Vicente L. Cebolla
Spanish National Research Council
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Featured researches published by Vicente L. Cebolla.
Critical Reviews in Analytical Chemistry | 2000
Bhajendra N. Barman; Vicente L. Cebolla; Luis Membrado
Recent developments in chromatographic techniques for the separation and quantitative characterization of petroleum and related products are highlighted. Specifically, scope, applicability, and versatility of individual techniques such as gas chromatography, liquid chromatography, supercritical fluid chromatography, thin-layer chromatography, and sizeexclusion chromatography are discussed in some detail. In general, analytical approaches vary widely depending on the chromatographic technique, instrumentation, minimum detection limit, and sample type. Specific applications include chromatographic separation followed by identification and determination of individual components, measurement of boiling range distribution, and determination of hydrocarbon group types. With the exception of gaseous samples and light distillates (up to gasoline range materials), the inherent complexity arising from the presence of numerous isomers and compound types, and the finite resolution afforded by chromatographic methods preclude precise identification and quantitative determination of individual components in fossil fuels and oils. For the middle and heavy distillates, chromatographic techniques have been applied mostly for the isolation and determination of compound classes. Several techniques such as open-column liquid chromatography, medium pressure liquid chromatography, high-performance liquid chromatography, and supercritical fluid extraction provide separation of compound classes for subsequent characterization by highresolution chromatography, spectroscopy, or other methods. Hyphenated or multitechnique chromatographic approaches have also been described. These simplify the characterization of complex samples by incorporating multiple separation mechanisms and detection schemes.
Journal of Organic Chemistry | 2010
Maialen Aginagalde; Yosu Vara; Ana Arrieta; Ronen Zangi; Vicente L. Cebolla; Arantzazu Delgado-Camón; Fernando P. Cossío
The reaction between benzynes and imidazo[1,2-a]pyridines (pyrimidines) to form benzo[a]imidazo[5,1,2-cd]indolizines and 2,3,9c-triazocyclopenta[j,k]fluorenes has been studied computationally and experimentally. It is found that these reactions take place via tandem [(pi)8(s) + (pi)2(s)] and [(sigma)2(s) + (pi)6(s) + (sigma)2(s)] processes. The [8 + 2] cycloaddition steps are essentially barrierless, and the aromatization steps occur via highly synchronous aromatic transition structures. From an experimental standpoint, the reaction is feasible under microwave irradiation and using 2-(trimethylsilyl)phenyl triflates as benzyne precursors. Depending on the substitution pattern in the starting triflate a complete regiocontrol of the reaction can be achieved. The tetracyclic compounds thus prepared emitted blue light when excited at 365 nm and exhibited interesting photophysical properties.
Biosensors and Bioelectronics | 2014
Melisa del Barrio; Susana de Marcos; Vicente L. Cebolla; Josef Heiland; Stefan Wilhelm; Thomas Hirsch; Javier Galbán
A new approach for the design of a fluorometric biosensor for continuous monitoring of glucose levels in biological samples based on near-infrared (NIR) excitation is described. The sensor combines the fluorescence of the enzyme glucose oxidase (GOx) chemically modified with a fluorescein derivative (FS) and the luminescent properties of upconverting luminescent nanoparticles (UCLNPs). Both, the chemically modified enzyme (GOx-FS) and the UCLNPs are immobilized in a poly(acrylamide) film as a physical support. The excitation of the UCLNPs with NIR light is of major advantage, since fluorescence background from the matrix is minimized. The upconverted luminescence is used to excite GOx-FS, which undergoes a change in the fluorescence intensity during the enzymatic reaction with glucose. The sensor comprises sufficient stability and covers the physiological range of glucose levels in blood. Furthermore, in a proof of principle experiment, the sensor system responds linearly to glucose concentrations in the range from 3.3 to 16.6 mM in flow injection analysis mode.
Fuel Processing Technology | 1993
M.T. Martínez; Isaías Fernández; Ana M. Benito; Vicente L. Cebolla; J.L Miranda; H.H. Oelert
Abstract A Spanish subbituminous coal has been processed in two-stage liquefaction in a non-integrated process. The first-stage coal liquefaction has been carried out in a continuous pilot plant in Germany at Clausthal Technical University at 400°C of temperature, 20 MPa hydrogen pressure and anthracene oil as solvent. The second-stage coal liquefaction has been performed in continuous operation in a hydroprocessing unit at the Instituto de Carboquimica at 450°C and 10 MPa hydrogen pressure, with two commercial catalysts: Harshaw HT-400E (Co-Mo/Al 2 O 3 ) and HT-500E (Ni-Mo/Al 2 O 3 ). The total conversion for the first-stage coal liquefaction was 75.41 wt% (coal d.a.f.), being 3.79 wt% gases, 2.58 wt% primary condensate and 69.04 w% heavy liquids. The heteroatoms removal for the second-stage liquefaction was 97–99 wt% of S, 85–87 wt% of N and 93–100 wt% of O. The hydroprocessed liquids have about 70% of compounds with boiling point below 350°C, and meet the sulphur and nitrogen specifications for refinery feedstocks. Liquids from two-stage coal liquefaction have been distilled, and the naphtha, kerosene and diesel fractions obtained have been characterized.
Journal of Chromatography A | 2011
Vicente L. Cebolla; Carmen Jarne; Pilar Domingo; Aránzazu Delgado-Camón; Rosa Garriga; Javier Galbán; Luis Membrado; Eva M. Gálvez; Fernando P. Cossío
Changes in emission of berberine cation, induced by non-covalent interactions with lipids on silica gel plates, can be used for detecting and quantifying lipids using fluorescence scanning densitometry in HPTLC analysis. This procedure, referred to as fluorescence detection by intensity changes (FDIC) has been used here in combination with automated multiple development (HPTLC/AMD), a gradient-based separation HPTLC technique, for separating, detecting and quantifying lipids from different families. Three different HPTLC/AMD gradient schemes have been developed for separating: neutral lipid families and steryl glycosides; different sphingolipids; and sphingosine-sphinganine mixtures. Fluorescent molar responses of studied lipids, and differences in response among different lipid families have been rationalized in the light of a previously proposed model of FDIC response, which is based on ion-induced dipole interactions between the fluorophore and the analyte. Likewise, computational calculations using molecular mechanics have also been a complementary useful tool to explain high FDIC responses of cholesteryl and steryl-derivatives, and moderate responses of sphingolipids. An explanation for the high FDIC response of cholesterol, whose limit of detection (LOD) is 5 ng, has been proposed. Advantages and limitations of FDIC application have also been discussed.
Chromatographia | 2002
Vicente L. Cebolla; M. Matt; Eva M. Gálvez; Luis Membrado; María Pilar Domingo; J. Vela; N. Beregovtsova; V. Sharypov; B. N. Kuznetsov; N. Marin; J.V. Weber
SummaryTwo alternative methods, based on Thin-Layer Chromatography (TLC) with Fluorescence Scanning Densitometry have been developed for characterization of heavy liquids from copyrolysis of different kinds of biomass and plastics in autoclaves under inert atmosphere.A conventional TLC system, which includes a vertical developing tank, and a High Performance TLC (HPTLC) system, with a horizontal developing chamber and the use of HPTLC plates, have been used. The analytical method involves in both cases the measurement of two chromatograms per sample: the first, on a silica gel berberine-impregnated plate, for detection of saturates using the phenomenon of berberine-induced fluorescence; and the second, on a silica gel plate, for detection of aromatic-polars and polars, by native fluorescence.Although the HPTLC system is more sensitive and faster, both techniques represent an improvement with regard to current methods for analyzing these kinds of products. However their application depends on the particular solubility of each sample and on its slope of the fluorescent response-sample load regression.
Chromatographia | 1996
Vicente L. Cebolla; J. Vela; Luis Membrado; Ana C. Ferrando
SummaryA rapid and quantitative method for compound class characterization of coal-tar pitches without previous fractionation, using an improved TLC method with an FID system, has been developed. Results show adequate accuracy and precision, including the sampling step.A fast calibration method, based on a variation of the internal normalization procedure, can be used for up to 18 μg of whole sample application, avoiding the usually tedious absolute calibration in such analyses. This range is more than sufficient in view of the small amounts usually spotted in this technique.Speed of sample application by autospotter influences the shape of the peak nearest the point of application. For the coal tar pitch studied (9 wt.% non-eluted), slow application (0.5 μL min−1) gives a non-eluted Gaussianintegratable peak. A faster speed (10 μL min−1) is usable for analysing fossil products with lower non-eluted content. Total analysis time is less than 2 h, a considerably improvement on current methods.
Fuel | 2001
D. Cagniant; Igor E. Nosyrev; Vicente L. Cebolla; J. Vela; Luis Membrado; René Gruber
Abstract The reductive alkylation of a French petroleum asphaltene (Lagrave) was studied with potassium in THF, in absence of an electron transfer reagent. From the number of butyl and benzyl groups added to the starting asphaltene, the difference of reactivity of the alkyl reagents, butyl iodide and benzyl bromide, was pointed out. Special attention was focused on the cleavage of C–S and C–O linkages in relation to the structural modifications. From the number of hydrogen atoms added during the reduction step, it was concluded that the sulphide linkages are mainly of aryl-S-aryl, aryl-S-alkyl or alkyl-S-alkyl types. The TLC-FID (Iatroscan) analysis was found to be very suitable to follow the “depolymerization” process of the asphaltene, qualitatively as well as quantitatively, by the application of quantitative hydrocarbon group type analysis.
ChemPhysChem | 2012
Vicente L. Cebolla; Elena Mateos; Rosa Garriga; Carmen Jarne; Luis Membrado; Fernando P. Cossío; Eva M. Gálvez; Muriel Matt; Arantzazu Delgado-Camón
Changes in fluorescence emission due to non-covalent analyte-fluorophore interactions in silica gel plates are studied and used as a general detection procedure for thin-layer chromatography (TLC). The presence of the analyte modifies the microenvironment of the fluorophore and thus changes the balance between radiative (k(r)) and non-radiative (k(nr)) emission constants. A model is proposed for analyte-fluorophore induced electrostatic interactions, which depend on analyte polarizability and are responsible for fluorescence enhancements. As consequence of these induced interactions, the analyte creates an apolar environment that prevents non-fluorescent decay mechanisms, decreasing k(nr). On the other hand, the effect of an increase in refractive index on k(r) is investigated, as it contributes to some extent to fluorescence enhancements in silica gel medium. Changes in fluorescence emission should be regarded as a general property of fluorophores in the presence of analytes, and criteria that fluorophores should meet to be used as sensitive TLC probes are discussed here.
Fuel | 1985
A.M. Mastral; Vicente L. Cebolla; JoséMa Gavilán
The FT-i.r. and 1H n.m.r. spectroscopic analyses of oils or maltenes from a Spanish lignite (Utrillas, Teruel), are reported. These oils were obtained by depolymerization with alkyl aromatic ethers (anisole, 3-methylanisoleand 1,3-dimethoxybenzene) catalyzed by Lewis acids ZnCl2, AlCl3, SbCl3and BF3 (as boron trifluoride etherate), at atmospheric pressure and temperatures <220 °C. Bands due to aromatic ethers in the i.r. and n.m.r. spectra of the oils obtained by depolymerization indicate solvent incorporation. Oils obtained by direct lignite extraction showed 25% aromatic H and some Hα (≈3%) without OH groups. These appeared in some oils obtained by depolymerization with AlCl3 and were due to secondary reactions with the aromatic extract. Oils derived from processes with good yields showed increases in aromaticity. The extent of substitution of aromatic rings in oils obtained by depolymerization was less than for oils directly extracted. All the oils studied show a low degree of condensation.