1,721,036 research outputs found
Accurate determination of total biophenols in unfractionated extra-virgin olive oil with the fast blue BB assay
Full text linkThe phenolic compounds of extra-virgin olive oil (EVOO) are key contributors of nutritional and sensory quality as well as chemical stability. The reference method for their determination is the HPLC-UV, which is cost-/time-expensive. In this work, total phenolic compounds were evaluated in unfractionated EVOO adapting the Fast Blue BB (FBBB) assay, which involves the spectrophotometric (absorbance at 420 nm) determination of azo derivatives resulting from the coupling of phenolic compounds with FBBB diazonium salt in alkali pH. When tested on 26 EVOO samples, the FBBB assay and HPLC-determinations were strikingly correlated (R2 = 0.9653), differently from FBBB and Folin-Ciocalteu assays, which showed poor correlation. The assay is simple, repeatable, robust, rapid and cheap, and results might be evaluated on a printed colorimetric scale. This protocol of the FBBB assay could be routinely used to categorize EVOO according to the health claim allowed by EFSA concerning the content of phenolic compounds
Mercury(II) Speciation in Natural Waters
No full textMercury(II) speciation in natural waters is proposed as a tutorial example for students interested in
equilibrium analysis. Accurate literature survey and database analysis are recommended as the starting point in
the study. Through a step-by-step approach students are invited to build up a speciation model in which the
contribution of Hg2+–chloride complexes, the hydrolysis of Hg2+, and the ternary HgOHCl(aq) species are taken
into account in that sequence. Observations from simple potentiometric and ESI-MS experiments are suggested
for the model refinement. It is shown how to use graphical methods and simple algebra to obtain a pictorial view
of the equilibria and a quantitative interpretation of it, which nicely fits data processing software results. Changes
in Mercury(II) speciation in passing from freshwaters to seawater are highlighted
Rare Earth Elements in Human and Environmental Health: Chapter 11 Rare Earth Elements Equilibria in Aqueous Media
No full textIn a chemical environment, the speciation, the distribution of an element within all the species that it may form, is necessary to know. Once the formation constants of the complexes that in each oxidation state the element may form with all the ligands present in the tissue are available, a still more detailed picture of the system can be obtained. Pressure, temperature, pH, total concentration of all the elements and the ligands, redox potential, ionic strength, determine the speciation of each element in any thermodynamic system at equilibrium. In this chapter a description of Equilibrium Analysis methodologies for speciation studies of real-world systems is proposed
Determination of metals in multicomponent system by differential pulse and alternating current anodic stripping voltammetry
No full textA combination of sensitive and selective voltammetric methods, namely differential pulse (DPASV) and fundamental and second harmonic alternating current anodic stripping voltammetry (ACASV) were found to be very suitable techniques for the simultaneous determination of metal species having half-wave potentials close to one another. The simultaneous determination of traces of CuII, BIII, SbIII, PbII, CdII and SnII is described using 0.1 M HCl as the supporting electrolyte with the subsequent addition of 0.02 M EDTA or 1.0 M NaOH (for the analysis of CuII, SbIII and SnII, respectively). A semistationary mercury electrode (long lasting sessile drop mercury electrode) was used as the working electrode. A saturated calomel electrode (SCE) and a platinum electrode were used as the reference and auxiliary electrodes, respectively. The analytical procedure was verified with the analysis of standard reference material NBS-SRM 631 Spectrographic Zinc Spelter LV1. Precision and accuracy, expressed as relative standard deviation and relative error, respectively, were 3 to 5%, while the detection limits were of the order of 10-8 to 10-10 M in the case of element examined
ACID BASE CHARACTERIZATION OF TRIAZOLO-TRIAZOLE HETEROCYCLIC SYSTEMS
No full textHeterocycles are key compounds of synthetic chemistry. Besides their long standing
and relevant application as drugs and bioactive compounds, aromatic heterocycles are
playing a fundamental role in modern material chemistry as building blocks of
conjugated active molecules in many emerging fields of organic electronics and
optoelectronics: conducting polymers, organic field-effect transistors,[1] organic solar
cells,[2] nonlinear optically active compounds.[3] In this work we propose a study of
acid-base properties of four [1,2,4]triazolo[3,2-c][1,2,4]triazole systems[4]. The
experimental method elected consists of potentiometric, spectrophotometric titrations,
in constant ionic medium NaCl 0.5M at 25.00±0.02°C. Electronic absorption spectra
have been interpreted with the following equilibria:
These results shown that the acid-base properties of [1,2,4]triazolo[3,2-
c][1,2,4]triazole derivatives critically depends on the substituents at the heterobicycle.
[1] J. Zaumseil, H. Sirringhaus, Chem. Rev., 2007, 107, 1296-1323; b) Y. Wen, Y. Liu, Adv.
Mater., 2010, 22,1-15.
[2] J. Li, A. C. Grimsdale, Chem. Soc. Rev. 2010, 39, 2399-2410.
[3] S. H. Jang, A. K. Jen, Introduction to Organic Electronic and Optoelectronic Materials
and Devices (Eds. S. S. Sun, L. R. Dalton) CRC Press, Boca Raton (FL), 2008.
[4] R. Centore, S. Fusco, A. Capobianco, V. Piccialli, S. Zaccaria, and A. Peluso, European
Journal of Organic Chemistry, 2013, 18, 3721-37
COMPLEX FORMATION BETWEEN PHYTIC ACID AND DIVALENT METAL IONS: A SOLUTION EQUILIBRIA AND SOLID STATE INVESTIGATION
No full text
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
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