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Mass Selection (mass + selection)

Distribution by Scientific Domains

Chemistry	41%

Selected Abstracts

C20 Carbon Clusters: Fullerene,Boat,Sheet Generation, Mass Selection, Photoelectron Characterization

CHEMISTRY - A EUROPEAN JOURNAL, Issue 24 2006
Horst Prinzbach Prof. Dr.
Abstract Electron-impact ionization in a time-of-flight mass spectrometer of C20H0,3Br14,12 probes,secured from C20H20 dodecahedrane by a "brute-force" bromination protocol,provided bromine-free C20H0,2(3) anions in amounts that allowed the clean mass-separation of the hydrogen-free C20, ions and the photoelectron (PE) spectroscopic characterization as C20 fullerene (electron affinity (EA)=2.25±0.03 eV, vibrational progressions of 730±70). The extremely strained C20 fullerene ions surfaced as kinetically rather stable entities (lifetime of at least the total flight time of 0.4 ms); they only very sluggishly expel a C2 unit. The HOMO and LUMO are suggested to be almost degenerate (,E=0.27 eV). The assignment as a fullerene was corroborated by the PE characterization of the C20 bowl (EA=2.17±0.03 eV, vibrational progression of 2060±50 cm,1) analogously generated from C20H10 corannulene (C20H1,3Br9,8 samples) and comparably stable. Highly resolved low-temperature PE spectra of the known C20 ring (EA=2.49±0.03 eV, vibrational progressions 2022±45 and 455±30 cm,1), obtained from graphite, display an admixture of, most probably, a bicyclic isomer (EA=3.40±0.03 eV, vibrational progression 455±30 cm,1). The C20+(,) and C20H2+(,) cluster ions generated from polybrominated perylene (C20H0,2Br12,10) have (most probably) retained the planar perylene-type skeleton (sheet, EA=2.47±0.03 eV, vibrational progressions of 2089±30 and 492±30 cm,1 and EA=2.18±0.03 eV, vibrational progressions of 2105±30 and 468±30 cm,1). [source]

A mass filter based on an accelerating traveling wave

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 5 2008
Michael Wiedenbeck
We describe a novel mass filtering concept based on the acceleration of a pulsed ion beam through a stack of electrostatic plates. A precisely controlled traveling wave generated within such an ion guide will induce a mass-selective ion acceleration, with mass separation ultimately accomplished via a simple energy-filtering system. Crucial for successful filtering is that the velocity with which the traveling wave passes through the ion guide must be dynamically controlled in order to accommodate the acceleration of the target ion species. Mass selection is determined by the velocity and acceleration with which the wave traverses the ion guide, whereby the target species will acquire a higher kinetic energy than all other lighter as well as heaver species. Finite element simulations of this design demonstrate that for small masses a mass resolution M/,M,,,1000 can be achieved within an electrode stack containing as few as 20 plates. Some of the possible advantages and drawbacks which distinguish this concept from established mass spectrometric technologies are discussed. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Experimental evaluation of mass selection to improve red body colour in Fijian hybrid tilapia (Oreochromis niloticus × Oreochromis mossambicus)

AQUACULTURE RESEARCH, Issue 5 2001
P B Mather
Abstract Mass selection was trialed on Fijian hybrid tilapia (Oreochromis niloticus × Oreochromis mossambicus) to reduce the amount of black spots on otherwise red phenotypes. The responses of two selection intensities (low-selection line, top 50% , L) and (high-selection line, top 30% , H) were compared with that of a control line (no selection , C) across three generations. The relative growth performance of treatments (C, L and H) was examined in parallel in each generation to assess whether mass selection had a correlated negative effect on growth performance. The results show clearly that red phenotype can be improved significantly by applying mass selection, without affecting growth performance. We propose that black spots on an otherwise red phenotype could represent the allelic products of a second genetic locus influencing skin colour, which can be expressed in red individuals (genotype Rr) but which may be masked in black individuals (genotype rr). [source]

Fragmentation of the (Cyclam-acetato)iron Azide Cation in the Gas Phase

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 6 2007
Detlef Schröder
Abstract Mass spectrometry is used to investigate the fragmentation of the ligated azidoiron cation [(cyclam-acetato)Fe(N3)]+, which is accessible in the gas phase by electrospray ionization of a solution of its hexafluorophosphate salt in methanol/water. Upon collisional activation, mass-selected [(cyclam-acetato)Fe(N3)]+ undergoes competing loss of dinitrogen or HN3 as the prevailing fragmentations. The former dissociation pathway is investigated in detail in order to determine whether or not the free, high-valent iron nitride [(cyclam-acetato)FeN]+ is formed. The evidence obtained indeed supports the formation of the iron nitride species as an intermediate, although the long-lived ion sampled after mass selection may also have undergone further rearrangements.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

Activation of large lons in FT-ICR mass spectrometry

MASS SPECTROMETRY REVIEWS, Issue 2 2005
Julia Laskin
Abstract The advent of soft ionization techniques, notably electrospray and laser desorption ionization methods, has enabled the extension of mass spectrometric methods to large molecules and molecular complexes. This both greatly extends the applications of mass spectrometry and makes the activation and dissociation of complex ions an integral part of these applications. This review emphasizes the most promising methods for activation and dissociation of complex ions and presents this discussion in the context of general knowledge of reaction kinetics and dynamics largely established for small ions. We then introduce the characteristic differences associated with the higher number of internal degrees of freedom and high density of states associated with molecular complexity. This is reflected primarily in the kinetics of unimolecular dissociation of complex ions, particularly their slow decay and the higher energy content required to induce decomposition,the kinetic shift (KS). The longer trapping time of Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) significantly reduces the KS, which presents several advantages over other methods for the investigation of dissociation of complex molecules. After discussing general principles of reaction dynamics related to collisional activation of ions, we describe conventional ways to achieve single- and multiple-collision activation in FT-ICR MS. Sustained off-resonance irradiation (SORI),the simplest and most robust means of introducing the multiple collision activation process,is discussed in greatest detail. Details of implementation of this technique, required control of experimental parameters, limitations, and examples of very successful application of SORI-CID are described. The advantages of high mass resolving power and the ability to carry out several stages of mass selection and activation intrinsic to FT-ICR MS are demonstrated in several examples. Photodissociation of ions from small molecules can be effected using IR or UV/vis lasers and generally requires tuning lasers to specific wavelengths and/or utilizing high flux, multiphoton excitation to match energy levels in the ion. Photodissociation of complex ions is much easier to accomplish from the basic physics perspective. The quasi-continuum of vibrational states at room temperature makes it very easy to pump relatively large amounts of energy into complex ions and infrared multiphoton dissociation (IRMPD) is a powerful technique for characterizing large ions, particularly biologically relevant molecules. Since both SORI-CID and IRMPD are slow activation methods they have many common characteristics. They are also distinctly different because SORI-CID is intrinsically selective (only ions that have a cyclotron frequency close to the frequency of the excitation field are excited), whereas IRMPD is not (all ions that reside on the optical path of the laser are excited). There are advantages and disadvantages to each technique and in many applications they complement each other. In contrast with these slow activation methods, the less widely appreciated activation method of surface induced dissociation (SID) appears to offer unique advantages because excitation in SID occurs on a sub-picosecond time scale, instantaneously relative to the observation time of any mass spectrometer. Internal energy deposition is quite efficient and readily adjusted by altering the kinetic energy of the impacting ion. The shattering transition,instantaneous decomposition of the ion on the surface,observed at high collision energies enables access to dissociation channels that are not accessible using SORI-CID or IRMPD. Finally, we discuss some approaches for tailoring the surface to achieve particular aims in SID. © 2004 Wiley Periodicals, Inc., Mass Spec Rev 24:135,167, 2005 [source]

MS3 using the collision cell of a tandem mass spectrometer system

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 11 2002
Lisa M. Cousins
We report the feasibility of multistage fragmentation in combination with a fast background subtraction method, yielding the equivalent of MS3. The first quadrupole selects an ion of interest, and the ion is axially accelerated into Q2 to generate fragment ions. Subsequent stages of mass selection and fragmentation are obtained by quadrupolar resonant excitation within the Q2 collision cell. The fragments are analyzed downstream by either a resolving quadrupole or a time-of-flight (TOF) mass spectrometer, and multistage spectra are obtained by subtraction (MSn,,,MSn,1) for n,=,3 or 4. We discuss the characterization of this method, including product ion arrival times, fragmentation efficiencies, and ion selectivity. We report accurate TOF mass spectra of background-subtracted MS3 for protonated molecules reserpine (m/z 609), bosentan (m/z 1552), and taxol (m/z 854). Copyright © 2002 John Wiley & Sons, Ltd. [source]

Divergent selection and realized heritability for growth in the Japanese scallop, Patinopecten yessoensis Jay

AQUACULTURE RESEARCH, Issue 9 2010
Jun Liang
Abstract In order to improve the production and accurately estimate response to selection, divergent selection for growth in shell height was conducted in a cultured population of the Japanese scallop Patinopecten yessoensis. Applying the same selection intensity ± 1.756 in upward and downward directions, three groups including two selected groups of Fast and Slow and one non-selected Control group were created, which were reared under the same environmental conditions at any stage. Differences always significantly existed among the three groups (P<0.05), except for larvae at day 1 and at day 5, and in the order of Fast>Control>Slow. The average standardized response to selection (SR), realized heritability (hR2) and genetic gain (GG) was 0.473%, 0.269% and 7.85% for the Fast group and 0.381%, 0.217% and 6.60% for the Slow group respectively. Moreover, significant differences (P<0.05) were detected between the fast and the slow lines in both SR and hR2, providing evidence for an asymmetric response in two directions. Performance in shell height is improved by 7.85% in the fast line after one generation selection, suggesting that mass selection for faster growth in a cultured population of the Japanese scallop is effective. [source]

Realized heritability and response to selection for shell height in the pearl oyster Pinctada fucata (Gould)

AQUACULTURE RESEARCH, Issue 8 2008
Maoxian He
Abstract The common pearl oyster, Pinctada fucata (Gould), is the most important species that is cultured for production of marine pearls in China. Heavy mortality and the decline of pearl quality have resulted in a breeding programme being established in recent years. In this study, we conducted selective breeding for the second generation of pearl oyster P. fucata (JCS-2) by mass selection for shell height (SH) with a selection intensity of 1.614, and analysed the growth of the selected line (JCS-2) and the non-selected control line (JCC) during a 1-year grow-out period. The results show that the selected line grew faster than the control one in the SH and total weight (TW) (P<0.05), and there were higher proportion of larger sized oysters. Coefficient of variation for SH of JCS-2 was smaller than that of JCC. The current genetic gains and realized heritability for JCS-2 averaged 16.03 ± 4.79% and 0.713 ± 0.208 at 3,15 months of age respectively. The findings indicated the selection response to faster growth for SH is markedly effective in the second generation, and there was a high correlated response of TW when selecting for SH. [source]

Efficacy of selection in sexually breeding Artemia (Artemia franciscana, Kellogg, 1906)

AQUACULTURE RESEARCH, Issue 13 2006
Mangesh M Shirdhankar
Abstract Bi-directional selection for smaller naupliar size (SNS) and bigger naupliar size (BNS) was practiced to develop two divergent lines. The efficacy of bi-directional mass selection in Artemia franciscana was evaluated by comparing the predicted genetic gains with the realized genetic gains. Two sets of predictions were made using two heritability estimates, e.g., the heritability estimate from full-sib analysis (h2) and the estimate from regression of offspring on mid parent (bop). Predictions with the full-sib heritabilities were of very high magnitude as compared with predictions with bop heritabilities. The predictions based on bop were more or less in agreement with realized genetic gain, while the predictions with heritability estimates based on full-sib analysis were much higher than the realized gains. Ratios of realized gain to predicted gain based on full-sib heritabilities were 0.2302 and 0.2152, respectively, for males and females of the SNS line, and 0.0471 and 0.2248, respectively, for males and females of the BNS line. Ratios of realized gain to predicted gain based on bop were 1.5348 and 0.6069 for males and females of the SNS line and 0.1028 and 0.9503 for males and females of the BNS line. Ratios of realized gain to predicted gain based on full-sib heritability were of low magnitude in all the cases as the heritability estimates based on full-sib analysis were inflated by non-additive genetic variance. The ratios of realized gain to predicted gain based on bop were high in both sexes of SNS and females of BNS, indicating high efficacy of selection as bop includes only additive genetic variance. However, it was of low magnitude in BNS males. Thus, the heritability estimates based on regression of offspring on mid parent (bop) are more reliable than that of heritability estimates based on full-sib analysis (h2) for predicting the selection response in Artemia. [source]

Experimental evaluation of mass selection to improve red body colour in Fijian hybrid tilapia (Oreochromis niloticus × Oreochromis mossambicus)

Genetic improvement in the Australian aquaculture industry

AQUACULTURE RESEARCH, Issue 1 2000
A J. Lymbery
Most aquaculture industries in Australia are at an early stage of development and would benefit from the introduction of genetic improvement programmes. Size at harvest is perceived by industry participants, managers and researchers as the trait that will most influence profitability. Although most current genetic improvement programmes in aquaculture use mass selection, inbreeding is widely regarded as an important problem, which could be overcome by the use of family data in selection decisions. The major research priority is the development of genetic markers to enable accurate pedigree determination. The major constraint upon the implementation of genetic improvement programmes by aquaculture industries is lack of available funds and resources. Industry ownership and national co-ordination of research and development is seen as the best way of addressing this constraint. [source]