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Barbara S. Larsen William J. Simonsick Charles N. McEwen 《Journal of the American Society for Mass Spectrometry》1996,7(3):287-292
Matrix-assisted laser desorption-ionization (MALDI) time of flight is shown to give a molar peak area response for isolated methylmethacrylate oligomers that have 25 and 50 repeat units when run on three different instruments in reflectron or linear mode and using three different matrix materials. In addition, fragmentation was not observed in any of the three different matrices or at higher laser power. No spectral differences were observed for syndiotactic and isotactic methylmethacrylate oligomers. These results suggest that the low most probable peak values observed for narrow distribution poly(methylmethacrylate) standards by MALDI mass spectrometry are not the result of mass discrimination or fragmentation. 相似文献
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Khoa Hoang Milan Pophristic Andrew J. Horan Murray V. Johnston Charles N. McEwen 《Journal of the American Society for Mass Spectrometry》2016,27(10):1590-1596
First results are reported using a simple, fast, and reproducible matrix-assisted ionization (MAI) sample introduction method that provides substantial improvements relative to previously published MAI methods. The sensitivity of the new MAI methods, which requires no laser, high voltage, or nebulizing gas, is comparable to those reported for MALDI-TOF and n-ESI. High resolution full acquisition mass spectra having low chemical background are acquired from low nanoliters of solution using only a few femtomoles of analyte. The limit-of-detection for angiotensin II is less than 50 amol on an Orbitrap Exactive mass spectrometer. Analysis of peptides, including a bovine serum albumin digest, and drugs, including drugs in urine without a purification step, are reported using a 1 μL zero dead volume syringe in which only the analyte solution wetting the walls of the syringe needle is used in the analysis. 相似文献
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M. R. McEwen J. P. Sephton P. H. G. Sharpe D. R. Shipley 《Radiation Physics and Chemistry》2003,68(6):1017-1022
A phantom composed of alanine dosimeter material has been constructed and depth–dose measurements made in a 10 MeV electron beam. The results have demonstrated the feasibility of using relative depth–dose measurements to determine stopping power ratios in materials of dosimetric interest. Experimental stopping power ratios for alanine dosimeter material and water agreed with the data of ICRU Report 37 within the uncertainty of the experiment (±1.2% at a 95% confidence level). 相似文献
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Koike Y Metoki N Haga Y McEwen KA Kohgi M Yamamoto R Aso N Tateiwa N Komatsubara T Kimura N Aoki H 《Physical review letters》2002,89(7):077202
The magnetic structure of the localized-5f uranium intermetallic compound U3Pd20Si6 has been determined by means of a neutron diffraction experiment. Our data demonstrate that this compound has a collinear coupling of the sublattice ordering of the uranium spins on the 4a and 8c sites. We conclude that higher-order exchange and/or quadrupole interactions are necessary to stabilize this unique collinear structure. We discovered a new type of spin-flop transition against the uniaxial anisotropy induced by this collinear coupling. 相似文献
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Fungal cells treated with various inhibitors to the ergosterol pathway were analyzed using an Orbitrap mass spectrometer equipped with an atmospheric solids analysis probe (ASAP). The technique is a rapid means for determining which of the multiple steps in the ergosterol pathway were interrupted by an inhibitor. Furthermore, in an inhibitor concentration study, the ASAP method was able to rapidly provide an estimate of the effectiveness of inhibition. In this method the cells are inserted directly into a hot nitrogen stream, thus eliminating extensive sample workup before analysis. Data indicating the point of pathway interruption are obtained in seconds. 相似文献
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Lake DA Johnson MV McEwen CN Larsen BS 《Rapid communications in mass spectrometry : RCM》2000,14(11):1008-1013
An automated sample preparation for high throughput accurate mass determinations by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) has been developed. Sample preparation was performed with an automated workstation and automated mass analyses were performed with a commercial MALDI-TOF mass spectrometer. The method was tested with a 41-sample library. MALDI-TOFMS was found to give the needed sensitivity, accurate mass measurement, and soft ionization necessary for structure confirmation, even of mixtures. A mass accuracy of 5 ppm or less was obtained in over 80% of known compound measurements. A mass accuracy better than 10 ppm was obtained for all measurements of known compounds. Analyses of parallel synthesis products resulted in 77% of the measurements with a mass accuracy of 5 ppm or better. 相似文献