1,720,961 research outputs found
Optimizing Separation Conditions for Riboflavin, Flavin Mononucleotide and Flavin Adenine Dinucleotide in Capillary Zone Electrophoresis with Laser-Induced Fluorescence Detection
No full textA method was developed for the quantitative determination of riboflavin, flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), using free solution capillary zone electrophoresis in uncoated fused-silica capillaries with laser-induced fluorescence (LIF) detection. Various factors influencing the separation and detection of flavin vitamers were investigated, including pH (5.5-10.5), concentration and nature of the run buffer (phosphate, borate and carbonate), applied voltage (15-30 kV), temperature (15-30degreesC) and injection time. Optimal resolution and detection were obtained with a pH 9.8, 30 mM aqueous phosphate buffer at 15degreesC and 30 kV of applied voltage. LIF detection was obtained with a He-Cd laser source using an excitation wavelength at 442 nm and lambda(cm)greater than or equal to515 nm. Riboflavin could be determined in the concentration ranges 0.5-350 mug/l with a rather low detection limit (LOD) down to 50 amol. The LODs of FAD and FMN were slightly higher, 300 and 350 amol, respectively. Combined with a simple clean-up procedure, the practical utility of this method is illustrated by the measurements of flavin derivates in foods and beverages, such as wines, milk, yoghurt and raw eggs. (C) 2002 Published by Elsevier Science B.V
Enhanced Stability and Electrocatalytic Activity of a Ruthenium-Modified Cobalt-Hexacyanoferrate Film Electrode
No full textThe electrochemical behaviour and electrocatalytic activity of a ruthenium-modified cobalt-hexacyanoferrate (CoHCF) thin film electrode, grown electrochemically on a glassy carbon substrate, is described. The modification, accomplished by potential cycling a freshly prepared CoHCF film electrode in acidic 50 mM NaCl solutions (pH 2-3 with HCl) containing ruthenium(III)chloride. represents a very effective contribution to the maintenance of electrode stability. Indeed, whereas a continuous decay over a few hundred redox scans at the parent CoHCF was observed, the resulting Ru-modified CoHCF film electrode exhibits greatly improved stability and enhanced electrocatalytic activity. Fifteen thousand redox scans at 100 mV/s caused the peak current to decrease by only about 10% by virtue of the strong stability of the Ru-modified CoHCF film electrode. Such an excellent stability is likely imparted by the formation of an extended network of dinuclear [Fe, Ru] ore-bridged, and has been interpreted by the insertion of Ru-O- moieties within the hydrated microparticles of CoHCF. Some examples are also presented which illustrate the excellent electrocatalytic capability in acidic solutions (pH 3) of the ruthenium-modified film towards the oxidation of hydrazine, thiosulfate, and p-chlorophenol. The catalytic oxidation currents observed are proportional to the concentration of hydrazine up to about 5 mM with a sensitivity of 2.7 mu A mM(-1) mm(-2) and correlation coefficient of 0.999. (C) 1999 Elsevier Science S.A. All rights reserved
Determination of hidden milk allergens in meat-based foodstuffs by liquid chromatography coupled to electrospray ionization and high-resolution tandem mass spectrometry
Full text linkThe issue of deliberate addition of antigenic proteins to foodstuffs for ameliorating bulk properties or the unintentional cross-contamination poses potentially life-threatening health problems to susceptible subjects. Even the intake of food products declaring the absence of allergens on their labels could lead to severe risks for sensitive consumers due to the presence of the so-called "hidden allergens". Thus, the quantification of low-abundant proteins as putative allergens has become mandatory. Herein, we present a sensitive and selective analytical method based on reversed-phase liquid chromatography coupled to electrospray ionization and hybrid orbitrap high-resolution mass spectrometry (RPLC-ESI-HRMS) and tandem MS, identifying, and quantifying allergenic milk proteins in complex meat-based foodstuffs from direct measurement of tryptic peptides. Two signature peptides of alpha-S1-casein and beta-lactoglobulin, i.e., FFVAPFPEVFGK (m/z 692.868(2+)) and TPEVDDEALEK (m/z 623.295(2+)), respectively, were chosen to search for hidden allergens in meat-based samples such as cooked meat, sausages, and sterilised pate. The marker peptides were identified and were exploited for method validation including recovery, matrix effect, precision, linearity, method variation, limit of detection, and limit of quantification. The undeclared occurrence of milk allergens as total milk protein content (TCMP) was verified in commercial meat products; beef and pork pate were meat-based products which require a major alert because up to 22 mu g(TCMP)/g of matrix i.e. more than 10 times the action level was determined
Phospholipidomics of human blood microparticles
No full textThe phospholipidome of blood microparticles
(MPs) obtained from platelet-rich plasma of healthy individuals
was characterized by hydrophilic interaction liquid chromatography
(HILIC) coupled to electrospray ionization tandem mass
spectrometry (ESI-MS/MS). The HILIC separation, performed
on a silica stationary phase using an acetonitrile/methanol gradient,
enabled the separation of several phospholipids (PL) classes, viz.,
phosphatidyl-cholines (PCs), -ethanolamines (PEs), -serines (PSs),
-inositoles (PIs), sphyngomielins (SMs), and lyso forms of PCs and
PEs. Structural characterization of species belonging to each class
was performed by MS/MS measurements, in either positive or
negative ion mode. The set of 131 phospholipids (including
regioisomers) here identified represents the most comprehensive
phospholipidomic characterization reported for human MPs. Although the phospholipidome composition of MPs and platelets,
collected from the same donors, was found to be qualitatively the same, quantitative differences were evidenced for lyso-PCs,
which appear to be significantly more abundant in MPs
Analysis of surfactants by mass spectrometry: Coming to grips with their diversity
No full textSurfactants are surface-active agents widely used in numerous applications in our daily lives as personal care products, domestic, and industrial detergents. To determine complex mixtures of surfactants and their degradation products, unselective and rather insensitive methods, based on colorimetric and complexometric analyses are no longer employable. Analytical methodologies able to determine low concentration levels of surfactants and closely related compounds in complex matrices are required. The recent introduction of robust, sensitive, and selective mass spectrometry (MS) techniques has led to the rapid expansion of the surfactant research field including complex mixtures of isomers, oligomers, and homologues of surfactants as well as their chemically and biodegradation products at trace levels. In this review, emphasis is given to the state-of-the-art MS-based analysis of surfactants and their degradation products with an overview of the current research landscape from traditional methods involving hyphenate techniques (gas chromatography-MS and liquid chromatography-MS) to the most innovative approaches, based on high-resolution MS. Finally, we outline a detailed explanation on the utilization of MS for mechanistic purposes, such as the study of micelle formation in different solvents
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Superbasic alkyl‐substituted bisphosphazene proton sponges: a new class of deprotonating matrices for negative ion matrix‐assisted ionization/laser desorption mass spectrometry of low molecular weight hardly ionizable analytes
No full textRATIONALE: Here hardly ionizable and low molecular weight compounds are detected in negative ion mode by using novel superbasic proton sponges based on 1,8-bisphosphazenylnaphthalene (PN) as MALDI matrices. Among the selected proton sponges, 1,8-bis(trispyrrolidinophosphazenyl)naphthalene (TPPN) has shown the best behaviour as matrix since it allows the direct detection of intact cholesterol without derivatization also in real challenging samples. METHODS: Very weakly acidic compounds such as sterols, steroids, fatty alcohols and saccharides were detected in reflectron negative ion mode by a MALDI TOF/TOF systemequipped with a neodymium-doped yttriumlithiumfluoride (Nd:YLF) laser (345 nm) with typical mass accuracy of 10 ppm. MS/MS experiments were performed by using ambient air as the collision gas. RESULTS: Contrary to traditional MALDI matrices, superbasic proton sponges allowed the easy deprotonation of an alcohol functional group without a previous chemical derivatization step. Experimental evidence indicates that analyte deprotonation is achieved in the condensed phase, i.e. PN superbasic proton sponges operate according to a recently proposed model named matrix assisted ionization/laser desorption (MAILD). A detection limit of 3 pmol/spot of cholesterol (model compound) with a signal-to-noise ratio = 10 was typically obtained. CONCLUSIONS: For the first time, the usefulness of novel superbasic proton sponges is demonstrated for MALDI detection of hardly ionizable compounds such as sterols, steroids, fatty alcohols and saccharides. The leading candidate TPPN has been successfully applied for negative ion MAILD-MS analysis of cholesterol, fatty acids and phospholipids in egg yolk and brain tissue extracts
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