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A low-cost disposable lipase activity sensor was developed and characterized overcoming the main drawbacks of the already existing disposable ones: insufficient reproducibility to be applied for automatic lipase activity quantification and complicated and long manual analytical procedure performed by qualified personnel. The sensor is based on a capacitor formation on an electrode surface by a substrate layer deposition possessing high electrical resistivity and dielectric constant (composite of olive oil mixed with BaTiO3 nanoparticles) serving as both: sensor sensitive layer and capacitor dielectric. Its decomposition by lipase catalyzed hydrolysis causes its thickness decrease resulting in capacitance increase proportional to the lipase activity. The sensor was characterized in terms of limit of quantification, linear quantification range, sensitivity, response time, precision, repeatability, storage time and the results are presented and discussed. The validation experiment showed excellent agreement with the standardized titrimetric method.

The simultaneous voltammetric determination of species with close peak potentials presents some difficulties, because of the overlapping of their redox peaks at conventional solid electrodes. Therefore, two approaches were proposed to overcome this drawback: (i) chemometric resolution of the overlapped peaks by semi-derivative or multivariate analysis and (ii) development of chemically modified electrodes with better electrochemical performances, permitting peaks separation. However, the mathematical treatment habitually results in a precision decrease, while the electrode modification often requires the use of expensive materials and involves sophisticated techniques. Hence, another strategy for the direct simultaneous species determination is suggested in this work. It involves the application of Differential Alternative Pulses Voltammetry (DAPV) [1], which provides the great resolution of the second order voltammetric techniques, as Radio-Frequency Polarography, Second Harmonic AC Voltammetry, and Differential Faradaic Rectification Polarography (DFRP), in combination with the high sensitivity, precision, and instrumental and operational simplicity of the most common voltammetric technique, the differential pulse voltammetry (DPV). The second order voltammetric techniques including DAPV are based on the nonlinearity of the electrochemical system I/E characteristic yielding voltammograms shaped as a derivative of voltammetric peak resulting from small sinusoidal or rectangular bipolar deviations of the DC potential. Two single pulses of small amplitude, one cathodic and one anodic are successively applied in DAPV for every value of the scanned DC potential with delay time between the pulses equal to the delay time between the scan step and the first one (Fig. 1). The sum of the two pulse faradaic current components with opposite polarities is registered vs. the scanned potential as DAPV voltammogram. The experimentally determined half-width of the DAPV peaks (37 mV at 2 electrons reduction) is 1.22 times smaller than that of the most common voltammetric technique DPV (45.3 mV) at the same conditions and equals that obtained by the application of another second order technique, the DFRP. Thus, the DAPV voltammogram’s shape as second derivative of voltammetric wave combined with the small half-widths of the anodic and the cathodic peaks allows simultaneous quantification of species having very small peak potential difference. Taking advantage from the great resolution power of DAPV, it was applied for the simultaneous determination of a range of organic (catechol and hydroquinone [2]; o-nitrophenol, m-nitrophenol and p-nitrophenol [3]) and inorganic species (Cd2+/In3+; Tl+/Pb2+ [1, 4]) with close peak potential difference, as shown in Figs. 2-5. The proposed approach offers a very simple alternative route for the simultaneous determination of a broad range of species and overcomes the disadvantages of the currently applied strategies involving electrode modification or mathematical data processing. References 1. Zlatev, M. Stoytcheva, B. Valdez, J.P. Magnin, P. Ozil. Electrochem. Communications, 2006, 8, 1699-1706. 2. Ayala, M. Stoytcheva, R. Zlatev, Z. Velkova, V. Gochev, B. Valdez, G. Montero. Electroanalysis, 2018, 30, 1913-1917. 3. Stoytcheva, R. Zlatev, Z. Velkova, V. Gochev, A. Ayala, G. Montero, B. Valdez. Electroanalysis, 2019, 31, 652-660. 4. Zlatev, M. Stoytcheva, B. Valdez. Electroanalysis, 2018, 30, 1902-1905. Figures captions Fig. 1. DAPV potential-time waveform. M1-M4 are the current measuring intervals; DT is the wait time for the pulse capacitive current decay. Fig. 2. HQ (30 mmol L-1) and CC (10 mmol L-1) determination by DAPV. PBS 0.1 mol L-1, pH 7; Spectroscopic graphite electrode. Fig. 3. Nitrophenol (NP) isomers simultaneous determination by DAPV (m-NP 125 mmol L-1, p-NP 125 mmol L-1, and increasing o-NP concentrations: 25, 50, 75, 100 and 125 mmol L-1). PBS 0.1 mol L-1; pH 6.5; glassy carbon electrode modified by a nanocomposite of graphite nanopowder and Au nanoparticles. Fig. 4. Cd2+ and In3+ (E1/2 difference 45 mV) simultaneous determination by DAPV, 0.1 mol L-1 HCl; Hanging Mercury Drop Electrode. Fig. 5. Tl+ and Pb2+ (E1/2 difference 50 mV) simultaneous determination at 12:1 concentration ratio by DAPV and DPV. 0.1 mol L-1 HCl; Hanging Mercury Drop Electrode. Figure 1

The authors describe a graphite immobilized bismuth film electrode with enhanced sensitivity for the organophosphorus pesticide paraoxon. The film was formed by ex-situ electroplating of bismuth onto the large surface of a glassy carbon electrode modified with graphite nanopowder (Bi/Gr/GCE). The modified GCE was characterized by chronoamperometry using p-nitrophenol as a model nitro compound. The modification of the GCE results in an increase of the electroactive area (to 27.7 mm2) and of the electrocatalytic activity (the catalytic rate constant being 4140 L·mol−1·s−1). This results in an enhancement of the current for the electroreduction of paraoxon by a factor of 4.3 (compared to a plain GCE). The modified GCE was applied to the sensitive determination of paraoxon by differential pulse voltammetry. At a typical working potential of −0.45 V vs. Ag/AgCl, the LOD is 2 nmol·L−1 of paraoxon, which is comparable to the LOD of some cholinesterases-based electrochemical sensors and is lower than the LOD of the organophosphorus hydrolase-based electrochemical sensors for paraoxon. In addition, the new GCE is more stable than enzyme-based sensors, and it can be renewed.

The medical diagnostic, the industry, and the biotechnology require rapid, sensitive, and easy to use methods for trypsin activity determination. A simple approach, which meets all these requirements, based on Quartz Crystal Microbalance (QCM) was developed, analytically characterized and described in the present work. QCM application allows rapid trypsin activity evaluation by real time monitoring of the enzymatic degradation of the substrate. The new approach suggested in this work takes advantage of nanoparticles loaded gelatin employment as a trypsin substrate, deposited on the QCM crystal. The heavy nanoparticles leave the substrate layer together with the products of its enzymatic degradation provoking thus a greater decrease of the total QCM crystal mass compared with the non charged substrate. As a result, a higher sensor frequency response occurs. A 10 fold improvement of the LOD was achieved for trypsin activity evaluation applying the proposed method with Ag nanoparticles loaded gelatin (7.5×10 −4 U mL −1 vs. 7.5×10 −3 U mL −1 obtained by the “classic” QCM method). The approach subject of this work can be applied with any substrate degrading enzyme.

The present work discusses the problem of induced external electrical noise as well as its removal from the electrical potential obtained from Scanning Vibrating Electrode Technique (SVET) in the pitting corrosion process of aluminum alloy A96061 in 3.5% NaCl. An accessible and efficient solution of this problem is presented with the use of virtual instrumentation (VI), embedded systems, and the discrete wavelet transform (DWT). The DWT is a computational algorithm for digital processing that allows obtaining electrical noise with Signal to Noise Ratio (SNR) superior to those obtained with Lock-In Amplifier equipment. The results show that DWT and the threshold method are efficient and powerful alternatives to carry out electrical measurements of potential signals from localized corrosion processes measured by SVET., The authors acknowledge the Materials Corrosion Laboratory of the UABC Institute of Engineering for the economic support and facilities provided for the development of electronic instrumentation and testing of the experimental processes. They are grateful for the international collaboration with the National Center of Metallurgical Research (CENIM) Madrid, the Spanish State Council for Scientific Research (CSIC), for the support provided in the research and experimentation process in this work.

Carbon nanohybrid material (CNF/γ-FeO) was obtained via a modified sol-gel technique consisting of two steps: functionalization of carbon nanofibers (CNF) in HSO/HNO followed by synthesis using Fe(NO)·9HO. As a result, the iron content of the CNF/γ-FeO was increased by more than twice from about 40% to about 87% mass percent, compared to the pristine CNF and oxidized CNF specimens, as proved by energy dispersive X-ray fluorescence. Scanning electron microscopy images exhibited >cumulus> on the CNF/γ-FeO specimen surface, which showed the highest iron mass percentage, proved by energy dispersive X-ray spectroscopy. Transmission electron microscopy images confirmed attachment of γ-FeO cumulus to the inner and outer surfaces of the CNF walls after synthesis. The characteristic peaks of Fe 2p and Fe 2p appeared in the XPS spectra obtained on CNF/γ-FeO. In addition, X-ray diffraction (XRD) results indicated formation of γ-FeO during the synthesis process. The Raman spectrum of the CNF/γ-FeO sample displays peaks with positions close to characteristic peaks of highly crystalline and monodisperse maghemite nanocrystallites. The synthesis of CNF/γ-FeO leads to an increase in the hydrophilicity of CNF and magnetic properties at room temperature., The authors acknowledge the support of the Engineering Institute of the Autonomous University of Baja California (UABC), Mexico, and the National Center for Metallurgical Research (CENIM-CSIC), Spain, during the performance of this research. The authors are also thankful to the Center of Nanoscience and Nanotechnology of the National Autonomous University of Mexico (UNAM), for the help with XPS and TEM analysis. Finally, the authors are grateful to theNational Council of Science and Technology of Mexico (CONACYT) for supporting this research through MYDCI Program Scholarship Grant (no. 257875).

Extracellular lipase production by Penicillium chrysogenum, Trichoderma harzianum and Aspergillus flavus was carried out through solid state fermentation using agro-industrial residues as substrates. For all three strains, the growth temperature was 29±1 °C, and 65% w (g/gds) moisture content. The effect of three factors on lipase production rate was investigated: initial pH (6.0 and 7.0), time of fermentation (72 h, 96 h and 120 h), and type of mixed substrate (wheat bran-olive oil, and wheat bran-castor oil cake). The process was optimized applying a mixed level factorial design. Fermentation time and pH were found to have positive effects on lipase production and secretion rates. However, the time effect was larger than initial pH. Type of substrate demonstrated minor effective importance than the other two factors, and Aspergillus flavus showed the larger lipase production among the three strains. Results indicated that the three fungal strains were able to grow and produce lipase in both cult...

The rates of hydrogen production by B10 and the genetically modified IR3 varieties of the bacterial strain R. capsulatus employing DL-sodium lactate as a carbon source and parts of the visible spectrum light as energy source were compared. The influence of parameters such as: light spectrum (blue, green, red, white light), light luminance (from 2500 to 17000 lux), reactor geometry (flat and cylindrical), was studied to maximize the bacterial hydrogen production. Maximal results were achieved in a flat reactor at 700 nm (red light) and 2500 lux light luminance by both varieties, but the hydrogen production obtained by the genetically modified variety IR3 exceeded the B10 production up to 64 % in spite of the superior biomass quantity of the latter.

The aim of this study was to characterise the corrosion phenomena occurring in the marine and fluvial, fixed and mobile infrastructure, including ships and ports and shipyard installations. Carbon steel and naval aluminium are the main materials used in the construction of these vessels and installations. Immersion corrosion tests were carried out at the laboratory and at two seaports in Mexico and Israel. Corrosion was identified in pieces tal

La industria electrónica ha crecido en los últimos cincuenta años, sobre todo en los países desarrollados, contribuyendo a su progreso económico. Particularmente en el Estado de Baja California ubicada en el noroeste de México, estas empresas han prosperado en los parques industriales de Mexicali considerada como una zona árida y Ensenada, un puerto y ciudad en el Océano Pacífico, que es una región marina. En ambos ambientes, durante el invierno y el verano los principales factores climáticos en ambientes de interiores son la humedad y temperatura, que aunados a los contaminantes del aire generan corrosión en dispositivos y equipos electrónicos, disminuyendo su rendimiento operativo. El cambio de clima en interiores de plantas industriales se debe a la variación de humedad, temperatura, radiación solar, así como a la concentración de contaminantes atmosféricos como el CO, SO2, H2S, NOX, O3 y partículas sólidas PM2.5 y PM10 provenientes de exteriores de la industria electrónica. Los gases y partículas contaminantes del aire son detectados por Estaciones de Monitoreo Ambiental (EMA) en Mexicali, mientras, que el SOX y Cl- se determinaron en Ensenada por la técnica de platos de sulfatación (TPS) y el método de la vela húmeda (MVH). Las probetas metálicas en ambas ciudades fueron analizadas por microscopia de barrido por electrones (MBE) y espectroscopia de electrones Auger (EEA) para determinar los productos de corrosión. Los equipos electrónicos instalados en las plantas están constituidos por componentes de cobre, siendo un metal muy utilizado por su buena conductividad eléctrica y térmica. Debido a que están expuestos a una amplia gama de ambientes agresivos, se origina deterioro del cobre, generando fallas en los equipos y con ello pérdidas económicas. Los materiales metálicos utilizados en los dispositivos electrónicos son susceptibles a la corrosión en interiores de plantas industriales por la variaciones de humedad y temperatura que generan el tiempo de humectación (TH), originando formación de una película delgada de agua sobre la superficie metálica, además de la exposición principalmente de sulfuros en Mexicali y cloruros en Ensenada, generan el proceso de corrosión.

A novel electrochemical biosensor integrating the strictly autotrophic bacterial strain Leptospirillum ferrooxidans as a recognition element and a Clark type oxygen probe as a transducer was designed, metrologically and analytically characterized and applied for the specific Fe(2+) determination. The bacterial Fe(2+) oxidation involves O(2) consumption, thus the quantification was performed registering the decrease of the oxygen reduction current. The limit of detection was found to be 2.4 micromol L(-1) and the sensitivity of the determinations-3.94 nAL micromol(-1). The response time of the biosensor is 18s for Fe(2+) concentrations of 10(-5) to 10(-4) mol L(-1). The biosensor was applied as well for the indirect determination of Fe(2+) oxidizing species such as Cr(2)O(7)(2-), reaching a sensitivity of 2.47 nAL micromol(-1). The transducer characteristics were evaluated and optimized to obtain short response time and high sensitivity. The analytical performances of the biosensor subject of the present work were found to be similar to that of the At. ferrooxidans based one developed by the authors earlier, avoiding however the sulfur compounds interference, because of the substrate specificity of the applied bacterial strain.

Purpose - Colonies of Actynomyces israelii bacteria have been found in removed copper intra-uterine devices (IUD) used as a long-term contraceptive method. The purpose of this paper is to characterize the biofilm developed under anaerobic conditions by Actynomyces israelii on IUD surface, and its influence in the copper corrosion processes. Design/methodology/approach - The dissolution of copper on the intra-uterine cavity prevents conception because of the toxic effect of the ions released. Nevertheless, microbiological growths have been detected on the IUD devices retired after long periods of insertion. In order to know about the influence of the biofilm on the corrosion of copper, electrochemical, spectroscopic and surface analysis techniques were applied to study the phenomenon. Findings - A porous Actynomyces israelii biofilm was formed on the copper IUD surface. The bacteria colony had developed in an exopolimeric substrate, which protects it from the toxic effect of copper ions. The corrosion process was not inhibited by the biofilm, due to the pores present which permit the transport of species through them. Practical implications - The results of this study show that there is no decay in the contraceptive function of the IUDs due to the presence of a bacterial biofilm on its surface. Originality/value - The relationship between microbial colonization and the corrosion process of copper IUD under anaerobic conditions was characterized. These results will complement previous investigations performed on the study of corrosion of copper IUDs under different conditions. © Emerald Group Publishing Limited.

An amperometric bacterial sensor with current response to Fe 2+ and S 2 O 3 2− ions has been designed by immobilizing an acidophilic biomass of Acidithiobacillus ferrooxidans on a multi disk flat-front oxygen probe. The bacterial layer was located between the oxygen probe and a membrane of cellulose. A filtration technique was used to yield the bacterial membranes having reproducible activity. The decrease of O 2 flow across the bacterial layer is proportional to the concentration of the dosed species. The dynamic range appeared to be linear for the Fe 2+ ions up to 2.5 mmol L −1 with a detection limit of 9 × 10 −7 mol L −1 and a sensitivity of 0.25 A L mol −1 . The response of the biosensor is 84 s for a determination of 2 × 10 −4 mol L −1 Fe 2+ . Optimizing the Fe 2+ determination by A. ferrooxidans sensor was carried out owing to Design of Experiments (DOE) methodology and empirical modelling. The optimal response was thus obtained for a pH of 3.4, at 35 °C under 290 rpm solution stirring. S 2 O 3 2− concentration was determined at pH 4.7, so avoiding its decomposition. The concentration range was linear up to 0.6 mmol L −1 . Sensitivity was 0.20 A L mol −1 with a response time of 207 s for a 2 × 10 −4 mol L −1 S 2 O 3 2− concentration.

Un reacteur bioelectrochimique a cathode volumique de grains de carbone regenere les ions ferreux, substrat de la bacterie acidophile autotrophe Thiobacillus ferrooxidans DSM 583. L'implantation d'un regulateur, non lineaire linearisant, controle efficacement l'intensite delivree au reacteur electrochimique. La concentration proteique, correlee a la concentration en biomasse, est multipliee par un facteur 6,4 lors d'une culture de 55 h dont 20 h sous electrolyse. Les capacites de la biomasse de Thiobacillus ferrooxidans pour la tolerance aux metaux et pour la fixation des metaux dans un effluent monometallique, bimetallique ou industriel sont presentees dans le but de concevoir un procede bioelectrochimique de recuperation de metaux en solution.

El uso de micro dispositivos electronicos como sensores opticos en las operaciones de deteccion de microorganismos (MO), es de gran importancia por las faciles y rapidas respuestas para detectar y enviar las senales electricas a indicadores que pueden ser luminosos o de conexion a computadoras, principalmente. Los procesos de deteccion de los MO, son aplicados en las actividades de envasado de alimentos en plantas industriales de este tipo, con el objetivo de eliminar al maximo todos los microorganismos que puedan generar corrosion microbiologica (CMB). Estos dispositivos operan a velocidades de microsegundos cuando estan en buenas condiciones, detectando los MO rapidamente en toda la superficie interna de las latas metalicas usadas para el envasado de alimentos. Los micro sensores opticos (MSO) se ubican en los equipos electronicos en interiores de una planta industrial dedicada a la manufactura y comercializacion de alimentos. Estos MSO estuvieron expuestos a variaciones de clima principalmente en los meses de marzo y octubre, siendo las epocas del ano donde se presentan los vientos Santa Ana (VSA). Dichos VSA modificaron las condiciones climaticas en el interior de la empresa, del ano 2010 al 2011 cuando se realizo la investigacion. Esto contribuyo a cambios en los rangos de humedad relativa (HR) desde 30% hasta 80% y de temperatura de 1 °C a 2 °C en periodos diarios en lugares sin flujo de viento principalmente donde se realizaban los procesos de manufactura de alimentos. Aunado a las variaciones de los factores climaticos, se observaron procesos de corrosion uniforme y por picaduras por la presencia de contaminantes del aire como cloruros principalmente y sulfuros como segundos agentes contaminantes con un efecto que contribuia al deterior de los MSO. Los MSO operaron en condiciones en mal estado o dejaron de operar, sin realizar el proceso de deteccion adecuado y se genero CMB que deterioro los alimentos y origino perdidas economicas.

La corrosion es un problema permanente, tanto en ambientes naturales como en industriales, incluyendo los campos geotermicos, danando la infraestructura civil e industrial. La fuente de la energia geotermica (EG) es el calor del agua subterranea, usado para generar electricidad y calentamiento de viviendas. La EG es renovable, local, confiable y economica. Los fluidos geotermicos: agua, vapor y salmuera a elevadas temperaturas, interactuan con la superficie de los equipos e instalaciones, afectando la produccion de energia y su eficiencia. El principal factor de la corrosion es la mezcla de gases disueltos: O 2 , CO 2 , H 2 S, NH 3 , su salinidad y acidez, en particular los cloruros (Cl - ). El acero es el mas importante material estructural que se encuentra expuesto a la corrosion neutra y acida, segun el pH del fluido. La corrosion y la incrustacion causan un evidente impacto economico, ya que afectan la produccion de los pozos de vapor. El control de la corrosion contribuye a la proteccion y preservacion de la calidad del ambiente en los campos geotermicos, evita elevados costos de mantenimiento y la reparacion o reemplazo de equipos danados. Este articulo presenta una descripcion ilustrada de los aspectos tecnologicos y ambientales, basada en el conocimiento y experiencia de los autores en Mexico.

Hydrogen sulphide (H2S) is considered one of the most corrosive atmospheric pollutants. It is a weak, diprotic, reducing acid, readily soluble in water and dispersed into the air by winds when emitted from natural, industrial, and anthropogenic sources. It is a pollutant with a high level of toxicity impairing human health and the environment quality. It attacks copper forming thin films of metallic sulphides or dendrite whiskers, which are cathodic to the metal substrate, enhancing corrosion. H2S is actively involved in microbially influenced corrosion (MIC) which develops in water, involving sulphur based bacteria, in oxidizing and reducing chemical reactions. H2S is found in concentrated geothermal brines, in the atmosphere of geothermal fields, and in municipal sewage systems. Other active atmospheric pollutants include SOX, NOX, and CO. This investigation reports on the effects of H2S on copper in microelectronic components of equipment and devices, with the formation of nonconductive films that lead to electrical failures.

The economic development of any region, state or country, depends not only on its natural re‐ sources and productive activities, but also on the infrastructure that account for the exploita‐ tion, processing and marketing of goods. Irrigation systems, roads, bridges, airports, maritime, land and air transport, school buildings, offices and housing, industrial installations are affect‐ ed by corrosion and therefore susceptible to deterioration and degradation processes.

The microelectronic industry applies materials with good electrical and corrosion resistance properties for the manufacturing of the microelectronic devices. Silver and copper are materials with this characteristics used for that purpose. Some of their main applications are as high thermal conductive die attach paste that had silver flakes as conductive filler material, silver plated over copper frames, Sn-Ag and Sn-Cu alloys for solder paste used in Surface Mount Technology (SMT) process, conductive internal copper layers in printed circuit boards, copper wire bonding, and more. Other metals and alloys, widely used for support frames, heat diffusers and case wares in the electronics industry are tin, nickel, aluminum, carbon steel and galvanized steel.

The electrochemical biosensors are analytical devices designed by coupling biological recognition elements and electrochemical transducers. The transducer converts the analytical signal produced as a result of the biochemical and electrochemical interactions into measurable electrical one (Thevenot et al., 1999). The electrochemical biosensors are self-contained, simple to handle, and able to provide specific, sensitive, accurate and cost-effective in situ and on line measurements in real time, without or with a minimum sample preparation. Because of these advantages over the conventional analytical methods, they are well suited for the detection of a large spectrum of compounds, entering food and subjects of analytical control. The present work is intended to demonstrate the applicability of the electrochemical biosensors for arsenic determination in beverages.

From ancient times human beings have survived on a diet consisting on a relatively few species of plants and animals, domesticated and then cultivated and grown. Three cereals, wheat, rice and corn, supply the need of human energy, protein and vitamins requirements for the network of metabolic processes to maintain normal body function and temperature. In a prehistoric era, indigenous peoples all over the world were moving in inhospitable grounds obtaining their daily sustenance by hunting and gathering fruits, seeds and roots. Actually, the three largest markets worldwide, according to their production extent, the number of consumers and their economic and social significance are the food, energy and water markets. Furthermore, their increasing scarcity and soaring prices lead to a global critical situation. The demand for increased food supply is related both, to population increase and personal and family income. Consequently, the food market is the largest one, including all the inhabitants of this planet, about seven billion, since everyone eats! The organized food production and supply starts with the agricultural revolution, developed and implemented in the fertile valleys of the rivers Tigris-Euphrates in Mesopotamia and the Nile in ancient Egypt. Afterwards the food industry expanded, avoided widespread famine and ensured that sufficient food is supplied for all people to stay healthy. Current food research had been largely stimulated by rapidly growing world demand but technological advances in food processing, equipment and production plants have also contributed. A most significant aspect in the search of new nutritional food is the requirement for adequate protein in regions where meat and fish are not available. Additionally, advances in the food industry (FI) such as preservation, packaging and storage facilitate food delivery and minimized health hazards. Space flight conditions have stimulated the creation of space food which meets highly demanding standards for conservation and to be ready for easy digestion e.g. solid dehydrated food easily converted into liquid or paste food. Techniques for preserving food from natural deterioration following harvest or slaughter dated to prehistoric times applying drying, salting, fermentation of milk and fruits and pickling of vegetables. Modern techniques include canning, freezing, dehydration, cooking under vacuum and addition of chemicals. The principal causes of food spoilage are growth

The organophosphorus (OP) pesticides are synthetic esters, amides, or thiol derivatives of the phosphoric, phosphonic, phosphorothioic, or phosphonothioic acids (Corbett et al., 1984; Eto, 1974; Gupta, 2006; Hassall, 1982; Quin, 2000). The structural diversity of this family of compounds is reflected in their physicochemical and biological properties: vapour pressure, solubility in water, chemical stability and toxicity (Corbett et al., 1984; Hassall, 1982; WHO, 1986), which determine their specific application (Hassal, 1982). Compared to the mostly banned in U.S. and Europe organochlorine pesticides, the OP ones are less persistent in the environment, are not subject of bioaccumulation and biomagnification, and do not release toxic break down products (Krieger, 2001). These features justify their application in the agricultural and veterinary practices of the modern world. In 1999 the OP insecticides represented ≈37% of the pesticides in use at a global scale (Table 1) and 72% of the insecticides used in U.S. (Kiely et al., 2004). The top ten OP insecticides active ingredients include malathion, chlorpyrifos, terbufos, diazinon, methyl-parathion, phorate, acephate, phosmet, azinphos-methyl, and dimethoate (Kiely et al., 2004).

The purpose of this paper is to evaluate the electrochemical behaviour of corrosion inhibition of the copper-carbon steel galvanic couple (Cu-CS), exposed to reverse osmosis water (RO) used for rinsing of heat exchangers for heavy duty machinery, during manufacture. Molybdate and nitrite salts were utilized to evaluate the inhibition behaviour under galvanic couple conditions. Cu-CS couple was used as working electrodes to measure open circuit potential (OCP), potentiodynamic polarization (PP), and electrochemical impedance spectroscopy (EIS). The surface conditions were characterized by scanning electron microscopy (SEM) and electron dispersive X-ray spectroscopy (EDS). The most effective concentration ratio between molybdate and nitrite corrosion inhibitors was determined. The morphological study indicated molybdate deposition on the anodic sites of the galvanic couple. The design of molybdate-based corrosion inhibitor developed in the present work should be applied to control galvanic corrosion of the Cu-CS couple during cleaning in the manufacture of heat exchangers.

The anticorrosive properties of cerium based conversion coatings deposited on AA6061-T6 alloy by immersion in unbuffered cerium chloride and cerium nitrate solutions in the presence of hydrogen peroxide were investigated and characterized by potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) in 0.5 mol/L NaCl aqueous solution. The microstructure and chemical composition of the protective films were examined by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). It was found that the best corrosion protection was afforded by the samples treated during 600 s in cerium chloride solution at pH values ∼5.5-4, showing higher amounts of cerium and polarization resistance values greater than 10 Ω m2. Moreover, an ennoblement of the corrosion potential and decreasing of the cathodic and anodic currents were obtained compared with the cerium nitrate solutions application. This behavior was attributed to the influence of the deposition parameters such as type of the salt anion, i.e., chelating effect and chaotropic characteristics, pH fluctuations in the conversion solution and deposition time. © 2011 The Chinese Society of Rare Earths.

The goal of this work is the evaluation of the analytical characteristics of the determinations performed using glucose oxidase and acetylcholinesterase based electrochemical sensors, developed applying original or optimized conventional methods of enzyme immobilization. It was found that the sensitivity of glucose determination, for example, varies from 0.048 to 3.36 mA L mol -1 cm -2 and the response time of the glucose oxidase based sensors – from 5 to 30 s, according to the method of the bioreceptor immobilization. The sensitivity of the analysis is affected from the activity of the immobilized biocomponent, from the composition of the solution (concentration of the substrate, of the mediator and of the inhibitor), and from the experimental conditions (pH, temperature, agitation), as well as from the kinetic parameters of the studied process. It was found that the immobilized glucose oxidase conserves its substrate specificity in the presence of a number of glucides (galactose, maltose, fructose, and saccharose) in 100 fold higher concentrations. The selectivity of glucose analysis is ensured applying a suitable potential. Interferences free glucose amperometric determination was performed at 0.00 V/SCE, in the presence of ascorbates and urates. The electrochemical quantification of enzyme inhibitors allows reaching particularly low limits of detection (10 -9 -10 -14 mol L -1 ).

International audience; A new voltammetric technique providing high resolution – Differential Alternative Pulses Voltammetry (DAPV) based on the nonlinearity of I/E characteristic of the electrochemical systems was developed, suitable for simultaneous determination of species without their preliminary separation. Superimposition of couples of single rectangular pulses separated by a constant delay time and having same amplitude and opposite polarity, combined with appropriate signal processing yields first derivative of peak shaped curve. The DAPV faradaic current response equation for reversible electrochemical reactions was theoretically derived, graphically presented and experimentally tested. DAPV was applied for determination of species having very near E1/2 potentials: Pb2+/Tl+ and In3+/Cd2+ under increasing concentration ratios. The experimental results compared with those obtained by Differential Pulse Polarography (DPP) and Second Harmonic Alternating Current Polarography show superiority of DAPV resolution power which is combined with high sensitivity, similar to that providing by DPP, employing a simple electronic equipment.

International audience; The sensors applied recently for determination of cholinesterase activity are mostly enzymatic amperometric sensors, in spite of their disadvantages: short life-time at ambient temperature, instability of the response, interferences, as well as passivation of the electrode surface. In the present paper a new approach for determination of cholinesterase activity was proposed, overcoming the main drawbacks of the analysis performed with amperometric enzymatic sensors. Instead of the immobilization of enzymes on a conducting electrode surface, whole cells of Arthrobacter globiformis, containing choline oxidase were fixed on a Clark type oxygen probe. Current proportional to bacteria respiration is registered as a sensor response. The application of whole cells of bacteria as a sensing element permits to achieve high stability of the response and long life-time of the sensor at ambient temperature, due to the conservation of the enzyme in its natural micro-environment inside the immobilized cells. The proposed sensor keeps its functionality more than 7 weeks stored in deionized water at ambient temperature. For the first 2 weeks the amplitude of the response decreases with only 10% and at the end of the studied 7 weeks period the response was 50% of the initial. The other advantages of the proposed sensor are: the dissolved oxygen is used as a mediator which concentration can be reliably and interferences free measured by the aim of a Clark type oxygen probe applied as a transducer; reproducible bacterial membranes can be elaborated by filtration of resuspended bacterial culture after preliminary determination of its activity; application of membranes containing lyophilized bacteria capable to be conserved infinitely long time and activated just before their application; negligible cost compared with the sensors based on immobilized enzymes. The steady-state response of the proposed bacterial sensor to choline obtained in 200 s is linear in the investigated concentration range up to 2 × 10–4 mol dm–3, with detection limit of 8 × 10–8 mol dm–3 and sensitivity of 4 × 10–1 μA cm3 mol–1, at pH 6, temperature of 25 °C and stirring rate of 300 rpm. Choline is formed as a result of the catalytic hydrolysis (depending on the cholinesterase activity) of the substrate acetylcholine. Linear calibration graph for cholinesterase activity determination was obtained in the range up to 11 mU cm–3, with a slope of 1.97 × 10–2 μA cm3 mU–1, at pH 6, temperature of 25 °C and stirring rate of 300 rpm. The tests with reconstituted lyophilized serum with known activity used as a control sample confirm the accuracy of the proposed method. The relative error of the determination was only 2.82%.

International audience; The adsorption (fixation) of bacteria Acidithiobacillus ferrooxidans on Hg and Cu metallic surfaces was qualitatively studied owing to two independent methods: frequency measurement using a quartz crystal microbalance and light absorption measuring at the Hg/bacterial culture interface. A method using a dropping mercury electrode (DME) allowed quantifying this bacterial fixation. Determining the superficial tension at Hg/bacterial culture interface led to determine bacteria adsorption on Hg through the Gibbs isotherm. A modified stripping voltammetry was proposed taking benefit of both bacterial adsorption on Hg surface and metal fixation capacity on biomass. Metal preconcentration on the biologically modified Hg electrode appeared to improve the measurement sensitivity of differential pulse anodic stripping voltammetry (DPASV). The height of the detected peaks was thus increased of 17.6% for copper, 48.4% for lead, and 132% for cadmium determinations compared to those obtained with an unmodified mercury electrode. Such augmentation depended on bulk bacteria concentration and bacteria preconcentration.

The aerobic acidophilic bacterium Acidithiobacillus ferrooxidans oxidizes Fe(2+) and S(2)O(3)(2-) ions by consuming oxygen. An amperometric biosensor was designed including an oxygen probe as transducer and a recognition element immobilized by a suitable home-made membrane. This biosensor was used for the indirect amperometric determination of Cr(2)O(7)(2-) ions owing to methods based on a mediator (Fe(2+)) or titration. Using the mediator, the biosensor response versus Cr(2)O(7)(2-) was linear up to 0.4 mmol L(-1), with a response time of, respectively, 51 s (2 x 10(-5) mol L(-1) Cr(2)O(7)(2-)) and 61 s (6 x 10(-5) mol L(-1) Cr(2)O(7)(2-)). The method sensitivity was 816 microA L mol(-1). Response time and measurement sensitivity depended on membrane material and technique for biomass immobilization. For example, their values were 90 s-200 microA L mol(-1) when using a glass-felt membrane and 540 s-4.95 microA L mol(-1) with a carbon felt one to determine a concentration of 2 x 10(-5) mol L(-1) Cr(2)O(7)(2-). For the titration method, the biosensor is used to determine the equivalence point. The relative error of quantitative analysis was lower than 5%.

An amperometric bacterial sensor with current response to Fe(2+) and S(2)O(3)(2-) ions has been designed by immobilizing an acidophilic biomass of Acidithiobacillus ferrooxidans on a multi disk flat-front oxygen probe. The bacterial layer was located between the oxygen probe and a membrane of cellulose. A filtration technique was used to yield the bacterial membranes having reproducible activity. The decrease of O(2) flow across the bacterial layer is proportional to the concentration of the dosed species. The dynamic range appeared to be linear for the Fe(2+) ions up to 2.5 mmol L(-1) with a detection limit of 9 x 10(-7) mol L(-1) and a sensitivity of 0.25 A L mol(-1). The response of the biosensor is 84 s for a determination of 2 x 10(-4) mol L(-1) Fe(2+). Optimizing the Fe(2+) determination by A. ferrooxidans sensor was carried out owing to Design of Experiments (DOE) methodology and empirical modelling. The optimal response was thus obtained for a pH of 3.4, at 35 degrees C under 290 rpm solution stirring. S(2)O(3)(2-) concentration was determined at pH 4.7, so avoiding its decomposition. The concentration range was linear up to 0.6 mmol L(-1). Sensitivity was 0.20 A L mol(-1) with a response time of 207 s for a 2 x 10(-4) mol L(-1) S(2)O(3)(2-) concentration.

The impurities determination in Ni electrolysis baths is of a great importance for the quality of the Ni electroplating protective and decorative coatings. Inclusions having more negative potential than Ni form corrosion anodic zones in the presence of humidity, corrupting the Ni layer protective properties. One of the most dangerous inclusions is Zn. Zn often appears in the Ni coatings deposited on brass, as a result of the brass detail dissolution in the low pH Ni baths before the beginning of the electrolysis: the deposition of the first Ni layer. As known, the maintenance of the Zn2+ concentration in the Ni bath bellow 3 ppm can prevent Zn inclusions formation in the Ni coatings, which requires on-line Zn2+ determination. Nevertheless, spectral analytical methods such as AAS and ICP cannot be applied after Zn2+ extraction from the high concentrated matrix, because the huge Ni2+ concentration will provoke crystallization in the nebulizer area corrupting the analysis. The direct application of some voltammetric techniques also cannot yield any results, because of the very small difference of the E½ of the two species, which will cause peak overlapping. Some specific properties of the Ni2+ and Zn2+ ions however can be used to avoid the interferences. It is known that Zn2+ forms soluble hydroxyl complex in the presence of excess of OH-, while Ni2+ forms the very stable Ni(OH)2 precipitation product. Thus, KOH or NaOH can be applied as a supporting electrolyte, in which a well defined peak of Zn2+ is registered as shown in Fig. 1, while no peak of Ni2+will appear because of its precipitation. The effect of the NaOH concentration applied as a supporting electrolyte, of the Zn2+ adsorption by the formed Ni(OH)2 precipitation product, and of the Ni2+/Zn2+ concentration ratio on the analytical characteristics of the Zn2+ determination are the subject of this study. The results are presented and discussed. It is demonstrated that the developed method consisting in adding of a small volume of Ni electroplating bath solution to the NaOH supporting electrolyte, followed by DPV determination can be applied for the on-line Zn2+ determination.