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排序方式: 共有114条查询结果,搜索用时 953 毫秒
61.
Victor Sadanory Takekawa Letícia Aparecida Marques Ethan Strubinger Thiago Pinotti Segato Stanislau Bogusz Junior Laís Canniatti Brazaca Emanuel Carrilho 《Electrophoresis》2021,42(16):1560-1569
Electrochemical techniques are commonly applied to micro total analysis system (μTAS) devices mainly due to its high sensitivity and miniaturization capacity. Among many electrochemical techniques, capacitively coupled contactless conductivity detection (C4D) stands out for not requiring direct electrode-solution contact, avoiding several problems such as electrolysis, bubble formation, and metal degradation. Furthermore, the instrumentation required for C4D measurements is compact, low cost, and easy to use, allowing in situ measurements to be performed even by nonspecialized personal. Contrarily, the production of metallic electrodes and microchannels adequate for C4D measurements commonly requires specialized facilities and workers, increasing the costs of applying these methods. We propose alternatives to batch manufacture metallic electrodes and polymeric microchannels for C4D analysis using more straightforward equipment and lower-cost materials. Three devices with different dielectric layer compositions and electrode sizes were tested and compared regarding their analytical performance. The constructed platforms have shown a reduction of more than 64% in cost when compared to traditional techniques and displayed good linearity (R2 ≥ 0.994), reproducibility (RSD ≤ 4.07%, n = 3), and limits of detection (≤0.26 mmol/L) when measuring standard NaCl samples. Therefore, the proposed methods were successfully validated and are available for further C4D applications such as diagnosis of dry-eye syndrome. 相似文献
62.
Letícia F. da Silva Celito C. Guerra Alana Foresti Ana M. Bergold 《Chemical Papers》2017,71(3):661-672
Quantification of bioactive phenols, like stilbenes and flavonols (SaF), has been conducted to evaluate the nutraceutical potential of red wines. However, there is still a lack of full validated, fast and accessible liquid chromatography methods offering high selectivity and a simple procedure. We present here the use of a high-resolution mass spectrometer to evaluate the selectivity of a feasible and traditional liquid chromatography technique (HPLC–DAD) to analyze markers of aglycone SaF in red wines. The SaF compounds were tested: trans-resveratrol, trans-ε-viniferin, quercetin, myricetin, and kaempferol, as well as trans-cinnamic acid, one of their precursors. System suitability and validation tests were employed for the selected conditions (octylsilane column, methanol mobile phase, and gradient elution). The validation process ensured the HPLC–DAD method was selective, linear, sensitive, precise, accurate and robust. The method was then applied to red wine samples from the Campanha Gaúcha region, Southern Brazil. The real samples contained different SaF levels, showing that the method is applicable to routine use. Furthermore, this was the first SaF characterization of red wines from the Campanha Gaúcha, contributing to regional and product development. 相似文献
63.
Determination of tetrakis(hydroxymethyl)phosphonium sulfate in commercial formulations and cooling water by capillary electrophoresis with contactless conductivity detection 下载免费PDF全文
Thaís Tamye Marques Letícia Sayuri Shiroma Dosil Pereira de Jesus 《Journal of separation science》2015,38(5):852-857
A novel capillary electrophoresis method using capacitively coupled contactless conductivity detection is proposed for the determination of the biocide tetrakis(hydroxymethyl)phosphonium sulfate. The feasibility of the electrophoretic separation of this biocide was attributed to the formation of an anionic complex between the biocide and borate ions in the background electrolyte. Evidence of this complex formation was provided by 11B NMR spectroscopy. A linear relationship (R2 = 0.9990) between the peak area of the complex and the biocide concentration (50–900 μmol/L) was found. The limit of detection and limit of quantification were 15.0 and 50.1 μmol/L, respectively. The proposed method was applied to the determination of tetrakis(hydroxymethyl)phosphonium sulfate in commercial formulations, and the results were in good agreement with those obtained by the standard iodometric titration method. The method was also evaluated for the analysis of tap water and cooling water samples treated with the biocide. The results of the recovery tests at three concentration levels (300, 400, and 600 μmol/L) varied from 75 to 99%, with a relative standard deviation no higher than 9%. 相似文献
64.
Laís E. Scheeren Daniele R. Nogueira-Librelotto Joana R. Fernandes Letícia B. Macedo Ana Isa P. Marcolino M. Pilar Vinardell 《Analytical letters》2018,51(10):1445-1463
Analytical methods by reversed-phase high-performance liquid chromatography (HPLC) and ultraviolet–visible spectrophotometry were developed and validated to determine doxorubicin in pH-sensitive chitosan nanoparticles. Chromatographic separation was performed on a reversed-phase C18 column, with ultraviolet detection at 254?nm and a mobile phase composed by 90% (v/v) acetonitrile in water and water pH 3.0 (33:67, v/v). The spectrophotometry method had the wavelength set at 480?nm and pH 3.0 water was used as a diluent. Calibration curves were linear from 1 to 30?µg/?mL (r?>?0.9995) and the specificity was demonstrated by verifying the absence of interferences from nanoparticle components. The values of accuracy and precision were within the acceptable limits, and robustness studies were performed by a two-level full factorial design. The validated methods were further tested to assess doxorubicin content in six different batches of pH-sensitive chitosan nanoparticles. The comparative analyses showed nonsignificant differences (p?>?0.05). Likewise, the HPLC method was successfully applied to determine the drug encapsulation efficiency as well as to measure doxorubicin during in vitro release assays and degradation kinetic studies under ultraviolet light C irradiation. Both methods fulfilled all validation parameters and were shown to be suitable for the characterization of doxorubicin-loaded pH-sensitive chitosan nanoparticles, without interferences from nanoparticle matrix. 相似文献
65.
A. T. Soldatenkov T. P. Khristoforova A. W. Temesgen B. N. Anissimov B. B Averkiev L. N. Kuleshova V. N. Khrustalev M. Yu. Antipin 《Chemistry of Heterocyclic Compounds》2001,37(6):715-722
On treating 4-aryl substituted 1-methyl-1,2,3,6-tetrahydropyridines with potassium permanganate in the presence of arylamines a previously unknown intermolecular oxidative imination reaction occurs leading to the formation of 2-(arylimino)-1,2,5,6-tetrahydropyridines. The molecular structure of 1-methyl-2-(4-nitrophenylimino)-4-phenyl-1,2,5,6-tetrahydropyridine was studied by X-ray analysis and it was shown that the hydropyridine ring of the molecule has a sofa conformation and its amidine fragment is in the E-configuration. 相似文献
66.
67.
Jéssica Santos Stefano Luiz Otávio Orzari Habdias Araujo Silva-Neto Vanessa Neiva de Ataíde Letícia Francine Mendes Wendell Karlos Tomazelli Coltro Thiago Regis Longo Cesar Paixão Bruno Campos Janegitz 《Current Opinion in Electrochemistry》2022
Electrochemistry combined with economical and sustainable platforms (such as paper) provides portable, affordable, robust, and user-friendly devices. In general, techniques, such as photolithography and sputtering, are excellent alternatives for producing these platforms. However, owing to the requirement of expensive and sophisticated instrumentation, as well as cleanroom facilities, these techniques have limited access. Thus, the search for easy to use and produce approaches have been reported, using consumables, including adhesives, carbon ink, graphite, pencil, office paper, paperboard, among others. In this sense, in this mini-review, we discuss various strategies explored to fabricate low-cost electrochemical sensors, including its main applications. Different manufacturing methods, such as screen and stencil printing, laser-scribing, and pencil drawing, will be discussed here, emphasizing the performance of the obtained devices, in addition to their advantages and disadvantages. 相似文献
68.
Graminha AE Rodrigues C Batista AA Teixeira LR Fagundes ES Beraldo H 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2008,69(4):1073-1076
Reaction of [RuCl(3)(dppb)H(2)O] (dppb=1,4 bis(diphenylphospine)butane) with 2-benzoylpyridine thiosemicarbazone (H2Bz4DH) and its N(4)-methyl (H2Bz4M) and N(4)-phehyl (H2Bz4Ph) derivatives gave [RuCl(dppb)(H2Bz4DH)]Cl (1), [RuCl(dppb)(H2Bz4M)]Cl (2) and [RuCl(dppb)(H2Bz4Ph)]Cl (3). The cytotoxic activity of the studied compounds was tested against the MCF-7, TK-10 and UACC-62 human tumor cell lines. The precursor [RuCl(3)(dppb)H(2)O] exhibits cytocidal activity against the tree cell lines. H2BzDH, H2Bz4M, and [RuCl(dppb)(H2Bz4M)]Cl (2) show a selective cytocidal effect against the UACC-62 cell line which makes them the most promising compounds. 相似文献
69.
70.
Tereza Auxiliadora Nascimento Ribeiro Letícia Ricette da Silva Paulo Teixeira de Sousa Júnior Rosane Nora Castro Mário Geraldo de Carvalho 《Helvetica chimica acta》2012,95(6):935-939
A new cyclopeptide, cyclozanthoxylane A ( 1 ), the lignans cis‐ and trans‐methylpluviatolide, the flavonoid isoquercitrin, along with a mixture of benzoic and cinnamic acid derivatives, were isolated from the MeOH extract of the leaves of Zanthoxylum rigidum (Rutaceae). The structures of the compounds were determined on the basis of 1D‐ and 2D‐NMR, and MS analysis. It is the first time that a natural cyclic peptide has been isolated from the genus Zanthoxylum. 相似文献