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

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

Tectomer-mediated optical nanosensors for tyramine determination

The development of optical sensors for in situ testing has become of great interest in the rapid diagnostics industry. We report here the development of simple, low-cost optical nanosensors for the semi-quantitative detection or naked-eye detection of tyramine (a biogenic amine whose production is commonly associated with food spoilage) when coupled to Au(III)/tectomer films deposited on polylactic acid (PLA) supports. Tectomers are two-dimensional oligoglycine self-assemblies, whose terminal amino groups enable both the immobilization of Au(III) and its adhesion to PLA. Upon exposure to tyramine, a non-enzymatic redox reaction takes place in which Au(III) in the tectomer matrix is reduced by tyramine to gold nanoparticles, whose reddish-purple color depends on the tyramine concentration and can be identified by measuring the RGB coordinates (Red–Green–Blue coordinates) using a smartphone color recognition app. Moreover, a more accurate quantification of tyramine in the range from 0.048 to 10 μM could be performed by measuring the reflectance of the sensing layers and the absorbance of the characteristic 550 nm plasmon band of the gold nanoparticles. The relative standard deviation (RSD) of the method was 4.2% (n = 5) with a limit of detection (LOD) of 0.014 μM. A remarkable selectivity was achieved for tyramine detection in the presence of other biogenic amines, especially histamine. This methodology, based on the optical properties of Au(III)/tectomer hybrid coatings, is promising for its application in food quality control and smart food packaging

Size and branching effects on the fluorescence of benzylic dendrimers possessing one apigenin fluorophore at the core

Different generations of dendrimers incorporating one fluorescent core of apigenin and three Fréchet benzylic dendrons have been prepared. The chief geometric features of these dendrimers have been obtained by Molecular Dynamics simulations. These computational data suggest that the asphericities of dendrimers belonging to the third and fourth generations are considerably larger than those associated with lower radii of gyration. Fluorescence spectra of high generation dendrimers evolve along time and quantum yields show an appreciable lowering for the fourth generation dendrimer. All these data suggest aggregation phenomena and lower quantum yields for nonspheric dendrimers in solution.Financial support by the Spanish Ministry of Economy and Competitiveness, with the participation of European Union (MINECO, projects CTQ2010-16959/BQU, CTQ2012- 35535 and Consolider-Ingenio CSD2007-00006), from the University of the Basque Country (UPV/EHU, UFI11/22 QOSYC), from the Basque Government (GV/EJ, grant IT-324-07), from the Donostia International Physics Center (DIPC), from the Ministry of Education, Youth and Sports of the Czech Republic (grant MSM6046137305), and Czech Science Foundation (projects 304/10/1951, P503/11/0616) is acknowledged. M. d. B. thanks the CSIC for the JAE-Pre contract funding for her PhD. The authors also thank the SGI/IZO-SGIker UPV/EHU and the DIPC for generous allocation of computational resources.Peer reviewe

Probing the interaction between 2D materials and oligoglycine tectomers

Heterostructures of 2D materials using graphene and MoS2, have enabled both pivotal fundamental studies and unprecedented sensing properties. These heterosystems are intriguing when graphene and MoS2 are interfaced with 2D sheets that emulate biomolecules, such as amino-terminated oligoglycine self-assemblies (known as tectomers). The adsorption of tectomer sheets over graphene and MoS2 modulates the physicochemical properties through electronic charge migration and mechanical stress transfer. Here, we present a systematic study by Raman spectroscopy and tectomer-functionalised scanning probe microscopy to understand mechanical strain, charge transfer and binding affinity in tectomer/graphene and tectomer/MoS2 hybrid structures. Raman mapping reveals distinctive thickness dependence of tectomer-induced charge transfer to MoS2, showing p-doping on monolayer MoS2 and n-doping on multilayer MoS2. By contrast, graphene is n-doped by tectomer independently of layer number, as confirmed by X-ray photoelectron spectroscopy (XPS). The interfacial adhesion between the amino groups and 2D materials are further explored using tectomer-functionalised probe microscopy. It is demonstrated here that these probes have potential for chemically sensitive imaging of 2D materials, which will be useful for mapping chemically distinct domains of surfaces and the number of layers. The facile tectomer-coating approach described here is an attractive soft-chemistry strategy for high-density amine-functionalisation of AFM probes, therefore opening promising avenues for sensor applications

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

Rapid enzymatic method for the determination of phosphoryl choline using the fluorescence of the enzyme choline oxidase. Sequential determination of choline and phosphorylcholine in milk powder for children

In this paper we present a rapid method for determining phosphorylcholine (ChoP). ChoP was first hydrolyzed by the enzyme alkaline phosphatase (AP); the choline formed was then submitted to a reaction with Choline Oxidase (ChOx). Both reactions were carried out simultaneously, in the same test without previous steps of incubation. The analytical signals used were the intrinsic fluorescence of ChOx due to FAD and that corresponding to a fluorescein derivative bonded to ChOx (ChOx-FS); both can be related with the concentration of ChoP. Once the conditions were optimized, the response range for ChoP was 5.2·10-7 - 1.0·10-5 M using the peak area as the analytical parameter with a precision of about 4% (RSD) at both ChOx and ChOx-FS wavelengths. In the experimental conditions found, it was also possible to determine free choline (Ch) with figures of merit similar to those obtained for ChoP. These results have made possible the sequential determination of Ch and ChoP in milk powder, using only one aliquot of the mixture, with good results. The recoveries obtained for both analytes were close to 100 %. The method is rapid because an incubation step is not necessary. Moreover, the enzymatic reaction is autoindicating and thus the additional detection step required by other published enzymatic methods is avoided. other published enzymatic methods is avoided.This work was supported by the Spanish Ministerio de Economía y Competitividad (MINECO) (CTQ 2012-34774) (CTQ 2012-35535), FEDER (EU) (CTQ 2008 06751 C02-01/BQU) and by the Regional Government of Aragón (DGA) (Support to Research Group E-74). Thanks to Dr. Jesús Martínez de la Fuente for providing the opportunity to use the BioTek Synergy HT Multi-Mode Microplate Reader.Peer reviewe

Validation of an automated extraction procedure for amino acids and acylcarnitines for use with tandem mass spectrometry for newborn screening

3 Tablas.- 1 Figura.- Datos suplementarios disponibles en la página web del editor.A certified reagent kit for newborn screening was transferred on a fully automated dried blood spot platform. The dried blood spot cards are directly eluted and the extract is online guided to tandem mass spectrometry instrument, where the amino acid and acyl carnitine panel is detected. The method takes 2 minutes per sample and requires no human interaction for up to 500 samples. The method is fully standardized through the automation and the usage of only certified consumables and reference material. The manual reagent kit was first modified to fit the automated platform, secondly validated and third, successfully transferred into a routine newborn screening laboratory.Peer reviewe