Plasticized PVC Membrane Research Articles

Optimization of the polyaniline solid contact in potentiometric sensors for detection of paralytic shellfish toxins in mussels

The present study optimized the properties of the electropolymerized polyaniline (PANI) solid inner contact for a potentiometric chemical sensor by varying the thickness of the polymer layer. A potentiometric sensor for detecting one of the paralytic shellfish toxins, decarbamoyl saxitoxin (dcSTX), in mussel extracts was selected as a case study. The plasticized PVC membrane composition, developed in previous work for the detection of this toxin, was used. The structure and electrical properties of PANI layers of different thicknesses were studied using scanning electron microscopy and electrochemical impedance spectroscopy. The effect of PANI solid contact thickness on the characteristics of the potentiometric sensor, including sensitivity, detection limit, and selectivity to dcSTX in buffer solutions and mussel extracts, was evaluated. The formation of a water layer at the inner solid contact and PVC membrane interface was investigated using electrochemical impedance spectroscopy and a water test. PANI layer thickness 1.1 µm was found to be optimal for solid inner contact for potentiometric sensor with PVC membrane providing highest sensitivity and selectivity.

Eco-conscious potentiometric sensing: a multiwalled carbon nanotube-based platform for tulathromycin monitoring in livestock products

Tulathromycin (TUL) is a widely used veterinary antibiotic for treating bovine and porcine respiratory infections. Consuming animal-derived food contaminated with this medication may jeopardize human health. This work adopted the first portable potentiometric platform for direct TUL sensing in pharmaceutical and food products. The sensor employed a plasticized PVC membrane on a glassy carbon electrode doped with calix[6]arene and multi-walled carbon nanotubes (MWCNT) in a single solid contact layer for selective binding and signal stability. Characterization via scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) confirmed the material’s integrity. The MWCNT-based sensor produced a stable Nernstian response (1.0 × 10−7 to 1.0 × 10−3 M) and a limit of detection (LOD) of 9.76 × 10–8 M with instantaneous response (8 ± 2 s). IUPAC validation revealed high selectivity for TUL against interfering ions, minimal drift (0.6 mV/h), and functionality over a broad pH range (2.0–7.0), allowing direct application to dosage form, spiked milk, and liver samples. Eco-Scale, AGREE, and Whiteness assessment proved the method's ecological sustainability, economic viability, and practical feasibility, surpassing traditional approaches.Graphical

Plasticizer-based and polymer-free ion-selective optodes on cellulose paper

Paper-based ion-selective optodes (ISOs) allow for low-cost ion measurements using widely accessible optical detectors such as smartphones, representing an attractive analytical platform for medical testing and environmental monitoring. Previously reported paper-based ISOs rely on plasticized PVC membranes or PVC/plasticizer-free adsorption layers containing hydrophobic sensing chemicals. In this paper, we studied a new format of paper-based ISOs, in which a plasticizer phase containing sensing chemicals is deposited onto cellulose paper without using a hydrophobic polymer like PVC. Compared to ISOs without plasticizers and polymers, the plasticizer-based ISOs show much higher pH sensitivity when using chromoionophore I and tetrakis[3,5-bis(trifluoromethyl)phenyl]borate as the sensing chemicals. When the sensing layer further contains a solid ionophore with high molecular rigidity, the plasticizer-based ISOs for cations also exhibit enhanced sensitivity than the plasticizer-free ISOs. However, when the ionophore is a liquid at room temperature or has a long alkyl chain, the plasticizer-based and plasticizer-free ISOs have comparable responses because the ionophore behaves as a pseudo-plasticizer. Compared to ISOs with both plasticizers and polymers, the elimination of hydrophobic polymers like PVC makes inkjet printing more efficient and preserves the capillary action of the porous paper. By using the newly launched Samba cartridge with smaller nozzles, the plasticizer-based and polymer-free optodes for sodium, potassium, and calcium ions are prepared by inkjet printing for the first time. In an example application, the inkjet-printed plasticizer-based and polymer-free ISOs are used for colorimetric measurements of urine calcium.

Colorimetric probe for the determination of osmium through a novel optical sensor in environmental samples

A novel optical probe has been successfully developed for the selective detection of Os(VIII) ions. This osmium-sensing platform was intricately designed by incorporating 4-(thiazol-2-yldiazenyl)benzene-1,3-diol (TDBD) as the ionophore within a plasticized PVC membrane, and tributylphosphate (TBP) serving as the plasticizer. Upon exposure to Os(VIII) ions in a 0.5 M HClO4 acid milieu, the sensing membrane undergoes a distinctive chromatic transition, shifting from a yellow to a pink hue. The preparation of the sensor and the methodology for Os(VIII) determination were meticulously refined to achieve optimal performance. Under these carefully optimized experimental conditions, the proposed optode demonstrated an impressive linear detection range spanning from 2.5 × 10−9 to 2.5 × 10−5 M for Os(VIII), alongside remarkable detection and quantification limits of 7.24 × 10−10 and 2.4 × 10−9 M, respectively. The sensor consistently delivered highly reproducible results, as evidenced by relative standard deviation (RSD) values of 1.45% and 1.30% for Os(VIII) concentrations at 7.5 × 10−7 and 2.5 × 10−6 M, respectively, underscoring its precision and reliability. Furthermore, the sensor exhibited a swift response time of 3.0 min, further emphasizing its efficiency. The incorporation of PIMs into the sensor architecture led to a remarkable eight-fold enhancement in its response compared to counterparts lacking PIMs, signifying a significant performance improvement. In assessing potential interference, an investigation into the influence of other ions on Os(III) determination revealed that the prepared sensor displayed exceptional selectivity for Os(VIII) ions, with negligible responses observed in the presence of common ions. Collectively, these experimental findings underscore the sensor's efficacy as an invaluable tool for the precise analysis of osmium content in water samples, aligning it with the rigorous standards of international scientific research.

Highly selective potentiometric determination of nitrate ions using silver bisdiethyldithiocarbamate based membrane electrodes

A new all-solid-state PVC membrane nitrate electrode was developed and nitrate ions were potentiometrically analyzed. Silver (I) bisdiethyldithiocarbamate ((C2H5)2NCS2)2Ag+) (Ag(dtc)2) compound was used as electroactive positive charged carrier (ionophore) in the plasticized PVC membrane structure of the developed electrode. The developed nitrate selective polymeric membrane electrode (nitrate-ISE) exhibited linear potentiometric behavior in the concentration range of nitrate ions from 1.0 × 10−1 to 1.0 × 10−5 mol L−1 and the detection limit was determined as 6.71 × 10−6 mol L−1. Although nitrate-ISE has good reproducibility, the pH working range is determined to be 4 – 9. The proposed nitrate-ISE has been successfully applied for the determination of nitrate ions in different water samples and fruit juices.

Novel (E)−2-((1-(thiophen-2-yl)ethylidene)-amino) phenol Manganese(II) as an Ionophore Based on Thiocyanate-Selective Electrodes and Its Applications

Novel highly selective potentiometric sensor based on aquadichloro(E)−2-((1-(thiophen-2-yl)ethylidene)-amino)phenol manganese(II)trihydrate as an anion carrier. The thiocayanate electrode displayed a very high selectivity compared with others inorganic anions. Different sensors with plasticized PVC membranes have been investigated. The sensors construction containing different amounts of ionophore with and without additives. The pH over 3.5–6.5 range has been studied. Optimized membrane electrode included 66 mg PVC, 132 mg o-nitrophenyloctylether, 10 mol % tetrakis(trifluoromethyl)phenyl borate and 2% [Mn(C12H11NOS)(Cl2)(H2O)]· 3H2O. The optimized sensors exhibit Nernstian response for thiocyanate through a linear concentration ranging from (5 × 10−8 to 9.06 × 10−1 M) with a detection limit of 3 × 10−8 M and a slope of −57.7 mV decade−1, the measurement carried out in acetate buffer pH 4.7. The response time of electrode <10 s and the lifetime of the sensor more than 6 weeks. The proposed electrode was effectively utilized to estimation of thiocyanate in saliva sample, the results revealed a valid agreement with reference colorimetric method.

Determination of Single-Ion Partition Coefficients between Water and Plasticized PVC Membrane Using Equilibrium-Based Techniques.

An experimentally simple method for the direct determination of single-ion partition coefficients between water and a PVC membrane plasticized with o-NPOE is suggested. The method uses the traditional assumption of equal single-ion partition coefficients for some reference cation and anion, in this case tetraphenylphosphonium (TPP+) and tetraphenylborate (TPB−). The method is based on an integrated approach, including direct study of some salts’ distribution between water and membrane phases, estimation of ion association constants, and measurements of unbiased selectivity coefficients for ions of interest, including the reference ones. The knowledge of distribution coefficients together with ion association constants allows for direct calculation of the multiple of the single-ion partition coefficients for the corresponding cation and anion, while the knowledge of unbiased selectivity coefficients together with ion association constants allows for immediate estimation of the single-ion partition coefficients for any ion under study, if the corresponding value for the reference ion is known. Both potentiometric and extraction studies are inherently equilibrium-based techniques, while traditionally accepted methods such as voltammetry and diffusion are kinetical. The inner coherent scale of single-ion partition coefficients between water and membrane phases was constructed.

Coulometric ion sensing with Li+-selective LiMn2O4 electrodes

A coulometric signal readout method, which was originally developed for solid-contact ion-selective electrodes, was investigated in this work using LiMn2O4 (LMO) as a combined ion-recognition and signal-transduction layer. The redox process of LMO, which is associated with reversible intercalation/expulsion of Li+ ions, allowed coulometric sensing of Li+ ions in aqueous solutions. On increasing the active area (mass loading) of LMO, the coulometric signal increased for a given change in Li+ ion activity. The excellent redox reversibility of LMO and its relatively low resistance were instrumental in achieving a high signal amplification together with a relatively fast response. Coating the LMO layer with a conventional Li+-selective plasticized PVC membrane was found to dramatically lower the coulometric response. Hence, the application of LMO as a combined Li+-selective electrode material and ion-to-electron transducer was found to be highly compatible with the coulometric signal readout method, especially for detecting small Li+ activity changes at high Li+ concentrations.

Hydrogels Doped with Redox Buffers as Transducers for Ion-Selective Electrodes.

Solid-contact ion-selective electrodes (ISEs) with an unintentional water layer between the sensing membrane and underlying electron conductor are well known to suffer from potential drift caused by the instability of the phase boundary potential between the sensing membrane and the water layer with its uncontrolled ionic composition. The reproducibility and long-term emf stability of ISEs with a miniaturized inner filling solution comprising a hydrogel and a hydrophilic electrolyte have not been studied as thoroughly. Here, such devices are discussed with a view to electrode-to-electrode reproducibility, using both hydrophilic ion-exchange and plasticized PVC membranes, along with a hydrophilic redox buffer composed of ferrocyanide and ferricyanide to control the potential between the hydrogel and the underlying electron conductor. With plasticized PVC sensing membranes, these electrodes showed an E0 reproducibility of ±1.1 mV or better, while with hydrophilic ion-exchange membranes, this variability was slightly larger. Long-term drifts were also assessed with both membranes, and the effect of osmotic pressure on drift was shown to be insignificant for the PVC membranes and very small at most for the hydrophilic membranes.

Electrochemical sensor for tricyclic antidepressants with low nanomolar detection limit: Quantitative Determination of Amitriptyline and Nortriptyline in blood

Amitriptyline and its metabolite, Nortriptyline are commonly used tricyclic antidepressant (TCA) drugs that are electrochemically active. In this work, the performance characteristics of a plasticized PVC membrane-coated glassy carbon (GC) electrode are described for the voltammetric quantification of Amitriptyline and Nortriptyline in whole blood. The highly lipophilic Amitriptyline and Nortriptyline preferentially partition into the plasticized PVC membrane where the free drug is oxidized on the GC electrode. The concentrations of the drugs in the membrane are orders of magnitude larger than in the sample solution, resulting in superb limit of detection (LOD) of the membrane-coated voltammetric sensor: 3 nmol/L for Amitriptyline and 20 nmol/L for Nortriptyline. Conversely, hydrophilic components of the sample solution, e.g., proteins, the protein-bound fraction of the drugs, and electrochemically active small molecules are blocked from entering the membrane, which provides exceptional selectivity for the membrane-coated sensor and feasibility for the measurements of Amitriptyline in whole blood. In this work, the concentrations of Amitriptyline and Nortriptyline were determined in whole blood using the sensor and the results of our analysis were compared to the results of the standard HPLC-MS method. Based on our experience, the one-step voltammetric methods with the membrane-coated sensor may become a real alternative to the significantly more complex HPLC-MS analysis.

Gold-modified paper as microfluidic substrates with reduced biofouling in potentiometric ion sensing

Microfluidic sampling media based on paper and its modifications with either gold nanoparticles or sputtered gold were evaluated for potentiometric determination of Na+, K+, and Cl– ions in clinically relevant samples. The measurements were conducted in comparison to other commonly considered microfluidic substrates, i.e. sponge, polyester textile, and polyamide textile. Ion determination was done by using solid-contact ion-selective electrodes based on plasticized PVC membranes for Na+, K+, and Cl– ions and utilizing PEDOT(PSS) or PEDOT(Cl) as the ion-to-electron transducer. The solid-contact ion-selective electrodes and a solid-state reference electrode were placed directly on the substrate into which the sample solution was wicked. Transport of bovine serum albumin (BSA) through the paper substrate was studied by ellipsometry. Modification of the paper substrates by gold nanoparticles (AuNPs) was found to slow down the transport of BSA through the paper, when compared with unmodified paper substrates and when compared with all the other alternative sampling matrices studied. The retention of BSA obtained with AuNP-modified paper substrates significantly improved the accuracy of the potentiometric ion determinations in sweat, saliva, artificial tears, and artificial serum. The potentiometric results were validated by inductively coupled plasma optical emission spectrometry (ICP-OES) and ion chromatography (IC). The study indicates that modification of paper by AuNPs is a feasible approach to reduce biofouling of sensors that are used in the paper-based analysis of clinically relevant samples.

Surface plasmon resonance based fiber optic potassium ion disposable sensing probe for soil testing

Fabrication and characterization of a fiber optic surface plasmon resonance (SPR) based potassium ion (K+) sensor utilizing the coating of dicyclohexeno-18-crown-6 ionophore incorporated in plasticized PVC membrane along with lipophilic pH sensitive dye chromoionophore-I over the silver coated unclad core of the fiber have been carried out. The interaction between ion selective cocktail layer and incoming K+ changes the effective refractive index of the sensing layer which affects the resonance wavelength in the SPR spectrum. To achieve best sensor performance, the thickness of the sensing layer has been optimized. The sensor probe has been found to be irreversible due to the very strong interaction between ionophore and target K+. The ring type structure of ionophore used provides a close fit to the incoming K+ and hence interacts strongly with it which makes K+ incapable of leaving the cavity of the ionophore. The washing of sensor probe with DI water could not break this bonding. This results in one time use of the probe or disposable type sensor probe. However, the probe works for 0 to 180 µg/mL concentration range of K+. The sensor is highly selective to K+ and is not affected by nitrate, phosphate, calcium and sodium ions and can be used to check the concentration of K+ in soil. In addition, the sensor possesses a response time of around 50 sec. Since the probe has been fabricated on optical fiber it has various advantages such as miniaturization, low cost, fast response, capability of real time monitoring and remote sensing.

Potentiometric Sensor for Naproxen Determination

Anaproxen-sensitive potentiometric sensor with a plasticized PVC membrane was designed. The sensor contains an ion associate of naproxen with rhodamine 6G dye and exhibits a linear response to naproxen anion in the range from 8 × 10–5 to 1 × 10–1 M with an electrode function slope characteristic of singly charged ions. The minimum determined concentration is 4 × 10–5 M. This sensor can be used for the detection and determination of naproxen in drugs.

Lipophilic Fluorescent Dye Liquids: Förster Resonance Energy Transfer-Based Fluorescence Amplification for Ion Selective Optical Sensors Based on a Solvent Polymeric Membrane.

Optical sensors based on solvent polymeric membranes have the potential to measure analytes present in an aqueous solution through the development of a tailored method for a specific target. However, limits in the concentrations of the component dyes have prevented improvements in sensitivity. We propose a Förster resonance energy transfer (FRET)-based fluorescence amplification system for ion-selective optical sensors using a highly fluorescent liquid material composed of a lipophilic phosphonium cation and a pyrene modifying sulfonate anion ([P66614][HP-SO3]), as both the plasticizer and donor, in addition to a combination of the lipophilic phosphonium cation and the fluorescein dodecyl ester anion ([P66614][12-FL]) as the fluorescent sensing dye acceptor. For ion extraction-based sensing, the donor and acceptor were retained in the plasticized PVC membrane with negligible leaching upon exposure to acidic and basic aqueous solutions. Systematic investigation of the donor and acceptor ratios clarified the effect of the amplification factor and the sensitivity of the sensor. At an acceptor doping level of 0.5 mol % (vs donor), an approximately 22-fold higher sensitivity was obtained compared to that of a conventional PVC membrane optical sensor. During ion measurement based on the coextraction of protons and anions, selectivity following the Hofmeister order was observed, which was controlled by the addition of ionophores. The proposed FRET system based on a lipophilic fluorescent liquid material has the potential to significantly improve the sensitivities of optical sensors using solvent polymeric membranes with high selectivities for various target analytes.

Inexpensive ion-selective electrodes for the simultaneous monitoring of potassium and nitrate concentrations in nutrient solutions.

A fast, simple and inexpensive potentiometric method has been developed for the determination of the major ions potassium and nitrate in nutrient solutions, by means of ion-selective electrodes (ISEs) based on plasticized polyvinyl membranes containing an ion-exchanger. Tridodecylmethylammonium chloride (TDMACl) and potassium tetrakis(4-chlorophenyl)borate (KTClPB) were used as ion-exchangers for the nitrate and potassium electrodes, respectively. Electrode membranes built with different plasticizers, bis-[2-ethylhexyl]-sebacate (DOS), tricresyl phosphate (TCP) and 2-nitrophenyloctyl ether (NPOE), were tested, and NPOE was selected. The electrodes were calibrated over both wide and narrow concentration ranges and residual analysis was made. Based on the results of these calibrations, the method of standard addition was developed and found to be suitable for the simultaneous determination of potassium and nitrate in nutrient solutions. A large group of samples taken from different stages of hydroponic crops was analysed. Several approaches recommended for statistical comparisons of the results obtained by potentiometric and by reference methods were tested, obtaining satisfactory results. The potentiometric methodology developed is promising for monitoring the concentration of these essential nutrients in nutrient solutions.

Liquid chromatographic and potentiometric methods for deteminations of clopidogrel

Two different techniques are developed for the determination of clopidogrel in pharmaceutical preparations. HPLC method has been developed where chromatographic analysis is performed on Nova-Pak(superscript ®) C18 column (3.9 mm×150 mm, 5 μm) with an ammonium formate buffer adjusted with formic acid to pH 4.0, acetonitrile (40:60, v/v) as mobile phase, and detection at 225 nm. Good linearity (0.9993, r), accuracy (≥99.20%) and precision (≤0.6 RSD) were obtained. Potentiometric measurments are based on tetrakis (p-chlorophenyl) borate-clopidogrel ion-pair as an electroactive material incorporating a plasticized PVC membrane with o-nitrophenyl octyl ether or dioctyl phthalate. The sensor is conditioned for at least two days in 0.1 M drug solution before use. It exhibits fast and stable Nernstian response for clopidogrel over the concentration range of 1.0×10^(-5)~1.0×10^(-2) M and pH range of 1.5-4.0. Results with an average recovery of 100.6% and a mean standard deviation of 0.86% of the nominal were obtained. The sensor shows reasonable selectivity towards clopidogrel hydrogen sulphate in presence of many cations. No significant interferences are caused by drug excipients and diluents.

PH-dependent distribution of the indicator dye tetrabromophenolphthalein ethyl ester between aqueous solution and plasticized polymeric phase: Predicting the lifetime of ion-selective optical sensors

The pH-dependent distribution of the indicator dye tetrabromophenolphthalein ethyl ester (TBPE, chromoionophore VIII) between plasticized polymeric phase and aqueous solution is studied. The commonly utilized algorithms for partition properties calculation are evaluated experimentally in terms of their suitability for the ionized species. The physical-chemical characteristics of TBPE that determine its applicability for use in chemical sensors, namely, the lipophilicity and acidity constant are estimated in the hydrophobic polymeric phase for the first time. The distribution coefficients of the neutral (protonated) and ionized (deprotonated) forms of TBPE are determined in plasticized PVC/water biphase system as 7.2 and 3.8, respectively (logk, ionic strength 1 M, 25 °C). The acidity constant of TBPE in plasticized PVC membrane, pKaPVC−DOS, is estimated spectrophotometrically as 6.1 ± 0.2 log units. The results can be used for developing optical chemical sensors based on TBPE (chromoionophore VIII), in particular for predicting the sensor lifetime, optimization of the sensor operating range and measuring conditions.

Ionic Liquid-Based Dye for Highly Sensitive Optical Sensing Based on FRET and Ion Extraction System Using Plasticized PVC Membrane

Ionic Liquid-Based Dye for Highly Sensitive Optical Sensing Based on FRET and Ion Extraction System Using Plasticized PVC Membrane

Characterization of Calcium Ion Release from a Polymer-Coated Electrode with a Plasticized PVC Membrane Containing Calcium Salts, and Its Contraction Examination of Vorticella Convallaria

Abstract Up to now several bio-imaging methods have taken very good pictures and/or recordings. With bio-imaging growing, a micro-stimulation method to limit in a fine region is required. Conventional chemical stimulation methods face difficulty in fulfilling this requirement, however, an electrochemical device is a potential response to this issue. This paper reports on the fabrication and the use of an electrochemical Ca2+-releasing device. The device consists of a three-layer electrode, including two transducers, a PVC membrane, PEDOT layer, and gold or carbon. The dynamic behavior of Ca2+ released from the device is evaluated by a two-dimensional 16 K pixel array Ca2+ image sensor, and is simulated using a diffusion model of Ca2+. Both experimental and calculated time and distance dependent profiles are almost in agreement when the PVC membrane is thin. As its biological application, a permeabilized Vorticella convallaria was set at a distance of ca. 0.1 mm from the Ca2+-releasing device. There was no response for some time just after switching-on, and then it gradually contracted. The gradual contraction after the interval proved that the Ca2+-releasing device can be used as a soft insertion based on the concentration diffusion.

Monitoring the lead-and-copper rule with a water-gated field effect transistor.

We use the natural zeolite clinoptilolite as the sensitive element in a plasticised PVC membrane. Separating a sample pool and a reference pool with such a membrane in water-gated SnO2 thin-film transistor (SnO2 WGTFT) leads to membrane potential, and thus transistor threshold shift in response to the common drinking water pollutants Pb2+ or Cu2+ in the sample pool. Threshold shift with ion concentration, c, follows a Langmuir-Freundlich (LF) characteristic. As the LF characteristic shows the steepest slope in the limit c → 0, this opens a window to limits-of-detection (LoDs) far below the 'action levels' of the 'lead-and-copper rule' for drinking water: Pb2+: LoD 0.9 nM vs 72 nM action level, Cu2+: LoD 14 nM vs 20.5 μM action level. LoDs are far lower than for membranes using organic macrocycles as their sensitive elements. Threshold shifts at the lead and copper action levels are more significant than shifts in response to variations in the concentration of non-toxic co-cations, and we discuss in detail how to moderate interference. The selective response to lead and copper qualifies clinoptilolite-sensitised WGTFTs as a low footprint sensor technology for monitoring the lead-and-copper rule, and to confirm the effectiveness of attempts to extract lead and copper from water.