A novel potentiometric membrane sensor for determination of Co based on 5-amino-3-methylisothiazole

A new poly(vinylchloride) (PVC) membrane electrode for trace level determination of Co²⁺ ions has been developed based on 5-amino-3-methylisothiazole as an ionophore, o-nitrophenyloctylether as a plasticizer and oleic acid (OA) as a good lipophilic additive. The electrode exhibits a Nernstian slope of 29.5 ± 0.2 mV/decade in a linear range of 1.0 × 10⁻¹ to 6.3 × 10⁻⁷ M for Co²⁺ ions. The detection limit of this electrode is 3.9 × 10⁻⁷ M. It has a fast response time of 12 s and can be used for a period of 4 months without any divergence in potentials. The proposed electrode reveals a good selectivity for Co (II) over a wide variety of other tested cations and could be used in the pH range 3.3–9.0. The electrode was successfully applied as an indicator electrode for the potentiometric titration of cobalt ions with EDTA as well as for the direct determination of Co (II) in real samples.     

Construction of a highly selective PVC-based membrane sensor for Ce(III) ions

A highly Ce(III) ion-selective poly vinyl chloride (PVC) membrane sensor based on N′-[(2-hydroxyphenyl)methylidene]-2-furohydrazide (NHMF) as an excellent sensing material is successfully developed. The electrode shows a good selectivity for Ce(III) ions with respect to most common cations including alkali, alkaline earth, transition and heavy metal ions. The proposed sensor exhibits a wide linear response with a slope of 19.4 ± 0.3 mV/decade over the concentration range of 1.0 × 10⁻⁵ to 1.0 × 10⁻¹ M, and a detection limit of 7.6 × 10⁻⁶ M of Ce(III) ions. The sensor response is independent of pH in the range of 3.5–10.0. The proposed electrode was applied as an indicator electrode in potentiometric titration of Ce(III) ions with EDTA and C₂O₄². It was also successfully applied in the determination of cerium ions in aqueous samples.     

Determination of reduced glutathione using an amperometric carbon paste electrode chemically modified with TTF–TCNQ

The development of an amperometric sensor for the determination of reduced glutathione (GSH) is described. The sensor is based on tetrathiafulvalene–tetracyanoquinodimethane (TTF–TCNQ) incorporated into the graphite powder/Nujol oil matrix. The electrooxidation of GSH was monitored amperometrically at 200 mV versus SCE (saturated calomel electrode). The amperometric response of the sensor was linearly proportional to the GSH concentration between 20 and 300 μmol l⁻¹, in 0.1 mol l⁻¹ phosphate buffer (pH 8.0), containing 0.1 mol l⁻¹ KCl and 0.5 mmol l⁻¹ Na₂H₂EDTA, as supporting electrolyte.

The detection limit, considering signal/noise ratio equal three, was 4.2 μmol l⁻¹ for GSH and the repeatability obtained as relative standard deviation was of 5.1% for a series of 10 successive measurements.     

Direct electrochemistry and electrocatalysis of myoglobin immobilized in zirconium phosphate nanosheets film

Myoglobin (Mb) is incorporated on a novel matrix—zirconium phosphate nanosheets (ZrPNS) and immobilized at a glassy carbon electrode surface. UV–vis spectra and electrochemical measurements show that the matrix is well biocompatible and can retain the bioactivity of immobilized Mb. The direct electron transfer between Mb and electrode exhibits a couple of well-defined redox peaks. The cathodic and anodic peaks are located at −0.340 and −0.280 V vs. Ag/AgCl, respectively. The ZrPNS can improve the electron transfer between Mb and electrode with an electron transfer constant of 5.6 s⁻¹. Meanwhile, the catalytic ability of the protein toward the reduction of H₂O₂, O₂, NaNO₂, trichloroacetic acid (TCA) is also studied and a third-generation biosensor is subsequently fabricated. The linear range of biosensor to H₂O₂ is from 8 × 10⁻⁷ to 1.28 × 10⁻⁵ M with the limit detection of 1.4 × 10⁻⁷ M. The small apparent Michaelis–Menten constant (34 μM) suggests that Mb/ZrPNS film performs good affinity with H₂O₂. The biosensor also exhibits acceptable stability and reproducibility. This work paves a way to develop other biologic active materials in this kind of nanosheets for constructing novel biosensors.     

Development of a bienzyme system based on sugar–lectin biospecific interactions for amperometric determination of phenols and aromatic amines

Bienzyme electrode with horseradish peroxidase (HRP) and glucose oxidase (GOD) multilayers was constructed based on sugar–lectin biospecific interactions for amperometric determination of phenolic compounds and aromatic amines. Atomic force microscopy (AFM) was applied to monitor the uniform layer-by-layer assembly of concanavalin A (Con A) and HRP or GOD on polyelectrolyte precursor film-modified Au electrode. Substituted phenolic compounds and aromatic amines could be determined with in situ generation of H₂O₂ by GOD-catalyzed oxidation of glucose. The parameters of the biosensor including the number of assembled HRP and GOD layer, and the concentrations of glucose were optimized. The linear range for the determination of catechol and p-phenyldiamine was 6.0–60.0 μmol L⁻¹ and 7.6–68.4 μmol L⁻¹ with detection limit of 0.9 μmol L⁻¹ and 0.4 μmol L⁻¹, respectively. The biosensor possessed high sensitivity and fast response for phenolic compounds and 95% of the maximum response could be reached in about 3 s. Glucose, ascorbic acid, tartaric acid, citric acid and starch exhibited no interference for the detection. The biosensor presented high stability due to the design for in situ generation of H₂O₂ with bienzyme system.     

Fabrication of a highly selective and sensitive Gd(III)-PVC membrane sensor based on N-(2-pyridyl)-N′-(4-nitrophenyl)thiourea

In this work we report the development of a highly selective and sensitive Gd(III) membrane based on N-(2-pyridyl)-N′-(4-nitrophenyl)thiourea (PyTu4NO₂) as an excellent neutral ion carrier. The Gd(III) sensor exhibits a Nernstian slope of 19.95 ± 0.3 mV per decade over the concentration range of 3.0 × 10⁻⁷ to 1.0 × 10⁻¹ M, and a detection limit of 3.0 × 10⁻⁷ M of Gd(III) ions. The potentiometric response of the sensor is independent of the solution pH in the range of 4.0–9.0. It manifests advantages of low detection limit, fast response time (10 s), and most significantly, very good selectivity with respect to a number of lanthanide ions (La, Ce, Sm, and Eu ions). It can be used at least for a period of 8 weeks without any significant divergences in its potential response. To assess its analytical applicability the proposed Gd(III) sensor was successfully applied as an indicator electrode in the titration of Gd(III) ion solutions with EDTA and for the determination of the fluoride ion in two mouth wash preparations. It was also used for the direct monitoring of Gd(III) ions in binary mixtures.     

A hydrogen peroxide biosensor based on direct electrochemistry of hemoglobin in Hb–Ag sol films

Hemoglobin (Hb) was used as a template to fabricate hemoglobin–silver (Hb–Ag) sol in which the hemoglobin showed direct electrochemistry on a glass carbon (GC) electrode. Ultraviolet–visible (UV–vis) spectra and reflectance absorption infrared (RAIR) spectra suggested that hemoglobin in Hb–Ag sol retained its native secondary structure. Scanning electron microscopy (SEM) demonstrated that the morphology of the Hb film was much different from the Hb–Ag sol film. The Hb–Ag film proved to exhibit a good electrocatalytic activity for the reduction of hydrogen peroxide. Based on this, a novel amperometric hydrogen peroxide biosensor was developed, which showed a sensitive response to the reduction of H₂O₂ without any electron mediator. Under optimum conditions, the biosensor responded linearly to H₂O₂ in the concentration range of 1 × 10⁻⁶ to 2.5 × 10⁻² M with detection limit of 1 × 10⁻⁷ M at 3σ. Moreover, the studied biosensor exhibited high sensibility, good reproducibility, and long-term stability.     

Perchlorate selective membrane electrodes based on synthesized platinum(II) complexes for low-level concentration measurements

Three synthesized platinum(II) complexes, [PtR₂(NN)] (R = Me, p-MeC₆H₄ and p-MeOC₆H₄; NN = 2,2′-bipyridyl), were studied to characterize their ability as an anion carrier in a PVC membrane electrode. The polymeric membrane electrodes (PME) and also coated glassy carbon electrodes (CGCE) prepared with [Pt(p-MeOC₆H₄)₂(NN)] showed excellent response characteristics to perchlorate ions. The electrodes exhibited Nernstian responses to ClO₄⁻ ions over a wide concentration range from 5 × 10⁻⁷ to 4.0 × 10⁻¹ M for PME and 1.5 × 10⁻⁷ to 2.7 × 10⁻¹ M for CGCE with low detection limits (4.0 × 10⁻⁷ M for PME and 1.0 × 10⁻⁷ M for CGCE). The electrodes possess fast response time, satisfactory reproducibility, appropriate lifetime and, most importantly, good selectivity toward ClO₄⁻ relative to a variety of other common anions. The potentiometric response of the electrodes is independent of the pH of the test solution in the pH range 2.5–9.5. The proposed sensors were used in potentiometric determination of perchlorate ions in mineral water, urine samples and also samples containing interfering anions. The interaction of the ionophore with perchlorate ions was shown by UV–vis spectroscopy.     

Perchlorate-selective membrane sensors based on two nickel-hexaazamacrocycle complexes

The perchlorate salts of nickel(II) complexes of 1,3,5,8,10,13-hexaazacyclotetradecane (1) and 1,8-tert-butyl-1,3,5,8,10,13-hexaazacyclotetradecane (2) were used in construction of PVC based membrane electrodes. These sensors show very good selectivity for ClO₄⁻ ions over a wide variety of anions. These electrodes exhibit Nernstian behavior with the slopes of 59.5 and 59.3 mV per decade for (1) and (2), respectively. The working concentration ranges of the sensors are 1.0 × 10⁻¹–9.0 × 10⁻⁷ M (1) and 1.0 × 10⁻¹–5.0 × 10⁻⁷ M (2) with the detection limits of 6.0 × 10⁻⁷ and 2.0 × 10⁻⁷ M, respectively. The response time of the both sensors is very fast, and can be used for 2 (I) and 12 (II) weeks in a pH range of 3.0–11.0. These electrodes were applied to the determination of perchlorate ions in wastewater and cattle urine samples.     

A selective modified bentonite–porphyrin carbon paste electrode for determination of Mn(II) by using anodic stripping voltammetry

A novel voltammetric sensor based on chemically modified bentonite–porphyrin carbon paste electrode (MBPCE) has been introduced for the determination of trace amount of Mn(II) in wheat flour, wheat rice and vegetables. In this method Mn(II) gives well-defined voltammetric peak at the pH range of 3.5–7.5. For the preliminary screening purpose, the catalyst was prepared by modification of bentonite with porphyrin and characterized by thermogravimetric method (TG) and UV–vis spectroscopy. The detection limit (three times signal-to-noise) with 4 min accumulation is 1.07 × 10⁻⁷ mol L⁻¹ Mn(II). The peak currents increases linearly with Mn(II) concentration over the range of 6.0 × 10⁻⁷ to 5.0 × 10⁻⁴ mol L⁻¹ (r² = 0.9959). Statistical treatment of the results gave a relative standard deviation lower than 2.30%. The chemical and instrumental parameters have been optimized and the results showed that 1000-fold excess of the additive ions had not interferences on the determination of Mn(II).     

Development of a highly sensitive and selective optical chemical sensor for batch and flow-through determination of mercury ion

A very sensitive, highly selective and reversible optical chemical sensor (optode) for mercury ion is described. The sensor is based on the interaction of Hg²⁺ with 2-mercapto-2-thiazoline (MTZ) in plasticized PVC membrane incorporating a proton-selective chromoionophore (ETH5294) and lipophilic anionic sites (sodium tetraphenylborate, NaTPB). The membranes were cast onto glass substrates and used for the determination of mercury ion in aqueous solutions by batch and flow-through methods. The sensor could be used in the range 2.0 × 10⁻¹⁰ to 1.5 × 10⁻⁵ M (0.04 ng mL⁻¹ to 3 μg mL⁻¹) Hg²⁺ with a detection limit of 5.0 × 10⁻¹¹ M and a response time of <40 s. It can be easily and completely regenerated by dilute nitric acid solution. The sensor has been incorporated into a home-made flow-through cell for determination of mercury ion in flowing streams with improved sensitivity, precision and detection limit. The sensor showed excellent selectivity for Hg²⁺ with respect to several common alkali, alkaline earth and transition metal ions. The results obtained for the determination of mercury ion in river water samples using the proposed optode was found to be comparable with the well-established cold-vapor atomic absorption method.     

Sol–gel derived polycrystalline Cr1.8Ti0.2O3 thick films for alcohols sensing application

The powder sample of Cr_1.8Ti_0.2O₃ (CTO) was obtained by a sol–gel method. The thick films were developed on identical ceramic tubes of 4 mm length comprising of two Au-electrodes and printing an eight-layer film prepared by mixing CTO with glass powder and -terpinol as an organic vehicle. X-ray powder diffraction (XRD) patterns showed the formation of a single phase. The scanning electron microscope (SEM) images of the ceramic sensor treated at 850 °C revealed that the grain size was larger than 400 nm for the individual isolated grains on the surface, and the agglomerated dense spheroidal platelets had the size of 1–4 μm in diameter. The AC impedance measurement in ambient air showed that the resistance decreased nearly by two orders of magnitude with an increase in temperature in the range of 400–600 °C for both the powder sample and the thick film, and the activation energy E_a derived from the measurement was found to be 0.35 and 0.36 eV for the powder and the film, respectively. The films were exposed to various concentrations of alcohols (0.4–1.2 ppm of methanol and 1.0–5.0 ppm of ethanol), followed by determination of sensor response, sensitivity and reversibility and reproducibility. The origin of the gas response was attributed to the surface reaction of R-OH (R = methyl and ethyl group) with O⁻_(ads) to form adsorbed R-CHO, which was desorbed as a gas at 400 °C after the sensor departing from the gas.     

Layer-by-layer construction of an active multilayer enzyme electrode applicable for direct amperometric determination of cholesterol

A biosensor for direct amperometric determination of cholesterol was constructed by a layer-by-layer nanothin film formation using cholesterol oxidase (COx) and poly(styrenesulfonate) on a monolayer of microperoxidase covalently-immobilized on Au–alkanethiolate electrodes. Cyclic voltammograms (CVs) of microperoxidase covalently-immobilized on mercaptopropionic acid- and aminoethanethiol-monolayer electrodes showed a redox wave with the formal potential of 0.40 V (versus Ag | AgCl | NaCl (sat.)). The formal potential and the apparent heterogeneous electron-transfer rate of immobilized microperoxidase were not specific with the inner Au–alkanethiolate layer. The biosensor shows a linear current response for cholesterol at the applied potential of 0 V in the concentration range of 0.2–3.0 mM with a correlation coefficient of 0.969. The current response of the biosensor for cholesterol was very rapid (response time <20 s) and was highly reproducible; sample standard deviation of the current response at the concentration of 1.5 mM in five individual determinations was 0.09. The magnitude of the amperometric response for cholesterol was 0.13 μA cm⁻² at the concentration of 1.5 mM. The inertness and stability of the biosensor towards the potential electrical interferents, -ascorbic acid, pyruvic acid and uric acid, was tested, and it was found that the biosensor rapidly responses to the addition of cholesterol even in the presence of these interferents.     

Calorimetric hydrocarbon sensor for automotive exhaust applications

We have developed a calorimetric sensor utilizing a thermoelectric device supported on a planar alumina substrate. By using a highly selective carbon monoxide (CO) oxidation catalyst and a non-selective platinum (Pt) catalyst, the device can be built to detect either CO or hydrocarbons with high selectivity. The CO oxidation catalyst comprises lead-modified platinum and exhibits excellent selectivity over the 200–400 °C temperature range. The thermoelectric device consists of two thick film junctions made of niobium pentoxide (Nb₂O₅)-doped titanium dioxide (TiO₂) and a lithiated nickel (Ni), which are supported on a planar alumina substrate. The thermocouple detects the difference in temperature due to different catalytic reactions over the two junctions and shows a high output signal because of the high Seebeck coefficient of Nb₂O₅-doped TiO₂ (−400 μV/°C). In gas bench tests, the sensor has a linear output of 0–2.75 mV over 0–1000 ppm of propylene and a response time of 2.5 s (at 90% of amplitude) at a gas temperature of 350 °C. An engine dynamometer evaluation shows that the response of the sensor parallels the change in CO and hydrocarbon constituent concentrations when the engine air-to-fuel ratio is varied.     

Electrocatalytic oxidation of methanol and other short chain aliphatic alcohols on glassy carbon electrodes modified with conductive films derived from Ni-(N,N′-bis(2,5-dihydroxybenzylidene)-1,2-diaminobenzene)

Complexes of nickel(II) with the ligand N,N′-bis(2,5-dihydroxybenzylidene)-1,2-diaminobenzene (Ni^II-DHS) can be electropolymerized onto glassy carbon surfaces in alkaline solution to give electroactive films strongly adhered on the electrode surface. In alkaline solution, these poly-[Ni^II-DHS]/GC films present the typical voltammetric response of a surface-immobilized redox couple, as can be anticipated for the Ni²⁺/Ni³⁺ transitions into the film. In addition, the films exhibit a potent and persistent electrocatalytic activity towards the oxidation of methanol. The electrocatalytic currents are, at least, 80 times higher than those obtained for the oxidation of methanol at electrodes modified with nickel hydroxide films in alkaline solutions. In addition, the current is proportional to the concentration of methanol from 0.050 to 0.30 μM. The detection limit and the sensitivity were found to be 26 ± 2 nM and 7.4 × 10⁻² ± 6 × 10⁻³ A cm² mol⁻¹ M⁻¹, respectively. Electrodes modified with poly-[Ni^II-DHS]/GC films show a moderate electrocatalytic activity towards the oxidation of other aliphatic short chain alcohols, such as: ethanol, 1-propanol, 2-propanol and n-butanol. In all cases the catalytic currents present linear dependences with the concentration of alcohol in alkaline solution. The analytical properties of these potential alcohol sensors have also been studied.     

The assessment of heat radiation

Approximately 900 climatic chamber experiments were performed with 16 male subjects to study the thermal strain at climates including increased heat radiation. Based on the reactions of heart rate, rectal temperature and sweat rate, a heat stress index was developed for the assessment of climates with effective heat radiation intensities up to 1400 W m⁻². The index considers different combinations of dry air temperature (5–55°C), globe temperature (25–76°C), mean radiant temperature (25–160°C), air velocity (0.5–2.0 m s⁻¹), clothing, physical work load and directions of radiation and air flow.

The index integrates combinations of the variables producing the same degree of thermal strain into a single value. This value indicates the temperature of the physiologically equivalent climate in which air and radiant temperature are equal. It can be determined from a simple formula or from correspondent graphs.

In comparison, the international recommended heat stress indices are less capable to evaluate heat radiation correctly. The incorporation of the new partial index into the used indices may improve substantially their physiological validity in the assessment of climates with radiant heat stress.

Relevance to industry

The goal of this paper is to provide an improved assessment of thermal stress in working environments in which heat radiation is an important heat stress factor.     

Nano levels detection of beryllium by a novel beryllium PVC-based membrane sensor based on 2,3,5,6,8,9-hexahydro-1,4,7,10-benzotetra oxacyclododecine-12-carbaldehyde-12-(2,4-dinitrophenyl)hy

A novel poly(vinyl chloride)-based 2,3,5,6,8,9-hexahydro-1,4,7,10-benzotetra oxacyclododecine-12-carbaldehyde-12-(2,4-dinitrophenyl)hy (PBC) with sodium tetraphenyl borate (NaTPB) as an anion excluder, benzyl acetate (BA), acetophenon (AP) and o-nitrophenyloctyl ether (NPOE) as plasticizing solvent mediators was prepared and investigated as a beryllium selective sensor. The best performance was observed with the membrane having the PVC–NaTPB–NPOE–PBC composition 30%:3%:62%:5%, which worked well over a very wide concentration range (1.0×10⁻⁷ M to 1.0×10⁻¹ M). The sensor exhibits a Nernstian slope of 29.9 mV per decade of Be²⁺ activity. The detection limit of the sensor is 7.0×10⁻⁸ M (630 ppt). The proposed electrode shows excellent discriminating ability toward Be²⁺ ion with regard to alkali, alkaline earth, transition and heavy metal ions. It was successfully applied to the determination of beryllium in a mineral sample.     

Trace detection of nitroaromatic compounds with layer-by-layer assembled {SBA/PSS}n/PDDA modified electrode

The {SBA/PSS}_n/PDDA films modified electrode was prepared by layer-by-layer (LBL) assembly with mesoporous SiO₂ (SBA), poly(sodium 4-styrene-sulfonate) (PSS) and poly(diallyldimethylammonium chloride) (PDDA) in this paper. SBA is a large pore-size mesoporous material with highly ordered hexagonally arranged mesochannels and high thermal stability etc. The electrochemical characteristics of the {SBA/PSS}_n/PDDA films have been studied by electrochemical impedance spectroscopy in 0.1 M KCl solution containing 5.0 mM Fe(CN)₆³⁻/Fe(CN)₆⁴⁻ at the formal potential of 0.230 V. The ultratrace nitroaromatic compounds (NACs) such as TNT, TNB, DNT and DNB were determined by differential pulse voltammetry (DPV) measurement. The sensitivities for NACs determination with {SBA/PSS}_n/PDDA modified electrode were dependent on the number of layers, pH and ionic strength of electrolyte, based on which a set of optimized conditions for film fabrication was inferred. The current responses were linear with NACs ranging from 10⁻⁹ to 10⁻⁷ mol/l. The results showed that the {SBA/PSS}_n/PDDA modified electrode established a new way for fast, simple and sensitive analysis of NACs.     

Fabrication of a highly selective Eu(III) membrane sensor based on a new S–N hexadentates Schiff''s base

A novel potentiometric membrane Eu (III) ion sensor is described based on a new S–N hexadentates Schiff's base, bis(thiophenol)butane2,3-dihydrazone (SNSB). The sensor exhibited a Nernstian response over a concentration range of 1.0 × 10⁻⁵ to 1.0 × 10⁻² M, with a detection limit of 5.0 × 10⁻⁶ M. The best performance was achieved with a membrane composition of 30% PVC, 63% o-nitrophenyloctyl ether (NPOE), 5% SNSB, and 5% (0.010 mmol) potassium tetrakis(p-chlorophenyl) borate (KTpClPB). It was found that in the pH range of 3.0–8.5, the potential response of the sensor was not affected by the pH. Furthermore, the electrode presented satisfactory reproducibility, very fast response time (<5 s), and relatively good discriminating ability for Eu(III) ions with respect to many common cations and lanthanide ions, including sodium, potassium, magnesium, calcium, copper, nickel, cobalt, zinc, lead, lanthanum, cerium, gadolinium, samarium, ytterbium, presidium, terbium, neodymium, holmium, erbium, thulium, lutetium, dysprosium, iron and chromium metal ions. The sensor was applied to the determination of fluoride ions in two mouth wash preparations and binary mixtures.     

Manufacture and characterization of sol–gel V1−x−yWxSiyO2 films for uncooled thermal detectors

V_1−x−yW_xSi_yO₂ films for uncooled thermal detectors were coated on sodium-free glass slides with sol–gel process, followed by the calcination under a reducing atmosphere (Ar/H₂ 5%). The V_1−x−yW_xSi_yO₂ films as prepared inherit various phase transition temperatures ranging from 20 to 70 °C depending on the dopant concentrations and the fabrication conditions. Compared to the hysteresis loop of plain VO₂ films, a rather steep loop was obtained with the addition of tungsten components, while a relaxed hysteresis loop with the tight bandwidth was contributed by Si dopants. Furthermore, the films with switching temperature close to room temperature were fabricated to one-element bolometers to characterize their figures of merit. Results showed that the V_0.905W_0.02Si_0.075O₂ film presented a satisfactory responsivity of 2600 V/W and detectivity of 9 × 10⁶ cm  Hz^1/2/W with chopper frequencies ranging from 30 to 60 Hz at room temperature. It was proposed that with appropriate amount of silicon and tungsten dopants mixed in the VO₂, the film would characterize both a relaxed hysteresis loop and a fair TCR value, which effectively reduced the magnitude of noise equivalent power without compromising its performance in detectivity and responsivity.