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91.
Recent developments in solid-phase microextraction for on-site sampling and sample preparation 总被引:1,自引:0,他引:1
Chunfeng DuanZheng Shen Dapeng WuYafeng Guan 《Trends in analytical chemistry : TRAC》2011,30(10):1568-1574
On-site sampling and sample preparation favor portable, solventless or even solvent-free techniques. Solid-phase microextraction (SPME) has these advantages. This review focuses on developments between 2007 and early 2011 in microextraction techniques for on-site sampling and sample preparation, including fiber SPME, stir-bar sorptive extraction (SBSE), thin-film microextraction (TFME) and different types of in-needle SPME. The major trends in on-site applications of SPME appear to be fiber and thin-film SPME, microextraction by packed sorbent (MEPS) and the sorbent-packed needle-trap device (NTD). We discuss and compare several aspects of these types of SPME in on-site applications. We also describe sorbent phases for SPME that benefit on-site applications. Finally, we provide a perspective on SPME-based techniques for on-site applications. 相似文献
92.
A single step on-line concentration and separation method for peptides in non-aqueous capillary electrophoresis was developed. ACN containing 50 mM tetraethylammonium perchlorate was used as the electrophoretic medium; angiotensins I-IV were separated as a result of the differences in the magnitudes of their interactions with perchlorate anions. When the sample solution (ACN containing 0.5% trifluoroacetic acid and angiotensins) was injected as a large-volume plug, the analytes were concentrated at the inlet end of the capillary by both sweeping and stacking mechanisms; the separation procedure then started automatically without any operations such as polarity change. It was found that the concentration of analytes, injection period, and concentration of tetraethylammonium perchlorate in the electrophoretic medium were important factors for both separation and concentration efficiencies. The angiotensins were concentrated and separated with the large-volume injection of up to 80% of the effective capillary length. 相似文献
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94.
Ultrafast on‐Chip Remotely‐Triggered All‐Optical Switching Based on Epsilon‐Near‐Zero Nanocomposites
《Laser \u0026amp; Photonics Reviews》2017,11(5)
On‐chip‐triggered all‐optical switching is a key component of ultrahigh‐speed and ultrawide‐band information processing chips. 1 - 4 This switching technique, the operating states of which are triggered by a remote control light, paves the way for the realization of cascaded and complicated logic processing circuits and quantum solid chips. Here, a strategy is reported to realize on‐chip remotely‐triggered, ultralow‐power, ultrafast, and nanoscale all‐optical switching with high switching efficiency in integrated photonic circuits. It is based on control‐light induced dynamic modulation of the coupling properties of two remotely‐coupled silicon photonic crystal nanocavities, and extremely large optical nonlinearity enhancement associated with epsilon‐near‐zero multi‐component nanocomposite achieved through dispersion engineering. Compared with previous reports of on‐chip direct‐triggered all‐optical switching, the threshold control intensity, 560 kW/cm2, is reduced by four orders of magnitude, while maintaining ultrafast switching time of 15 ps. This not only provides a strategy to construct photonic materials with ultrafast and large third‐order nonlinearity, but also offers an on‐chip platform for the fundamental study of nonlinear optics. 相似文献
95.
The present work describes the field emission characteristics of conducting polymer coated multi walled carbon nanotubes (MWNTs) field emitters fabricated over flexible graphitized carbon cloth. Nanocomposites involving the combination of MWNTs and conducting polymers polyaniline (PANI) and polypyrrole (PPy) have been prepared by in-situ polymerization method and have been characterized using scanning electron microscopy and transmission electron microscopy. Using spin coating method, field emitters based on PANI/MWNTs and PPy/MWNTs over flexible graphitized carbon cloth have been prepared. The field emission characteristics have been studied using an indigenously fabricated set up in a vacuum chamber with a base pressure of 2 × 10−5 Pa and the results are discussed. Our results display that the field emission performance of the emitters depends strongly on the work function of the emitting material. Low turn on emission field of 2.12 V/μm at 10 μA/cm2 and high emission current density of 1 mA/cm2 at 3.04 V/μm have been observed for PANI/MWNTs field emitter. 相似文献
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97.
Abstract Derivatization, or chemical modification of analytes, is often required for species that are only weakly detectable by common spectroscopic methods. Derivatization is most commonly performed in homogeneous solution or using phase‐transfer catalyzed reactions. However, the use of solid phase supports for performing the same reactions has a number of advantages. The sample can be “cleaned up” on the same phase, eliminating interfering matrix components or excess reagent. The process naturally concentrates the analyte, providing higher sensitivity, but also, under favorable circumstances, provides for more efficient reactions relative to solutions of the same original concentration. This review explores the uses to which such supports have been put, primarily in fluorescence derivatization for chromatographic applications. Some of the considerations in applying these techniques are described, and they are shown to be an extremely useful format for derivatization. 相似文献
98.
Summary A mixture of eleven priority pollutant phenols (PPP) have been separated using a Dionex 4000 chromatograph; VAL-U-PAK ODS (250 × 4.6 mm I.D.) column; eluents A: CH3CN/0.2M NaH2PO4/CH3COOH 40/60/1 and B: CH3CN with/without gradient; detectors: UV-254 nm and Pulse Amperometric Detector (PAD) with glassycarbon electrode (+1.20V). With preconcentration unit (guard RP-18 column) on line and PAD, detectability limit at ten ppt was achieved. The method has been applied for determination of PPP in tap-water and in leachates from sanitary and industrial landfill sites. 相似文献
99.
A microchip for integrated isotachophoretic (ITP) preconcentration with gel electrophoretic (GE) separation to decrease the detectable concentration of sodium dodecyl sulfate (SDS)-proteins was developed. Each channel of the chip was designed with a long sample injection channel to increase the sample loading and allow stacking the sample into a narrow zone using discontinuous ITP buffers. The pre-concentrated sample was separated in GE mode in sieving polymer solutions. All the analysis steps including injection, preconcentration, and separation of the ITP-GE process were performed continuously, controlled by a high-voltage power source with sequential voltage switching between the analysis steps. Without deteriorating the peak resolution, four SDS-protein analyses with integrated ITP-GE system resulted in a decreased detectable concentration of approximately 40-fold compared to the GE mode only. A good calibration curve for molecular weights of SDS-proteins indicated that the integrated ITP-GE system can be used for qualitative analysis of unknown protein samples. 相似文献
100.
A multibed on-line sorption trap is used to preconcentrate organic vapors from air samples and inject the analytes into a GC separation column. Injection plug widths depend on the boiling point for the lipophilic compounds and on the polarity and boiling point for the polar compounds. Injection plug widths are sufficiently small (0.7-0.8 s) as to allow the direct injection of the most volatile compounds into the GC column without the need for a second focusing device. The presence of water in the samples has an effect on the retention of polar compounds by the trap. However, this effect is reproducible for a fixed water content and so can be overcome by using calibration standards under the same conditions of humidity as the samples. The thermal decomposition of many volatile organic compounds in an on-line sorption trap during the GC analysis of air samples is examined. The results show that degradation of unstable compounds is governed by the amount of heat transferred to the compounds during desorption (i.e., applied temperature and pulse duration). The use of an on-line trap results in the immediate transfer of desorbed compounds to the analytical column, which can reduce the formation of artifacts. 相似文献