In situ electrochemical generation of gold nanostructured screen-printed carbon electrodes. Application to the detection of lead underpotential deposition

In the present work, an electrochemical method for the reproducible and stable generation of gold nanostructures on the surface of screen-printed carbon electrodes was developed. This technique is based on the application of a constant current over an appropriate time interval. Gold nanostructured screen-printed carbon electrodes were characterized using both SEM and electrochemical methods. The mean diameter and the dispersion of gold nanoparticles that were generated electrochemically depended on the gold concentration, the time deposition and the current intensity. Smaller diameters and better distribution of nanoparticles were obtained when a shift of potential to −0.70 V occurred during the gold electrodeposition process. Moreover, the underpotential deposition (UPD) of lead on these nanostructured surfaces was studied, as was their behavior as array electrodes. The best results, using UPD combined with square wave stripping voltammetry, were obtained for gold nanostructured surfaces with a mean diameter of 78 ± 24 nm and a density of 4.4 × 10⁷ nanoparticles/mm². These gold nanostructured screen-printed carbon electrodes were obtained by applying a current intensity of −100 μA for 300 s using a gold concentration of 0.5 mM. The reproducibility and limit of detection obtained using these nanostructured electrodic surfaces were 2.4% (in terms of RSD) and 0.8 ng/mL, respectively.     

Comparative study of the effects of 1‐MCP treatment on apple quality by instrumental and multivariate analysis

BACKGROUND: The main aim of this work was to define how 1‐methylcyclopropene (1‐MCP) treatment affects apple fruit quality by two complementary approaches. RESULTS: The results confirmed that 1‐MCP treatment maintained firmness and acidity of the fruit. Multivariate analysis distinguished treated and untreated fruits and showed that a relationship exists between 1‐MCP treatment and firmness, and also between 1‐MCP and the physiological disorder, ‘diffuse skin browning’ (DSB). Relationships for acidity were low and absent for soluble‐solids concentration (SSC). The PCA model built only with 1‐MCP treated fruit showed a positive correlation between DSB incidence and firmness, and a negative correlation between DSB and SSC or a* values. Collectively, these correlations indicated that the more immature fruits are more susceptible to DSB. This last model also characterised acidity as the best parameter to discriminate the 1‐MCP fruits. CONCLUSION: It is the first time that such a comparative study has been conducted on 1‐MCP treated fruits. The results are of interest because they (1) help to discriminate treated and untreated fruits, and (2) allow discrimination of 1‐MCP‐treated fruit during storage. Copyright © 2008 Society of Chemical Industry     

Modeling of the Low-Frequency Noise in Thermal Lens Spectrometry

The low-frequency noise observed in thermal lens spectrometry (TLS) can be modeled by assuming that the heated region, constituted by the thermal lens gradient and associated convective stream, behaves as a weakly damped harmonic oscillator with a natural frequency, v_o, which is forced to move at an externally imposed pump frequency, v_p. Out-of-phase lower-frequency oscillations of the TLS signal can be produced both by transient events, such as the beginning of the TLS experiment and small changes in the pump beam stability, and by drift of boundary conditions, such as the temperature of the surroundings. A model is developed and checked using 1-(2-pyridylazo)-2-napthol (PAN) solutions in silicone oil. Consequences of analytical interest are drawn; e.g., the signal-to-noise ratio of the TLS experiments is improved by pumping at the resonance frequency, where v_p = v_o.     

Antioxidant and antimutagenic activity of phenolic compounds in three different colour groups of common bean cultivars (Phaseolus vulgaris)

Total phenolic content of seven improved common bean cultivars (Phaseolus vulgaris L.) namely, Negro Altiplano, Negro Durango, Negro Sahuatoba, Flor de mayo sol, Flor de Mayo Bajío, Flor de Mayo 94044MX and Bayo Madero were analyzed. Acetone and methanol extracts from bean cotyledons were obtained by successive extractions. Total phenolic content was evaluated following Folin–Ciocalteu method; antioxidant activity by the DPPH technique; antimutagenic potential by the Ames method; and preliminary identification was realized by 2D-TLC. Results indicated high correlation between total phenol content and antioxidant activity for acetone extracts, and also high correlation between antioxidant and antimutagenic activities. In contrast, low correlation coefficients were obtained for methanol extracts. Three cultivars (two Negro cultivars and a Flor de Mayo type) showed lower antimutagenic activity than catechin.     

Influence of traditional smoking on the triglyceride composition during the ripening of Idiazabal cheese

 The influence of traditional smoking on the triglyceride (TG) composition of Idiazabal cheese during ripening was studied using HPLC. The partition numbers (PNs) of the TGs ranged between 22 and 53, the groupings of TG peaks with PN values of 36, 34, and 38 being the main contributors. Statistically significant differences between the smoked and the unsmoked cheeses were recorded during the ripening period. Smoking had a significant effect on certain groups of TGs at different ripening times and no effect on others. The differences in the TG profiles of the cheeses were the result of differing levels of lipolytic activity, which was heightened by smoking. Received: 29 December 1997 / Revised version: 9 March 1998     

Micromorphological characterization of zinc/silver particle composite coatings

The aim of this study was to evaluate the three‐dimensional (3D) surface micromorphology of zinc/silver particles (Zn/AgPs) composite coatings with antibacterial activity prepared using an electrodeposition technique. These 3D nanostructures were investigated over square areas of 5 μm × 5 μm by atomic force microscopy (AFM), fractal, and wavelet analysis. The fractal analysis of 3D surface roughness revealed that (Zn/AgPs) composite coatings have fractal geometry. Triangulation method, based on the linear interpolation type, applied for AFM data was employed in order to characterise the surfaces topographically (in amplitude, spatial distribution and pattern of surface characteristics). The surface fractal dimension D_f, as well as height values distribution have been determined for the 3D nanostructure surfaces. Microsc. Res. Tech. 78:1082–1089, 2015. © 2015 The Authors published by Wiley Periodicals, Inc.     

Role of predation by zooplankton in transport and fate of protozoan (oo)cysts in granular activated carbon filtration

The significance of zooplankton in the transport and fate of pathogenic organisms in drinking water is poorly understood, although many hints of the role of predation in the persistence of microorganisms through water treatment processes can be found in literature. The objective of this study was to assess the impact of predation by natural zooplankton on the transport and fate of protozoan (oo)cysts in granular activated carbon (GAC) filtration process. UV-irradiated unlabelled Cryptosporidium parvum and Giardia lamblia (oo)cysts were seeded into two pilot-scale GAC filtration columns operated under full-scale conditions. In a two-week period after seeding, a reduction of free (oo)cysts retained in the filter bed was observed. Zooplankton was isolated from the filter bed and effluent water on a 30 μm net before and during the two-week period after seeding; it was enumerated and identified. Rotifers, which are potential predators of (oo)cysts, accounted for the major part of the isolated zooplankton. Analytical methods were developed to detect (oo)cysts internalized in natural zooplankton isolated from the filter bed and effluent water. Sample sonication was optimized to disrupt zooplankton organisms and release internalized microorganisms. (Oo)cysts released from zooplankton after sonication were isolated by IMS and stained (EasyStain™) for microscopic counting. Both Cryptosporidium and Giardia (oo)cysts were detected in association with zooplankton in the filter bed samples as well as in the effluent of GAC filters. The results of this study suggest that predation by zooplankton can play a role in the remobilization of persistent pathogens such as Cryptosporidium and Giardia (oo)cysts retained in GAC filter beds, and consequently in the transmission of these pathogens in drinking water.     

Phenomenon of phase inversion in high impact polystyrene: Physico‐chemical,rheological and morphological study in the presence of chain transfer agent and using different tapered block copolymers as the precursor rubber

Different high impact polystyrenes were synthesized using styrene/butadiene copolymers (SB) with PS/PB composition: 30/70 and 20/80 as the precursor rubber, benzoyl peroxide (BPO) as the initiator, and ter‐dodecyl mercaptane (TDM) as the chain transfer agent. During the polymerization, several samples were taken and analyzed under different techniques to evaluate the phase inversion (PI) phenomenon. The PI was determined through transmission electron microscopy (TEM) and through dynamic oscillatory behavior, where the PI takes places when the relaxation process presents the lower value of activation energy. Finally, the Choi and Schowalter emulsion model was employed to elucidate the PI, and relevant information was revealed about the interfacial tension in the PI. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Pile burning of cutting debris in stands of hazel (Corylus avellana): An experimental study of smouldering combustion towards the validation of a burning protocol

Smouldering combustion in burning piles was experimentally investigated by studying temperature changes in six piles of 2 m of diameter of cutting debris of hazel (Corylus avellana) for three days after extinction. The piles were monitored using an IR camera and K-type thermocouples. The experiment was designed in order to study how the maximum temperature of the charcoal might be influenced by the individual and interaction effects of both the quality of extinction and the elapsed time until the start of extinction of the piles. The piles that were properly extinguished (i.e. using a high-pressure, homogeneously distributed water flow of 50 l/min for 4 min) had a uniform temperature profile and did not have significant hot spots. The temperature reached equilibrium with the environment in less than 10 h after extinction. In contrast, a smouldering front moved throughout the poorly extinguished piles, which had a wide temperature distribution and hot spots of up to 700 °C. A simulation of windy conditions after three days of experiments on a poorly extinguished pile showed that the reactivation of charcoal combustion was possible. It gave a high-risk scenario to cause a wildfire, with hot smouldering embers being transported by wind flow. The results are of interest to improve pile burning protocols so that the number of wildfires caused by such practices may be reduced.