Search results for "Analytical"
showing 10 items of 9586 documents
A spectroelectrochemical study of poly(dithienothiophenes)
1997
Abstract The use of n- and p-dopable conjugated polymers as both the working and counter electrodes in an electrochemical device has always attracted chemists and has stimulated the design of new molecules with a low energy gap that can be p- and n-doped efficiently. The present paper reports the spectroelectrochemical study of polymers obtained from several dithienothiophene isomers, molecules with three thiophene rings fused in different positions. Of the six isomers, poly(dithieno[3,4-b:3′,2′-d]thiophene) and poly(dithieno[3,4-b:2′,3′-d] thiophene) were tested against poly(dithieno[3,2-b:2′,3′-d]thiophene) and poly(dithieno[3,4-b:3′,4′-d]thiophene). The differences in their performance, …
Atomic force microscopy study of conducting polymer films near electrode's edge or grown on microband electrode
2013
Abstract Polypyrrole (PPy) films of different thicknesses (within the range from 200 nm to 2.5 μm) were electrodeposited on two types of inhomogeneous substrates, single band and double-band Pt electrodes. Topographic images of the polymer layers were obtained by means of ex situ large-scale AFM technique to demonstrate how the propagation rates of the film growth above the electrode (in the normal direction to the electrode surface) and along the insulating surface surrounding the single- or double-band electrodes (in the horizontal direction) change with the deposition charge. It is proved that variations in the film thickness over the double band electrodes and progressive changes of the…
Photoelectrochemical Synthesis of Polypyrrole on Anodic Ta[sub 2]O[sub 5] Films
2007
Polypyrrole film was photoelectrochemically grown on insulating Ta 2 O 5 anodic film in acetonitrile solution. A characterization by photocurrent spectroscopy (PCS) of metal/oxide/polypyrrole interface was carried out. The PCS results suggest that a metallic-like PPy is formed under illumination at constant anodic potential. By polarizing the polypyrrole at cathodic potentials a photocurrent spectrum typical of p-type semiconducting film was recorded. A scanning electron microscopy study of PPy surfaces solution side and oxide side allowed us to obtain information on the morphology of the polymer as well as a rough estimate of the film thickness and of the diameter of PPy globules at the tw…
Impedance spectroscopy characterization of functionalized alumina membranes
2005
Abstract Anodic alumina membranes have been impregnated with a protonic conductor either by immersion or by vacuum permeation of a saturated aqueous solution of CsHSO4 for different times. Synthetized salt, obtained through the reaction of cesium carbonate with sulphuric acid (in excess), contained a small quantity of Cs2SO4. Unmodified membranes consist of amorphous Al2O3 with a regular distribution of pores (average diameter: 200 nm) and are stable up to 850 °C. Long impregnation times caused partial dissolution of alumina, with formation of Al(HSO4)3 on the front surfaces as well as into pore walls. From the frequency dispersion of the impedance, the “macroscopic conductivity” of membran…
Pressure Effect Studies on the Spin Transition of Microporous 3D Polymer [Fe(pz)Pt(CN)4]
2018
Pressure effects on the spin transition of the three-dimensional (3D) porous coordination polymer {Fe(pz)[Pt(CN)4]} have been investigated in the interval 105 Pa–1.0 GPa through variable-temperature (10–320 K) magnetic susceptibility measurements and spectroscopic studies in the visible region at room temperature. These studies have disclosed a different behavior of the compound under pressure. In the magnetic experiments, a temperature independent paramagnetic behavior has been observed under 0.4 GPa. In contrast, at room temperature and at 0.8 GPa, a complete HS-to-LS transition has been evidenced. The differences in the magnetic behavior are strongly related with the porous structure of …
Analysis of amino acids using serially coupled columns.
2017
Single conventional columns in reversed-phase LC are insufficient for analysing the isoindoles of primary amino acids, due to their limited functionality. An interesting possibility for increasing the separation power is the combination of several columns of different nature, where the length is modified by coupling small segments. This approach may require a considerable investment to have multiple lengths for each stationary phase. However, the combination of only two columns of fixed length can be enough to resolve satisfactorily relatively complex mixtures, provided that an optimised gradient program is applied. In this work, a mixture of 19 primary amino acid isoindoles found in protei…
Dynamics of cross polarization in solid state nuclear magnetic resonance experiments of amorphous and heterogeneous natural organic substances
2008
Nuclear magnetic resonance (NMR) experiments on carbon-13 in the solid state were done with cross polarization (CP) and magic angle spinning (MAS) in order to overcome the low NMR sensitivity of (13)C and the chemical shift anisotropy, respectively. In the present research, CPMAS (13)C-NMR spectra were collected by modulating the contact time needed for cross polarization (variable contact times experiments, VCT) on two different humic acids (a soil-HA and a coal-HA). VCT data were fitted by a model containing either a monotonic or a non-monotonic cross polarization term. The non-monotonic model, which fitted the experimental results better than the monotonic one, provided two cross-polariz…
Prediction of the curing time of Spanish hams using peptide profiles established by capillary zone electrophoresis
2009
Abstract A capillary zone electrophoresis procedure for the prediction of curing time of Spanish hams using peptide profiles has been developed. Excellent resolution between the seven peptide peaks was achieved within 30 min analysis time with a BGE containing 60 mM MgSO 4 and 50 mM phosphate at pH 2.5. Using hams with curing times of 6, 8 and 12 months, both linear discriminant analysis (LDA) and multiple linear regression (MLR) models were constructed. In both cases, two different normalisation procedures of the peak areas were compared. Using LDA, all the ham samples corresponding to the three categories were correctly classified. Using MLR, the ham curing time could be predicted with av…
Optical planar Bragg grating sensor for real-time detection of benzene, toluene and xylene in solvent vapour
2012
Abstract We report on an optical planar Bragg grating sensor functionalized by a comparatively simple method to detect substances such as benzene, toluene and xylene (BTX). The functionalization is performed by allyl substituted γ -cyclodextrin derivatives which are immobilized on the sensor surface by dip coating. Our results prove the capability of this functionalized sensor system to detect lowest concentrations of BTX in solvent vapour in real-time with a sensitivity of 3±0.4 pm/100 ppm for benzene, 8±1 pm/100 ppm for toluene and 32±1 pm/100 ppm for m-xylene. Taking into account the spectral resolution and repeatability of the interrogation system this corresponds to a minimum concentra…
Polarimetry as a useful tool for the determination of binding constants between cyclodextrins and organic guest molecules
2006
Binding constants for cyclodextrin inclusion complexes can be easily estimated by means of simple polarimetric measurements. Determinations are as reliable and accurate as those obtained by means of other more sophisticated techniques, and take advantage by the limited waste of material required. Our results are briefly compared with literature values obtained by means of different techniques.