Determination of trace constituents in biological and environmental samples usually requires a pre-concentration step. While solid-phase extraction (SPE) has been widely used, it is slow, labor intensive and adversely affected by analytical errors from handling. On-line SPE eliminates some of the flaws but often suffers from solvent compatibility problems with the subsequent chromatography separation. In this study, we are presenting a technical solution for overcoming some of these compatibility issues, by utilizing a fully automated, focused SPE sample transfer technique utilizing narrow-band solvent plugs, for seamless hyphenation with high-performance liquid chromatography (HPLC) or flow injection mass spectrometry (MS). A wide range of pharmaceutical compounds was studied in different sample matrices. Short plugs of high elution strength solvent were generated by means of an electrically actuated sample loop and enrichment and transfer steps monitored using on-line SPE-MS. The impact of the solvent plugs on chromatographic separation was studied using hyphenated SPE-LC-MS. By carefully examining elution profiles of solvent plugs of different compositions, optimum conditions for quantitative elution within well-defined volumes were found for all substances. In addition, the highly focused elution bands resulted in excellent retention time and peak area reproducibilities when injected on-line onto HPLC columns. Finally, to demonstrate proof-of-principle, the fully integrated on-line SPE-LC-MS system was applied to the analysis of spiked urine and river water samples. 相似文献
CaAl12O19 powders doped with Er3+, Yb3+, and Mg2+ ions have been prepared by a low-temperature combustion synthesis technique. Formation and chemical compositions were analysed
by powder X-ray diffraction and energy-dispersive spectroscopy. The visible luminescence spectra of the doped phosphor upon
excitation with ∼378 nm radiation from a Xenon lamp have been studied. A broad band emission in the range of 1400–1700 nm
with a peak around 1.5 μm and FWHM of about ∼80 nm responsible for the eye-safe telecommunication window has been observed
upon direct excitation with a NIR laser into the 4I11/2 level of Er3+. The effect of co-doping with Yb3+ and Mg2+ ions in the CaAl12O19:Er3+ matrix on the photoluminescence intensity corresponding to the 2H11/2,4S3/2→4I15/2, 4F9/2→4I15/2 and 4I13/2→4I15/2 transitions of Er3+ is elaborated and discussed in detail. 相似文献
The red emitting Cr3+ activated α-Al2O3 powder phosphor has been prepared by easy combustion reactions from mixed metal nitrate reactants and urea with ignition temperatures of 500 °C. The as-synthesized powder was characterized by X-ray diffraction, scanning electron microscopy, and Fourier-transform infrared techniques. The X-ray diffraction pattern reveals that the phosphor crystallized in the hexagonal α-Al2O3 phase directly from the combustion reaction. The EPR spectrum exhibits an intense resonance signal with effective g value at g=3.33 along with a few weak resonance signals with effective g values at g=13.7, 2.34, 1.95, 1.49, and 1.26. The spin concentration (N) and its paramagnetic susceptibility (χ) have been evaluated. The excitation spectrum consists of two broad intense bands at 415 nm and 555 nm and are assigned to 4A2g(F)→4T1g(F) and 4A2g(F)→4T2g(F) transitions, respectively. The intense fluorescence peak around 691 nm is attributed to 2Eg→4A2g transition of Cr3+ ion. By correlating EPR and optical data, the crystal field splitting parameter (Dq), Racah inter-electronic repulsion parameter (B) have been evaluated and discussed. The EPR and optical studies reveal that Cr3+ ions are occupying in Al3+ sites in octahedral coordination. 相似文献
The spontaneous spreading of non-volatile liquid droplets on solid substrates poses a classic problem in the context of wetting phenomena. It is well known that the spreading of a macroscopic droplet is in many cases accompanied by a thin film of macroscopic lateral extent, the so-called precursor film, which emanates from the three-phase contact line region and spreads ahead of the latter with a much higher speed. Such films have been usually associated with liquid-on-solid systems, but in the last decade similar films have been reported to occur in solid-on-solid systems. While the situations in which the thickness of such films is of mesoscopic size are fairly well understood, an intriguing and yet to be fully understood aspect is the spreading of microscopic, i.e. molecularly thin, films. Here we review the available experimental observations of such films in various liquid-on-solid and solid-on-solid systems, as well as the corresponding theoretical models and studies aimed at understanding their formation and spreading dynamics. Recent developments and perspectives for future research are discussed. 相似文献
Defect-free microporous carbon layers on graphite can be produced by DABCO-catalyzed twin polymerization of 2,2'-spirobi[4H-1,3,2-benzodioxasiline] in a slurry polymerization and subsequent thermal transformation of the resulting phenolic resin into carbon. 相似文献
Experimental N K-edge NEXAFS data of surface immobilized azide, 1,2,3-triazole and terpyridyl groups are interpreted with the help of DFT spectrum simulations. Assignments of π* resonances in experimental N K-edge NEXAFS spectra to nitrogen atoms within these functional groups have been made. The azide was immobilized on gold as the head group of a thiol SAM, 1,2,3-triazole was formed on this SAM by click reaction and terpyridyl groups were introduced as substituents of the acetylene used for the click reaction. For azide-terminated molecules, DFT spectrum simulations are found to be useful to find measurement conditions delivering experimental N K-edge NEXAFS data with negligible X-ray damage. The 1,2,3-triazole group is found to be rather stable under X-ray irradiation. 相似文献
Surface properties of mixtures of charged platelike colloids and salt in contact with a charged planar wall are studied within density functional theory. The particles are modeled by hard cuboids with their edges constrained to be parallel to the Cartesian axes corresponding to the Zwanzig model [J. Chem. Phys. 39, 1714 (1963)] and the charges of the particles are concentrated at their centers. The density functional applied is an extension of a recently introduced functional for charged platelike colloids. It provides a qualitative approach because it does not determine the relation between the actual and the effective charges entering into the model. Technically motivated approximations, such as using the Zwanzig model, are expected not to influence the results qualitatively. Analytically and numerically calculated bulk and surface phase diagrams exhibit first-order wetting for sufficiently small macroion charges and isotropic bulk order as well as first-order drying for sufficiently large macroion charges and nematic bulk order. The asymptotic wetting and drying behaviors are investigated by means of effective interface potentials which turn out to be asymptotically the same as for a suitable neutral system governed by isotropic nonretarded dispersion forces. Wetting and drying points as well as predrying lines and the corresponding critical points have been located numerically. A crossover from monotonic to nonmonotonic electrostatic potential profiles upon varying the surface charge density has been observed. Nonmonotonic electrostatic potential profiles are equivalent to the occurrence of charge inversion. Due to the presence of both the Coulomb interactions and the hard-core repulsions, the surface potential and the surface charge do not vanish simultaneously, i.e., the point of zero charge and the isoelectric point of the surface do not coincide. 相似文献