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231.
Gika H Theodoridis G Mattivi F Vrhovsek U Pappa-Louisi A 《Journal of separation science》2012,35(3):376-383
The analysis of amino acids presents significant challenges to contemporary analytical separations. The present paper investigates the possibility of retention prediction in hydrophilic interaction chromatography (HILIC) gradient elution based on the analytical solution of the fundamental equation of the multilinear gradient elution derived for reversed‐phase systems. A simple linear dependence of the logarithm of the solute retention (ln k) upon the volume fraction of organic modifier (φ) in a binary aqueous‐organic mobile is adopted. Utility of the developed methodology was tested on the separation of a mixture of 21 amino acids carried out with 14 different gradient elution programs (from simple linear to multilinear and curved shaped) using ternary eluents in which a mixture of methanol and water (1:1, v/v) was the strong eluting member and acetonitrile was the weak solvent. Starting from at least two gradient runs, the prediction of solute retention obtained under all the rest gradients was excellent, even when curved gradient profiles were used. Development of such methodologies can be of great interest for a wide range of applications. 相似文献
232.
Fedrizzi B Carlin S Franceschi P Vrhovsek U Wehrens R Viola R Mattivi F 《The Analyst》2012,137(16):3725-3731
In recent times we have seen the development of many "-omics" technologies. One of the youngest is undoubtedly metabolomics, which aims to define the whole chemical fingerprint unique to each specific organism. The development and optimisation of an untargeted high-throughput method capable of investigating the volatile fraction of a biological system represents a crucial step for the success of such holistic approaches, and specific optimisation criteria must be developed in connection with suitable experimental designs. In this paper experimental designs (D-optimal) were applied for the first time as an automatic optimisation tool to an untargeted HS-SPME-GC-TOF method. In this case, optimal conditions correspond to a maximal number of detected features, in order to provide a fingerprint that is as complete as possible. The system under study is the grape berry. Four variables were considered: the type of fibre, extraction time, equilibration time and temperature. The results show that the D-optimal design methodology provides an easily interpretable assessment of experimental settings. This and other specific properties of the D-optimal design, such as the possibility to explicitly exclude certain experimental conditions, make it an extremely suitable strategy for method optimisation in untargeted metabolomics. 相似文献
233.
Gika H Theodoridis G Mattivi F Vrhovsek U Pappa-Louisi A 《Analytical and bioanalytical chemistry》2012,404(3):701-709
The development and application of new separation mechanisms such as hydrophilic interaction chromatography (HILIC) is of high importance for the simultaneous analysis of polar molecules such as primary metabolites. However the retention mechanism in HILIC is not fully understood and as a result retention prediction tools are not at hand for this chromatographic approach. In the present report we study the utility of a simple algorithm, based on a simple linear and/or a simple logarithmic retention model, for retention prediction in HILIC gradient separation of a mixture of 23 selected compounds including (poly)amines, amino acids, saccharides, and other molecules. Utilizing two types of gradient elution programs with or without an isocratic part, retention data were collected in order to build prediction models. Starting from at least three gradient runs the prediction of analyte retention was very satisfactory for all gradient programs tested, providing useful evidence of the value of such retention time prediction methodologies. 相似文献
234.
The branching ratio of the excited-state population at the conical intersection between the S(1) and S(0) energy surfaces (Φ(CI)) of a protonated Schiff base of all-trans retinal in protic and aprotic solvents was studied by multipulse ultrafast transient absorption spectroscopy. In particular, pump-dump-probe experiments allowed to isolate the S(1) reactive state and to measure the photoisomerization time constant with unprecedented precision. Starting from these results, we demonstrate that the polarity of the solvent is the key factor influencing the Φ(CI) and the photoisomerization yield. 相似文献
235.
236.
Antonio Monopoli Giovanni Ventura Andrea Aloia Fulvio Ciriaco Angelo Nacci Tommaso R. I. Cataldi Cosima D. Calvano 《Molecules (Basel, Switzerland)》2022,27(8)
A significant area of study and upgrading for increasing sensitivity and general performances of matrix-assisted laser-desorption ionization (MALDI) mass spectrometry (MS) is related to matrix design. Several efforts have been made to address the challenge of low-mass-region interference-free for metabolomics analysis and specifically for lipidomics. To this aim, rationally designed matrices as 4-chloro-α-cyanocinnamic acid (ClCCA) were introduced and reported to provide enhanced analytical performances. We have taken this rational design one step further by developing and optimizing new MALDI matrices with a range of modifications on the CHCA core, involving different functionalities and substituents. Of particular interest was the understanding of the electron-withdrawing (e.g., nitro-) or donating (e.g., methoxy-) effects along with the extent of conjugation on the ionization efficiency. In the present work, ten matrices were designed on a reasonable basis, synthesized, and characterized by NMR and UV spectroscopies and laser desorption ionization. With the assistance of these putative MALDI matrices, samples containing phospholipids (PL), and neutral di-/tri-acylglycerols (DAG, TAG) were investigated using milk, fish, blood, and human plasma extracts. In comparison with CHCA and ClCCA, four of them, viz. [(2E,4E)-2-cyano-5-(4-methoxyphenyl)penta-2,4-dienoic acid] (1), [(2E,4E)-2-cyano-5-(4-nitrophenyl)penta-2,4-dienoic acid] (2), [(E)-2-cyano-3-(6-methoxynaphthalen-2-yl)acrylic acid] (6) and [(E)-2-cyano-3-(naphthalen-2-yl)acrylic acid] (7) displayed good to even excellent performances as MALDI matrices in terms of ionization capability, interference-free spectra, S/N ratio, and reproducibility. Especially compound 7 (cyano naphthyl acrylic acid, CNAA) was the election matrix for PL analysis and matrix 2 (cyano nitrophenyl dienoic acid, CNDA) for neutral lipids such as DAG and TAG in positive ion mode. 相似文献
237.
Fulvio Melia 《Annalen der Physik》2023,535(9):2300157
The energy conditions in general relativity are introduced to establish powerful theorems without having to restrict their applicability to specific choices of the stress-energy tensor. They are famously invoked, e.g., to prove the singularity theorems of Penrose and Hawking, but have also been applied elsewhere, including various tests of certain cosmological theories. These conditions have become somewhat controversial, however, because they appear to be violated by commonly accepted scenarios, such as inflation shortly after the Big Bang and late-time acceleration of the cosmic expansion. But accommodating these processes by abandoning all of the energy conditions will promote other disquieting possibilities, including the breakdown of causality with traversable wormholes and closed timeloops. This paper advocates for the opposite viewpoint, demonstrating that the ‘numen’ scalar field, derived from the zero active mass condition in general relativity, satisfies all of the energy conditions in the early Universe. This unique feature among scalar fields adds to its success in accounting for the observed properties of the cosmic microwave background better than its inflationary counterpart. Specifically, numen's complete consistency with all of the energy conditions, and inflation's violation of at least one of them, provides additional justification for theoretically favoring the former over the latter. 相似文献