Determination of Microcystin-LR in waters in the subnanomolar range by sol–gel imprinted polymers on solid contact electrodes

The present work reports new sensors for the direct determination of Microcystin-LR (MC-LR) in environmental waters. Both selective membrane and solid contact were optimized to ensure suitable analytical features in potentiometric transduction. The sensing layer consisted of Imprinted Sol–Gel (ISG) materials capable of establishing surface interactions with MC-LR. Non-Imprinted Sol–Gel (NISG) membranes were used as negative control. The effects of an ionic lipophilic additive, time of sol–gel polymerization, time of extraction of MC-LR from the sensitive layer, and pH were also studied. The solid contact was made of carbon, aluminium, titanium, copper or nickel/chromium alloys (80 : 20 or 90 : 10). The best ISG sensor had a carbon solid contact and displayed average slopes of 211.3 mV per decade, with detection limits of 7.3 1010 M, corresponding to 0.75 mg L1 . It showed linear responses in the range of 7.7 1010 to 1.9 109 M of MC-LR (corresponding to 0.77–2.00 mg L1 ), thus including the limiting value for MC-LR in waters (1.0 mg L1 ). The potentiometric-selectivity coefficients were assessed by the matched potential method for ionic species regularly found in waters up to their limiting levels. Chloride (Cl) showed limited interference while aluminium (Al3+), ammonium (NH4 + ), magnesium (Mg2+), manganese (Mn2+), sodium (Na+ ), and sulfate (SO4 2) were unable to cause the required potential change. Spiked solutions were tested with the proposed sensor. The relative errors and standard deviation obtained confirmed the accuracy and precision of the method. It also offered the advantages of low cost, portability, easy operation and suitability for adaptation to flow methods.

New and low cost plastic membrane electrode with low detection limits for sulfadimethoxine determination in aquaculture waters

Sulfadimethoxine (SDM) is one of the drugs, often used in the aquaculture sector to prevent the spread of disease in freshwater fish aquaculture. Its spread through the soil and surface water can contribute to an increase in bacterial resistance. It is therefore important to control this product in the environment. This work proposes a simple and low-cost potentiometric device to monitor the levels of SDM in aquaculture waters, thus avoiding its unnecessary release throughout the environment. The device combines a micropipette tip with a PVC membrane selective to SDM, prepared from an appropriate cocktail, and an inner reference solution. The membrane includes 1% of a porphyrin derivative acting as ionophore and a small amount of a lipophilic cationic additive (corresponding to 0.2% in molar ratio). The composition of the inner solution was optimized with regard to the kind and/or concentration of primary ion, chelating agent and/or a specific interfering charged species, in different concentration ranges. Electrodes constructed with inner reference solutions of 1 × 10−8 mol/L SDM and 1 × 10−4 mol/L chromate ion showed the best analytical features. Near-Nernstian response was obtained with slopes of −54.1 mV/decade, an extraordinary detection limit of 7.5 ng/mL (2.4 × 10−8 mol/L) when compared with other electrodes of the same type. The reproducibility, stability and response time are good and even better than those obtained by liquid contact ISEs. Recovery values of 98.9% were obtained from the analysis of aquaculture water samples.

The presence of fungi on contact electrical stimulation electrodes and ultrasound transducers in physiotherapy clinics

Objectives To evaluate the presence of fungi on contact electrodes and ultrasound transducers from physiotherapy clinics.Design Quantitative study conducted at the Laboratory of Microbiology and Immunology, Faculty of Health Sciences and Technology of Piaui - NOVAFAPI, Teresina, Brazil.Setting Sample collection was performed in 10 clinics ( 20 ultrasound transducers and 20 contact electrodes).Main outcome measures Swabs were soaked with saline solution, inoculated in culture and incubated for filamentous fungi and yeast growth.Results Fourteen taxons were identified: Acremomium hyalinulum (Sacc.), Aspergillus terreus, Candida albicans, Cladosporium cladosporioides, Cladosporium elatum, Cladosporium oxysporum, Cladosporium sphaerospermum, Cladosphialophora bantiana, Curvularia clavata, Curvularia senegalensis, Fusarium oxysporum, Penicillium decumbens, Scopulariopsis candida and Sporothrix schenckii. Aspergillus terreus, Cladosporium oxysporum, Sporothrix shenckii and Candida albicans were found most often on contact electrodes, and Penicillium decumbens and Cladosporium cladosporioides were found most often on ultrasound transducers.Conclusion Fungi were found on all of the contact electrodes and ultrasound transducers. Physiotherapy professionals need to improve the disinfection procedures for this equipment. (C) 2010 Chartered Society of Physiotherapy. Published by Elsevier Ltd. All rights reserved.

Label-free Detection of Microcystin-LR in Waters Using Real-Time Potentiometric Biosensors Based on Single-Walled Carbon Nanotubes Imprinted Polymers

Microcystin-LR (MC-LR) is a dangerous toxin found in environmental waters, quantified by high performance liquid chromatography and/or enzyme-linked immunosorbent assays. Quick, low cost and on-site analysis is thus required to ensure human safety and wide screening programs. This work proposes label-free potentiometric sensors made of solid-contact electrodes coated with a surface imprinted polymer on the surface of Multi-Walled Carbon NanoTubes (CNTs) incorporated in a polyvinyl chloride membrane. The imprinting effect was checked by using non-imprinted materials. The MC-LR sensitive sensors were evaluated, characterized and applied successfully in spiked environmental waters. The presented method offered the advantages of low cost, portability, easy operation and suitability for adaptation to flow methods.

PVC Supported Liquid Membrane and Carbon Paste Potentiometric Sensors Incorporating a Mn(III)-Porphyrin for the Direct Determination of Undissociated Paracetamol

PVC supported liquid membrane and carbon paste potentiometric sensors incorporating an Mn(III)-porphyrin complex as a neutral host molecule were developed for the determination of paracetamol. The measurements were carried out in solution at pH 5.5. Under such conditions paracetamol exists as a neutral molecule. The mechanism of molecular recognition between the Mn(III)-porphyrin and paracetamol, leading to potentiometric signal generation, is discussed.The sensitivity and selectivity toward paracetamol of carbon paste and polymeric liquid membrane electrodes incorporating an Mn(III)-porphyrin host were compared. The applicability of these sensors to the direct determination of paracetamol was checked by performing a recovery test in human plasma.

Optimizing potentiometric ionophore and electrode design for environmental on-site control of antibiotic drugs: Application to sulfamethoxazole

Potentiometric sensors are typically unable to carry out on-site monitoring of environmental drug contaminants because of their high limits of detection (LODs). Designing a novel ligand material for the target analyte and managing the composition of the internal reference solution have been the strategies employed here to produce for the first time a potentiometric-based direct reading method for an environmental drug contaminant. This concept has been applied to sulfamethoxazole (SMX), one of the many antibiotics used in aquaculture practices that may occur in environmental waters. The novel ligand has been produced by imprinting SMX on the surface of graphitic carbon nanostructures (CN) < 500 nm. The imprinted carbon nanostructures (ICN) were dispersed in plasticizer and entrapped in a PVC matrix that included (or not) a small amount of a lipophilic additive. The membrane composition was optimized on solid-contact electrodes, allowing near-Nernstian responses down to 5.2 μg/mL and detecting 1.6 μg/mL. The membranes offered good selectivity against most of the ionic compounds in environmental water. The best membrane cocktail was applied on the smaller end of a 1000 μL micropipette tip made of polypropylene. The tip was then filled with inner reference solution containing SMX and chlorate (as interfering compound). The corresponding concentrations were studied for 1 × 10−5 to 1 × 10−10 and 1 × 10−3 to 1 × 10−8 mol/L. The best condition allowed the detection of 5.92 ng/L (or 2.3 × 10−8 mol/L) SMX for a sub-Nernstian slope of −40.3 mV/decade from 5.0 × 10−8 to 2.4 × 10−5 mol/L.

Introduzione agli elettrodi senza contatto per uso medico

I segnali biopotenziali cardiaci e neurali nelle forme di elettroencefalogramma (EEG) ed elettrocardiogramma (ECG) sono due indicatori fisiologici molto importanti che ben si prestano ad un monitoraggio sanitario wireless a lungo termine. Nonostante gli innumerevoli progressi compiuti nel campo della tecnologia wireless e della microelettronica, l’utilizzo dell'EEG/ECG risulta essere ancora limitato dai disagi e dalle scomodità dovute all’impiego di elettrodi a contatto bagnato (wet contact electrodes). Gli elettrodi adesivi ad uso clinico sono spesso percepiti dai pazienti su cui vengono applicati come irritanti e scomodi, riducendo notevolmente l’accondiscendenza ad un loro utilizzo costante nell'ambiente domestico, ovvero al di fuori dello stretto controllo medico-sanitario. Come alternativa si ricorre all’uso di elettrodi a secco (dry electrodes), questi però, in mancanza della capacità di conduzione del gel, sono molto più sensibili alle condizioni della pelle e pertanto suscettibili agli artefatti legati al movimento. Questa tesi si ripropone di illustrare in maniera il più possibile organica e precisa il principio di funzionamento degli elettrodi senza contatto, con particolare attenzione al ruolo rivestito dai segnali EEG ed ECG. L’analisi intende inoltre mettere in evidenza l’entità dei vantaggi derivanti dall’impiego degli elettrodi senza contatto rispetto a quelli tradizionali.

Computational fluid dynamical studies of structured distillation packings

In recent years structured packings have become more widely used in the process industries because of their improved volumetric efficiency. Most structured packings consist of corrugated sheets placed in the vertical plane The corrugations provide a regular network of channels for vapour liquid contact. Until recently it has been necessary to develop new packings by trial and error, testing new shapes in the laboratory. The orderly repetitive nature of the channel network produced by a structured packing suggests it may be possible to develop improved structured packings by the application of computational fluid dynamics (CFD) to calculate the packing performance and evaluate changes in shape so as to reduce the need for laboratory testing. In this work the CFD package PHOENICS has been used to predict the flow patterns produced in the vapour phase as it passes through the channel network. A particular novelty of the approach is to set up a method of solving the Navier Stokes equations for any particular intersection of channels. The flow pattern of the streams leaving the intersection is then made the input to the downstream intersection. In this way the flow pattern within a section of packing can be calculated. The resulting heat or mass transfer performance can be calculated by other standard CFD procedures. The CFD predictions revealed a circulation developing within the channels which produce a loss in mass transfer efficiency The calculations explained and predicted a change in mass transfer efficiency with depth of the sheets. This effect was also shown experimentally. New shapes of packing were proposed to remove the circulation and these were evaluated using CFD. A new shape was chosen and manufactured. This was tested experimentally and found to have a higher mass transfer efficiency than the standard packing.

Trimethoprim-selective electrodes with molecularly imprinted polymers acting as ionophores and potentiometric transduction on graphite solid-contact

This work proposes a new biomimetic sensor material for trimethoprim. It is prepared by means of radical polymerization, having trimethylolpropane trimethacrylate as cross-linker, benzoyl peroxide as radicalar iniciator, chloroform as porogenic solvent, and methacrylic acid and 2-vinyl pyridine as monomers. Different percentages of sensor in a range between 1 and 6% were studied. Their behavior was compared to that obtained with ion-exchanger quaternary ammonium salt (additive tetrakis(p-chlorophenyl)borate or tetraphenylborate). The effect of an anionic additive in the sensing membrane was also tested. Trimethoprim sensors with 1% of imprinted particles from methacrylic acid monomers showed the best response in terms of slope (59.7 mV/decade) and detection limit (4.01×10−7 mol/L). These electrodes displayed also a good selectivity towards nickel, manganese aluminium, ammonium, lead, potassium, sodium, iron, chromium, sulfadiazine, alanine, cysteine, tryptophan, valine and glycine. The sensors were not affected by pH changes from 2 to 6. They were successfully applied to the analysis of water from aquaculture.

Solid contact PVC membrane electrodes based on neutral or charged carriers for the selective reading of anionic sulfamethoxazole and their application to the analysis of aquaculture water

Sulfamethoxazole (SMX) is among the antibiotics employed in aquaculture for prophylactic and therapeutic reasons. Environmental and food spread may be prevented by controlling its levels in several stages of fish farming. The present work proposes for this purpose new SMX selective electrodes for the potentiometric determination of this sulphonamide in water. The selective membranes were made of polyvinyl chloride (PVC) with tetraphenylporphyrin manganese (III) chloride or cyclodextrin-based acting as ionophores. 2-nitrophenyl octyl ether was employed as plasticizer and tetraoctylammonium, dimethyldioctadecylammonium bromide or potassium tetrakis (4-chlorophenyl) borate was used as anionic or cationic additive. The best analytical performance was reported for ISEs of tetraphenylporphyrin manganese (III) chloride with 50% mol of potassium tetrakis (4-chlorophenyl) borate compared to ionophore. Nersntian behaviour was observed from 4.0 × 10−5 to 1.0 × 10−2 mol/L (10.0 to 2500 µg/mL), and the limit of detection was 1.2 × 10−5 mol/L (3.0 µg/mL). In general, the electrodes displayed steady potentials in the pH range of 6 to 9. Emf equilibrium was reached before 15 s in all concentration levels. The electrodes revealed good discriminating ability in environmental samples. The analytical application to contaminated waters showed recoveries from 96 to 106%.

Trimethoprim-selective electrodes with molecularly imprinted polymers acting as ionophores and potentiometric transduction on graphite solid-contact

This work proposes a new biomimetic sensor material for trimethoprim. It is prepared by means of radical polymerization, having trimethylolpropane trimethacrylate as cross-linker, benzoyl peroxide as radicalar iniciator, chloroform as porogenic solvent, and methacrylic acid and 2-vinyl pyridine as monomers. Different percentages of sensor in a range between 1 and 6% were studied. Their behavior was compared to that obtained with ion-exchanger quaternary ammonium salt (additive tetrakis(p-chlorophenyl)borate or tetraphenylborate). The effect of an anionic additive in the sensing membrane was also tested. Trimethoprim sensors with 1% of imprinted particles from methacrylic acid monomers showed the best response in terms of slope (59.7 mV/decade) and detection limit (4.01 × 10− 7 mol/L). These electrodes displayed also a good selectivity towards nickel, manganese aluminium, ammonium, lead, potassium, sodium, iron, chromium, sulfadiazine, alanine, cysteine, tryptophan, valine and glycine. The sensors were not affected by pH changes from 2 to 6. They were successfully applied to the analysis of water from aquaculture.

Stability of a nanofiltration membrane after contact with a low-level liquid radioactive waste

This study investigated the treatment of a liquid radioactive waste containing uranium (235U + 238U) using nanofiltration membranes. The membranes were immersed in the waste for 24-5000 h, and their transport properties were evaluated before and after the immersion. Surface of the membranes changed after immersion in the waste. The SW5000 h specimen lost its coating layer of polyvinyl alcohol, and its rejection of sulfate ions and uranium decreased by about 35% and 30%, respectively. After immersion in the waste, the polyamide selective layer of the membranes became less thermally stable than that before immersion.

Nickel hydroxide electrodes as amperometric detectors for carbohydrates in flow injection analysis and liquid chromatography

The present paper describes the utilization of nickel hydroxide modified electrodes toward the catalytic oxidation of carbohydrates (glucose, fructose, lactose and sucrose) and their utilization as electrochemical sensor. The modified electrodes were employed as a detector in flow injection analysis for individual carbohydrate detection, and to an ionic column chromatography system for multi-analyte samples aiming a prior separation step. Kinetic studies were performed on a rotating disk electrode (RDE) in order to determine both the heterogeneous rate constant and number of electrons transferred for each carbohydrate. Many advantages were found for the proposed system including fast and easy handling of the electrode modification, low cost procedure, a wide range of linearity (0.5-50 ppm), low detection limits (ppb level) and high sensitivities. (C) 2009 Elsevier B.V. All rights reserved.

Wedged analog tunable beam steering device based on cholesteric liquid crystals

In this work we propose a novel cholesteric liquid crystal beam steering device based on the Kerr effect. The first version of the device consists of two ITO coated glass plates, with intentionally prepared electrodes, assembled together with a thickness gradient between both sides of the device. One side of the cell has two substrates at direct contact; the other side has separated substrates to form the wedge. The cell was filled with a cholesteric liquid crystal. The liquid crystal material is an innovative mixture called 1892E with extremely low viscosity doped with a ZLI chiral nematogen. The proposed beam steering device based on cholesteric liquid crystals has great potential for many photonic applications. Results describing the performance of the device and the properties of the selected liquid crystals are presented.

Characterization of the interfaces between Au(hkl) single crystal basal plane electrodes and [Emmim][Tf2N] ionic liquid

The interface between Au(hkl) basal planes and the ionic liquid 1-Ethyl-2,3-dimethyl imidazolium bis(trifluoromethyl)sulfonil imide was investigated by using both cyclic voltammetry and laser-induced temperature jump. Cyclic voltammetry showed characteristic features, revealing surface sensitive processes at the interfaces Au(hkl)/[Emmim][Tf2N]. From laser-induced heating the potential of maximum entropy (pme) is determined. Pme is close to the potential of zero charge (pzc) and, therefore, the technique provides relevant interfacial information. The following order for the pme values has been found: Au(111) > Au(100) > Au(110). This order correlates well with work function data and values of pzc in aqueous solutions.