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21.
On‐Site Determination of Carbendazim,Cathecol and Hydroquinone in Tap Water Using a Homemade Batch Injection Analysis Cell for Screen Printed Electrodes 下载免费PDF全文
Ricardo Pini Caramit Bruno Gabriel Lucca Valdir Souza Ferreira Rodrigo Alejandro Abarza Munoz Eduardo Mathias Richter Rodrigo Amorim Bezerra da Silva 《Electroanalysis》2015,27(2):271-275
In this work, we present a simple homemade batch‐injection analysis cell for screen‐printed electrodes (BIA‐SPE). The potential of the proposed system for on‐site analysis was demonstrated by the determination of carbendazim, catechol, and hydroquinone in tap water. The system provided reduced injection volume (30 µL), high analytical frequency (≈200 h?1) and low detection limits (nanomolar level). Moreover, the BIA‐SPE cell presented better stability (RSD≈0.4 %) than a conventional flow injection cell for SPE (RSD≈5.0 %) in organic media. The proposed homemade BIA‐SPE cell is very simple, inexpensive and can be easily constructed in any laboratory. 相似文献
22.
L. Giorgio Soldi Yizhak Marcus Michael J. Blandamer Paul M. Cullis 《Journal of solution chemistry》1995,24(3):201-209
Enthalpic pairwise interaction parameters, hjj, were determined by titration calorimetry at 25°C for dilute solutions of glycerol, D-threitol, manitol, and D-glucitol in water. The parameters for these and other polyols conform to the expression hjj (J-kg–1)=145+135nOH–21.5n
OH
2
–41.7
dl
2
-160.5ndlld, where nOH=nC is the number of hydroxyl groups (carbon atoms), ndl is the number of dl configuration of a vicinal pair of OH-groups, and ndlld is the number of such configurations in the polyol molecules. A rationalization of this expression is given. 相似文献
23.
The present study covers the problem of rotation of a porous disk under a viscous incompressible fluid that fills the half-space above the disk, which is the generalization of the von Karman’s problem. It is found that, instead of solving the exact problem, which is rather complicated by coupling the motions of the free fluid and that contained inside the permeable disk, it is sufficient to solve a much simpler problem of the motion of the free fluid placed onto a permeable plane. Assuming the flow in the permeable disk is described by the Brinkman equations, we obtain a self-similar formulation of the problem. Employing this formulation, we also show that the boundary condition associated with continuity of the tangential strains and tangential velocity components is satisfied at the fluid–porous body interface. The coefficient for the vertical velocity component is furthermore obtained. Various extreme cases are identified. 相似文献
24.
Antonio Marcos Jacques Barbosa Tatiane Alfonso de Araujo Magno Aparecido Gonalves Trindade Valdir Souza Ferreira 《Microchemical Journal》2011,98(2):297-302
In this paper we present a new electroanalytical method for determination of ceftiofur based on the hydrolysis of this antibiotic in 0.04 mol L−1 Britton–Robinson buffer at pH 10 and 60 °C for 60 min (reduction peak at − 0.70 V). Conditions were optimized for complete hydrolysis and quantitative determination of ceftiofur in milk. The method can be successfully used for determination of the antibiotic directly from samples of fluid milk and powder milk spiked to concentrations of 6.0 × 10−8, 8.0 × 10−8, and 10 × 10−8 mol L−1, respectively. Recovery test ranged from 98.28% to 100.83%. The limits of detection and quantification were 3.73 × 10−10 and 1.24 × 10−9 mol L−1, respectively. The method has the advantage of eliminating interference from proteins present in the sample, thus obviating the need for exhaustive extraction, which often renders other procedures unfeasible in terms of time and reagent cost. In addition, waste generation was found to be lower than in other methods. 相似文献
25.
Jayasundara DR Cullen RJ Soldi L Colavita PE 《Langmuir : the ACS journal of surfaces and colloids》2011,27(21):13029-13036
Self-assembled organic layers are an important tool for modifying surfaces in a range of applications in materials science. Covalent modification of metal surfaces with aryldiazonium cations has attracted much attention primarily because this reaction offers a route for spontaneously grafting a variety of aromatic moieties from solution with high yield. We have investigated the kinetics of this process by performing real-time, in situ nanogravimetric measurements. The spontaneous grafting of 4-nitrobenzene diazonium salts onto gold electrodes was studied via quartz crystal microbalance (QCM) from aqueous solutions of the salt at varying concentrations. The concentration dependence of the grafting rate within the first 10 min is best modeled by assuming a reversible adsorption process with free energy comparable to that reported for arylthiols self-assembled on gold. Multilayer formation was observed after extended grafting times and was found to be favored by increasing bulk concentrations of the diazonium salt. Modified gold surfaces were characterized ex situ with cyclic voltammetry, infrared reflection absorbance spectroscopy, and X-ray photoemission spectroscopy. Based on the experimentally determined free energy of adsorption and on the observed grafting rates, we discuss a proposed mechanism for aryldiazonium chemisorption. 相似文献
26.
Maximiliano A. Sortino Valdir Cechinel Filho Susana A. Zacchino 《Tetrahedron: Asymmetry》2009,20(10):1106-1108
The CC double bond of non-substituted and substituted maleimides were hydrogenated to the corresponding succinimides by fungal strains. 2- and 2,3-methylated-phenyl-maleimides were enantioselectively reduced to (R)-N-phenyl-3-methylsuccinimide and to trans-(R,R)-N-phenyl-2,3-dimethylsuccinimide respectively by Aspergillus niger, A. flavus and A. fumigatus (conversion 96 to 99%), Fusarium graminearum and Penicillium sp (conversion: 37 and 39%), with 99% ee. 相似文献
27.
Juliana M. OliveiraJuliano C. R. Freitas João Valdir ComassetoPaulo Henrique Menezes 《Tetrahedron》2011,67(16):3003-3009
A new approach for the synthesis of α,β-unsaturated δ-lactones, a unit present in many natural products with interesting biological activities is described. The approach was based on the use of a vinyl telluride, and it is complementary to the methods using ring-closing metathesis. The sequence was performed in good overall yield with retention of the Z-double bond geometry. 相似文献
28.
Suellen Cadorin Fernandes Iolanda Cruz Vieira Antonio Marcos Jacques Barbosa Valdir Souza Ferreira 《Electroanalysis》2011,23(7):1623-1630
A sol–gel derived carbon ceramic biosensor was used for methomyl determination in vegetable extract samples based on the immobilization of laccase from Aspergillus oryzae. Esculetin was chosen as the substrate for laccase in order to measure inhibition by this pesticide. The analytical curve was linear for methomyl concentrations of 0.5 to 12.2 µM with a detection limit of 0.2 µM. The lifetime of the proposed biosensor was 60 days and the recovery from vegetable extract samples ranged from 98.0 to 104.2 %. The results using the proposed method are in agreement with those using HPLC at the 95 % confidence level. 相似文献
29.
M. J. Blandamer P. M. Cullis L. G. Soldi K. Chowdoji Rao M. C. S. Subha 《Journal of Thermal Analysis and Calorimetry》1996,46(6):1583-1588
In a titration calorimetric study an aqueous solution held in a syringe and containing hexadecyltrimethylammonium bromide (CTAB; 15.4×10–3 mol dm–3) is injected in aliquots (5×l0–3 dm3) into a sample cell containing initially water. Analysis of the data shows that thecmc equals 0.97×l0–3 dm–3 and the enthalpy of micelle formation equals –10.3 kJ mol–1. When the solution in the syringe is replaced by a mixed surfactant solution, CTAB+dodecyltrimethylammonium bromide, at the same total concentration of surfactant, thecmc of CTAB decreases gradually with increasing mole fraction of DOTAB but the enthalpy of CTAB micelle formation is hardly affected. We conclude, therefore, that incorporation of DOTAB monomers into the CTAB micelles stabilizes entropically the CTAB micelles.We thank EPSRC for their support; the Commonwealth Scholarship Commission for an award to MCSS and the Royal Society for a grant awarded to PMC for the purchase of the Titration Microcalorimeter. 相似文献
30.
Juliano Carvalho Cardoso Bruna Milca Lenzi Armondes Tatiane Alfonso de Araújo Jorge Luiz Raposo Jr. Nilva R Poppi Valdir Souza Ferreira 《Microchemical Journal》2007,85(2):301-307
The voltammetric behavior of 4-methylbenzelidene camphor (MBC) was studied by square wave voltammetry (SWV) using mercury electrode. The experimental condition that provided the highest peak current with the best reduction signal definition of MBC was found in Britton-Robinson buffer and cationic surfactants, cetyltrimethylammoniun bromide (CTABr). A single peak of MBC reduction was observed at − 1.21 V versus Ag/AgCl. The developed methodology was applied for determination of MBC in commercial sunscreen SPF 15, 20 and 30 and for the simultaneous determination when other protection agents were associated, such as benzophenone-3 (BENZO) and octyl methoxycinammate (OMC). Both methodologies had shown good determination values for the analyzed samples. The calculated detection limit was 2.99 × 10− 9 mol L− 1 and the quantification limit was 9.98 × 10− 9 mol L− 1. 相似文献