An evaluation of hydration and thermal decomposition of HAlg and its sodium salt is described using thermogravimetry (TG) and differential scanning calorimetry (DSC). TG curves in N2 and air, were obtained for alginic acid showed two decomposition steps attributed to loss of water and polymer decomposition respectively. The sodium alginate decomposed in three steps. The first attributed to water loss, followed by the formation of a carbonaceous residue and finally the Na2CO3. DSC curves presented peaks in agreement with the TG data. In the IR alginic acid presented bands at 1730 and 1631 cm-1, while sodium alginate presented a doublet at 1614 e 1431 cm-1, evidencing the presence of salified carboxyl groups.

No abstract

Chitosan is a linear polysaccharide obtained from the deacetylation of chitin. The physico-chemical properties of chitosan dependent on the average degree of acetylation ( DA ) and of the average molar mass ( M ). Several applications of chitosan have been proposed in the literature, mainly in water treatment, cosmetic and drug manufacturing, food additives, semipermeable membranes and development of biomaterials. In this work, three commercial chitosan samples were characterized by proton nuclear magnetic resonance ( 1 H NMR), infrared spectroscopy (IR), conductimetric titration and thermal analysis (TG and DSC) in order to compare commercial chitosans from different supplies. The average viscosimetric molecular weight M v was estimated from the intrinsic viscosity. The results confirmed remarkable differences in relation to the mean degree of acetylation ( DA ) (or desacetylation, DD ). The thermal analysis data permitted to follow the dehydration, decomposition, and glass transition temperature (Tg).

Nanostructured carbon fiber microdisk electrodes were prepared by a combination of mechanical polishing and electrolytic treatment, where the latter involved moderate oxidation of the surface, followed by a reduction. A high density of surface defects contributed to a high capacitance of the nanostructured electrodes. Facilitated proton transfer was observed at the nanostructured surface and was associated with cation-exchanged oxide defects. The nanostructured surfaces intercalated uric acid and adenosine and engaged in fast electron/proton transfer in the oxidation of both analytes. As a result, electrolytic treatment followed by fast-scan voltammetry determinations led to a sensitive response to both analytes in physiological buffers. The nanostructured electrodes showed remarkable stability and could be easily regenerated and reused. With long use, electrode activity decreased. Kinetic discrimination of the surface-mediated reaction of ascorbate was achieved at high scan rates.

No abstract

No abstract

No abstract

Bismuth films (BiF) deposited in situ on graphite-polyurethane composite electrodes were successfully used for the determination of Zn, Cd, Pb, Cu and Hg, simultaneously in acetate buffer solution pH 4.5 using square wave anodic stripping voltammetry. It is possible to determine metals reoxidized at potentials more negative and more positive than Bi using in situ deposited BiF; reoxidation was studied by electrochemical impedance spectroscopy. The BiFmodified electrode was applied to analyse tap water. The influence of surface-active compounds, Triton X-100 and bovine serum albumin, on the stripping of these metals was investigated; Nafion coatings did not significantly improve the performance.