Comparison of different sample preparation treatments for the analysis of wine phenolic compounds in human plasma by reversed phase high-performance liquid chromatography

Phenolic compounds are common constituents of wine. Due to their healthy properties the analysis in human fluids is interesting within bioavailability evaluation. They have been reported not to be stable in human plasma, particularly at room temperature. Most sample treatments have been reported for a single compound. Our aim in this paper is to study sample handling control conditions and improve phenolic stability in human plasma samples. We tested various sample treatments to determine whether they could be used for analysing a set of phenolic compounds usually present in wines.The compounds studied were six phenolic acids, five flavonoids, trans-resveratrol and tyrosol. The effect of the following factors was explored: temperature, pH, the addition of antioxidants and the addition of anticoagulants.The results suggest that the plasma samples should be kept at temperatures below −20 °C before analysis and that 1% ascorbic acid plus 10 μl/ml o-phosphoric acid should be added. Anticoagulants (heparin or EDTA) do not play a significant role in the stability of polyphenolic compounds.The recovery values of a number of sample treatments (solid phase extraction, extraction with methanol, deproteinization, inhibition of enzymatic plasma activity) were compared. The recovery values for most phenolic compounds were better if the enzymatic plasma activity was inhibited and acidified ethanol was used for deproteinization.     

Headspace solid-phase microextraction method for determining 3-alkyl-2-methoxypyrazines in musts by means of polydimethylsiloxane-divinylbenzene fibres

A method for determining 2-methoxypyrazine, 3-methyl-, 3-ethyl-, 3-isopropyl-, 3-sec.-butyl- and 3-isobutyl-2-methoxypyrazine in musts is described. It involves headspace solid-phase microextraction (SPME) and determination by capillary gas chromatography using nitrogen–phosphorous detection. Pyrazines were satisfactorily separated under isothermal conditions, and quantification was carried out using 3-isopropyl-2-ethoxypyrazine as the internal standard. Ionic strength, time and temperature were studied in order to make SPME as efficient as possible. The developed method enabled detection limits at the 0.1 ng l⁻¹ levels for some of the analytes. The method was successfully applied to identify and quantify different 3-alkyl-2-methoxypyrazines in experimental musts of Cabernet Sauvignon and Merlot. Their evolution during the ripening was also monitored.     

Patterns in the precision of quantitative data from multicomponent gas chromatographic or gas chromatographic-mass spectrometric analysis

The dispersion of the quantitative results in the analysis of volatile compounds from multicomponent mixtures by different fractionation techniques (solid-phase microextraction and direct thermal desorption) followed by GC or GC-MS presents nonrandom patterns related to the existence of different factors in the fractionation process or in the chromatographic separation which affect, to a different extent, the recovery of the sample components. Statistical techniques have been used to show the relative importance of these factors. The improvement in data precision achieved by using volatile compound concentration ratios is discussed.     

A two-stage approach to automatic determination of 1H NMR coupling constants

(1)H NMR scalar coupling constants are a rich source of information on molecular structure, but their extraction from spectra can be less than straightforward. Previous approaches to J extraction include methods proposed by Hoye, Golotvin, and the 'modified J-doubling' method. Here we describe the ACCA method, currently implemented in the NMR package MestReC, which allows a high degree of automation in the extraction of coupling patterns even in the case of complex multiplets with sublinewidth splitting. The new approach is illustrated by application to strychnine, for which it has detected previously unreported couplings.     

Extraction of the [(C4H9)4N]3[Fe(SCN)6] ion-pair with chloroform: Spectrophotometric determination of iron

When excesses of ammonium thiocyanate and tetrabutylammonium chloride are added to an iron(III) solution, a water-insoluble ion-pair is formed. This compound is soluble in chloroform and other organic solvents. The variables affecting extraction with CHCl₃ are studied in order to obtain the optimal conditions and an extraction procedure is proposed. The separation of iron as a previous step to its spectrophotometric determination is studied.     

Interaction of UO2 2+ with sodium dodecyl sulfate micelles: association of phenols to micelles through fluorescence quenching data

Time-resolved laser-induced fluorescence (TRLIF) has been used to study the interaction of uranyl ion with sodium dodecyl sulfate (SDS) micelles in H(3)PO(4) 1 M. The titration curve consists of two curved regions with different slopes, one of them more pronounced at low concentration of SDS and the other, with a less pronounced positive slope at larger [SDS] until a plateau is reached. The fluorescence quenching of uranyl ion by para-substituted phenol compounds was studied by TRLIF and steady-state emission intensity measurements. The results were interpreted in terms of binding of phenolic compounds to the micelle. The binding constant (K(Q)) as well as the entrance and exit rate constants were determined for all the quenchers used.     

Multiple-steering QM-MM calculation of the free energy profile in chorismate mutase

A novel technique for computing free energy profiles in enzymatic reactions using the multiple steering molecular dynamics approach in the context of an efficient QM-MM density functional scheme is presented. The conversion reaction of chorismate to prephenate catalyzed by the Bacillus subtilis enzyme chorismate mutase has been chosen as an illustrative example.     

Synthesis and photoluminescent properties of 1,1'-binaphthyl-based chiral phenylenevinylene dendrimers

New chiral, soluble binaphthyl derivatives that incorporate stilbenoid dendrons at the 6,6'-positions have been prepared. The synthesis of the new enantiopure dendrimers was performed in a convergent manner by Horner-Wadsworth-Emmons (HWE) reaction of the appropriately functionalized 1,1'-binaphthyl derivative (R)-1 and the appropriate dendrons (R)(2n)G(n)-CHO. Different electroactive units were incorporated in the peripheral positions of the dendrons in order to tune both the optical and electrochemical behavior of these systems. Fluorescence measurements on the chiral dendrimers reveal a strong emission with maxima between 409 and 508 nm depending upon the substitution pattern. Finally, the redox properties of the dendrimers were determined by cyclic voltammetry, showing the influence of the functional groups at the peripheral positions of the dendrimer on the redox behavior of these systems.     

Sensitive determination of diquat by a kinetic method using the stopped-flow mixing technique

A simple, sensitive, selective, fast and inexpensive assay for the determination of diquat is proposed. The method is based on the reduction of the herbicide to a strongly fluorescent monocation radical with sodium dithionite. The initial rate of this reaction is directly proportional to the diquat concentration. The stopped-flow mixing technique was used because the kinetic data can be obtained in only 7 s, meaning that the method can be automated. The calibration graph is linear over the range 5-500 ng ml-1 and the precision (RSD) is close to 1.2%. The applicability of the method was demonstrated by determining the herbicide in different kinds of samples.     

Neutron activation analysis for chromium(III) and (VI) in lixiviated liquid through a calcined chromium(VI) adsorbed hydrotalcite

Summary Electrophoresis followed by neutron activation analysis was utilized to determine chromium(III) and (VI) in mixed solutions. These solutions proceeded from Cr(VI) adsorbed hydrotalcites heated at 800 °C to partially immobilize Cr in the Mg-Al oxide solid solution. Immobilization was studied by Cr lixiviation with NaCl solutions through the heated hydrotalcites. The results have shown that Cr lixiviated was in the form of CrO₄^2- ions, mainly because some Cr(VI) was not completely reduced to Cr(III) during heating. Chromium lixiviated from HT-Cr sample, heated at 800 °C and γ-irradiated at 1000 kGys, was found, as well, in the form of CrO₄^2- ions. Although γ-irradiation increases Cr immobilization in the solid, it does not reduce completely all CrO₄^2- ions present in the solid and, therefore, some Cr is lixiviated through the solid in the form of CrO₄^2- ion.