Supercritical Fluid Extraction of Bivalve Samples for Simultaneous GC-MS Determination of Polychlorobiphenyls and Polycyclic Aromatic Hydrocarbons

Abstract

A method is presented for the simultaneous determination of polychlorobiphenyls and polycyclic aromatic hydrocarbons in bivalve samples. The method implies the fortification of the freeze-dried sample with isotopically labeled internal standards; followed by extraction with supercritical carbon dioxide modified with 3% methanol, then a simple clean-up step on a silicagel packed Pasteur pipette and, finally, determination by gaschomatography-mass spectrometry. The method requires little time and labor compared to traditional methods, uses negligible amounts of solvents and produces little wastes. Sixty different PCB congeners and seven selected PAHs are analyzed. Six replicate analyses were performed on the SRM 2974 certified material and the results are discussed.     

Microfluidic housing system: a useful tool for the analysis of dye-sensitized solar cell components

In order to understand the behavior of the different dye-sensitized solar cell (DSC) components, an in-situ analysis should give fundamental help but it is impossible to be performed without compromising the integrity of the cell. Our recently proposed novel microfluidic approach for the fabrication of DSCs is based on a reversible sealing of the two transparent electrodes and it allows the easy assembling and disassembling of the cell, making possible an analysis of the components over time. The aim of this work is not to investigate the different degradation mechanisms of a standard DSC: we want to show that, by using a microfluidic architecture, it is possible to perform a non-destructive analysis and to monitor the photoanode and the counter electrode properties during their lifetime. Morphological (field emission scanning electron microscopy), wetting (contact angle), optical (UV-visible spectroscopy) and electrical (current?Cvoltage and electrochemical impedance spectroscopy measurements under standard AM1.5G illumination) characterizations have been performed over a period of three weeks. The results show how the variation of the wetting and morphological properties at the counter electrode and of the dye absorbance at the photoanode are strongly related to the decrease of the cell performances as evidenced by electrical characterization, thus demonstrating the effectiveness of the use of our structure in this kind of studies.     

Finite planar spaces with projective points

In this paper a class of finite planar spaces with projective points is characterized.     

Organocatalytic Stereoselective α‐Alkylation of Aldehydes with Stable Carbocations

The organocatalytic stereoselective alkylation of aldehydes is carried out with the four stable carbocations 1 , 2 , 3 , 4 in the presence of a catalytic amount (20 mol%) of MacMillan imidazolidinones 5 , 6 . In all reactions, lutidine was used as a base. The alkylation reactions are investigated at different temperatures with linear and branched aldehydes. In the case of carbocation tropylium fluoroborate, an interesting reversal of alkylation product configuration was observed, which is driven by entropic effects in the reaction. The absolute configuration of the products obtained is determined by chemical correlation and found to be in general agreement with the model proposed by MacMillan to justify the stereoselectivity obtained in the reactions promoted by catalysts of type 5 , 6 .     

On-line Calibration and Determination of the Heat of Reaction for Laboratory Scale Heat Transfer Calorimeters

A simple method for the on-line calibration, in which both the heat transfer coefficient and the heat capacity of the reactor contents are determined, is described for laboratory scale heat transfer calorimeters. The calorimeter is operated in the isoperibolic mode for the calibration and a constant power is supplied to a resistor placed inside the reactor. The reactor heat balance differential equation is used to produce a set of linear simultaneous equations with each data acquisition cycle giving one equation. The heat transfer coefficient and the heat capacity are obtained from this set of equations by linear least squares. The application of the calibration procedure is illustrated by experiments in which the heat of reaction is determined on-line fora simulated reaction with first order kinetics and for the hydrolysis of acetic anhydride. This revised version was published online in July 2006 with corrections to the Cover Date.     

A computational model of the 5-HT3 receptor extracellular domain: search for ligand binding sites

A three-dimensional model of the 5-HT₃ receptor extarcellular domain has been derived on the basis of the nicotinic acetylcholine receptor model recently published by Tsigelny et al. Maximum complementarity between the position and characteristics of mutated residues putatively involved in ligand interaction and the pharmacophoric elements derived by the indirect approach applied on several series of 5-HT₃ ligands have been exploited to gain insights into the ligand binding modalities and to speculate on the mechanistic role of the structural components. The analysis of the three-dimensional model allows one to distinguish among amino acids that exert key roles in ligand interactions, subunit architecture, receptor assembly and receptor dynamics. For some of these, alternative roles with respect to the ones hypothesized by experimentalists are assigned. Different binding modalities for agonists and antagonists are highlighted, and residues which probably play a role in the transduction of binding into a change in conformational state of the receptor are suggested. Received: 27 July 2000 / Accepted: 15 September 2000 / Published online: 21 December 2000     

A weak gel model for foods

From a general point of view food can be seen as either a continuous aqueous or lipidic phase in which other components are dispersed (for example long fibres, droplets). While these systems seem to be very different one from the other, they generally show similar behaviour due to the presence of a supramolecular structure, comprised of ordered or interacting droplets, particles etc. that determine these characteristics. Many food systems can be treated as gels, characterised by a three-dimensional network where weak interactions (like Wan der Waals interactions or hydrogen bonding) ensure the stability of the structure. The gel is assumed to coincide with the critical gel of Winter's theory, but a finite relaxation time is assumed to account for the flowing character of foods, that is interpreted in terms of theory of cooperative flow. Thus, apart from the usual two continuum material function, i.e. a truncated relaxation spectrum and an apparent elastic modulus, other two material parameters were determined and proposed to describe the network extension and its strength. This kind of approach, named weak gel model, was applied to different foods such as jams, dough and yoghurt and it proved to be quite adherent to food reality. Received: 6 February 2000 Accepted: 10 October 2000     

Capillary electrophoresis of nicotinamide—adenine dinucleotide and nicotinamide—adenine dinucleotide phosphate derivatives in coated tubular columns

HPCE was shown to be an effective and convenient method for the determination of nicotinamide—adenine dinucleotide (oxidized, NAD⁺; reduced, NADH), nicotinamide—adenine dinucleotide phosphate (oxidized, NADP; reduced, NADPH) and their synthetic derivatives. The coenzymes were easily separated among themselves and from their degradation products, which are inhibitors of dehydrogenases, in 15 min in a coated capillary. Several coenzyme derivatives such as N⁶-(2-aminoethyl)-NAD(P)⁺ and N(1)-(2-aminoethyl)-NAD(P)⁺ were separated by zone electrophoresis in uncoated or coated capillaries using 50 mM 3-(N-morpholino)propanesulphonic acid (pH 7.0) or Tris—HCl (pH 8.0) as buffer systems. Capillary zone electrophoresis and micellar electrokinetic capillary chromatography can also be used to monitor continuously coenzyme chemical modifications.     

“One pot” synthesis of 2,9-disubstituted 8-azaadenines (3,5-disubstituted 7-amino-3H-1,2,3-triazolo[4,5-d]pyrimidines)

A new simple method for the synthesis of title compounds is described starting from malononitrile, benzyl-azide and an aliphatic or aromatic nitrile.