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This paper describes how electrochemical trace analysis can be performed in micro samples based on the precipitation of a sparingly soluble compound and its immobilization on an electrode surface. Precipitation is performed in a solution droplet put on the electrode in an upside-down position in air. The solvent of the droplet is then evaporated and the immobilized residue is subjected to a voltammetric measurement after introducing the electrode to an electrolyte solution. This methodology can be used for the quantification of dissolved ions (after precipitation) as well as for that of dispersed solids. As example, here the quantification of silver ions following precipitation as AgCl is described. Keywords: Stripping voltammetry, Precipitation, Immobilization, Electrochemistry, Microanalysis

We have revisited correlations between catalytic activity and formal potentials of MN4 catalysts for the reduction of O2 (ORR). When comparing the activities of Cr, Mn, Co and Fe MN4 complexes for ORR as a plot of (log i/n)E versus the M(III)/(II) formal potential of the catalyst (n = number of electrons involved in the ORR), two linear correlations are obtained: one for Cr, Mn and Fe complexes and another for Co complexes. Mn and Fe are 4-electron reduction catalysts and Cr and Co are 2-electron reduction catalysts for ORR in alkaline media. We show that instead of plotting the formal potential E°′ of the catalyst but the difference between this parameter and the reversible potential Erev of the corresponding catalytic reaction (O2/OH−) or (O2/HO2−), as (E°′ − Erev) and using the Co(II)/(I) formal potential for cobalt macrocyclics, instead of the Co(III)/(II) redox couple, all data points merge into one single linear correlation of slope +0.170 V/decade. It is possible that when (E°′ − Erev) approaches zero, the maximum activity could be achieved and this is especially important for 4-electron catalysts and the linear correlation might be part of an incomplete volcano correlation. Keywords: Linear correlations, Phthalocyanines, Fe porphine, O2 reduction catalyst, Redox potentials

Salmon gelatin and chitosan are high potential biopolymer to obtain edible films with antimicrobial effect for fresh meat. Therefore, it is important to characterize the structural (glassy or rubbery) state of the gelatin film on antimicrobial properties of chitosan. Extracted salmon (Salmo Salar) gelatin (acid-basic extraction) and low molecular weight chitosan solutions (0; 0.25; 0.5 and 1% w/w) at pH 5.5 were prepared to obtain a final concentration to 7% w/w (gelatin + chitosan). Films were obtained by casting at 5°C and equilibrated at 33% and 85% of relative humidity (RH) in order to obtain a glassy and rubbery state, respectively. Water content, specific volume and glass transition temperature (Tg) were measured and antimicrobial properties against Escherichia coli (E.c.) (105 ufc/ml) were obtained by agar plate diffusion and kinetic measurements at 37°C. Chitosan diffusion in agar plate was determined using liquid solutions and films over agar plate. The results showed diminution of Tg (maintaining structural state) as increase chitosan concentration, increasing also specific volume and water content due their high capacity to adsorb water. Although inhibition by chitosan of bacteria growth kinetic was 100%, solutions and films samples could not diffuse in the agar. In conclusion, the chitosan could not diffuse on the films matrix and also in agar plate and therefore in food when is combined with salmon gelatin. The implication of this work have been investigate the use of edible films from marine sources with antimicrobial effects in an effort to growing demand from consumers for safer and better quality foods.

Article history:Received 18 August 2011Received in revised form 25 August 2011Accepted 30 August 2011Available online 10 September 2011Keywords:O 2 reductionSAMsFe phthalocyaninesAu(111) We have obtained and characterized self assembled monolayers (SAMs) of 4-aminothiophenol (4-ATP) and1-(4-mercaptophenyl)-2,6-diphenyl-4-(4-pyridyl)pyridinium tetrafluoroborate (MDPP) functionalized withiron phthalocyanine (FePc) adsorbed on gold (111) electrodes. The catalytic activity of these SAMs/FePc wasexamined for the reduction of O 2 in aqueous media (pH=4) and compared with that of bare gold and of goldcoated directly with FePc molecules. Scanning tunneling microscopy (STM) studies confirm the functionali-zation of the 4-ATP by FePc. The electrocatalytic studies carried out with Au/FePc, Au/4-ATP/FePc and Au/MDPP/FePc electrodes show that the O 2 reduction takes place by a 4-electron transfer to give water in con-trast to a 2-electron-transfer processobserved on the bare gold. The activity of the electrodes increases as fol-lows: AubAu/FePcbAu/4-ATP/FePcbAu/MDPP/FePc.© 2011 Elsevier B.V. All rights reserved.