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排序方式: 共有122条查询结果,搜索用时 31 毫秒
91.
92.
C. J. Proctor E. A. Larka Z. V. I. Zaretskii J. H. Beynon 《Journal of mass spectrometry : JMS》1982,17(3):131-135
It is shown that two configurational steroidal isomers, 14α-equilenin and 14β-isoequilenin, may be easily distinguished by the unimolecular mass analysed ion kinetic energy spectra of their corresponding molecular ions. Furthermore, many of the peaks in these spectra are found to be due to consecutive reactions, whereby product ions of an initial reaction are themselves reactive and can undergo further fragmentation. In each of these cases, the individual steps of the reaction sequence have been separated in the different field free regions of a reversed geometry, double focusing mass spectrometer. Isotopic labelling with 18O in the 17-position has also helped to clarify reaction sequences. 相似文献
93.
Phase correction in double-pass quasi-phase-matched second-harmonic generation with a wedged crystal
Compensation for dispersive elements is necessary for efficient multiple-pass and intracavity nonlinear frequency-conversion devices. We describe the use of a wedged quasi-phase-matched crystal to compensate for the phase shifts introduced by mirrors in such devices, taking advantage of the periodic variation in the relative phases of the interacting waves in a quasi-phase-matching grating. A representative double-pass second-harmonic generation experiment with a 5-cm -long periodically poled lithium niobate crystal showed the expected conversion efficiency enhancement. 相似文献
94.
95.
Marcus L. Cole Glen B. Deacon Craig M. Forsyth Peter C. Junk Kathryn M. Proctor Janet L. Scott Christopher R. Strauss 《Polyhedron》2007
Direct treatment of HOdbp (= 2,6-dibenzylphenol) with strontium or barium metal in the absence of solvent at high temperature provides the corresponding phenolates Sr(Odbp)2 and Ba(Odbp)2. Recrystallisation of Ba(Odbp)2 from THF gave a good yield of the crystalline dimer [Ba(Odbp)2(THF)]2 · 2THF. Attempted recrystallisation of Sr(Odbp)2 from THF mostly yielded microcrystalline material characterized as [Sr(Odbp)2]n but on one occasion gave a small crop of crystalline [Sr9(Odbp)8(O2SiMe2)4(OH)2(THF)6(OH2)2] · 6THF derived from the adventitious reaction of Sr(Odbp)2 with dimethylsilicone grease ({OSiMe2}∞). In the solid-state [Ba(Odbp)2(THF)]2 · 2THF displays significant intramolecular Ba?π-arene interactions with the pendant benzyl substituents. [Sr9(Odbp)8(O2SiMe2)4(OH)2(THF)6(OH2)2] · 6THF features a square prismatic [Sr(O2SiMe2)4]6− core capped by two inverse crown-like square [Sr4(Odbp)4(OH)(L)4]3+ units, where L = OH2 or THF, that are staggered with respect to the cuboidal core. 相似文献
96.
C. J. Proctor B. Kralj A. G. Brenton J. H. Beynon 《Journal of mass spectrometry : JMS》1980,15(12):619-631
Over thirty consecutive reactions of a type m1+ → m2+ → m3+ have been studied in a variety of organic compounds using a reversed geometry mass spectrometer. Two field free regions allow the separation of the two steps that make up the consecutive reaction sequence. Translational energy release measurements are used in the comparison of m2+ ions formed as a result of a high energy process in the ion source with m2+ ions formed as a product of a metastable decomposition. In some cases the structures of such ions have been found to be different. Examples have also been found where consecutive fragmentations of metastable ions do not occur although, when higher energy ions within the source are studied, the two-step reaction does take place. Furthermore, it has been found that a control over ion internal energy may be achieved by selecting portions of a peak due to the fragmentation of a metastable ion. Unimolecular reactions may then be used to study the reactivity of such ‘energy-selected’ ions; collision induced reactions can be used to study the structure of both the reactive and unreactive energy selected ions. 相似文献
97.
98.
Standard cotinine solutions, controls and human serum samples containing cotinine have been measured by both radioimmunoassay (RIA) and gas chromatographic (GC) techniques. Cross-checks on standards and controls showed good agreement. However, for samples containing greater than 50 ng ml-1 of cotinine, RIA gave results on average 60% higher than GC. Determinations by using RIA and GC on samples containing less than 7 ng ml-1 of cotinine gave no significant correlation. The importance of the age of the serum sample has been investigated, and it is suggested that the age may affect the determination when dealing with low levels of cotinine. 相似文献
99.
Richard D. Chambers Lee D. Proctor Gerardo Caporiccio 《Journal of fluorine chemistry》1995,70(2):241-247
Telomerisation reactions have been investigated for the alkenes 1,1-difluoroethene (5) and hexafluoropropene (3) with the telogens CF2Br2 (1), CF3CFBr2 (8) and CF3CBr3 (9), as a means of preparing telomers and co-telomers. The efficiency of chain transfer increases as 18<9. Surprisingly, co-telomerisations of 5 with 3 occurred more efficiently than the corresponding telomerisations with 5 alone. The effects of solvent are described. 相似文献
100.
A host-guest optical sensor for the determination of aliphatic amines as exemplified by octylamine is proposed. It is based
on the reversible fluorescence enhancement of heptakis(2,6-di-O-isobutyl)-β-cyclodextrin(DOB-β-CD) hosting tetraphenylporphyrin
(TPP) immobilized in poly(vinyl chloride) (PVC) membrane by aliphatic amine extracted from aqueous phase into membrane phase.
The optimum membrane contained 1.15 wt % TPP, 6.15 wt % DOB-β-CD as sensing reagent and other membrane materials. The fluorescence
enhancement of the membrane resulted from the formation of a stable three-component complex among DOB-β-CD, TPP, and aliphatic
amines. With the optimum conditions described, the fluorescence response of the sensor to octylamine shows a good correlation
with the theoretically derived equation in the range 1.0 × 10–6 to 8.0 × 10–4 mol/L. The response characteristics including reversibility, response time, reproducibility and lifetime and selectivity
of this optical device are also discussed in detail. This sensor has also been applied for the determination of octylamine
in water samples containing interferents with satisfactory recovery.
Received: 21 November 1999 / Revised: 10 January 2000 / Accepted: 15 January 2000 相似文献