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131.
Muscat D Henderickx H Kwakkenbos G van Benthem R de Koster CG Fokkens R Nibbering NM 《Journal of the American Society for Mass Spectrometry》2000,11(3):218-227
Hyperbranched polyesteramides (DA2), prepared from hexahydrophthalic anhydride (D) and diisopropanolamine (A) have been characterized, by use of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS), field desorption (FD)-MS, and electrospray ionization (ESI)-MS. MALDI of polyesteramides produces protonated molecules. The spectra show a complex chemical composition distribution and end-group distribution which are mainly composed of two series of homologous oligomers DnA(n)+1 - mH2O and DnA(n) - mH2O, where m = 1-2. Signals from protonated molecules DnAn+1 and DnAn are almost absent in the MALDI spectrum, whereas these ions are responsible for the base peak of DnA(n)+1 - mH2O and DnA(n) - mH2O (m = 1-2) clusters in the ESI spectrum. The absence of -OH end-groups signals in the MALDI spectrum is due to a metastable decay of protonated DnA(n)+1 and DnAn ions in the ion source of the MALDI mass spectrometer prior to ion extraction. In-source decay results in the formation of protonated lower DnA(n)+1 - mH2O and DnA(n) - mH2O oligomers and their corresponding neutrals, leading to wrong conclusions concerning the relative end-group distribution as a function of the degree of polymerization and the chemical composition. 相似文献
132.
EH. Miller und R. W. Page 《Fresenius' Journal of Analytical Chemistry》1903,42(4-5):322-324
Ohne Zusammenfassung 相似文献
133.
Report on the Algorithmic Language ALGOL 68 总被引:2,自引:0,他引:2
134.
135.
Experiments were performed with a new radioscopic flow visualization technique on natural convection during melting of a binary metallic Ga-In alloy. This technique provides visualization of the density fields within opaque low Prandtl number fluids and their solids. Upon applying a horizontal temperature gradient to a gallium melt alloyed with 5 weight percent indium, the binary melt developed a vertical concentrational stratification and heat transfer was by conduction only. Convective flow developed at a higher temperature difference, which may be termed “critical”. After reducing the temperature difference the thermosolutal convection breaks down and a conductive state reappears at ΔT0 K. This threshold for onset of natural convection in binary Ga-In melts is in need of a theoretical explanation. 相似文献
136.
F. T. Arecchi G. Giusfredi E. Petriella P. Salieri E. Giacobino S. Cribier G. Grynberg F. Biraben H. M. Gibbs J. L. Jewell J. V. Moloney M. C. Rushford K. Tai S. S. Tarng D. A. Weinberger A. C. Gossard S. L. McCall A. Passner W. Wiegmann P. Martinot A. Koster S. Laval W. Carvalho A. Miller J. R. Hill G. Parry R. R. Puri R. K. Bullough S. S. Hassan A. M. Scott C. K. Wu P. Agostini G. Petite F. Fabre 《Applied physics. B, Lasers and optics》1982,29(3):169-175
137.
Koster S Duursma MC Boon JJ Heeren RM Ingemann S van Benthem RA de Koster CG 《Journal of the American Society for Mass Spectrometry》2003,14(4):332-341
Electron capture dissociation (ECD) of doubly protonated hyperbranched polyesteramide oligomers (1100-1900 Da) was examined and compared with the structural information obtained by low energy collisionally activated dissociation (CAD). Both the ester and amide bonds of the protonated species were cleaved easily upon ECD with the formation of odd electron (OE(.+)) or even electron (EE(+)) fragment ions. Several mechanistic schemes are proposed that describe the complex ECD fragmentation behavior of the multiply charged oligomers. In contrast to studies of biomolecules, the present results indicate that consecutive cleavages induced by intramolecular H-shifts are significant for ECD and of less importance for low energy CAD. The capture of an electron by the ionized species results in fragmentation associated with a redistribution of the excess internal energy over the products and the subsequent bond cleavage. Low energy, multiple collision CAD is found to be a more selective dissociation method than ECD in view of the observation that only amide bonds are cleaved for most of the hyperbranched polymers examined with CAD in this study. ECD appears not to provide complementary structural information compared to CAD in the study of hyperbranched polymers, even though a significantly more complex ECD fragmentation behavior is observed. ECD is shown to be of use for the structural characterization of large oligomers that may not dissociate upon low energy CAD. This is a direct result of the fact that ECD produces ionized hyperbranched oligomers with a relatively high internal energy. 相似文献
138.
Koster S Duursma MC Boon JJ Nielen MW de Koster CG Heeren RM 《Journal of mass spectrometry : JMS》2000,35(6):739-748
The molecular structure of a series of homo- and copolyesters was studied using sustained off-resonance irradiation collisionally activation dissociation on a Fourier transform ion cyclotron resonance mass spectrometer. Electrospray ionization was used as an ionization technique. The most important fragmentation pathways of the homopolyesters poly(dipropoxylated bisphenol-A/adipic acid) and poly(dipropoxylated bisphenol-A/isophthalic acid) were studied. Six different dissociation mechanisms were observed which are very similar to the mechanisms found to occur during pyrolysis of these compounds. Four of these mechanisms are a result of cleavages of the ester bond and the others are due to cleavages of the ether bond or bisphenol-A unit. Some of the fragments expected are not present in the spectrum, indicating that each fragment has a specific sodium affinity. Sequence-specific fragments of two of the three copolyester sequences that theoretically can exist were experimentally observed. Fragments that originate from the third sequence are not unique and can also be formed from other sequences. Therefore, it was not possible to determine the presence of the third sequence. Copyright 2000 John Wiley & Sons, Ltd. 相似文献
139.
Summary An anodic stripping voltammetric method for the determination of zinc in silicates is described and discussed. The method is sensitive and is not affected by interferences resulting from varying sample composition.
Dedicated to Prof. Dr. M. von Stackelberg on his 70th birthday.
This work was performed under the sponsorship of the U.S.National Bureau of Standards. Reproduction of this article, with the customary credit to the source, is permitted. 相似文献
Zusammenfassung Ein Verfahren zur Bestimmung von Zink in Silicaten mit Hilfe der anodischen Amalgamvoltammetrie wird beschrieben und diskutiert. Das Verfahren ist empfindlich und wird durch verschiedenartige Zusammensetzung der Probe nicht beeinflußt.
Dedicated to Prof. Dr. M. von Stackelberg on his 70th birthday.
This work was performed under the sponsorship of the U.S.National Bureau of Standards. Reproduction of this article, with the customary credit to the source, is permitted. 相似文献
140.