Determination of monoacylglycerides in biodiesel

As a modular and flexible technique, HPTLC-based hyphenated systems can be designed by combining different approaches concerning chromatographic development systems and detectors in a sequential mode. A hyphenated procedure is reported that provides quantitative determination of the monoacylglycerides as a compound class in the BX sample as well as the BX composition profile, all obtained from a single plate.Thanks to the Spanish Ministerio de Economia y Competitividad (MINECO) and FEDER (UE) (Plan Nacional de I+D+I, project CTQ2012-035535) and to DGA-ESF for financial support. MPL thanks MINECO for the grant BES-2013-063673.Peer reviewe

Gradient high-performance thin-layer chromatography for characterizing complex hydrocarbon-containing products

Classic saturates, aromatics, resins, and asphaltenes (SARA) analysis has long enabled the chromatographic separation of complex hydrocarbon-containing products into these four families. This simplification often does not provide sufficient or correct information on the relationship between the composition of the products and the process variables studied. The obtention of profiles by gradient automated multiple development (AMD) is an interesting alternative to obtain extended SARA separations with increasing level of complexity for heavy petroleum products that adequately represent the entirety of the sample. An optimized 20-step gradient based on tetrahydrofuran (THF)‒dichloromethane‒n-heptane over a total migration distance of 83 mm is proposed here to characterize all types of heavy oil products. The combination of ultraviolet (UV)–densitometry (at 201, 228, and 273 nm), fluorescence detection by intensity changes using berberine cation, together with on-plate recording of UV spectra of separated peaks and the comparison with those of standards, allow for a deep characterization of chemical families. In the apolar zone of the chromatogram saturates, naphthenes, naphteno-aromatics, alkyl-aromatics, and aromatics with different degrees of condensation are detected. The use of THF, both in the plate precleaning stage and in the first stages of the gradient, is responsible for the satisfactory resolution of the resins in the polar zone. AMD chromatographic zones can be related to peaks from hydrocarbon groups in classical SARA. The application of this gradient to different types of products allowed for the relation of the profiles of bitumen to their origin, differentiation of the resin part trapped in asphaltenes, control performance of deasphalting in hydrorefining products, and the control of the composition of base oils

About the stability of the dodecatoplet

A new investigation is done of the possibility of binding the "dodecatoplet", a system of six top quarks and six top antiquarks, using the Yukawa potential mediated by Higgs exchange. A simple variational method gives a upper bound close to that recently estimated in a mean-field calculation. It is supplemented by a lower bound provided by identities among the Hamiltonians describing the system and its subsystems.Comment: 5 pages, two figures merged, refs. added, typos correcte

Separation, determination and composition profile of lipids in biodiesel using hyphenation of gradient HPTLC with fluorescence detection by intensity changes and mass spectrometry

Trabajo presentado al 250th ACS National Meeting, celebrado en Boston (US) del 16 al 20 de agosto de 2015.Spanish MINECO and FEDER (UE) (Plan Nacional I+D+I, project CTQ2012-035535) and to DGA-ESF. M.P.L. thanks MINECO for grant BES-2013-063673).Peer Reviewe

Revisiting molecular weight distribution of polystyrenes using adsorption highperformance thin-layer chromatography

A repeatable separation of polystyrenes according to MW, from 1920 to 520000 u.m.a, has been obtained under adsorption conditions using a method that comprises the use of Lichrospher HPTLC plates, and a controlled, isocratic elution with a 78:22 (v/v) mixture of cyclohexane (Cy)-tetrahydrofuran (THF). Likewise, UV-densitometric quantification of polystyrenes in mixtures can be achieved, by an intra-plate or an inter-plate procedure, using the corresponding polystyrene calibration curve. In the case or overlapped, unresolved peaks, an average curve of the corresponding polystyrenes can be used. Migration of polystyrenes strongly varies with slight variations in the relative proportion of Cy and THF in the mobile phase. This allows different ranges of MW to be separated as a function of mobile phase composition. Other factors influencing repeatability have been identified. Some reasons have been advanced to explain the current lack of activity in the research on polymer characterization by HPTLC. Old literature results concerning polystyrene separation have also been discussed in the light of modern HPTLC instrumentation. Developed method provides similar information on Molecular Weight Distribution (MWD) to that obtained using Gel Permeation Chromatography (GPC). Advantages and limitations of HPTLC for obtaining polymer MWD have also been discussed.Authors thank the Spanish Ministerio de Ciencia e Innovación (MICINN) and FEDER (UE) for financial support (Plan Nacional de I+D+I, project CTQ2008-00959)Peer reviewe

Application of AMD to petrochemical analysis: improved separation and expanded hydrocarbon group type analysis of heavy petroleum products

P-123.-- Presented at the International Symposium for High‐Performance Thin‐Layer Chromatography, Lyon (France), 02nd-04th July, 2014.A complete molecular separation of heavy petroleum products is not feasible for their quality control. They are instead characterized in terms of chemical family composition, using classical Hydrocarbon Group Type Analysis such as SARA (Saturates, Aromatics, Resins, Asphaltenes). However, SARA does not provide information enough to correlate chemical differences of products with their conversion parameters in the case of heavy products. AMD appears as an interesting alternative to obtain different separations with increasing level of complexity for these products

Dark energy versus

We explore the possibility of discriminating dark energy models from the study of the growth of matter perturbations. For the sake of simplicity, instead of dealing with a great number of models, we have chosen a simple model of dark energy ($p_x=\omega_0\rho_{x}^{\gamma}$, with $\omega_00$; px, and $\rho_x$ being pressure and energy density), which is able to reproduce a great number of different behaviours. A combination of WMAP data with other results have been used to estimate model parameters. The study has been made for collapsing shells in spherical clusters virialized at redshifts $z=1$, 0.1 and 0.025 with line-of-sight velocity dispersion $\sigma_{\rm los}= 750$ and $1000~\rm km\, s^{-1}$. According to shell velocities, our dark energy models are clearly differentiated from the $\Omega_{\rm m0}=1$ model (the greater the $\sigma_{\rm los}$ is, the more differentiated the models are). However, the differences among dark energy models are not so large. From our results, the nearest clusters with large $\sigma_{\rm los}$ are the idoneous ones to discriminate models. In fact, we think that from observations of caustics in nearby spherical clusters, it would be possible to make an estimation of $\Omega_{\rm m0}$.

Separation, determination and composition profile of lipids in biodiesel using hyphenation of gradient HPTLC with fluorescence detection by intensity changes and mass spectrometry

Póster presented at the 250th ACS National Meeting, Boston (USA), 2015, 16th-20th august.We report here an on-line, hyphenated High-Performance Thin-Layer Chromatography (HPTLC)-based procedure on a unique silica gel plate that provides separation and quantitative determination of monoglycerides, diglycerides, and fatty acids in biodiesel (BX, X>5), as well as their composition profile in the sample. Sequential steps of hyphenation include: AMD gradient separation of lipid classes (using a 4-step gradient based on t-butyl methyl ether-dichloromethane-n-heptane; followed by a post-chromatographic impregnation of the plate with primuline (200 ppm), and densitometric detection and quantification using Fluorescence Detection by Intensity Changes (FDIC, >exc= 365 nm). Finally, the peaks are directly transferred from the impregnated plate to an ESI-MS spectrometer using a head elution-based TLC-MS interface for peak identification and obtention of fatty acid-related composition profiles of each lipid classAuthors thank the Spanish Ministerio de Economia y Competitividad (MINECO), FEDER (UE) (Plan Nacional de I+D+I, project CTQ2012-035535) and to DGA-ESF, for financial support. C.J. thanks CSIC and ESF for a JAE-doc grant