Urea sensors based on PVC membrane pH electrode

Several procedures of urease immobilization on the surface of the polymeric membrane pH electrode with tri-n-dodecylamine as a neutral carrier were compared. The best results were obtained for the urea sensor with covalently bound urease. The sensor characteristics including the effect of buffer, pH and concentration and the effect of stirring rate are presented. These effects are in good agreement with theoretical expectations.     

PVC membrane based potentiometric sensors for uranium determination

Two novel uranyl PVC matrix membrane sensors responsive to uranyl ion are described. The first sensor incorporates tris(2-ethylhexyl)phosphate (TEHP) as both electroactive material and plasticizer and sodium tetraphenylborate (NaTPB) as an ion discriminator. The sensor displays a rapid and linear response for UO₂²⁺ ions over the concentration range 1×10⁻¹–2×10⁻⁵ mol l⁻¹ UO₂²⁺ with a cationic slope of 25.0±0.2 mV decade⁻¹. The working pH range is 2.8–3.6 and the life span is 4 weeks. The second sensor contains O-(1,2-dihydro-2-oxo-1-pyridyl)-N,N,N′,N′-bis(tetra-methylene)uronium hexafluorophosphate (TPTU) as a sensing material, sodium tetraphenylborate as an ion discriminator and dioctyl phenylphosphonate (DOPP) as a plasticizer. Linear and stable response for 1×10⁻¹–5×10⁻⁵ mol l⁻¹ UO₂²⁺ with near-Nernstian slope of 27.5±0.2 mV decade⁻¹ are obtained. The working pH range is 2.5–3.5 and the life span of the sensor is 6 weeks. Interference from many inorganic cations is negligible for both sensors. However, interference caused by some ions (e.g. Th⁴⁺, Cu²⁺, Fe³⁺) is eliminated by a prior ion exchange or solvent extraction step. Direct potentiometric determination of as little as 5 μg ml⁻¹ uranium in aqueous solutions shows an average recovery of 97.2±1.3%. Application for the determination of uranium at levels of 0.01–1 wt.% in naturally occurring and certified ores gives results with good correlation with data obtained by X-ray fluorescence.     

Novel applications of fluorescence sensors

Typically, NAD(P)H-sensitive culture probes have been used to estimate biomass concentrations in suspended-cell cultivations, but these sensors have other uses as well. A number of applications, ranging from biosensors to immobilized-cell metabolic studies, are presented.     

Novel potentiometric sensors for pyrilamine maleate

The fabrication and electrochemical response characteristics of four novel potentiometric sensors for determination of pyrilamine maleate (PyraH) were described. The sensors include polymeric membrane electrodes (PME₁, PME₂) and carbon paste electrodes (CPE₁, CPE₂). The fabricated sensors were based on the ion-pair of pyrilamine with sodium tetraphenylborate (NaTPB) and ammonium reineckate (NH₄RN) using dibutyl phthalate (DBP) as plasticizing solvent. The sensors showed linear, stable and near-Nernstian slopes of 56.4 ± 0.4, 54.2 ± 0.2, 58.8 ± 0.3 and 57.9 ± 0.4 mV decade^?1 at 25 ± 0.1 °C and detection limits of 2.0 × 10^?5, 1.8 × 10^?5, 1.0 × 10^?5 and 9.5 × 10^?6 mol L^?1 for PME₁, PME₂, CPE₁ and CPE₂ sensors, respectively. The response time was less than 10 and 8 s for polymeric membrane and carbon paste sensors. The proposed sensors displayed good selectivity for pyrilamine with respect to a number of common inorganic and organic species. The thermal temperature coefficients of the investigated sensors were 0.9508, 0.7012, 0.9450 and 0.6497 mV °C^?1. Modified carbon paste sensors showed lower detection limits, higher thermal stability and faster response time than those of polymeric membrane sensors. The proposed sensors displayed useful analytical characteristics for determination of pyrilamine in pharmaceutical preparation and biological fluids (Human urine and plasma).     

Comparative studies on Tb (III)-selective PVC membrane sensors

A new terbium selective sensor based on N-(2-hydroxyphenyl)-3-(2-hydroxyphenylhydroxyphenylimino)-N-phenylbutanamidine (L₁) and N,N′-bis((1H-indole-3-yl)methylene)butane-1,4 diamine (L₂) as a ionophore is reported. Effect of various plasticizers; 2-nitrophenyloctylether (o-NPOE), dibutyl butylphosphonate (DBBP), chloronaphthelene (CN), dioctylphthalate (DOP) and tri-(2-ethylhexyl)phosphate (TEHP) with anion excluder, potassium tetrakis (p-chloropheny1)borate (KTpClPB) have been studied. The membrane with a composition of ionophore (L₁):KTpClPB:PVC:o-NPOE (w/w, %) in ratio of 3.0:5.0:30.0:62.0 exhibited enhanced selectivity towards terbium ions (III) in the concentration range of 3.5 × 10⁻⁷ to 1.0 × 10⁻² M with a detection limit of 1.2 × 10⁻⁷ M and a Nernstian slope (20.0 ± 0.5 mV dec⁻¹ activity). The sensors showed the working pH range to be 3.5-7.5 with response time of 11 s. The sensor has been found to work satisfactorily in partially non-aqueous media up to 15% (v/v) content of methanol, ethanol or acetonitrile and could be used for a period of 3 months. The selectivity coefficients indicated high selectivity for terbium (III). The fast and stable response, good reproducibility and long-term stability of the sensors were observed. The application of the sensor has been demonstrated in determination of terbium (III) ions in spiked water samples.     

Comparative studies of neodymium (III)-selective PVC membrane sensors

Sensors based on two neutral ionophores, N,N′-bis((1H-pyrrol-2-yl)methylene)cyclohexane-1,2-diamine (L₁) and 3,3′-(cyclohexane-1,2-diylbis(azan-1-yl-1-ylidene)bis(methan-1-yl-1-ylidene)bis(5-hydroxymethyl)pyridine-2-ol) (L₂) are described for quantification of neodymium (III). Effect of various plasticizers; 2-nitrophenyloctylether (o-NPOE), dibutyl butylphosphonate (DBBP), tri-n-butyl phosphates (TBP), dioctylpthalate (DOP) and chloronapthalen (CN) and anion excluder, sodiumtetraphenylborate (NaTPB) has been studied. The membrane composition of PVC:o-NPOE:ionophore (L₁):NaTPB (w/w; mg) of 150:300:5:5 exhibited best performance. The sensor with ionophore (L₁) exhibits significantly enhanced selectivity towards neodymium (III) in the concentration range 5.0 × 10⁻⁷ to 1.0 × 10⁻² M with a detection limit of 1.0 × 10⁻⁷ M and a Nernstian compliance (19.8 ± 0.3 mV decade⁻¹ of activity) within pH range 4.0-8.0. The response time of sensor was found as 10 s. The influence of the membrane composition and possible interfering ions has also been investigated on the response properties of the electrode. The fast and stable response, good reproducibility and long-term stability of the sensor are observed. The sensor has been found to work satisfactorily in partially non-aqueous media up to 20% (v/v) content of methanol, ethanol or acetonitrile and could be used for a period of 3 months. The selectivity coefficients determined by using fixed interference method (FIM) indicate high selectivity for neodymium. The proposed electrode shows fairly good discrimination of neodymium (III) from other cations. The application of prepared sensor has been demonstrated in the determination of neodymium (III) in spiked water samples.     

Potentiometric determination of moxifloxacin in some pharmaceutical formulation using PVC membrane sensors

Background

The construction and electrochemical response characteristics of Poly (vinyl chloride) membrane sensors for moxifloxacin HCl (MOX) are described. The sensing membranes incorporate ion association complexes of moxifloxacin cation and sodium tetraphenyl borate (NaTPB) (sensor 1), phosphomolybdic acid (PMA) (sensor 2) or phosphotungstic acid (PTA) (sensor 3) as electroactive materials.

Results

The sensors display a fast, stable and near-Nernstian response over a relative wide moxifloxacin concentration range (1 × 10^-2 - 4.0 × 10^-6, 1 × 10^-2 - 5.0 × 10^-6, 1 × 10^-2 - 5.0 × 10^-6 M), with detection limits of 3 × 10^-6, 4 × 10^-6 and 4.0 × 10^-6 M for sensor 1, 2 and 3, respectively over a pH range of 6.0 - 9.0. The sensors show good discrimination of moxifloxacin from several inorganic and organic compounds. The direct determination of 400 μg/ml of moxifloxacin show an average recovery of 98.5, 99.1 and 98.6% and a mean relative standard deviation of 1.8, 1.6 and 1.8% for sensors 1, 2 and 3 respectively.

Conclusions

The proposed sensors have been applied for direct determination of moxifloxacin in some pharmaceutical preparations. The results obtained by determination of moxifloxacin in tablets using the proposed sensors are comparable favorably with those obtained using the US Pharmacopeia method. The sensors have been used as indicator electrodes for potentiometric titration of moxifloxacin.

     

Novel PVC-based membrane sensors selective for vanadyl ions

Poly(vinyl chloride) based membranes of di-(2-ethylhexyl)phosphoric acid (DEHPA) and dibutyl(butyl)phosphonate (DBBP) have been prepared and investigated as VO²⁺-selective sensors. The membranes containing DEHPA/DBBP and sodium tetraphenylborate, an anion excluder, show near-Nernstian/Nernstian response in the concentration range 10⁻⁵–10⁻¹ M. The sensors exhibit a fast response time and good selectivity for VO²⁺ over a number of other cations. Quantitative determination of vanadium in waste V₂O₅ catalyst has been achieved by these sensors and they have also been used as indicator electrodes for the determination of the end point in the potentiometric titration of VO²⁺ against EDTA.     

Novel clorsulon voltammetric sensors based on zinc oxide nanostructure

Herein, the fabrication and electrochemical characterization of a novel clorsulon (CLO) sensor were evaluated. Among the different tested metal oxides nanostructures, bulk modification of the carbon paste working electrode with zinc oxide exhibited the proper electrocatalytic activity towards CLO with irreversible anodic oxidation peak at 1.02 in universal buffer pH 7.0. Clorsulon molecule showed diffusion–reaction mechanism through the involvement of one-electron and one proton as illustrated by the sweep rate, pH studies, and sustained by the molecular orbital calculations. The fabricated sensors showed linear calibration curves within the CLO concentration range from 0.45 to 10.13 × 10^?9 mol L^?1 with LOD value of 0.14 × 10^?9 mol L^?1. Enhanced sensitivity with good measurement reproducibility and long operational lifetime were cited as shining futures of the fabricated sensor. The constructed sensors were utilized for clorsulon quantification in veterinary formulations and milk samples with high accuracy and precision compared with the traditional methods.     

Novel fused-LEDs devices as optical sensors for colorimetric analysis

The development of a novel, low power optical sensing platform based on light emitting diodes (LEDs) is described. The sensor is constructed from a pair of LEDs fused together at an angle where one LED functions as the light source and the other LED is reverse biased to function as a light detector. Sensor function is based on the level of light received by the detector diode, which varies with the reflectance of the interface between the device and its environment, or the chemochromic membrane that covers the device. A simple microprocessor circuit is used to measure the time taken for the photon-induced current to discharge the detector LED from an initial 5 V (logic 1) to 1.7 V (logic zero). This sensing device has been successfully used for colour and colour-based pH measurements and offers extremely high sensitivity, enabling detection down to the sub micro molar level of dyes.     

Synthesis of stilbene carboxylic acids as scaffolds for calcium sensors

This communication describes the synthesis and characterization of calcium binding stilbene carboxylic acids.     

Novel antimicrobial organic thermal stabilizer and co-stabilizer for rigid PVC

Biologically active N-benzoyl-4-(N-maleimido)-phenylhydrazide (BMPH) was synthesized and its structure was confirmed by elemental analysis and various spectral tools. It was examined as a thermal stabilizer and co-stabilizer for rigid poly (vinyl chloride) at 180 °C in air. Blending BMPH with reference samples in different ratios greatly lengthens the thermal stability value and improves the extent of discoloration of PVC. TGA confirmed the improved stability of PVC in presence of the investigated organic stabilizer. GPC measurements were done to investigate the changes occurred in the molecular masses of the degraded samples of blank PVC and PVC in presence of the novel stabilizer. BMPH showed good antimicrobial activity towards two kinds of bacteria and two kinds of fungi.     

新型有机高分子型PVC热稳定剂的合成

以经部分硝化和还原的低分子量聚苯乙烯为母链,利用其胺基和丙烯酰基异硫氰酸酯加成,合成了一种新型有机高分子型PVC热稳定剂——丙烯酰基硫脲接枝聚苯乙烯,其结构经IR和元素分析表征。     

A perfume odour-sensing system using an array of piezoelectric crystal sensors with plasticized PVC coatings

Using PVC polymer as membrane matrix and di-n-octylphenyl phosphate (DOPP) as plasticizer, a piezoelectric crystal sensor (PCS) array with 12 adsorptive materials selected from 68 compounds by cluster analysis has been constructed as a perfume odour-sensing system. The frequency shift data obtained from the sensor array responding to four commercial perfume odours are first autoscaled and then treated by principal component analysis. The experimental results show that the plasticized PVC membrane PCS array provides improved performance of pattern recognition compared with the single adsorptive coating PCS array. The frequency shift response characteristics of these sensors have been investigated experimentally. The proposed sensor array has also been applied to the classification of commercial spirituous liquor, wine and soft drink samples, as well as aliphatic alcohol homologues and isomers.     

Novel arene receptors as nitric oxide (NO) sensors

Nitric oxide sensors are based on the reversible, specific, and efficient binding to various types of arene receptors via intermolecular complexes, which are characterized by complete electron delocalization and strong interaction between the donor and acceptor moieties.     

Lanthanum-selective sensors based on 3-amino-2-mercapto-3H-quinazolin-4-one in PVC matrix

A new solvent polymeric membrane (PME) and coated graphite (CGE) electrodes based on 3-amino-2-mercapto-3H-quinazolin-4-one as a suitable carrier for La(III) ion are described. The sensors exhibited a Nernstian response for La(III) ion over a wide concentration range (3.0 × 10^?7 to 1.0 × 10^?1 M for PME and 1.0 × 10^?7 to 1.0 × 10^?1 M for CGE) with a slope of 20.1 ± 0.3 (PME) and 23.4 ± 0.4 (CGE) mV decade^?1. The lower detection limits by PME and CGE were 2.0 × 10^?7 and 7.1 × 10^?8 M, respectively. The potentiometric response of the proposed electrodes was independent of the pH of the test solution in the pH range 3.0–9.0 with a fast response time (<10 s). The applications of prepared sensors were demonstrated in the determination of lanthanum ions in spiked water sample and also utilized for indirect determination of fluoride content of two mouth wash preparation samples.     

Novel nanostructured materials to develop oxygen-sensitive films for optical sensors

Novel nanostructured materials, such as aluminum oxide (AlOOH), silicon oxide (SiO₂) or zirconium oxide (ZrO₂) embedded into PVA, were investigated as potential matrices to incorporate organometallic compounds (OMCs) for the development of optical oxygen-sensitive sensors which make use of the principle of luminescence quenching.In order to assess the benefits and drawbacks of the nanoporous material, the luminescence quantum yield and the Stern-Volmer constants were investigated and compared with the values shown for the same OMCs solubilized in polymer films (polystyrene). Referred to polymer films, the incorporation of the dyes into nanoporous membranes increased the Stern-Volmer constant by more than a factor of 100. Their response time was less than 1 s and the optode membranes were stable at room temperature for at least 9 months. Sterilization by autoclavation and gamma irradiation resulted in a marginal loss in activity. The photostability and sterilizability of the oxygen-sensitive membranes and the performance of the optodes with respect to of different types of metal oxides are discussed in the paper, as well as the influence of the total pore volume (TPV), the pore diameter (PD), the transparency of the film and the geometry of the pores. The OMCs used in this work were: ETH^T-3003 (tris(4,7-bis(4-octylphenyl)-1,10-phenanthroline) ruthenium(II)), N-926 (bis(2-phenylpyridinyl)-N⁴,N⁴,N⁴′,N⁴′-tetramethyl-(4,4′-diamine-2,2′-bipyridine) iridium(III) chlorate), N-833 (tetrabutylammonium bis(isothiocyanate) bis(2-phenylpyridinyl)-iridium(III)) and N-837 (tetrabutylammonium bis(cyanate) bis(2-phenylpyridinyl)-iridium(III)).     

Novel sol–gel reversible thermochromic materials for environmental sensors

Anhydrous cobalt(II) chloride has been encapsulated in several inorganic sol–gel matrices with different solvent/water ratios. Sols were cast into cuvettes and hermetically closed. Such sol–gel materials were found to be sensitive to temperature in the 10–50 °C range showing a change of colour. General characterisation of the sensitive materials was made by immersion into a thermostatic water bath and recording of the corresponding visible spectra. The optical response consisted of a change in colour from light pink to deep blue as the temperature increases. These temperature detectors behave as sensors showing good optical sensitivity in the range mentioned above and reversibility for more than 30 cycles. The sensors response time is at about 15 min and their lifetime is 2 months at least. These sol–gel materials have been designed to be applied for preservation and conservation purposes. High temperatures and cyclical temperature changes can yield severe consequences for the correct preservation of cultural heritage materials (textiles, archaeological ceramics and other remains, metallic objects and statues, stained glass windows, etc.) both in museums and outdoors.     

Novel potentiometric sensors based on polysulfone immobilized metallothioneins as metal-ionophores

We show here the use of immobilized metal-binding biomolecules for metal analysis by using novel potentiometric sensors. To this end and as a model, Ag⁺-ISEs were developed using polysulfone matrix embedding metallothioneins as ionophores (mouse MT1 (P1) or sea urchin SpMTA (P2)). Polysulfone, a porous polymer that was not used until the present in potentiometric biosensors, has the advantage of being compatible with biological materials. Also, the phase inversion procedure allows protein incorporation into the membrane with minima alterations, since it always remains in the aqueous phase. Construction of these biosensors required small amounts of protein; they can be dry-stored and have long lifetimes. They exhibited linear responses with slopes of ca. 61 mV per decade within the 10⁻⁵ to 10⁻² M Ag⁺ concentration range, detection limits of about 10⁻⁵ M, and worked in the 2-to-8 pH range. Except for Hg²⁺, the Pb²⁺, Zn²⁺, Cd²⁺, Cu²⁺ cations do not interfere with Ag⁺ determination. Significantly, different affinities of Pb²⁺ and Zn²⁺ towards P1- and P2-ISE were found, in good correlation with the higher affinity of these cations towards SpMTA than to MT1. Consequently, the distinct metal-binding features of each MT are conserved and determine the differential properties of their biosensors. These results open a broad range of possibilities for the use of proteins as ionophores in what could be considered a new type of potentiometric biosensor if their response mechanism is taken into account.     

Zinc(II)-selective sensors based on dibenzo-24-crown-8 in PVC matrix

Membranes of dibenzo-24-crown-8 (I) as an ion active material in poly(vinylchloride) (PVC) based matrix have been tried for zinc(II)-selective sensors. The effect of anion excluder, sodium tetraphenylborate (NaTPB) and plasticizers, tris(2-ethylhexyl)phosphate (TEP), tributylphosphate (TBP), dibutylphthalate (DBP), dibutyl(butyl)phosphonate (DBBP), 1-chloronaphthalene (CN) and dioctylphthalate (DOP) on the performance of the membrane electrodes has also been studied. It was observed that the membrane having the composition (I): PVC:NaTPB:DOP in the ratio 10:200:2:100 gave the best results with a wide working concentration range of 9.2 × 10⁻⁵ to 1.0 × 10⁻¹ M, Nernstian slope of 29.0 ± 0. 5 mV/decade of activity, fast response time of 12 s and good selectivity over a number of mono-, bi-, and trivalent cations. The sensor works well in a pH range 4.8-6.2 and can be employed for the estimation of zinc ions in partially non-aqueous medium having up to 10% (v/v) methanol, ethanol or acetone content. The practical utility of the sensor has been demonstrated by using it successfully as an indicator electrode in the potentiometric titration of Zn²⁺ with EDTA and also for the determination of Zn²⁺ in a real sample analysis of wastewater.