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Viñas P Martínez-Castillo N Campillo N Hernández-Córdoba M 《Journal of chromatography. A》2011,1218(5):639-646
A miniaturized liquid-phase extraction procedure based on directly suspended droplet microextraction is proposed for determining different classes of polyphenols. A derivatization reaction by means of in injection-port reaction with bis(trimethylsilyl)trifluoroacetamide is carried out to convert the polar non-volatile polyphenols into volatile derivatives. The separation and detection is carried out by coupling gas chromatography with mass spectrometry in the selected ion monitoring mode. The procedure uses undecanone, a low density organic solvent, and several factors influencing the extraction, collection efficiency and derivatization reaction are optimized. Excellent linearity was obtained for the range studied (0.05-500ngmL(-1)). The limits of detection are between 0.011 and 0.13ngmL(-1), depending on the compound, and the limits of quantification between 0.037 and 0.43ngmL(-1). The sensitivity and detection limits for polyphenols using the DSDME sample pretreatment method were very low. Enrichment factors are between 413 and 578. The recoveries obtained for spiked samples are satisfactory for all the compounds. The coupled miniaturized method is applied to the sensitive determination of both cis- and trans-resveratrol isomers, piceatannol, catechin, epicatechin, quercetin and fisetin in herbal infusions, fruits, juices and functional foods. 相似文献
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Directly suspended droplet liquid–liquid–liquid microextraction (LLLME) has been used to determine residues of diclofenac
(2-[2-(2,6-dichlorophenyl) aminophenyl] ethanoic acid), in environmental water samples. In this technique a free suspended
droplet of an aqueous solvent is delivered to the top-center position of an immiscible organic solvent floating on the top
of an aqueous sample while being agitated by a stirring bar placed on the bottom of the sample cell. Recently, diclofenac
was found as an environmental contaminant in sewage, surface, ground and drinking water samples. In the present work, diclofenac
was extracted from water samples by LLLME and analysed by HPLC with UV detection at 281 nm. Factors such as organic solvent,
extraction and back extraction times, stirring rate and the pH of acceptor and donor phases were optimized. Enrichment factor
and detection limit (LOD, n = 7) were 102 and 0.1 μg L−1, respectively. The linearity ranged from 0.5 to 2,000 μg−1 with a %RSD (n = 5) of 7.2 at S/N = 3. All experiments were carried out at room temperature (22 ± 0.5 °C). 相似文献
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Shah-Jye Tzeng 《Optics Communications》2006,259(1):127-132
A directly modulated CATV/radio-on-fiber (ROF) transport system based on external light injection technique, optical single sideband (SSB) filter, and RF amplifier predistorter is proposed and demonstrated. To the best of my knowledge, it is the first time to transmit CATV and ROF signals simultaneously in a directly modulated form. Good performances of carrier-to-noise ratio (CNR), composite second order (CSO) and composite triple beat (CTB) were obtained for CATV band; and low third order intermodulation distortion to carrier ratio (IMD3/C), and bit error rate (BER) values were achieved for ROF application. 相似文献
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《Arabian Journal of Chemistry》2022,15(4):103718
The present study attempts to prepare Al-substituted α-Ni(OH)2 and Al-substituted α-Ni(OH)2 with modified interlayer anions by directly immersing pure α-Ni(OH)2 into AlCl3-containing solutions. XRD and FT-IR analysis demonstrated Al-substituted α-Ni(OH)2 can be prepared directly by soaking pure α-Ni(OH)2 into AlCl3 solution. Al-substituted α-Ni(OH)2 with S2O32? as the primary anion in the interlayer can be obtained by immersing pure α-Ni(OH)2 into AlCl3-Na2S2O3 solution. The analysis of Al content in samples demonstrated the Al content in the Al-substituted α-Ni(OH)2 was regulated by adjusting the molar ratio of pure α-Ni(OH)2 soaked in the solution and Al3+ dissolved in the solution. The Al element entered the lattice of pure α-Ni(OH)2 through a process of pure α-Ni(OH)2 dissolved followed by the precipitation of Al3+, Ni2+ and OH?. The S2O32? entered the interlayer of Al-substituted α-Ni(OH)2 through the formation process of the Al-substituted α-Ni(OH)2 or though ion exchange with the intercalated Cl?. The strongly alkaline solution soaking results demonstrated that Al-substituted α-Ni(OH)2 prepared by soaking pure α-Ni(OH)2 into AlCl3-containing solutions could preliminary get stabilized in the strongly alkaline solution. 相似文献
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This study presented a directly modulated 1550 nm NTSC AM-VSB CATV longdistance transmission system using Fabry-Perot laser diode, optical isolator, fiber Bragg grating, quarter-split-band, and wavelength-division multiplexing techniques. Good carrier-to-noise ratio ( ≥48 dB), composite second-order ( ≥64 dB), and composite triple-beat ( ≥60 dB) performances were obtained after a 100 km standard single-mode fiber transmission. Our proposed system does not use an externally modulated 1550 nm transmitter and a sophisticated stimulated Brillouin scattering suppression technique. It reveals a prominent technique with simpler and more economical advantages than that of externally modulated 1550 nm transmission system. 相似文献
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Marianna Vehviläinen Taina Kamppuri Monika Rom Jaroslaw Janicki Danuta Ciechańska Stina Grönqvist Matti Siika-Aho Kristina Elg Christoffersson Pertti Nousiainen 《Cellulose (London, England)》2008,15(5):671-680
Novel cellulose fibres (Biocelsol) were spun by traditional wet spinning technique from the alkaline solution prepared by
dissolving enzyme treated pulp directly into aqueous sodium zincate (ZnO/NaOH). The spinning dope contained 6 wt.% of cellulose,
7.8 wt.% of sodium hydroxide (NaOH) and 0.84 wt.% of zinc oxide (ZnO). The fibres were spun into 5% and 15% sulphuric acid
(H2SO4) baths containing 10% sodium sulphate (Na2SO4). The highest fibre tenacity obtained was 1.8 cNdtex−1 with elongation of 15% and titre of 1.4 dtex. Average molecular weights and shape of molecular weight distribution curves
of the celluloses from the novel wet spun cellulosic fibre and from the commercial viscose fibre were close to each other. 相似文献
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The chaotic dynamics of directly modulated semiconductor lasers with delayed optoelectronic feedback is studied numerically.
The effects of positive and negative delayed optoelectronic feedback in producing chaotic outputs from such lasers with nonlinear
gain reduction in its optimum value range is investigated using bifurcation diagrams. The results are confirmed by calculating
the Lyapunov exponents. A negative delayed optoelectronic feedback configuration is found to be more effective in inducing
chaotic dynamics to such systems with nonlinear gain reduction factor in the practical value range.
相似文献
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Homeira Ebrahimzadeh Narges Mollazadeh Ali Akbar Asgharinezhad Nafiseh Shekari Fatemeh Mirbabaei 《Journal of separation science》2013,36(23):3783-3790
In this work, a novel procedure based on surfactant‐assisted directly suspended droplet microextraction for the determination of tramadol prior to GC with flame ionization detection is proposed. In this technique, a free microdroplet of solvent is transferred to the surface of an immiscible aqueous sample containing Triton X‐100 and tramadol while being agitated by a stirring bar placed on the bottom of the sample vial. After the predetermined time, the microdroplet of solvent is withdrawn by a syringe and analyzed. The effective parameters such as the type of organic solvent, extraction time, microdroplet volume, salt content of the donor phase, stirring speed, the source phase pH, concentration of Triton X‐100, and extraction temperature were optimized. For this purpose, a multivariate strategy was applied based on an experimental design in order to screen and optimize the significant factors. This method requires minimal sample preparation, analysis time, solvent consumption, and represents significant advantages over customary analytical methods. The linearity ranged from 10 to 2000 μg/L with RSDs (n = 5) of 7.3–10. Preconcentration factors and the LODs were 391–466 and 2.5–6.5 μg/L, respectively. Finally, this method was applied to the analysis of biological samples and satisfactory results were obtained. 相似文献