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51.
Sérgio L. C. Ferreira Marcus L. S. F. Bandeira Valfredo A. Lemos Hilda C. dos Santos A. C. Spinola Costa Djane S. de Jesus 《Analytical and bioanalytical chemistry》1997,357(8):1174-1178
A simple and very sensitive method has been developed for the determination of ascorbic acid based on the oxidation of ascorbic
acid to dehydroascorbic acid by iron(III), followed by a complexation of iron(II) with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol(Br-PADAP).
The iron(II) complex is formed immediately, with absorption maxima at 560 and 748 nm and a molar absorptivity of 1.31 × 105 l mole–1cm–1 and 5.69 × 104 l mole–1cm–1, respectively. The ascorbic acid determination is possible with a linear range up to 2.4 μg ml–1, a calibration sensitivity of 0.744 ml μg–1 at 560 nm and 0.323 ml μg–1 at 748 nm, and a detection limit of 15 ng ml–1 and 44 ng ml–1, respectively. The procedure was used for the ascorbic acid determination in several fruit juices and pharmaceutical formulations.
The results demonstrated a good precision (R.S.D. < 1%) and are in agreement with those obtained with others methods. The
Br-PADAP method proposed is six times more sensitive than the method using the iron(II)-1,10-phenanthroline system.
Received: 7 May 1996 / Revised: 1 July 1996 / Accepted: 8 August 1996 相似文献
52.
Denilson S.S. dos Santos Alete P. Teixeira José T.P. Barbosa Sérgio L.C. Ferreira Maria das Graças A. Korn Leonardo S.G. Teixeira 《Spectrochimica Acta Part B: Atomic Spectroscopy》2007
In this work, the use of cetyltrimethylammonium bromide as surfactant for the preparation of oil-in-water emulsions for the determination of Cu and Cr in gasoline by electrothermal atomic absorption spectrometry (ET AAS) was evaluated. The surfactant amount was tested in the range of 25 to 300 mg, added to 2 ml of gasoline, and completed to 10 mL with 0.1% (v/v) nitric acid solution. 150 mg of surfactant was found optimum, and a sonication time of 10 min sufficient to form an oil-in-water emulsion that was stable for several hours. The ET AAS temperature program was established based on pyrolysis and atomization curves. The pyrolysis temperatures were set at 700 and 1300 °C for Cu and Cr, respectively and the selected atomization temperatures were 2400 and 2500 °C. The time and temperature of the drying stage and the atomization time were experimentally tested to provide optimum conditions. The limits of detection were found to be 5 μg L− 1 and 1.5 μg L− 1 for Cu and Cr, respectively in the original gasoline samples. The relative standard deviation (RSD) ranged from 4 to 9% in oil-in-water emulsions spiked with 5 μg L− 1 and 15 μg L− 1 of each metal, respectively. Recoveries varied from 90 to 98%. The accuracy of the proposed method was tested by an alternate procedure using complete evaporation of the gasoline sample. The method was adequate for the determination of Cu and Cr in gasoline samples collected from different gas stations in Salvador, BA, Brazil. 相似文献
53.
AkshatKumar Nigam Robert Pollice Mario Krenn Gabriel dos Passos Gomes Aln Aspuru-Guzik 《Chemical science》2021,12(20):7079
Inverse design allows the generation of molecules with desirable physical quantities using property optimization. Deep generative models have recently been applied to tackle inverse design, as they possess the ability to optimize molecular properties directly through structure modification using gradients. While the ability to carry out direct property optimizations is promising, the use of generative deep learning models to solve practical problems requires large amounts of data and is very time-consuming. In this work, we propose STONED – a simple and efficient algorithm to perform interpolation and exploration in the chemical space, comparable to deep generative models. STONED bypasses the need for large amounts of data and training times by using string modifications in the SELFIES molecular representation. First, we achieve non-trivial performance on typical benchmarks for generative models without any training. Additionally, we demonstrate applications in high-throughput virtual screening for the design of drugs, photovoltaics, and the construction of chemical paths, allowing for both property and structure-based interpolation in the chemical space. Overall, we anticipate our results to be a stepping stone for developing more sophisticated inverse design models and benchmarking tools, ultimately helping generative models achieve wider adoption.Interpolation and exploration within the chemical space for inverse design. 相似文献
54.
Alvarez-Puebla RA dos Santos DS Blanco C Echeverria JC Garrido JJ 《Journal of colloid and interface science》2005,285(1):41-49
Illite clays are known to have a strong affinity for metallic pollutants in the environment and can be applied as low-cost adsorbents for industrial waste treatment. A crucial factor in the development of such applications, however, is the understanding of the chemical, mineralogical, and colloidal properties of these clays. It is also important to understand the mechanisms involved in the surface adsorption of metals by these adsorbants. In order to study the retention of transition metals on illite clays, we have applied surface characterization techniques such as FPIA, SEM-EDX, XRD, N2 (77 K) adsorption, and FTIR. In addition to these experimental techniques, we have also employed a theoretical model that accounts for the chemistry of transition metal ions, and considers the global retention process to be the sum of several single retention processes. This model adequately fits the experimental data and allows for the speciation of metal retention on illite surfaces. Between pH values of 2.53 and 3.01 the only adsorption processes are the electrostatic sorption of [Cu(H2O)6]2+, and the surface complexation of [Cu(H2O)6]2+ and [Cu(OH)(H2O)5]+ ions. Surface complexation of [Cu(OH)(H2O)5]+ ions increases with pH, overcoming [Cu(H2O)6]2+ retention, and thus contributing to the surface precipitation of Cu(OH)2. 相似文献
55.
Daniela P. Mesquita Cristiano Leal Jorge R. Cunha Adrian Oehmen A. Luís Amaral Maria A.M. Reis Eugénio C. Ferreira 《Analytica chimica acta》2013
The present study focuses on predicting the concentration of intracellular storage polymers in enhanced biological phosphorus removal (EBPR) systems. For that purpose, quantitative image analysis techniques were developed for determining the intracellular concentrations of PHA (PHB and PHV) with Nile blue and glycogen with aniline blue staining. Partial least squares (PLS) were used to predict the standard analytical values of these polymers by the proposed methodology. Identification of the aerobic and anaerobic stages proved to be crucial for improving the assessment of PHA, PHB and PHV intracellular concentrations. Current Nile blue based methodology can be seen as a feasible starting point for further enhancement. Glycogen detection based on the developed aniline blue staining methodology combined with the image analysis data proved to be a promising technique, toward the elimination of the need for analytical off-line measurements. 相似文献
56.
E. A. Reis M. H. M. Rocha-Leão S. G. F. Leite 《Applied biochemistry and biotechnology》2013,169(4):1241-1249
As the concern towards environmental deterioration grows worldwide, new technological achievements become essential for all countries. Among the technologies with great potential of bioremediation is microencapsulation of active material. Several studies have investigated the use of controlled release of active materials as a way of biostimulation and supplying the nutrients necessary for the bioremediation process. In fact, as the use of microorganisms has a great potential in degrading crude oils, this work aims to use that technology and to associate it to produce controlled-release capsules of nitrogen, phosphorus, and potassium (N, P, and K) for bioremediation purposes. For the capsule formulation, polymers of sodium alginate, Capsul®, and the commercial fertilizer NPK from Sempre Verde Inc. were used. Crude oil was the only carbon source and mineral medium for microorganism growth. Controlled-release nutrient capsules, with 4 mm in diameter, made of 3.0 % alginate (w/v) and 4.0 % Capsul® (w/v) were produced. Those capsules were used in association with a microbial consortium, in a liquid phase bioremediation process, having degraded 43.6 % of the total hydrocarbon within 240 h, evidencing thus as a promising tool for hydrocarbon bioremediation. 相似文献
57.
In this paper we report a simple methodology for obtaining (+) trans - 1,2 - epoxylimonene (1b) in high purity (>99% HRGC) and reasonable quantity. The mixture of 1a and 1b in CH2Cl2 is stirred with 1M NaHSO3 in water. Under these conditions 1a is completely destroyed, while 1b is only partially destroyed. 相似文献
58.
dos Santos Poli Anne Karoline Hilário Rodrigo Barbosa Gama Adriana Medeiros Baldan Mauricio Ribeiro Gonçalves Emerson Sarmento 《Journal of Solid State Electrochemistry》2019,23(1):33-52
Journal of Solid State Electrochemistry - Polyaniline was electrosynthesized using three voltammetric cycles on carbon fiber felts annealed at 1400, 1600, 2000, and 2300 K. Felts and... 相似文献
59.
Tanay Chattopadhyay Cláudia Reis Paulo André António Teixeira 《Optics Communications》2012,285(9):2266-2275
A novel scheme for an all-optical clocked D flip-flop, with very low complexity, is proposed and numerically demonstrated. This new flip-flop configuration is based on a semiconductor optical amplifier — Mach–Zehnder interferometer (SOA-MZI), with a feedback loop, and presents two stable states determined by the phase shift between the two MZI arms. 相似文献
60.
Benvenuti Jaqueline Capeletti Larissa Brentano Gutterres Mariliz dos Santos João Henrique Zimnoch 《Journal of Sol-Gel Science and Technology》2018,85(2):446-457
Journal of Sol-Gel Science and Technology - This study reports the development of a functional adsorbent synthesized by the molecular imprinting method in a sol–gel matrix. The adsorption... 相似文献