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91.
Diego A. Blanco-Martínez Liliana Giraldo Juan C. Moreno-Piraján 《Journal of Thermal Analysis and Calorimetry》2009,96(3):853-857
The immersion enthalpies of modified activated carbons were determined, with commercial CarbochemTM–PS230 (CAG) as the initial activated carbon, which was modified by: chemical treatment with HNO3 7 mol L−1 (CAO) and thermal treatment under flow of H2 (CAR) in function of the adsorbed quantity of monohydroxilated phenols, catechol, resorcinol and hydroquinone at a pH of
7 in aqueous dissolutions in order to characterize the solid–solution interaction and evaluate the influence of the chemical
characteristics of the activated carbon in the phenol adsorption. The results show a variation in the immersion enthalpy in
function of the adsorbed quantity of phenol and the initial dissolution concentration; which shows that the intensity of the
interaction changes in function of the composition of the liquid phase. The immersion enthalpies present the following arrangement:
catechol > resorcinol > hydroquinone, with a −ΔHinm of 35.7; 30.8 and 24.6 Jg−1, respectively, at a pH of 7 for a 100 mg L−1 phenol monohydroxilated solution. 相似文献
92.
A novel method of photoresist-free micropatterning coupled with electroless gold plating is described for the fabrication of an integrated gold electrode for electrochemical detection (ED) on a polycarbonate (PC) electrophoresis microchip. The microelectrode layout was photochemically patterned onto the surface of a PC plate by selective exposure of the surface coated without photoresist to 254 nm UV light through a chromium/quartz photomask. Thus, the PC plate was selectively sensitized by formation of reactive chemical moieties in the exposed areas. After a series of wet chemistry reactions, the UV-exposed area was activated with a layer of gold nanoparticles that served as a seed to catalyze the electroless plating. The gold microelectrode was then selectively plated onto the activated area by using an electroless gold plating bath. Nonselective gold deposition on the unwanted areas was eliminated by sonication of the activated PC plate in a KSCN solution before electroless plating, and the adhesion of the plated electrodes to the PC surface was strengthened with thermal annealing. Compared with the previously reported electroless plating technique for fabrication of microelectrodes on a microchip, the present method avoided the use of a membrane stencil with an electrode pattern to restrict the area to be wet-chemically sensitized. The CE with integrated ED (CE-ED) microchip was assembled by thermal bonding an electrode-plated PC cover plate to a microchannel-embossed PC substrate. The novel method allows one to fabricate low-cost, electrode-integrated, complete PC CE-ED chips with no need of a clean room. The fabricated CE-ED microchip was demonstrated for separation and detection of model analytes, including dopamine (DA) and catechol (CA). Detection limits of 0.65 and 1.03 microM were achieved for DA and CA, respectively, and theoretical plate number of 1.4 x 10(4) was obtained for DA. The plated gold electrode can be used for about 4 h, bearing usually more than 100 runs before complete failure. 相似文献
93.
Determination of phenol, resorcinol and hydroquinone in air samples by synchronous fluorescence using partial least-squares (PLS) 总被引:4,自引:0,他引:4
Pistonesi MF Di Nezio MS Centurión ME Palomeque ME Lista AG Fernández Band BS 《Talanta》2006,69(5):1265-1268
The determination of phenolic compounds is of great importance owing to their high toxicity. Some of them are present in tobacco smoke and it is important for their monitoring in air of closed room. A simple, rapid and sensitive method was developed for simultaneous determination of hydroquinone, resorcinol and phenol in this kind of samples. Synchronous fluorescence technique was used and the data were processed by using the partial least-squares (PLS) chemometric algorithm. The concentrations for experimental calibration matrix were varied between 0.02 and 0.2 mg L−1 for hydroquinone, between 0.05 and 0.6 mg L−1 for resorcinol and between 0.05 and 0.4 mg L−1 for phenol in accordance with the national legislation. The cross-validation method was used to select the number of factors. To check the accuracy of the proposed method a recovery study on real samples was carried out. 相似文献
94.
The bismuth film electrode (BiFE), in combination with anodic stripping voltammetry, offers convenient measurement of low concentrations of tin. The procedure involves simultaneous in situ formation of the bismuth film electrode on a glassy carbon substrate electrode, together with electrochemical deposition of tin, in a non-deaerated model solution containing bismuth ions, catechol as complexing agent and the metal analyte, followed by an anodic stripping scan. The BiFE is characterized by an attractive electroanalytical performance, with two distinct voltammetric stripping signals corresponding to tin, accompanied with low background contributions. Several experimental parameters were optimized, such as concentration of bismuth ions and catechol, deposition potential, deposition time and pH of the model solution. In addition, a critical comparison is given with bare glassy carbon and mercury film electrodes, revealing the superior characteristics of BiFE for measurement of tin. BiFE exhibited highly linear behavior in the examined concentration range from 1 to 100 μg L−1 of tin (R2 = 0.997), an LoD of 0.26 μg L−1 tin, and good reproducibility with a calculated R.S.D. of 7.3% for 10 μg L−1 tin (n = 10). As an example, the practical applicability of BiFE was tested with the measurement of tin in a real sample of seawater. 相似文献
95.
This work examines in deep the analytical performance of an example of “first-generation” microdevices: capillary electrophoresis microchip (CE) with end-channel electrochemical detection (ED). A hydroquinone and arbutin separation strategically chosen as route involving pharmaceutical-clinical testing, public safety and food control scenes was carried out. The reproducibility of the unpinched electrokinetic protocol was carefully studied and the technical possibility of working indiscriminately and/or sequentially with both simple cross-injectors was also demonstrated using a real sample (R.S.D.'s less than 7%). The robustness of the injection protocol allowed checking the state of the microchip/detector coupling and following the extraction efficiency of the analyte from real sample. Separation variables such as pH, ionic strength and, separation voltage were also carefully assayed and optimized. Analyte screening was performed using borate buffer (pH 9, 60 mM) in less than 180 s in the samples studied improving dramatically the analysis times used for the same analytes on a conventional scale (15 min), with good precision (R.S.D.'s ranging 5-10%), accuracy (recoveries ranging 90-110%) and acceptable resolution (Rs ≥ 1.0).In addition, the excellent analytical performance of the overall analytical method indicated the quality of the whole analytical microsystem and allowed to introduce the definition of robustness for methodologies developed into the “lab-on-a-chip” scene. 相似文献
96.
The analytical performance of lab-on-valve (LOV) system using irreversible biamperometry for the determination of catechol was evaluated. By integrating miniaturized electrochemical flow cell (EFC) designed and processed which is furnished with two identical polarized platinum electrodes, into the LOV unit, the lab-on-valve system combines sampling with analysis, realizing automated on-line analysis for catechol in a closed system. The biamperometric detection system was established to record the relationship between oxidation current and time by coupling the irreversible oxidation of catechol at one pretreated platinum electrode with the irreversible reduction of platinum oxide at the other pretreated platinum electrode. Factors influencing the analytical performance were optimized, including the potential difference (ΔE), buffer solution and pH, and flow variables in the LOV. A linear calibration curve was obtained within the range of 1.0 × 10−6-5.0 × 10−4 mol L−1 of catechol with the detection limit (3σ) of 5.09 × 10−7 mol L−1. The relative standard deviation (R.S.D.) was 2.39% for 11 successive determinations of 1 × 10−5 mol L−1 catechol and the sample throughput was 35 h−1. Moreover, this proposed method was applied to the analysis of catechol in beer sample, which was testified by high-performance liquid chromatography (HPLC). 相似文献
97.
Seijiro Hosokawa 《Tetrahedron letters》2010,51(42):5532-5536
The first total synthesis of epi-cochlioquinone A has been achieved in a highly convergent manner via [3+3] cycloaddition of catechol 2 and oxadecalin 3 as the key reaction. The synthesis of the catechol segment, possessing the side chain with multi stereogenic centers, features the asymmetric vinylogous Mukaiyama aldol reaction, the stereoselective conjugate addition to the nitroalkene, the stereospecific nitro-Dieckmann condensation, and the transformation of 6-nitrocyclohex-2-enone into catechol 2, using two new methodologies, such as (i) the hydrogen-transfer reaction to o-aminophenol and the subsequent auto-redox-catalysis to catechol and (ii) the direct oxidation of 6-nitrocyclohex-2-enone to o-quinone and the subsequent reduction. The oxadecalin segment was synthesized from a glycosyl cyanide by the [3+3] annulation with a ketone and an acetoacetate. These segments were connected by the [3+3] cyclization, and the resulting tetracyclic compound was subjected to a specific oxidation of the protected hydroquinone to provide epi-cochlioquinone A. 相似文献
98.
Polystyrene-supported hydroquinone (PS-HQ) is presented as an in situ polymeric cocatalyst to replace polystyrenesupported benzoquinone (PS-BQ) in the PdCl2-catalyzed acetalization of methyl acrylate with methanol in supercritical carbon dioxide (scCO2) under oxygen atmosphere. Due to deletion of H2O2 oxidation step, PS-HQ is more convenient and relatively inexpensive. 相似文献
99.
NADH在邻苯二酚紫修饰石墨电极上的电催化氧化 总被引:2,自引:0,他引:2
以吸附在石墨电极上的邻苯二酚紫作为电子传递媒介体构成修饰电极。在-0.40-+0.60V电位区间内,吸附态的邻苯二酚紫表现出相当可逆的氧化,还原行为,电极反应为单电子过程并有1个质子参加。在pH为7.0的磷酸盐缓冲溶液中,其式量电位E^o'为0.10V,表观电极反应速率常数ks为5.5s^-^1。邻苯二酚紫修饰电极对还原型烟酰胺腺嘌呤二核苷酸(NADH)的电化学氧化具有明显的催化作用。可使NADH 相似文献
100.
Muhammad Saeed 《Tetrahedron letters》2005,46(26):4449-4451
The human carcinogen diethylstilbestrol (DES) is metabolized into 3′-hydroxydiethylstilbestrol (3′-OH-DES) (1). Chemical oxidation of the catechol metabolites with silver oxide in CH2Cl2 affords a novel spiro-quinone (3) in quantitative yield. Protection of the phenolic OH group followed by oxidation gives 4″-OCH3-DES-3′,4′-Q (5) in excellent yield. 相似文献