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91.
Yulia B. Monakhova Svetlana P. Mushtakova Thomas Kuballa Dirk W. Lachenmeier 《Magnetic resonance in chemistry : MRC》2014,52(12):755-759
An eight‐fold suppression pulse sequence was recently developed to improve sensitivity in 1H NMR measurements of alcoholic beverages [Magn. Res. Chem. 2011 (49): 734–739]. To ensure that only one combined hydroxyl peak from water and ethanol appears in the spectrum, adjustment to a certain range of ethanol concentrations was required. To explain this observation, the structure of water–ethanol solutions was studied. Hydroalcoholic solutions showed extreme behavior at 25% vol, 46% vol, and 83% vol ethanol according to 1H NMR experiments. Near‐infrared spectroscopy confirmed the occurrence of four significant compounds (‘individual’ ethanol and water structures as well as two water–ethanol complexes of defined composition – 1 : 1 and 1 : 3). The successful multiple suppression can be achieved for every kind of alcoholic beverage with different alcoholic strengths, when the final ethanol concentration is adjusted to a range between 25% vol and 46% vol (e.g. using dilution or pure ethanol addition). In this optimum region, an individual ethanol peak was not detected, because the ‘individual’ water structure and the 1 : 1 ethanol–water complex predominate. The nature of molecular association in ethanol–water solutions is essential to elucidate NMR method development for measurement of alcoholic beverages. The presented approach can be used to optimize other NMR suppression protocols for binary water–organic solvent mixtures, where hydrogen bonding plays a dominant role. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
92.
Bilender P. Allahverdiev 《Mathematical Methods in the Applied Sciences》2019,42(1):229-236
In this study, maximal dissipative second‐order dynamic operators on semi‐infinite time scale are studied in the Hilbert space , that the extensions of a minimal symmetric operator in limit‐point case. We construct a self‐adjoint dilation of the dissipative operator together with its incoming and outgoing spectral representations so that we can determine the scattering function of the dilation as stated in the scheme of Lax‐Phillips. Moreover, we construct a functional model of the dissipative operator and identify its characteristic function in terms of the Weyl‐Titchmarsh function of a self‐adjoint second‐order dynamic operator. Finally, we prove the theorems on completeness of the system of root functions of the dissipative and accumulative dynamic operators. 相似文献
93.
Strategies for differentiation of isobaric flavonoids using liquid chromatography coupled to electrospray ionization mass spectrometry 下载免费PDF全文
Flavonoids are a class of secondary plant metabolites existing in great variety in nature. Due to this variety, identification can be difficult, especially as overlapping compounds in both chromatographic separations and mass spectrometric detection are common. Methods for distinguishing isobaric flavonoids using MS2 and MS3 have been developed. Chromatographic separation of various plant extracts was done with RP‐HPLC and detected with positive ESI‐MS operated in information‐dependent acquisition (IDA) mode. Two methods for the determination of flavonoid identity and substitution pattern, both featuring IDA criteria, were used together with the HPLC equipment. A third method where the collision energy was ramped utilized direct infusion. With the developed strategies, it is possible to differentiate between many isobaric flavonoids. Various classes of flavonoids were found in all of the plant extracts, in the red onion extract 45 components were detected and for 29 of them the aglycone was characterized, while the substituents were tentatively identified for 31 of them. For the strawberry extract, those numbers were 66, 30 and 60, and for the cherry extract 99, 56 and 71. The great variety of flavonoids, several of them isobaric, found in each of the extracts highlights the need for reliable methods for flavonoid characterization. Methods capable of differentiating between most of the isobars analyzed have been developed. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
94.
《Analytical letters》2012,45(9-10):939-962
Abstract The ET(30) scale of solvent polarity has been shown to be useful in examining many diverse analytical processes. It is based on the charge transfer absorption of 2,6-diphenyl-4-(2,4,6-triphenyl-N-pyridinio)phenolate (referred to as ET-30 in this paper). Unfortunately, use of the ET(30) scale has been hindered by (a) the lack of a commercial source of the ET-30 dye and (b) the lack of an English language synthetic procedure. Here we discuss recent applications of the ET(30) scale to analytical techniques, as well as a simplified procedure for the synthesis of ET-30. 相似文献
95.
Fabio Mazzotti Leonardo Di Donna Hicham Benabdelkamel Bartolo Gabriele Anna Napoli Giovanni Sindona 《Journal of mass spectrometry : JMS》2010,45(4):358-363
Pterostilbene (trans‐3,5‐dimethoxy‐4‐hydroxystilbene) is an active component found in several plant species, exhibiting important pharmacological properties. A new and reliable method of assaying this phyto compound in various matrices is presented; the assay is based on (1) the selectivity of liquid chromatography (LC) hyphenated with electrospray ionisation (ESI), (2) the specificity of a two‐step mass spectrometric analysis (MS/MS) and (3) the accuracy of the isotope dilution method. The labelled analogue may be conveniently synthesised in a few steps. The sensitivity of the method is confirmed by the very low limit of detection (LOD) and limit of quantitation (LOQ) values achieved in the assay of pterostilbene in two distinct fortified matrices, and is further supported by the observed accuracy values. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
96.
This paper deals with ultrasound medical image processing, particularly to filter the noise while preserving the edges and
structures of information. The mathematical processing consists in solving by a numerical way a nonlinear evolutive boundary
value problem. Several numerical semi-implicit time marching schemes are considered and analyzed. At each time step, parallel
synchronous or asynchronous Schwarz alternating methods are used to solve the linear system and its convergence is studied.
Lastly, the results of sequential and parallel simulations are presented.
相似文献
97.
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99.
A new family of univariate exponential slash distribution is introduced, which is based on elliptical distributions and defined by means of a stochastic representation as the scale mixture of an elliptically distributed random variable with respect to the power of an exponential random variable. The same idea is extended to the multivariate case. General properties of the resulting families, including their moments and kurtosis coefficient, are studied. And inferences based on methods of moment and maximum likelihood are discussed. A real data is presented to show this family is flexible and fits much better than other related families. 相似文献
100.