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901.
Md. Nur Alam Miro Antal Alvaro Tejado Theo G. M. van de Ven 《Cellulose (London, England)》2012,19(2):517-522
Chemical reactions in charged nanopores, such as present in cellulose fibers, can be accelerated by adding an inert salt,
that does not participate in the reaction. Due to a Donnan-like equilibrium between ions inside and outside the pores, the
concentration of co-ions in the nanopores (having a charge of the same sign as that of the pore wall), is lower than the concentration
in the bulk. The co-ion concentration in pores can be increased by adding an inert salt, which shifts the Donnan equilibrium.
The increased concentration of reactants in pores results in faster reaction kinetics. Reactions of cellulose with periodate
confirm these predictions. 相似文献
902.
Fernanda M. de Oliveira Affonso C. Gonçalves Jr Douglas C. Dragunski Mariana G. Segatelli 《International journal of environmental analytical chemistry》2013,93(10):1061-1071
The present paper describes the feasibility of on-line preconcentration of nickel ions from aqueous medium on Ni(II)-imprinted cross-linked poly(methacrylic acid) (IIP) synthesised through a double-imprinting method and their subsequent determination by FAAS. The proposed method consisted in loading the sample (20.0 mL, pH 7.25) through a mini-column packed with 50 mg of the IIP for 2 min. The elution step was performed with 1.0 mol L?1 HNO3 at a flow rate of 7.0 mL min?1. The following parameters were obtained: quantification limit (QL) – 3.74 µg L?1, preconcentration factor (PF) – 36, consumption index (CI) – 0.55 mL, concentration efficiency (CE) – 18 min?1, and sample throughput – 25 h?1. The precision of the procedure assessed in terms of repeatability for ten determinations was 5.6% and 2.5% for respective concentrations of 5.0 and 110.0 µg L?1. Moreover, the analytical curve was obtained in the range of 5.0–180.0 µg L?1 (r = 0.9973), and a 1.64-fold increase in the method sensitivity was observed when compared with the analytical curve constructed for the NIP (non-imprinted polymer), thus suggesting a synergistic effect of the Ni(II) ions and CTAB on the adsorption properties of the IIP. The practical application of the adsorbent was evaluated from an analysis of tap, mineral, lake and river water. Considering the results of addition and recovery experiments (90.2–100 %), the efficiency of this adsorbent can be ensured for the interference-free preconcentration of the Ni(II) ions. 相似文献
903.
D. Shooter S. J. de Mora A. Grout D. J. Wylie He Zhi-yun 《International journal of environmental analytical chemistry》2013,93(4):239-249
Abstract A technique was developed using sparging and pre-concentration onto a Tenax trap at ambient temperature allowing field measurements to be made of reduced sulfur gases in Antarctic marine and glacial melt waters. Following thermal desorption, gases were determined by gas chromatography using a flame photometric detector. Detection limits in ng 1?1 were: H2S 50, OCS 8, SO2 160, CH3SH 6, CH3SCH3 20 and CS2 2. Storage of melt water samples for more than 24 hours resulted in concentration changes of the reduced sulfur gases present. While the Antarctic environment imposed limitations on the analytical method, an investigation of various pond and marine waters was undertaken. 相似文献
904.
S. Sarmento P. Simeão Carvalho M. R. Chaves F. Pinto H. T. Nguyen 《Liquid crystals》2013,40(12):1839-1845
The SmC* phase of (R)-4-(1-methylheptyloxycarbonyl)phenyl 4'-(4-decyloxy-3-fluorobenzoyloxy)-benzoate, 10FHBBBM7*, shows an anomalous thermal hysteresis that is reflected in the values of the measured dielectric constant. When the cooling-heating cycle is repeated, a memory effect occurs. In this work, we present a detailed study and a tentative interpretation of this unusual effect. 相似文献
905.
Ultra‐high pressure LC for astaxanthin determination in shrimp by‐products and active food packaging
A. Sanches‐Silva T. Ribeiro T. G. Albuquerque P. Paseiro R. Sendón A. Bernaldo de Quirós J. López‐Cervantes D. I. Sánchez‐Machado H. Soto Valdez I. Angulo G. P. Aurrekoetxea H. S. Costa 《Biomedical chromatography : BMC》2013,27(6):757-764
Nowadays, there is increasing interest in natural antioxidants from food by‐products. Astaxanthin is a potent antioxidant and one of the major carotenoids in crustaceans and salmonids. An ultra‐high pressure liquid chromatographic method was developed and validated for the determination of astaxanthin in shrimp by‐products, and its migration from new packaging materials to food simulants was also studied. The method uses an UPLC® BEH guard‐column (2.1 × 5 mm, 1.7 µm particle size) and an UPLC® BEH analytical column (2.1 × 50 mm, 1.7 µm particle size). Chromatographic separation was achieved using a programmed gradient mobile phase consisting of (A) acetonitrile–methanol (containing 0.05 m ammonium acetate)–dichloromethane (75:20:5, v/v/v) and (B) ultrapure water. This method was evaluated with respect to validation parameters such as linearity, precision, limit of detection, limit of quantification and recovery. Low‐density polyethylene films were prepared with different amounts of the lipid fraction of fermented shrimp waste by extrusion, and migration was evaluated into food simulants (isooctane and ethanol 95%, v/v). Migration was not detected under the tested conditions. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
906.
Fernanda Cortez Lopes Deise Michele Tichota Jamile Queiroz Pereira Jéferson Segalin Alessandro de Oliveira Rios Adriano Brandelli 《Applied biochemistry and biotechnology》2013,171(3):616-625
The search for new sources of natural pigments has increased, mainly because of the toxic effects caused by synthetic dyes used in food, pharmaceutical, textile, and cosmetic industries. Fungi provide a readily available alternative source of natural pigments. In this context, the fungi Penicillium chrysogenum IFL1 and IFL2, Fusarium graminearum IFL3, Monascus purpureus NRRL 1992, and Penicillium vasconiae IFL4 were selected as pigments producers. The fungal identification was performed using ITS and part of the β-tubulin gene sequencing. Almost all fungi were able to grow and produce water-soluble pigments on agro-industrial residues, with the exception of P. vasconiae that produced pigments only on potato dextrose broth. The production of yellow pigments was predominant and the two strains of P. chrysogenum were the largest producers. In addition, the production of pigments and mycotoxins were evaluated in potato dextrose agar using TOF-MS and TOF-MS/MS. Metabolites as roquefortine C, chrysogine were found in both extracts of P. chrysogenum, as well fusarenone X, diacetoxyscirpenol, and neosolaniol in F. graminearum extract. In the M. purpureus extract, the pigments monascorubrin, rubropunctatin, and the mycotoxin citrinin were found. The crude filtrates have potential to be used in the textile industry; nevertheless, additional pigment purification is required for food and pharmaceutical applications. 相似文献
907.
Upon prolonged alkali reduction in ethereal solvents 1,3,5-triphenylbenzene (Tpb), 2,4,6-triphenyl-sym-triazine (Tpt) and 2,4,6-tritolyl-sym-triazine (Ttt) can be reduced to their dinegative ions. Dissolved in rigid solvent matrices these ions produce E.S.R. spectra which are characteristic for randomly oriented triplet systems. Hückel and SCF MO calculations indicate that these dianions have a twofold degenerate lowest anti-bonding level. Although the ions Tpb2- and Tpt2- are iso-electronic their magnetic properties prove to be strikingly different. While Tpb2- has a triplet ground state irrespective of solvent, counter ion and temperature, Tpt2- (and also Ttt2-) has a singlet ground state with a thermally accessible triplet state in solvents with poorly solvating properties and has a triplet ground state in better solvating media. Furthermore, the zero field splitting parameters D and E of the lowest triplet states of Tpt2- and Ttt2- are markedly different from those obtained from Tpb2-. The former show a considerably larger D value than Tpb2- and, in contrast to Tpb2-, the ions Tpt2- and Ttt2- have a non-zero E value in poorly solvating solvents, pointing to a non-trigonal spin distribution of the triplet systems. An explanation of the observed differences is given in terms of current MO theories. The results suggest that in the case of Tpt2- and Ttt2- the association with the counter ions even in strongly solvating solvents is very strong. 相似文献
908.
Eigenstates of a particle in a localized and unconfined harmonic potential well are investigated. Effects due to the variation of the potential parameters as well as certain results from asymptotic expansions are discussed. 相似文献
909.
910.
Ariana Borges Souza Monique Rodrigues Moreira Carly Henrique Gambeta Borges Marília Rodrigues Simão Jairo Kenupp Bastos João Paulo Barreto de Sousa Sérgio Ricardo Ambrosio Rodrigo Cassio Sola Veneziani 《Biomedical chromatography : BMC》2013,27(3):280-283
The Copaifera species (Leguminoseae) are popularly known as ‘copaíba’ or ‘copaíva’ and are grown in the states of Amazonas, Pará and Ceará in northern Brazil. The oleoresins obtained from these species have been extensively used owing to their pharmacological potential and their application in cosmetic and pharmaceutical preparations. In the present study, the development and validation of a novel, rapid and efficient RP‐HPLC methodology for the analysis of the diterpene (?)‐copalic acid (CA), pointed out as the only chemical marker of the Copaifera genus, are described. The regression equation (Y = 26,707x ? 29,498) was obtained with good linearity (r2 = 0.9993) and the limits of quantification and detection were 9.182 and 3.032 µg/mL, respectively. The precision and the accuracy of the method were adequate (lower than 4%). Finally, the validation parameters evaluated were satisfactorily met, so the developed method represents a suitable tool for application in the quality control of such natural products. Further studies aiming to develop analytical methodologies for each Copaifera species using a more representative number of chemical markers should be performed. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献