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51.
Method development for the analysis of trans-fatty acids in hydrogenated oils by capillary electrophoresis 总被引:8,自引:0,他引:8
A novel capillary electrophoresis methodology using UV indirect detection (224 nm) for the analysis of trans-fatty acids in hydrogenated oils was proposed. The electrolyte consisted of a pH 7 phosphate buffer at 15 mmol x L(-1) concentration containing 4 mmol.L(-1) sodium dodecylbenzenesulfonate, 10 mmol x L(-1) polyoxyethylene 23 lauryl ether (Brij 35), 2% 1-octanol and 45% acetonitrile. Under the optimized conditions, ten fatty acids, C12:0, C13:0 (internal standard), C14:0, C16:0, C18:0, C18:1c, C18:1t, C18:2cc, C18:2tt and C18:3ccc were baseline-separated in less than 12 min. The proposed methodology was applied to monitor the formation of trans-fatty acids during hydrogenation of Brazilnut oil. A crude oil sample (42.1% linoleic acid, 37.3% oleic acid, 13.4% palmitic acid, and 7.0% stearic acid) was mixed with 0.25% of a nickel-based catalyst and submitted to two independent hydrogenation conditions: 175 degrees C, 3 atm, 545 rpm for 60 min (GH(1) sample), and 150 degrees C, 1 atm, 545 rpm for 30 min (GH(2) sample). For the most severe hydrogenation condition (higher temperature and pressure, under longer reactional period), a more complete conversion of linoleic and oleic acids into stearic acid occurred with concomitant formation of the trans-species, elaidic acid (C18:1t). For the milder hydrogenation procedure that generated sample GH(2), larger amounts of linoleic and oleic acids remained, in addition to the transformations already observed in the GH(1) sample. 相似文献
52.
53.
We introduce local adaptive discrete Galerkin bases as a basis set in order to obtain geometrical and topological information about attractors of discrete dynamical systems. The asymptotic behavior of these systems is described by the reconstruction of their attractors in a finite dimensional Euclidean space and by the attractor topological characteristics including the minimal embedding dimension and its local dimension. We evaluate numerically the applicability of our geometrical and topological results by examining two examples: a dissipative discrete system and a nonlinear discrete predator–prey model that includes several types of self-limitation on the prey. 相似文献
54.
The mechanistic pathways for hydrogen evolution catalyzed by cobalt complexes with supporting diglyoxime ligands are analyzed with computational methods. The cobaloximes studied are Co(dmgBF(2))(2) (dmg = dimethylglyoxime) and Co(dpgBF(2))(2) (dpg = diphenylglyoxime) in acetonitrile. The reduction potentials and pK(a) values are calculated with density functional theory in conjunction with isodesmic reactions, incorporating the possibility of axial solvent ligand loss during the reduction process. The solvent reorganization energies for electron transfer between the cobalt complex and a metal electrode and the inner-sphere reorganization energies accounting for intramolecular rearrangements and the possibility of ligand loss are also calculated. The relative reduction potentials agree quantitatively with the available experimental values. The pK(a)s and reorganization energies agree qualitatively with estimates based on experimental data. The calculations suggest that a peak measured at ca. -1.0 V vs SCE in cyclic voltammetry experiments for Co(dmgBF(2))(2) is more likely to correspond to the Co(II)H/Co(I)H reduction potential than the Co(III)H/Co(II)H reduction potential. The calculations also predict pK(a) values of Co-hydride complexes and reduction potentials for both cobaloximes that have not been determined experimentally. The results are consistent with a mechanism in which the Co(III) and Co(II) complexes have two axial solvent ligands and the Co(I) complex has a single axial ligand along the reaction pathway. Analysis of the free energy diagrams generated for six different monometallic and bimetallic hydrogen production pathways identified the most favorable pathways for Co(dmgBF(2))(2) and tosic acid. The thermodynamically favored monometallic pathway passes through a Co(III)H intermediate, and Co(II)H reacts with the acid to produce H(2). The thermodynamically favored bimetallic pathways also pass through the Co(III)H intermediate, but the pathways in which two Co(III)H or two Co(II)H complexes react to produce H(2) are not thermodynamically distinguishable with these methods. On the basis of the electrostatic work term associated with bringing the two cobalt complexes together in solution, the preferred bimetallic pathway involves the reaction of two Co(III)H complexes to produce H(2). This mechanistic insight is important for designing more effective catalysts for solar energy conversion. 相似文献
55.
dos Santos CM Boyle EM De Solis S Kruger PE Gunnlaugsson T 《Chemical communications (Cambridge, England)》2011,47(44):12176-12178
The synthesis and binding investigations of first generation C(3v)-symmetrical hydrogen bonding urea-amide based tripodal receptors, 1-6, with various anions such as acetate, phosphate, sulfate and chloride in DMSO-d(6) are presented. Analysis of the (1)H NMR titrations of 1-6 showed on all occasions the selective formation of 1?:?1 stoichiometries. 相似文献
56.
We present a novel algorithm for baseline estimation in CE. The new algorithm which we have named as accelerated multiple-pass moving average (AMPMA) is combined to three preexisting low-pass filters, spike-removal, moving average, and multi-pass moving average filter, to achieve real-time baseline correction with commercial instrumentation. The successful performance of AMPMA is demonstrated with simulated and experimental data. Straightforward comparison of experimental data clearly shows the improvement AMPMA provides to the linear fitting, LOD, and accuracy (absolute error) of CE analysis. 相似文献
57.
F. L. Jones C. P. Ritz R. W. Miksad E. J. Powers R. S. Solis 《Experiments in fluids》1988,6(6):365-372
A digital technique is presented for experimentally measuring the local wavenumber-frequency spectrum S
L(k, f) of a fluctuating velocity field using two probes. From S
L(k, f), the local wavenumber spectrum S
L(k), the averaged dispersion relation, and the broadening of the wavenumber spectrum for a given frequency can be determined. The technique is demonstrated by applying it to the velocity field of a plane wake which is undergoing transition from laminar to turbulent flow. A specially designed two sensor hotwire probe is used to obtain simultaneous records of streamwise velocity fluctuations at two locations having a fixed streamwise separation. New information is obtained concerning: the spatial characteristics of instability waves in the wake; the importance of local wavenumber matching in nonlinear coupling among waves; and broadening of the dispersion relation associated with the transition to turbulence. The usefulness of the S
L(k, f) approach when Taylor's hypothesis is not valid is also discussed. 相似文献
58.
This study extends upon a multi-echelon inventory model developed by Graves, introducing in the one-warehouse, N-retailer case—as Graves suggested—stochastic leadtimes between the warehouse and the retail sites in place of the original deterministic leadtimes. Effects of stochastic leadtimes on required base stock levels at the retail sites in the case where the warehouse carries no stock (e.g., serves as a cross-dock point) were investigated analytically. Two alternative treatments of stochastic leadtime distributions were considered. Using as a baseline Graves’ computational study under deterministic leadtimes, results of the current study suggest that it may be better to use the deterministic model with an accurately estimated mean leadtime than a stochastic model with a poorly estimated mean leadtime. 相似文献
59.
Francisco J. Solis 《Applied mathematics and computation》1999,100(2-3):169-175
We give a numerical algorithm to compute the dimension and local structures of attracting sets or invariant manifolds of smooth dynamical systems. This algorithm is based on local adaptive Galerkin bases and is tested for several examples. The important degrees of freedom that are preferentially selected, from the geometrical point of view, are found. 相似文献
60.
The process of oxide removal in crystalline Ge using a pulsed ultraviolet laser has been studied by means of real-time reflectivity measurements with nanosecond resolution. The interaction of laser radiation with a clean, oxide-free surface has been characterized and the inhomogeneous and homogeneous energy density melting thresholds of c-Ge for 193 nm radiation have been determined. The values are 180 and 370 mJ/cm2, respectively. We have demonstrated that it is possible to remove an oxide overlayer by irradiation in vacuum and to produce a surface that shows the same response to laser radiation as a smooth, oxide-free, chemically cleaned surface. Under certain specific irradiation conditions it is even possible, after removing the oxide overlayer, to produce an enhanced crystalline quality in the near-surface region compared to that obtained upon chemical cleaning as evidenced by Rutherford backscattering/channeling measurements. 相似文献