence the dosimetry of high-doses that uses crystals agglutinated with this polymer. Preliminary results show that the Teflon® causes an increased sensitivity in the TL signal of the pellet compared to the crystalline powder without the polymer, and that even the pure Teflon® pellet is a material that can be exploited for high-doses dosimetry. 相似文献
697.
A. L. Nazareth da Silva S. C. S. Teixeira A. C. C. Widal F. M. B. Coutinho 《Polymer Testing》2001,20(8):895-899
The effect of the addition of methyl ethyl ketone peroxide (MEKP) and cobalt naphthenate (CoNaph) on the mechanical behavior of epoxy vinyl ester resin (EVER) laminates has been investigated by using a factorial experimental design, in which the MEKP and NaphCo contents were varied. Previous results showed that there is an interaction effect between the process variables analysed on the mechanical properties evaluated. It was also observed that the MEKP/CoNaph ratio affected the tensile behavior of the EVER/glass fiber composites. 相似文献
698.
M. L. A. Gonçalves M. A. G. Teixeira R. C. L. Pereira R. L. P. Mercury J. R. Matos 《Journal of Thermal Analysis and Calorimetry》2001,64(2):697-706
The thermal decomposition of asphaltenes is mainly responsible for the formation of coke in petroleum processing. Phenomena
involved are not clearly understood, because of the difficulties to characterize such heavy components. This paper reports
the application of thermal analysis techniques to study the thermal behavior of asphaltenes from Brazilian oil. The approach
involves kinetic studies of the thermal decomposition of asphaltenes under controlled conditions by thermogravimetry (TG),
characterization of volatile fractions by thermogravimetry and differential thermal analysis coupled with gas chromatography/mass
spectrometry (TG-DTA/GC/MS) and by gas chromatography/mass spectrometry (GC/MS) in the volatile recovered. The coke formed
was also studied after being decomposed into smaller molecules using selective oxidation.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
699.
Eliangela de Morais Teixeira Alessandra Luzia Da Róz Antonio José Felix de Carvalho Antonio Aprigio da Silva Curvelo 《Macromolecular Symposia》2005,229(1):266-275
Summary: Thermoplastic starches (TPS) based on cassava starch have been produced by extrusion at 120 °C, using glycerol as plasticizer. Three forms of cassava starch were employed, viz: cassava root (CR), cassava bagasse (CB) and purified cassava starch (PCS). The main differences between these are the presence of sugars and a few fibres in CR and high fibre concentration in CB. Conditions of processing and characteristics such as amylose and fibre content, crystallinity, water absorption and mechanical behaviour in the tension x deformation test were evaluated. The results demonstrated that the PCS and CR had amylose contents consistent with literature values (14–18%) and that CB is a material constituted mainly by amylopectin. It was found that fibres in high proportions (as in the bagasse) can confer reinforcement properties and are thus able to generate natural composites of TPS with cellulose fibre. The sugars naturally found in the root reduce the elongation of the TPS under tension. The PCS and CR TPS were stable with respect to indices of crystallinity after processing; and during a period of 90 d in a relative humidity of 53%, while the CB TPS tended to vary its crystallinity, probably because its amylose chain had low degree of polymerization. 相似文献
700.
We find, by counting the degrees of freedom of two-dimensional bubble clusters (finite or periodic) of given topology and
bubble areas, that the Plateau laws determine a unique configuration of a finite free cluster, but allow an infinite number
of configurations of a periodic cluster. Each of these configurations is associated with a particular strain (stress) state
of the cluster; there is in general one unstrained configuration, which corresponds to the minimum of the (surface) energy.
Configurations of given topology that satisfy Plateau's laws may only exist in certain ranges of bubble area ratios and/or
strains.
Received 31 May 2001 and Received in final form 12 September 2001 相似文献