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1.
The possibility of exciting the fluorescence of several elements with the “overlapping” lines of other elements and the effectiveness of exciting the fluorescence of Fe, Mn, Ni, Cr, Tl, Cu and Mg with a 90 W mercury discharge lamp, are discussed. A method of increasing the fluorescence radiation by suitable optics, with a simple adaptation of a Jarrell-Ash AA spectrometer, is described. A two-pass system of the incident radiation into the flame is coupled with a mirror, in the optical axis, which reflects the fluorescence radiation emitted at the opposite side to the monochromator slit. This produces an increase of 168% of the signal. Detection limits for 10 elements are reported. 相似文献
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Optical cavities are commonly used to increase the sensitivity of absorption measurements, but have not been extensively used below 300 nm, mainly owing to the limited light sources at these wavelengths. While some progress has been made using cavity ring-down spectroscopy, these systems rely on complex and expensive lasers. Here we investigate an approach combining Cavity-Enhanced Absorption Spectroscopy (CEAS) with an inexpensive low vapour pressure mercury lamp for sensitive absorption measurements at 253.7 nm. We demonstrate that the CEAS absorption in our system is 50 times greater than the absorption found in a single-pass configuration; using this approach, we obtained limits of detection of 8.1 pptv (66 ng m(-3)) for gaseous elemental mercury and 8.4 ppbv for ozone. We evaluate the performance of the system and discuss potential improvements and applications of this approach. 相似文献
3.
The literature about direct solid sample analysis of the past 10–15 years using electrothermal atomic absorption spectrometry
has been reviewed. It was found that in the vast majority of publications aqueous standards were reported as having been used
for calibration after careful program optimization. This means the frequently expressed claim that certified reference materials
with a matrix composition and analyte content close to that of the sample have to be used for calibration in solid sample
analysis is not confirmed in the more recent literature. There are obviously limitations, and there are examples in the literature
where even calibration with certified reference materials did not lead to accurate results. In these cases the problem is
typically associated with spectral interferences that cannot be corrected properly by the systems available for conventional
line source atomic absorption spectrometry, including Zeeman-effect background correction. Using high-resolution continuum
source atomic absorption spectrometry, spectral interferences become visible owing to the display of the spectral environment
at both sides of the analytical line at high resolution, which makes program optimization straightforward. Any spectrally
continuous background absorption is eliminated automatically, and even rapidly changing background absorption does not cause
any artifacts, as measurement and correction of background absorption are truly simultaneous. Any kind of fine-structured
background can be eliminated by “subtracting” reference spectra using a least-squares algorithm. Aqueous standards are used
for calibration in all published applications of high-resolution continuum source atomic absorption spectrometry to direct
solid sample analysis.
This contribution is based on a presentation given at the Colloquium for Analytical Atomic Spectroscopy (CANAS ‘07) held March
18–21, 2007 in Constance, Germany. 相似文献
4.
Atomic fluorescence of magnesium is possible in air-propane or air-acetylene flames at 285.21 nm, using a high-intensity hollow-cathode magnesium lamp for excitation. The technique permits determinations of magnesium in the range 0.01–5 p.p.m., i.e. with more than 10 times the sensitivity of the atomic absorption method even for this most sensitive element. The detection limit in either flame is 1 ng/ml (signal: noise ratio 1 : 0.75). In a nitrous oxide-acetylene flame, atomic fluorescence may be carried out with linear signal/concentration dependence up to 100 p.p.m. without interference even from metals such as aluminium, titanium, etc. at a 1000-fold excess ratio to magnesium. A brief comparison is made with atomic absorption using the same source and equipment. 相似文献
5.
《Rapid communications in mass spectrometry : RCM》2018,32(9):677-685
Rationale
Recent trends towards miniature and portable quadrupole mass spectrometry (QMS) entail challenges in instrumental sensitivity, which is influenced by 3D fringe field effects on ion transmission in the Quadrupole Mass Filter (QMF). The relationship of these effects with the gap from the ion source to the QMF entrance (source gap) is significant and little explored. We examine transmission characteristics experimentally and use the results to test the predictive accuracy of a recently developed 3D QMF simulation model. The model is then applied to directly investigate optimal transmission m/z ranges across multiple source gaps.Methods
A portable single filter quadrupole mass spectrometer is used to analyse transmission characteristics across a range of common gases. We use an experimental approach originally proposed by Ehlert, enhanced with a novel method for absolute calibration of the transmission curve. Custom QMF simulation software employs the boundary element method (BEM) to compute accurate 3D electric fields. This is used to study the effects of the source gap on transmission efficiency.Results
Experimental findings confirm a centrally peaked transmission curve; simulations correctly predict the optimal transmission location (in m/z) and percentage, and extend the experimental trend. We compare several methods for determining fringe field length, demonstrating how the size of the physical source gap influences both the length and the intensity of the fringe field at the QMF entrance. A complex relationship with ion transmission is revealed in which different source gaps promote optimal transmission at differing m/z ranges.Conclusions
The presented results map the relationship between the source gap and transmission efficiency for the given instrument, using a simulation method transferrable to other setups. This is of importance to miniature and portable quadrupole mass spectrometers design for specific applications, for the first time enabling the source gap to be tailored for optimal transmission in the desired mass range.6.
Masanori Fujinami Satoshi Jinno Masafumi Fukuzumi Takumi Kawaguchi Koichi Oguma Takashi Akahane 《Analytical sciences》2008,24(1):73-79
A production method for a positron microprobe using a beta+-decay radioisotope (22Na) source has been investigated. When a magnetically guided positron beam was extracted from the magnetic field, the combination of an extraction coil and a magnetic lens enabled us to focus the positron beam by a factor of 10 and to achieve a high transport efficiency (71%). A 150-nm-thick Ni(100) thin film was mounted at the focal point of the magnetic lens and was used as a remoderator for brightness enhancement in a transmission geometry. The remoderated positrons were accelerated by an electrostatic lens and focused on the target by an objective magnetic lens. As a result, a 4-mm-diameter positron beam could be transformed into a microprobe of 60 microm or less with 4.2% total efficiency. The S parameter profile obtained by a single-line scan of a test specimen coincided well with the defect distribution. This technique for a positron microprobe is available to an accelerator-based high-intensity positron source and allows 3-dimensional vacancy-type defect analysis and a positron source for a transmission positron microscope. 相似文献
7.
A scheme of photoabsorption spectroscopy based on scanning tunneling microscopy (STM) has been developed by using a supercontinuum light as the wideband light source of a Fourier transform interferometer for spectroscopic measurements. The performance was demonstrated for a sample of GaAs. The proof-of-concept test showed that the use of the supercontinuum light instead of halogen lamps greatly enhances the signal-to-noise ratio due to the high brilliance of the supercontinuum light emitted from a small core of the photonic crystal fiber that enables tight focusing of the spectroscopy light onto the sample beneath the STM tip. 相似文献
8.
[reaction: see text]. Rhodium complex-catalyzed carbonylative alkene-alkyne coupling proceeds using aldehydes as a CO source. Cinnamaldehyde is the best CO donor, and various cyclopentenones were provided in high isolated yields by a solvent-free system. 相似文献
9.
《Liquid crystals》1999,26(12):1849-1851
The TLM method uses the voltages and currents on a three-dimensional network of transmission lines to model the electric and magnetic field and loss components of Maxwell's equations. Optical fields within anisotropic media may be easily modelled and results are presented for calculation of the transmission spectra of a Freedericksz transition liquid crystal device. The method is well suited to the calculation of transmission spectra; calculations agree well with spectrometer measurements on an actual liquid crystal device. 相似文献
10.
Garry A. Lester 《Liquid crystals》2013,40(12):1849-1851
The TLM method uses the voltages and currents on a three-dimensional network of transmission lines to model the electric and magnetic field and loss components of Maxwell's equations. Optical fields within anisotropic media may be easily modelled and results are presented for calculation of the transmission spectra of a Freedericksz transition liquid crystal device. The method is well suited to the calculation of transmission spectra; calculations agree well with spectrometer measurements on an actual liquid crystal device. 相似文献
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Bisquert J Grätzel M Wang Q Fabregat-Santiago F 《The journal of physical chemistry. B》2006,110(23):11284-11290
A three-channel transmission line (TL) impedance model is proposed to address the charge transport behavior of molecular functionalized mesoscopic oxide electrodes at different bias conditions. A full general solution of the three-channel TL for the system is provided in this paper. Selected experimental results of impedance spectroscopy of mesoscopic Al2O3 and TiO2 networks, covered with a monolayer of Ru complex cis-RuLL'(NCS)2 (L = 2,2'-bipyridyl-4,4'-dicarboxylic acid, L' = 4,4'-dinonyl-2,2'-bipyridyl) (Z907), are briefly discussed. It shows that the model constitutes a useful tool for characterizing nanoporous electrodes functionalized with organic conducting layers in the surface. The model makes it possible to determine the separate conductivity of substrate oxide and molecular layer, and interfacial charge transfer, in the functionalized nanostructured electrodes. 相似文献
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This paper presents a study about moderation and collimation of a neutron radiography system using 252Cf. A Monte Carlo Code, MCNP4B, has been used to obtain a maximum and more homogeneous thermal neutron flux in the collimator outlet next to the image plane. Among the various moderator materials investigated, high density polyethylene proved to be the most efficient, with a thermalization factor of 56 cm2. Using a collimator design assembly it was possible to obtain a normalized thermal neutron flux, at the image plane of 6×10−6 n cm−2 s−1 at an effective collimator ratio of 7.5, or 3.2×10−7 n cm−2 s−1 at an effective collimator ratio of 50. 相似文献
16.
Sheathless capillary electrophoresis-mass spectrometry using a pulsed electrospray ionization source
A sheathless interface has been developed for coupling CE with electrospray IT mass spectrometer. This interface utilized a pulsed ESI source. The use of a pulsed electrospray source allows the use of a sprayer with larger orifice, and thus alleviates the problem of column clogging during conductive coating and CE analysis. A pulsed ESI source operated at 20 Hz and 20% duty cycle was found to produce the optimal signals. For better signals, the maximum ion injection time in the IT mass spectrometer has to be set to a value close to the actual spraying time (10 ms). Using a sprayer with 50 microm od, more stable and enhanced signals were obtained in comparison with continuous CE-ESI-MS under the same flow rate (150 nL/min). The utility of this design is demonstrated with the analysis of synthetic drugs by CE-MS. 相似文献
17.
L. Larsson M. Alpsten S. Mattsson 《Journal of Radioanalytical and Nuclear Chemistry》1987,114(1):181-185
A set up forin vivo determination of nitrogen has been built. Phantoms containing different amounts of nitrogen have been measured as well as a volunteer in a pilot study. A total body protein content of 18.8 kg was calculated, to be compared with 17.0 kg estimated from potassium measurements. 相似文献
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《Radiation Physics and Chemistry》2007,76(2):304-307
A procedure for calibrating a FAST-ComTec 2D-CDB spectrometer using a 133Ba source is presented. The energy calibration consisted of acquiring two-dimensional (2D) spectra by measuring simultaneously with two HPGe detectors the 356 and 511 keV peaks. As the 133Ba source only emits one photon per decay, the Ba contribution to the 2D spectra was built up by taking two successive and uncorrelated events, i.e. one from each detector (pseudo-coincidence technique). The FWHM of the spectrometer was estimated from the E1=E2 diagonal of the spectra. 相似文献