Non-enzymatic paper-based analytical device for direct potentiometric detection of urine creatinine

A paper-based analytical device (PAD) with an integrated composite electrode has been designed and fabricated for non-enzymatic creatinine sensing. Reduced graphene oxide (rGO) was employed to modify the PAD so that it could function as a solid-contact transducer. A new macrocyclic pyrido-hexapeptide derivative was made and used as a special ionophore in the creatinine membrane sensor. The synthesized PAD showed a detection limit of 1.0 µM (S/N = 3) and a potentiometric response towards creatinine throughout a log-linear range of 2.0 µM-10 mM (R2 = 0.9998). The sensor shows significant selectivity for a few related substances, including ephedrine, codeine, ketamine, caffeine, urea, urate, carbinoxamine, and dextromethorphan. It has been established that the testing method is appropriate for the direct potentiometric detection of creatinine in a variety of human urine sample types. When an indicating electrode and a reference electrode are put on the same flexible disposable, this lets applications with a small sample volume be done. For point-of-care creatinine measurement, the developed paper-based analytical equipment is a good choice because it is affordable, easily accessible, and self-pumping (especially when combined with potentiometric detection).

Current perspectives, challenges, and future directions in the electrochemical detection of microplastics

Microplastics (5 μm) are a developing threat that contaminate every environmental compartment. The detection of these contaminants is undoubtedly an important topic of study because of their high potential to cause harm to ecosystems. For many years, scientists have been assiduously striving to surmount the obstacle of detection restrictions and minimize the likelihood of receiving results that are either false positives or false negatives. This study covers the current state of electrochemical sensing technology as well as its application as a low-cost analytical platform for the detection and characterization of novel contaminants. Examples of detection mechanisms, electrode modification procedures, device configuration, and performance are given to show how successful these approaches are for monitoring microplastics in the environment. Additionally included are the recent developments in nanoimpact techniques. Compared to electrochemical methods for microplastic remediation, the use of electrochemical sensors for microplastic detection has received very little attention. With an overview of microplastic electrochemical sensors, this review emphasizes the promise of existing electrochemical remediation platforms toward sensor design and development. In order to enhance the monitoring of these substances, a critical assessment of the requirements for future research, challenges associated with detection, and opportunities is provided. In addition to-or instead of-the now-in-use laboratory-based analytical equipment, these technologies can be utilized to support extensive research and manage issues pertaining to microplastics in the environment and other matrices.

Synthesis and characterization of bio-nanocomposite based on chitosan and CaCO3 nanoparticles for heavy metals removal

Water is a vital component of life; therefore, it is critical to have access to pure water for various life-sustaining activities including agriculture and human consumption. An eco-friendly nanocomposite based on chitosan (Cs) and nanomaterials (CaCO3-NPs) were combined to amalgamate the advantages of biopolymers and nanomaterials to overcome the problems of instability, poor mechanical properties, and low removal percentage of biopolymers. The as-prepared samples were characterized and were used for the removal of heavy metal from wastewater. X-ray diffractometer, Fourier transform infrared spectroscopy, and transmission electron microscope were used to distinguish the prepared absorbents. The absorption of the heavy metals by as-prepared samples was examined at different conditions. The kinetic and isotherm models of the adsorption process were also studied. The data showed that the removal percentages of Cd, Cu, Pb, Zn, Cr and Ni by the composite were 98.0, 94.8, 99.0, 97.9, 97.4 and 98.3 %, respectively. The kinetic and isothermal studies showed that the absorption of these metal ions by the samples obeyed a pseudo-second-order mechanism and Langmuir isotherm model, respectively. In addition, the maximum adsorption capacities of Cd, Cu, Pb, Zn, Cr, and Ni ions by as-prepared nanocomposite were 83.33, 47.84, 98.03, 89.28, 62.11, and 63.69 mg/g, respectively.

Paper-Based Analytical Device Based on Potentiometric Transduction for Sensitive Determination of Phenobarbital

In medicine, barbiturates are a class of depressive medications used as hypnotics, anticonvulsants, and anxiolytics. For the treatment of specific forms of epilepsy and seizures in young children in underdeveloped countries, the World Health Organization recommends phenobarbital (PBAR), a barbiturate drug. This review describes the fabrication and characterization of a paper-based analytical apparatus for phenobarbital detection that is straightforward, affordable, portable, and disposable. All of the solid-state ion-selective electrodes (ISEs) for PBAR as well as a Ag/AgCl reference electrode were constructed and optimized on a nonconductive paper substrate. Using carbon nanotube ink, the sensors were made to function as an ion-to-electron transducer and to make the paper conductive. A suitable polymeric membrane is drop-cast onto the surface of the carbon ink orifice. The pyrido-tetrapeptide and pyrido-hexapeptide derivatives, which were recently synthesized, functioned as distinct ionophores in the PBAR-membrane sensor, enabling its detection. With a detection limit of 5.0 × 10-7 M, the manufactured analytical device demonstrated a Nernstian response to PBAR anions in 50 mM phosphate buffer, pH 8.5, over a linear range of 1.0 × 10-6 to 1.0 × 10-3 M. The PBAR-based sensors showed quick (less than 5 s) response times for PBAR ion detection. The modified separate solution method was utilized to evaluate the selectivity pattern of these novel ionophores with respect to PBAR ions in comparison to other common anions. The analytical instrument that was exhibited on paper had good precision both within and between days. The suggested technology assisted in the detection of trace amounts of PBAR in real pharmaceutical samples. A comparison was made between the data acquired using the HPLC reference method and the information obtained by the recommended potentiometric approach. The described paper-based analytical device may be a good choice for point-of-care PBAR determination because it is cheap and easy to find and can self-pump (especially when combined with potentiometric detection).

Spinel ferrite nanoparticles as potential materials in chlorophenol removal from wastewater

Persistent organic pollutants (POPs) including chlorophenols (CPs) are increasing in water effluents, creating serious problems for both aquatic and terrestrial lives. Several research attempts have considered the removal of CPs by functionalised nanomaterials as adsorbents and catalysts. Besides the unique crystal structure, spinel ferrite nanomaterials (SFNs) own interesting optical and magnetic properties that give them the potential to be utilised in the removal of different types of CPs. In this review, we highlighted the recent research work that focused on the application of SFNs in the removal of different CP substances based on the number of chlorine atom attached to the phenolic compound. We have also discussed the structure and properties of SFN along with their numerous characterisation tools. We demonstrated the importance of identifying the structure, surface area, porosity, optical properties, etc. in the efficiency of the SFN during the CP removal process. The reviewed research efforts applied photocatalysis, wet peroxide oxidation (WPO), persulfate activated oxidation and adsorption. The studies presented different paths of enhancing the SFN ability to remove the CPs including doping (ion substitution), oxide composite structure and polymer composite structure. Experimental parameters such as temperature, dosage of CPs and SFN structure have shown to have a major effect in the CP removal efficiency. More attention is needed to investigate the different properties of SFN that can be tailored through different techniques and expected to have major role in the removal mechanism of CPs.

Characterization of Some "Hashish" Samples in the Egyptian Illicit Trafficking Market Using a Thermal Separation Probe and Gas Chromatography-Mass Spectrometry

Drugs that are illegal have long been a part of Egyptian society. The most widely misused form of narcotic is marijuana, also known as "bango", and other cannabis-related products like "hashish". The chemical profile of some available "hashish" in the local Egyptian illegal market and its possible country of origin are investigated using a gas chromatography-mass spectrometry technique in conjunction with a thermal separation probe (TSP/GC/MS). The TSP/GC/MS method reveals the presence of 23 different terpenes, of which caryophylla-4(12),8(13)-dien-5α-ol, isoaromadendrene epoxide, caryophyllene, and alloaromadendrene oxide-(1) are detected in high relative proportions. Ten cannabinoid components are also detected. These are cannabiorcochromene (CBC-C1), tetrahydrocannabivarin (THCV), delta-8-tetrahydrocannabinol (delta-8-THC), exo-THC, cannabichromene, cannabidiol (CBD), cannabielsoin (CBE), dronabinol (delta-9-THC), cannabigerol (CBG), and cannabinol (CBN). Phenotypic index (THC % + CBN %)/CBD %) is measured for the test samples to identify both the nature of the samples (fiber- or drug-type cannabis) and the country of origin.

Screen‐printed electrochemical sensors for label‐free potentiometric and impedimetric detection of human serum albumin

Herein, two electrochemical methods based on potentiometric and impedimetric transductions were presented for albumin targeting, employing screen‐printed platforms (SPEs) to make easy and cost‐effective sensors with good detection merits. The SPEs incorporated ion‐to‐electron multi‐walled carbon nanotubes (MWCNTs) transducer. Sensors were constructed using either tridodecyl methyl‐ammonium chloride (TDMACl) (sensor I) or aliquate 336S (sensor II) in plasticized polymeric matrices of carboxylated poly (vinyl chloride) (PVC‐COOH). Analytical performances of the sensors were evaluated using the above‐mentioned electrochemical techniques. For potentiometric assay, constructed sensors responded to albumin with −81.7 ± 1.7 (r2 = 0.9986) and −146.2 ± 2.3 mV/decade (r2 = 0.9991) slopes over the linearity range 1.5 μM–1.5 mM with 0.8 and 1.0 μM detection limits for respective TDMAC‐ and aliquate‐based sensors. Interference study showed apparent selectivity for both sensors. Impedimetric assays were performed at pH = 7.5 in 10 mM PBS buffer solution with a 0.02 M [Fe(CN)6]−3/−4 redox‐active electrolyte. Sensors achieved detection limits of 4.3 × 10−8 and 1.8 × 10−7 M over the linear ranges of 5.2×10−8–1.0×10−4 M and 1.4×10−6–1.4×10−3 M, with 0.09 ± 0.004 and 0.168 ± 0.009 log Ω/decade slopes for sensors based on TDMAC and aliquate, respectively. These sensors are characterized with simple construction, high sensitivity and selectivity, fast response time, single‐use, and cost‐effectiveness. The methods were successfully applied to albumin assessment in different biological fluids.

Impact of pathogenic bacterial communities present in wastewater on aquatic organisms: Application of nanomaterials for the removal of these pathogens

Contaminated wastewater (WW) can cause severe hazards to numerous delicate ecosystems and associated life forms. In addition, human health is negatively impacted by the presence of microorganisms in water. Multiple pathogenic microorganisms in contaminated water, including bacteria, fungi, yeast, and viruses, are vectors for several contagious diseases. To avoid the negative impact of these pathogens, WW must be free from pathogens before being released into stream water or used for other reasons. In this review article, we have focused on pathogenic bacteria in WW and summarized the impact of the different types of pathogenic bacteria on marine organisms. Moreover, we presented a variety of physical and chemical techniques that have been developed to provide a pathogen-free aquatic environment. Among the techniques, membrane-based techniques for trapping hazardous biological contaminants are gaining popularity around the world. Besides, novel and recent advancements in nanotechnological science and engineering suggest that many waterborne pathogens could be inactivated using nano catalysts, bioactive nanoparticles, nanostructured catalytic membranes, nanosized photocatalytic structures, and electrospun nanofibers and processes have been thoroughly examined.

Point-of-care paper-based analytical device for potentiometric detection of myoglobin as a cardiovascular disease biomarker

One of the cardiac biomarkers, myoglobin (Mb), is important in the rapid identification of cardio-vascular disorders. Therefore, point-of-care monitoring is essential. Pursuing this goal, a robust, reliable, and affordable paper-based analytical apparatus for potentiometric sensing has been developed and characterized. The molecular imprint technique was used to create a customized biomimetic antibody for myoglobin (Mb) on the surface of carboxylated multiwalled carbon nanotubes (MWCNT-COOH). This was accomplished by attaching Mb to carboxylated MWCNTs' surfaces and then filling the empty spaces through the mild polymerization of acrylamide in N,N-methylenebisacrylamide and ammonium persulphate. The modification of the MWCNTs' surface was verified by SEM and FTIR analysis. A hydrophobic paper substrate coated with fluorinated alkyl silane (CF₃(CF₂)₇CH₂CH₂SiCl₃, CF¹⁰) has been coupled with a printed all-solid-state Ag/AgCl reference electrode. The presented sensors showed a linear range of 5.0 × 10^-8 to 1.0 × 10^-4 M with a potentiometric slope of -57.1 ± 0.3 mV decade^-1 (R² = 0.9998) and a detection limit of 28 nM at pH 4. Compared to creatinine, sucrose, fructose, galactose, sodium glutamate, thiamine, alanine, ammonium, uric acid, albumin, glutamine, guanine, troponine T, and glucose, the sensor showed good selectivity for Mb. It demonstrated a good recovery for the detection of Mb in several fake serum samples (93.0-103.3%), with an average relative standard deviation of 4.5%. The current approach might be viewed as a potentially fruitful analytical tool for obtaining disposable, cost-effective paper-based potentiometric sensing devices. These types of analytical devices can be potentially manufacturable at large scales in clinical analysis.

All-solid-state paper-based potentiometric combined sensor modified with reduced graphene oxide (rGO) and molecularly imprinted polymer for monitoring losartan drug in pharmaceuticals and biological samples

A cost-effective, highly selective and sensitive paper-based potentiometric combined sensor for losartan potassium drug (LOS) is fabricated, characterized and used for the drug monitoring. The sensor consists of 2 strips of filter paper (20 × 5 mm each) as platform, each imprinted with 4 mm diameter circular spot of carbon. One carbon spot is covered by a reduced graphene oxide (rGO) for use as a substrate for the recognition sensor and the other without rGO is used for the reference electrode. LOS molecularly imprinted drug polymer (MIP) is applied onto the graphene oxide containing strip to act as a drug recognition sensing material and a solid-state polyvinyl butyral (PVB) is applied onto the second carbon spot to act as a reference electrode. Performance characteristics of the combined sensor are examined with chronopotentiometry (CP) and electrochemical impedance spectroscopy (EIS). Increase effect of rGO on the interfacial double-layer capacitance of the sensing membrane and consequently on the potential stability is confirmed. The developed combined sensor (strip cell) displays a Nernstian slope of -58.2 ± 0.3 mV/decade (R² = 0.9994) over the linear range 8.5 × 10^-7 - 6.9 × 10^-2 M with a detection limit of 2.7 ± 0.3 × 10^-7 M. The sensor shows remarkable selectivity toward various related compounds especially those commonly used by the COVID-19 patients such as paracetamol, ascorbic acid and dextromethorphan. The assay method is validated and proved to be satisfactory for direct potentiometric determination of LOS-K in some pharmaceutical formulations and in spiked human urine samples. An average recovery of 96.3 ± 0.3-98.7 ± 0.6% of the nominal or spiked concentration and a mean relative standard deviation of ±0.6% are obtained. The use of an indicating and a reference electrodes combined into a single flexible disposable paper platform enables applications to a minimum sample volume due to the close proximity of the responsive membrane and the liquid junction. The efficiency of the proposed sensor in complex urine matrix suggests its application in hospitals for rapid diagnosis of overdose patients and for quality control/quality assurance tests in pharmaceutical industry.

Carbon Capture Materials in Post-Combustion: Adsorption and Absorption-Based Processes

Global warming and climate changes are among the biggest modern-day environmental problems, the main factor causing these problems is the greenhouse gas effect. The increased concentration of carbon dioxide in the atmosphere resulted in capturing increased amounts of reflected sunlight, causing serious acute and chronic environmental problems. The concentration of carbon dioxide in the atmosphere reached 421 ppm in 2022 as compared to 280 in the 1800s, this increase is attributed to the increased carbon dioxide emissions from the industrial revolution. The release of carbon dioxide into the atmosphere can be minimized by practicing carbon capture utilization and storage methods. Carbon capture utilization and storage (CCUS) has four major methods, namely, pre-combustion, post-combustion, oxyfuel combustion, and direct air capture. It has been reported that applying CCUS can capture up to 95% of the produced carbon dioxide in running power plants. However, a reported cost penalty and efficiency decrease hinder the wide applicability of CCUS. Advancements in the CCSU were made in increasing the efficiency and decreasing the cost of the sorbents. In this review, we highlight the recent developments in utilizing both physical and chemical sorbents to capture carbon. This includes amine-based sorbents, blended absorbents, ionic liquids, metal-organic framework (MOF) adsorbents, zeolites, mesoporous silica materials, alkali-metal adsorbents, carbonaceous materials, and metal oxide/metal oxide-based materials. In addition, a comparison between recently proposed kinetic and thermodynamic models was also introduced. It was concluded from the published studies that amine-based sorbents are considered assuperior carbon-capturing materials, which is attributed to their high stability, multifunctionality, rapid capture, and ability to achieve large sorption capacities. However, more work must be done to reduce their cost as it can be regarded as their main drawback.

All-Solid State Potentiometric Sensors for Desvenlafaxine Detection Using Biomimetic Imprinted Polymers as Recognition Receptors

Using single-walled carbon nanotubes (SWCNTs) as an ion-to-electron transducer, a novel disposable all-solid-state desvenlafaxine-selective electrode based on a screen-printed carbon paste electrode was created. SWCNTs were put onto the carbon-paste electrode area, which was protected by a poly (vinyl chloride) (PVC) membrane with a desvenlafaxine-imprinted polymer serving as a recognition receptor. Electrochemical impedance spectroscopy and chronopotentiometric techniques were used to examine the electrochemical characteristics of the SWCNTs/PVC coating on the carbon screen-printed electrode. The electrode displayed a 57.2 ± 0.8 mV/decade near-Nernstian slope with a 2.0 × 10^-6 M detection limit. In 10 mM phosphate buffer, pH 6, the ODV-selective electrodes displayed a quick reaction (5 s) and outstanding stability, repeatability, and reproducibility. The usefulness of electrodes was demonstrated in samples of ODV-containing pharmaceutical products and human urine. These electrodes have the potential to be mass produced and employed as disposable sensors for on-site testing, since they are quick, practical, and inexpensive.

Fabrication and characterization of electrospun nanofibers using biocompatible polymers for the sustained release of venlafaxine

Recently, drug-controlled release nanotechnology has gained special attention in biomedicine. This work focuses on developing novel electrospun polymeric nanofibers (NFs) for buccal delivery of VEN to avoid the hepatic metabolism and enzymatic degradation in the GIT and develop an effective control of drug release. The optimized NFs were obtained by blending polylactic acid (PLA), and poly (ɛ-caprolactone) (PCL) fixed at a ratio of 1:1. It was characterized for morphology, drug-loading, FTIR, XRD, DSC, and in vitro drug release. Ex vivo permeability of the blend NFs was assessed using chicken pouch mucosa compared to VEN suspension, followed by histopathological examination. Further, the cytotoxic effect in three different cell lines using WST-1 assay. SEM morphologies refer to defect-free uniform NFs of PLA, PCL, and PLA/PCL mats. These fibers had a diameter ranging from 200 to 500 nm. The physico-thermal characterization of NFs depicted that the drug was successfully loaded and in an amorphous state in the PLA/PCL NFs. In vitro release of NFs substantiated a bi-phasic profile with an initial burst release of about 30% in the initial 0.5 h and a prolonged cumulative release pattern that reached 80% over 96 h following a non-Fickian diffusion mechanism. Ex vivo permeation emphasizes the major enhancement of the sustained drug release and the noticeable decrease in the permeability of the drug from NFs. Cytotoxicity data found that IC₅₀ of VEN alone was 217.55 μg/mL, then VEN-NFs recorded an IC₅₀ value of 250.62 μg/mL, and plain NFs showed the lowest toxicity and IC₅₀ 440.48 μg/mL in oral epithelial cells (OEC). Histopathology and cell toxicity studies demonstrated the preserved mucosal architecture and the preclinical safety. The developed PLA/PCL NFs can be promising drug carriers to introduce a step-change in improved psychiatric treatment healthcare.

Molecularly Imprinted Polymer Modified with an MWCNT Nanocomposite for the Fabrication of a Barbital Solid-Contact Ion-Selective Electrode

For potentiometric sensing of barbital (BAR), unique micro-sized imprinted polymer/multiwalled carbon nanotube (MWCNT)-based sensors are introduced. MWCNT is a lipophilic ion-to-electron transducing substance. A synthetic, described, and integrated barbital sodium molecular imprinted polymer (MIP) was used as a recognition receptor for potentiometric transduction in a plasticized polyvinyl chloride membrane. Methacrylic acid and ethylene glycol dimethacrylic acid are used as the functional monomer and crosslinking agent, respectively, in the synthesis of the MIPs. In the operating concentration range of 1.0 × 10^-3 to 2.0 × 10^-7 M, the sensors' Nernstian slope was -56.8 ± 0.9 mV/decade, with a detection limit of 1.0 × 10^-7 M. The sensor displayed an accurate response time of 10 s and consistent potential response in the pH range of 8.5-11. Using chronopotentiometry tests, the interfacial capacitance of the presented ion-to-electron transducer was assessed. When compared to sensors without MWCNTs, the interfacial double-layer capacitance for sensors based on those layers reached 52.5 μF. After the addition of the MWCNTs nanocomposite layer, the water layer was eliminated between the sensing membrane and the conducting substrate. A wide range of applications for the proposed sensors for BAR detection in real samples can be provided by the sensors' strong selectivity over the interfering species. The suggested sensors were successfully used to determine BAR in urine samples that had been spiked.

New Potentiometric Screen-Printed Platforms Modified with Reduced Graphene Oxide and Based on Man-Made Imprinted Receptors for Caffeine Assessment

Caffeine is a psychoactive drug that is administered as a class II psychotropic substance. It is also considered a component of analgesics and cold medicines. Excessive intake of caffeine may lead to severe health damage or drug addiction problems. The assessment of normal caffeine consumption from abusive use is not conclusive, and the cut-off value for biological samples has not been established. Herein, new cost-effective and robust all-solid-state platforms based on potentiometric transduction were fabricated and successfully utilized for caffeine assessment. The platforms were modified with reduced graphene oxide (rGO). Tailored caffeine-imprinted polymeric beads (MIPs) based on methacrylic acid (MAA) and ethylene glycol dimethacrylate (EGDMA) were prepared, characterized, and used as recognition receptors in the presented potentiometric sensing devices. In 50 mM MES buffer, the sensors exhibited a slope response of 51.2 ± 0.9 mV/decade (n = 6, R2 = 0.997) over the linear range of 4.5 × 10−6−1.0 × 10−3 M with a detection limit of 3.0 × 10−6 M. They exhibited fast detection of caffeinium ions with less than 5 s response time (<5 s). The behavior of the presented sensors towards caffeinium ions over many common organic and inorganic cations was evaluated using the modified separate solution method (MSSM). Inter-day and intra-day precision for the presented analytical device was also evaluated. Successful applications of the presented caffeine sensors for caffeine determination in commercial tea and coffee and different pharmaceutical formulations were carried out. The data obtained were compared with those obtained by the standard liquid chromatographic approach. The presented analytical device can be considered an attractive tool for caffeine determination because of its affordability and vast availability, particularly when combined with potentiometric detection.

Removal of Uranium-238, Thorium-232, and Potassium-40 from Wastewater via Adsorption on Multiwalled Carbon Nanotubes

The optimum conditions for the removal of uranium-238, thorium-232, and potassium-40 from wastewater and the discharge of nuclear facilities using multiwalled carbon nanotubes (CNTs) are described. The adsorption mechanism is mainly attributed to chemical interactions between the metal ions and surface functional groups of the CNTs. Batch adsorption experiments are carried out in order to study the effect of different parameters such as pH, contact time, initial metal ion concentration, adsorbent dose, and temperatures. Maximum metal removal (>98%) from solutions containing 20-120 Bq/L metal ions is achieved using a contact time of 15 min, a pH of 6.0, and 10 mg/L CNTs. The effect of temperature on the kinetics and equilibrium of adsorption on CNT particles is examined. Consistent with an exothermic reaction, an increase in the temperature resulted in an increase in the adsorption rate. Langmuir, Freundlich, and Dubinin-Radushkevich isotherms are applied to the data obtained at various temperatures. The Langmuir adsorption model is the best for data interpretations. The kinetics of adsorption reveals a pseudo-second-order mechanism. Thermodynamic parameters at 293 K (ΔG°, ΔH°, and ΔS°) for U-238, Th-232, and K-40 are -14590.7 kJ/mol, -6.66 kJ/mol, and 26.47 J/(mol K), -96,96.5 kJ/mol, -2.48 kJ/mol, and 14.17 J/(mol K), and -3922.09 kJ/mol, -1.32 kJ/mol, and 6.12 J/(mol K), respectively.

Novel magnetic nickel ferrite nanoparticles modified with poly(aniline-co-o-toluidine) for the removal of hazardous 2,4-dichlorophenol pollutant from aqueous solutions

Chlorinated organic and phenolic compounds are still purely studied by many researchers because of their severe damage to the aquatic environment and their carcinogenic effect on many living organisms. Therefore, there is a great interest in removing these environmental pollutants from aqueous mediums by easy and inexpensive methods. Herein, novel nickel ferrite (NiFe₂O₄) nano composite modified with poly(aniline-co-o-toluidine) (PAOT) is prepared, characterized, and used for the removal of 2,4-dichlorophenol (2,4-DCP) as an organic chlorinated environmental pollutant. The morphological properties of the composite are characterized by Fourier transform infrared spectrometry (FTIR), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), and Brunauer–Emmett–Teller (BET) methods. The prepared composite is tested for the removal of the hazardous dichlorophenol pollutant from aqueous solutions. Under optimized conditions and with effective control of parameters including, contact time, pH of the test solution, adsorbent dose, and temperature, over 83% of the pollutant is adsorbed and removed. The adsorption capacity is 162 mg g⁻¹. Adsorption kinetics, adsorption isotherm and some physicochemical parameters of the reaction are evaluated. The Redlich–Peterson isothermal model is the appropriate model for describing the adsorption process. These results indicate that NiFe₂O₄/PAOT nanocomposites are promising adsorbents for the removal of persistent organic pollutants (e.g., DCP) from aqueous solutions. The results also reveal that modification of NiFe₂O₄ particles with poly(aniline-co-o-toluidine) (PAOT) significantly enhances the adsorption capacity of the adsorbent. This is probably due to the electrostatic attraction and non-covalent interactions (e.g. π–π) between the aromatic rings in both dichlorophenol and poly(aniline-co-o-toluidine) copolymer. Advantages offered by using NiFe₂O₄/PAOT nanocomposites are the high stability, reasonable efficiency, reusability for at least five adsorption–desorption cycles and the ability to remove the adsorbent from aqueous solutions for reuse using an external magnetic field.

Chlorinated organic and phenolic compounds are still purely studied by many researchers because of their severe damage to the aquatic environment and their carcinogenic effect on many living organisms.

Effective screen-printed potentiometric devices modified with carbon nanotubes for the detection of chlorogenic acid: application to food quality monitoring

All-solid state screen-printed electrodes were fabricated for chlorogenic acid (CGA) detection. The screen-printed platforms were modified with multi-walled carbon nanotubes (MWCNTs) to work as a lipophilic solid-contact transducer. The sensing-membrane was plasticized with a suitable solvent mediator and incorporating [NiII(bathophenanthroline)3][CGA]2 complex as a sensory material. In a 30 mM phosphate solution (buffer, pH 6), the sensor revealed a Nernstian-response towards CGA ions with a slope of -55.1 ± 1.1 (r 2 = 0.9997) over the linear range 1.0 × 10-7 to 1.0 × 10-3 (0.035-354.31 μg mL-1) with a detection limit 7.0 × 10-8 M (24.8 ng mL-1). It revealed a stable potentiometric response with excellent reproducibility and enhanced selectivity over several common ions. Short-term potential stability and the interfacial sensor capacitance was estimated using both electrochemical-impedance spectroscopy (EIS) and chronopotentiometry techniques. The presented electrochemical platform revealed the merits of design simplicity, ease of miniaturization, good potential-stability, and cost-effectiveness. It is successfully applied to CGA determination in different coffee beans extracts and juice samples. The data obtained were compared with those obtained by liquid chromatography reference method (HPLC).

Paper-Based Potentiometric Device for Rapid and Selective Determination of Salicylhydroxamate as a Urinary Struvite Stone Inhibitor

Novel paper-based potentiometric platforms for rapid, cost-effective, and simple determination of the salicylhydroxamic acid (SHAM) drug are presented. Both the SHAM sensor and the reference Ag/AgCl electrode were integrated together on the miniaturized paper platforms. The ion-sensing membrane for the presented sensor is based on the use of SnIV-tetraphenylporphyrin (SnIVTPP) as a charged carrier within a plasticized poly(vinyl chloride) (PVC) matrix. Multiwalled carbon nanotubes (MWCNTs) were used as an ion-to-electron transducer. The resulting sensor revealed a rapid and stable response with a Nernstian slope of -59.3 ± 0.7 mV/decade over the linear range of 1.0 × 10-6 to 1.0 × 10-3 M and a detection limit of 0.7 μM. All measurements were carried out in 30 mM phosphate-buffered solution (PBS) at pH 7.2. Intra- and interday precision were measured and found to be 1.7%. The relative standard deviation (RSD%) ( = 5) was calculated as 2.43% after utilizing five different electrodes (n = 5). The selectivity behavior of the prepared electrodes in the absence and presence of ionic additives was evaluated. The selectivity pattern showed a non-Hofmeister selectivity pattern in the existence of anionic additives with enhanced potentiometric selectivity for SHAM over different lipophilic anions (e.g., ClO4 -, SCN-, and I-). The presented device was successfully applied for SHAM determination in pharmaceutical preparations. This paper-based analytical device can be potentially manufactured at large scales and provides a portable, rapid, disposable, and cost-effective analytical tool for measuring the SHAM drug.

Low-cost potentiometric paper-based analytical device based on newly synthesized macrocyclic pyrido-pentapeptide derivatives as novel ionophores for point-of-care copper(ii) determination

A simple, cost-effective, portable and disposable paper-based analytical device is designed and fabricated for copper(ii) determination. All solid-state ion-selective electrodes (ISEs) for copper and a Ag/AgCl reference electrode were constructed and optimized on the paper substrate. The copper electrodes were built using carbon nano-tube ink as a conductive substrate and an ion-to electron transducer. A suitable polymeric membrane is drop-cast on the surface of the conductive carbon ink window. The copper-sensing membrane is based on newly synthesized macrocyclic pyrido-pentapeptide derivatives as novel ionophores for copper detection. Under the optimized conditions, the presented all-solid-state paper-based Cu²⁺-ISEs showed a Nernstian response toward Cu²⁺ ions in 30 mM MES buffer, pH 7.0 over the linear range of 5.0 × 10⁻⁷–1.0 × 10⁻³ M with a limit of detection of 8.0 × 10⁻⁸ M. The copper-based sensors exhibited rapid detection of Cu²⁺ ions with a short response time (<10 s). The selectivity pattern of these new ionophores towards Cu²⁺ ions over many common mono-, di- and trivalent cations was evaluated using the modified separate solution method (MSSM). The presented paper-based analytical device exhibited good intra-day and inter day precision. The presented tool was successfully applied for trace Cu²⁺ detection in real samples of serum and whole blood collected from different children with autism spectrum disorder. The data obtained by the proposed potentiometric method were compared with those obtained by the inductively-coupled plasma (ICP) as a reference method. The presented copper paper-based analytical-device can be considered as an attractive tool for point-of-care copper determination because of its affordability, vast availability, and self-pumping ability, particularly when combined with potentiometric detection.

A simple, cost-effective, portable and disposable paper-based analytical device is designed and fabricated for copper(ii) determination.

Paper-Based Potentiometric Sensors for Nicotine Determination in Smokers' Sweat

Herein, we describe for the first time, the design and fabrication of a novel nicotine paper-based sensor, in which a miniaturized paper reference electrode is integrated for potentiometric measurements. The paper-based sensors were designed using printed wax barriers to define the electrochemical cell and the sample zones. The electrodes were based on the use of the ion association complexes of the nicotinium cation (Nic) with either tetraphenylborate (TPB) or 5-nitrobarbiturate (NB) counter anions as sensing materials for nicotine recognition. A poly (3,4 ethylenedioxythiophene)/poly-(styrene sulfonate) (PEDOT/PSS) conducting polymer was used as an ion-to-electron transducer. The performance characteristics of the proposed sensors were evaluated and it revealed a rapid and stable response with a Nernstian slope of 55.2 ± 0.3 and 51.2 ± 0.6 mV/decade over the linear range of 1.0 × 10^-5 to 1.0 × 10^-2 M and detection limits of 6.0 and 8.0 μM for [Nic/TPB] and [Nic/NB], respectively. The sensors revealed a constant response over the pH range 3.5-6.5. The designed sensors provided a portable, inexpensive, and disposable way of measuring trace levels of nicotine coming from different cigarettes and in the collected human sweat of heavy smokers. All results were compared favorably with those obtained by the standard gas chromatographic method.

All-Solid-State Potentiometric Ion-Sensors Based on Tailored Imprinted Polymers for Pholcodine Determination

In recent times, the application of the use of ion-selective electrodes has expanded in the field of pharmaceutical analyses due to their distinction from other sensors in their high selectivity and low cost of measurement, in addition to their high measurement sensitivity. Cost-effective, reliable, and robust all-solid-state potentiometric selective electrodes were designed, characterized, and successfully used for pholcodine determination. The design of the sensor device was based on the use of a screen-printed electrode modified with multiwalled carbon nanotubes (MWCNTs) as a solid-contact transducer. Tailored pholcodine (PHO) molecularly imprinted polymers (MIPs) were prepared, characterized, and used as sensory receptors in the presented potentiometric sensing devices. The sensors exhibited a sensitivity of 31.6 ± 0.5 mV/decade (n = 5, R² = 0.9980) over the linear range of 5.5 × 10⁻⁶ M with a detection limit of 2.5 × 10⁻⁷ M. Real serum samples in addition to pharmaceutical formulations containing PHO were analyzed, and the results were compared with those obtained by the conventional standard liquid chromatographic approach. The presented analytical device showed an outstanding efficiency for fast, direct, and low-cost assessment of pholcodine levels in different matrices.

An all-solid-state potentiometric sensor modified with multi-walled carbon nanotubes (MWCNTs) for silicate assessment and water-quality testing

A simple and cost-effective approach is proposed for silicate ion determination. The approach is based on designing an all-solid-state potentiometric sensor. The plasticized polyvinyl chloride (PVC) membrane sensor is based on the ion-association complex [Ni(bphen)₃]²⁺[SiO₃]^2- as a sensory recognition material. The sensor is modified with multi-walled carbon nanotubes (MWCNTs) as an ion-to-electron transducer material. The performance characteristics of the new silicate-selective electrode were evaluated using a potentiometric water-layer test, potentiometric measurements, impedance spectroscopy, and current-reversal chronopotentiometry. The developed electrodes exhibited a low detection limit (0.11 μg mL^-1) over a wide linear range (4.0 × 10^-6 to 1.0 × 10^-3 M) and near-Nernstian sensitivity (slope = -28.1 ± 1.4 mV per decade). They presented a very short response time (<5 s) over the pH range 6-12 and provided acceptable reliability, ease of design and miniaturization, and high potential stability, in addition to good accuracy and precision. The sensors exhibited enhanced selectivity for silicate over many common interfering anions, such as SO₄^2-, NO₃^-, CH₃COO^-, CO₃^2-, Cl^-, S^2-, and PO₄^3-. These results could qualify the developed sensor to be used in a successful way for the trace determination of silicate ions in different matrices. The developed method was successfully applied to the potentiometric detection of silicate in different pre-packaged bottled drinking water samples.

Cacodylate Sensors and their Application in the Determination of Amino Acid Levels in Biological Samples

BACKGROUND

The importance of recognizing and quantifying chemical anions/cations found in various types of samples, including environmental and biological samples, has been extensively studied. Recent findings suggest the possibility of health risks caused by organic compound dimethylarsinic acid (DMAs) rather than its inorganic arsenic metabolite.

OBJECTIVE

This article aims to fabricate polymeric-membrane electrochemical sensors with high sensitivity and selectivity for the cacodylic acid sodium salt dimethylarsinate (DMAs) based on silver diethyldithiocarbamate (AgDDTC) and CuIIphthalocyanine (CuPC) as novel neutral carriers and their applications.

METHOD

DMAs calibration relations and titrations were carried out using a potentiometric workstation equipped with a double-junction reference electrode, in conjunction with the fabricated working electrodes.

RESULTS

Sensors revealed fast and stable anionic response with near-Nernstian slopes (-38.6 ± 0.9 and -31.5 ± 0.6 mV/decade), within concentration ranges (1.7 × 10-5 -1.0 × 10-2 and 3.0 × 10-5 -1.0 × 10-2 M) and detection limits (1.0 × 10-5 and 1.6 × 10-5 M) for AgDDTC- and CuPC-based sensors, respectively. Sensors are characterized by extended life-time, signal stability, high precision and short response times. Selectivity for the cacodylate anion over most common anions was tested for the proposed electrodes. Sensors were satisfactorily applied for DMAs quantification in biological matrices with recoveries ranging between 96.2 and 99.0%. Membrane sensors were interfaced with a flow-through system for continuous monitoring of DMAs. The sensors were tested for the assay of different amino acids based on their reaction with cacodylate, where reaction end points were monitored with the proposed electrodes using direct potentiometric determination and flow injection analysis (FIA).

CONCLUSIONS

Potentiometric ion-selective PVC-membrane electrodes based on silver diethyldithiocarbamate (AgDDTC) and CuIIphthalothyanine (CuPC) provide adequate and reliable means for the determination of dimethylarsenate anion (cacodylate anion, DMAs). These membrane electrodes are easy to manufacture, they have the advantages of high selectivity and sensitivity, broad dynamic ranges, low detection limits, quick response times and cost effectiveness. Such properties make these sensors suitable for the assay of DMAs levels in aqueous solutions by direct potentiometry, flow injection and potentiometric titration, as well as in monitoring of the titration end points of the reactions between various amino acids and DMAs anion in aqueous solutions.

HIGHLIGHTS

Simple electrochemical membranes for dimethylarsinate (DMAs) were prepared, based on diethyldithiocarbamate (AgDDTC) and CuIIphthalocyanine (CuPC). - DMAs sensors were fabricated in two different modules: batch (for static) and flow-through (for hydrodynamic) approaches. - Levels of DMAs were determined in spiked biological samples. - AgDDTC-based sensors were successfully applied in the determination of several amino acids via potentiometric titration with DMAs.

Integrated all-solid-state sulfite sensors modified with two different ion-to-electron transducers: rapid assessment of sulfite in beverages

An integrated all-solid-state screen-printed ion-selective potentiometric sensor for rapid assessment of sulfite ion in beverages, based on analytical transduction, is described. The constructed potentiometric cell incorporates a polymeric membrane sulfite ion-selective electrode based on cobalt(ii) phthalocyanine (CoPC) as a recognition material and an Ag/AgCl reference electrode with a polyvinyl butyral reference membrane. Two different solid-contact transducers, namely multi-walled carbon nanotubes (MWCNTs) and polyaniline (PANI) were used for a comparative study. The presented sensors exhibited a rapid Nernst response across the concentration ranges from 2.0 × 10-6 to 2.3 × 10-3 M and from 5.0 × 10-6 to 2.3 × 10-3 M with detection limits equal to 1.1 × 10-6 M and 1.5 × 10-6 M for sensors based on MWCNTs and PANI, respectively. The proposed sensors manifested high selectivity and sensitivity, enhanced stability and low cost that provides a wide number of potential applications for food analysis. Good performance characteristics were obtained for the proposed method after applying the validation requirements. Method precision, accuracy, bias, trueness, repeatability, reproducibility, and uncertainty are examined. These analytical capabilities support the rapid and direct determination of sulfite in different beverage samples. The analytical results were verified and compared with the standard iodometric method.

Solid-Contact Potentiometric Sensors Based on Main-Tailored Bio-Mimics for Trace Detection of Harmine Hallucinogen in Urine Specimens

All-solid-state potentiometric sensors have attracted great attention over other types of potentiometric sensors due to their outstanding properties such as enhanced portability, simplicity of handling, affordability and flexibility. Herein, a novel solid-contact ion-selective electrode (SC-ISE) based on poly(3,4-ethylenedioxythiophene) (PEDOT) as the ion-to-electron transducer was designed and characterized for rapid detection of harmine. The harmine-sensing membrane was based on the use of synthesized imprinted bio-mimics as a selective material for this recognition. The imprinted receptors were synthesized using acrylamide (AA) and ethylene glycol dimethacrylate (EGDMA) as functional monomer and cross-linker, respectively. The polymerization process was carried out at 70 °C in the presence of dibenzoyl peroxide (DBO) as an initiator. The sensing membrane in addition to the solid-contact layer was applied to a glassy-carbon disc as an electronic conductor. All performance characteristics of the presented electrode in terms of linearity, detection limit, pH range, response time and selectivity were evaluated. The sensor revealed a wide linearity over the range 2.0 × 10⁻⁷–1.0 × 10⁻² M, with a detection limit of 0.02 µg/mL and a sensitivity slope of 59.2 ± 0.8 mV/hamine concentration decade. A 40 mM Britton–Robinson (BR) buffer solution at pH of 6 was used for all harmine measurements. The electrode showed good selectivity towards harmine over other common interfering ions, and maintained a stable electrochemical response over two weeks. After applying the validation requirements, the proposed method revealed good performance characteristics. Method precision, accuracy, bias, trueness, repeatability, reproducibility, and uncertainty were also evaluated. These analytical capabilities support the fast and direct assessment of harmine in different urine specimens. The analytical results were compared with the standard liquid chromatographic method. The results obtained demonstrated that PEDOT/PSS was a promising solid-contact ion-to-electron transducer material in the development of harmine-ISE. The electrodes manifested enhanced stability and low cost, which provides a wide number of potential applications for pharmaceutical and forensic analysis.

Correction: Integrated all-solid-state sulfite sensors modified with two different ion-to-electron transducers: rapid assessment of sulfite in beverages

Correction for ‘Integrated all-solid-state sulfite sensors modified with two different ion-to-electron transducers: rapid assessment of sulfite in beverages’ by Hisham S. M. Abd-Rabboh et al., RSC Adv., 2021, 11, 3783–3791, DOI: 10.1039/D0RA09903A.

Paper-based potentiometric sensing devices modified with chemically reduced graphene oxide (CRGO) for trace level determination of pholcodine (opiate derivative drug)

Robust, reliable and cost-effective paper-based analytical device for potentiometric pholcodine (opiate derivative drug) ion sensing has been prepared and characterized. A printed pholcodinium (PHL)²⁺/5-nitrobarbiturate (NB)⁻ ion-association complex as a sensory material-based all-solid-state ion-selective electrode (ISE) on a chemically reduced graphene oxide (CRGO) solid-contact, and a printed all-solid-state Ag/AgCl reference electrode, has been combined on a hydrophobic paper substrate coated with fluorinated alkyl silane (CF₃(CF₂)₇CH₂CH₂SiCl₃, C^F₁₀). The sensors revealed a potentiometric slope of 28.7 ± 0.3 mV dec⁻¹ (R² = 0.9998) over a linear range starting from 2.0 × 10⁻⁷ M to 1.0 × 10⁻² M and a detection limit of 0.04 μg mL⁻¹. The repeatability and stability of the pholcodine paper-based sensor was found to be 2.32%. The RSD% (n = 6) was found to be 2.67% when using five different paper-based sensors. The sensor revealed an excellent selectivity towards PHL over dextromethorphan, codeine, ephedrine, carbinoxamine, caffeine, ketamine, and K⁺, Na⁺ and Ca²⁺ ions. It showed a good recovery (94–104%) for the determination of PHL in different artificial serum samples. The presented paper-based analytical device was successfully introduced for PHL determination in different pharmaceutical formulations (i.e. syrups and suspensions) containing pholcodine. The current work can be considered as a promising possible analytical tool to obtain cost-effective and disposable paper-based potentiometric sensing devices. These devices can be potentially manufacturable at large scales in pharmaceutical, clinical and forensic applications for opiate drug assessment.

Robust, reliable and cost-effective paper-based analytical device for potentiometric pholcodine (opiate derivative drug) ion sensing has been prepared and characterized.

Novel Potentiometric Screen-printed Carbon Electrodes for Bisphenol S Detection in Commercial Plastic Samples

Novel miniaturized poly(vinyl chloride) matrix membrane sensors based on screen-printed carbon electrodes and responsive to bisphenol S (BPS) were formulated. Polymeric membranes are based on an ion-pair complex of BPS anion with an Aliquat 336S counter cation. A solid conductive contact of multi-walled carbon nanotubes (MWCNTs) was used on screen-printed carbon platforms. After drop-casting and drying of the MWCNTs on a carbonaceous substrate, it was coated with a layer of polymeric poly(vinyl chloride) PVC sensing membrane containing the recognition complex. Prepared electrodes revealed a near-Nernstian response towards BPS with a -28.2 ± 0.8 mV/decade anionic slope, 0.02 μg/mL detection limit and 2.5 × 10-7 - 1.0 × 10-3 M concentration range (r2 = -0.9994). Signals were recorded in a 30 mM HCO3-/CO32- buffer, pH 10, with fast response times <10 s. A suggested sensing system was effectively applied in the quantitative determination of diminished BPS levels released from plastic bottle samples, and obtained results were statistically assessed against a chromatographic HPLC independent reference method.

Solid-State Membrane Sensors Based on Man-Tailored Biomimetic Receptors for Selective Recognition of Isoproturon and Diuron Herbicides

Solid-contact ion-selective electrodes (SC-ISEs) have shown great potential for routine and portable ion detection. The introduction of nanomaterials as ion-to-electron transducers and the adoption of different performance-enhancement strategies have significantly promoted the development of SC-ISEs. Herein, new solid-contact ion-selective electrodes, along with the implementation of multiwalled carbon nanotubes (MWCNTs) as ion-to-electron transducers and potassium tetrakis (p-chlorophenyl) borate (KTpClB) as lipophilic ionic additives, were presented for the detection of isoproturon (IPU) and diuron (DU) herbicides. Molecularly imprinted polymers (MIPs), with special molecule recognition properties for isoproturon (IPU) and diuron (DU), were prepared, characterized, and introduced as sensory recognition materials in the presented electrodes. Sensors revealed a near-Nernstian response for both isoproturon (IPU) and diuron (DU) with slopes of 53.1 ± 1.2 (r² = 0.997) and 57.2 ± 0.3 (r² = 0.998) over the linear ranges of 2.2 × 10^-6-1.0 × 10^-3 M and 3.2 × 10^-6-1.0 × 10^-3 M with detection limits of 8.3 × 10^-7 and 1.4 × 10^-6 M, respectively. The response time of the presented sensors was found to be <5 s and the lifetime was at least eight weeks. The sensors exhibited good selectivity towards isoproturon (IPU) and diuron (DU) in comparison with some other herbicides, alkali, alkaline earth, and heavy metal ions. The presented sensors were successfully applied for the direct determination of isoproturon (IPU) and diuron (DU) in real water samples.

Novel Validated Analytical Method Based on Potentiometric Transduction for the Determination of Citicoline Psychostimulant/Nootropic Agent

Herein, a novel validated potentiometric method is presented for the first time for citicoline determination. The method is based on measuring the potential using new constructed citicoline electrodes. The electrodes are based on the use of citicolinium/phosphomolybdate [Cit]₂[PM] (sensor I) and citicolinium/tetraphenylborate [Cit][TPB] (sensor II) ion association complexes. These sensory materials were dispersed in plasticized polyvinyl chloride (PVC) polymeric membranes. The sensors revealed a Nernstian response with the slopes 55.9 ± 1.8(r² = 0.9994) and 51.8 ± 0.9 (r² = 0.9991) mV/decade over a linearity range of 6.3 × 10⁻⁶–1.0 × 10⁻³ and 1.0 × 10⁻⁵–1.0 × 10⁻³ M and detection limits of 3.16 × 10⁻⁶ and 7.1 × 10⁻⁶ M for sensors I and II, respectively. To ensure the existence of monovalent citicoline, all measurements were performed in 50 mM acetate buffer at pH 3.5. All presented electrodes showed good performance characteristics such as rapid response, good selectivity, high potential-stability and long life-span. Method verification and validation in terms of response linearity, quantification limit, accuracy, bias, trueness, robustness, within-day variability and between-days variability were evaluated. The method was introduced for citicoline determination in different pharmaceutical formulations and compared with the standard high performance liquid chromatography (HPLC) method.

A New Validated Potentiometric Method for Sulfite Assay in Beverages Using Cobalt(II) Phthalocyanine as a Sensory Recognition Element

A simple potentiometric sensor is described for accurate, precise, and rapid determination of sulfite additives in beverages. The sensor is based on the use of cobalt phthalocyanine as a recognition material, dispersed in a plasticized poly(vinyl chloride) matrix membrane. o-Nitrophenyl octyl ether (o-NPOE) as a membrane solvent and tri-dodecylmethyl- ammonium chloride (TDMAC) as ion discriminators are used as membrane additives. Under the optimized conditions, sulfite ion is accurately and precisely measured under batch and flow injection modes of analysis. The sensor exhibits fast and linear response for 1.0 × 10-2-1.0 × 10-6 M (800-0.08 µg/mL) and 1.0 × 10-1-5.0 × 10-5 M (8000-4 µg/mL) sulfite with Nernstian slopes of -27.4 ± 0.3 and -23.7 ± 0.6 mV/concentration decade under static and hydrodynamic modes of operation, respectively. Results in good agreement with the standard iodometric method are obtained.Validation of the assay method is examined in details including precision, accuracy, bias, trueness, repeatability, reproducibility, and uncertainty and good performance characteristics of the method are obtained. The sensor response is stable over the pH range of 5 to 7 without any significant interference from most common anions. The advantages offered by the proposed sensor (i.e., wide range of assay, high accuracy and precision, low detection limit, reasonable selectivity, long term response stability, fast response, and long life span and absence of any sample pretreatment steps) suggest its use in the quality control/quality assurance routine tests in beverages industries, toxicological laboratories and by inspection authorities.

Porous Activated Carbon from Lignocellulosic Agricultural Waste for the Removal of Acetampirid Pesticide from Aqueous Solutions

A facile eco-friendly approach for acetampirid pesticide removal is presented. The method is based on the use of micro- and mesoporous activated carbon (TPAC) as a natural adsorbent. TPAC was synthesized via chemical treatment of tangerine peels with phosphoric acid. The prepared activated carbon was characterized before and after the adsorption process using Fourier- transform infrared (FTIR), X-ray diffraction (XRD), particle size and surface area. The effects of various parameters on the adsorption of acetampirid including adsorbent dose (0.02–0.2 g), pH 2–8, initial adsorbate concentration (10–100 mg/L), contact time (10–300 min) and temperature (25–50 °C) were studied. Batch adsorption features were evaluated using Langmuir and Freundlich isotherms. The adsorption process followed the Langmuir isotherm model with a maximum adsorption capacity of 35.7 mg/g and an equilibration time within 240 min. The adsorption kinetics of acetamiprid was fitted to the pseudo-second-order kinetics model. From the thermodynamics perspective, the adsorption was found to be exothermic and spontaneous in nature. TPAC was successfully regenerated and reused for three consecutive cycles. The results of the presented study show that TPAC may be used as an effective eco-friendly, low cost and highly efficient adsorbent for the removal of acetamiprid pesticides from aqueous solutions.

Synthesis and Characterization of CuFe2O4 Nanoparticles Modified with Polythiophene: Applications to Mercuric Ions Removal

In this research, CuFe₂O₄ nanoparticles were synthesized by co-precipitation methods and modified by coating with thiophene for removal of Hg(II) ions from aqueous solution. CuFe₂O₄ nanoparticles, with and without thiophene, were characterized by x-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), energy dispersive x-ray (EDX), high-resolution transmission electron microscopy (HRTEM) and Brunauer-Emmett-Teller (BET). Contact time, adsorbent dose, solution pH, adsorption kinetics, adsorption isotherm and recyclability were studied. The maximum adsorption capacity towards Hg²⁺ ions was 7.53 and 208.77 mg/g for CuFe₂O₄ and CuFe₂O₄@Polythiophene composite, respectively. Modification of CuFe₂O₄ nanoparticles with thiophene revealed an enhanced adsorption towards Hg²⁺ removal more than CuFe₂O₄ nanoparticles. The promising adsorption performance of Hg²⁺ ions by CuFe₂O₄@Polythiophene composite generates from soft acid-soft base strong interaction between sulfur group of thiophene and Hg(II) ions. Furthermore, CuFe₂O₄@Polythiophene composite has both high stability and reusability due to its removal efficiency, has no significant decrease after five adsorption-desorption cycles and can be easily removed from aqueous solution by external magnetic field after adsorption experiments took place. Therefore, CuFe₂O₄@Polythiophene composite is applicable for removal Hg(II) ions from aqueous solution and may be suitable for removal other heavy metals.

Imprinted Polymeric Beads-Based Screen-Printed Potentiometric Platforms Modified with Multi-Walled Carbon Nanotubes (MWCNTs) for Selective Recognition of Fluoxetine

Herein, we present a new validated potentiometric method for fluoxetine (FLX) drug monitoring. The method is based on the integration of molecular imprinting polymer (MIP) beads as sensory elements with modified screen-printed solid contact ion-selective electrodes (ISEs). A multi-walled carbon nanotube (MWCNT) was used as a nanomaterial for the ion-to-electron transduction process. The prepared MIP beads depend on the use of acrylamide (AAm) and ethylene glycol dimethacrylic acid (EGDMA) as a functional monomer and cross-linker, respectively. The sensor revealed a stable response with a Nernstian slope of 58.9 ± 0.2 mV/decade and a detection limit of 2.1 × 10⁻⁶ mol/L in 10 mmol/L acetate buffer of pH 4.5. The presented miniaturized sensors revealed good selectivity towards FLX over many organic and inorganic cations, as well as some additives encountered in the pharmaceutical preparations. Repeatability, reproducibility and stability have been studied to evaluate the analytical features of the presented sensors. These sensors were successfully applied for FLX assessment in different pharmaceutical formulations collected from the Egyptian local market. The obtained results agreed well with the acceptable recovery percentage and were better than those obtained by other previously reported routine methods.

Modified Screen-Printed Potentiometric Sensors based on Man-Tailored Biomimetics for Diquat Herbicide Determination

Screen-printed platforms integrated with molecularly imprinted polymers (MIP) were fabricated and characterized as potentiometric sensors for diquat (DQ). The synthesized MIP beads were studied as sensory carriers in plasticized poly(vinyl chloride) membranes. The sensors were constructed by using poly(3,4-ethylenedioxythiophene) (PEDOT) as solid-contact material to diminish charge-transfer resistance and water layer potential. Conventional ion-selective electrodes (ISEs) with internal filling solution were used for comparison. The designed electrodes showed near Nernstian slopes of 28.2 ± 0.7 (r² = 0.999) over the concentration range of 1.0 × 10-6-1.0 × 10-2 M with the limit of detection 0.026 µg/mL over the pH range 4.2-9.0. The electrode exhibited good selectivity for diquat cations over a large number of organic and inorganic cations. The sensor was successfully introduced for direct measurement of diquat content in commercial pesticide preparations and different spiked potato samples. The results showed that the proposed electrode has a fast and stable response, good reproducibility, and applicability for direct assessment of diquat content. The proposed potentiometric method is simple and accurate in comparison with the reported HPLC methods. Besides, it is applicable to turbid and colored sample solutions.

Paper Strip and Ceramic Potentiometric Platforms Modified with Nano-Sized Polyaniline (PANi) for Static and Hydrodynamic Monitoring of Chromium in Industrial Samples

Screen-printed membrane sensors based on the use of paper and ceramic substrates are fabricated, characterized, and used for rapid batch and continuous monitoring of CrIII in the form of CrO42- in some industrial products and wastewater samples. Strips of paper and ceramic platforms (15 × 5 mm) were covered with conductive carbon paint and then modified with polyaniline (PANI) film, to act as an ion-to-electron transducer, followed by a drop casting of plasticized poly (vinyl chloride) (PVC) Rhodamine-B chromate membrane as a recognition sensing material. In a 5.0 mmol L-1 Trizma buffer solution of pH ~8, the fabricated paper and ceramic based membrane sensors exhibited a near Nernstian response for CrVI ion with slopes of -29.7 ± 0.5 and -28.6 ± 0.3 mV decade-1, limit of detection 2.5 × 10-5 and 2.4 × 10-6 mol L-1 (1.3-0.12 µg mL-1), and linear concentration range 7.5 × 10-3-5.0 × 10-5 and 7.5 × 10-3-1.0 × 10-5 mol L-1 (390-0.5 µg mL-1), respectively. Both sensors exhibited fast and stable potentiometric response, excellent reproducibility, and good selectivity with respect to a number of common foreign inorganic species. Impedance spectroscopy and chronopotentiometry data revealed a small resistance and a larger double layer capacitance due to the presence of the intermediate polyaniline (PAN) conductive layer. Furthermore, the formation of a water layer between the ion selective membrane (ISM) and the underlying conductor polymer and between the conducting polymer and the carbon conducting surface was greatly reduced. The developed disposable solid-contact potentiometric sensors offer the advantages of simple design, long term potential stability, flexibility, miniaturization ability, short conditioning time, and cost effectiveness that enable mass production. The sensors were successfully used for static and hydrodynamic measurements of total chromium in some leather tanning wastewater and nickel-chrome alloy samples. The results compare favorably with data obtained by atomic absorption spectrometry.

Novel Solid-State Potentiometric Sensors Using Polyaniline (PANI) as A Solid-Contact Transducer for Flucarbazone Herbicide Assessment

Novel potentiometric solid-contact ion-selective electrodes (SC/ISEs) based on molecularly imprinted polymers (MIPs) as sensory carriers (MIP/PANI/ISE) were prepared and characterized as potentiometric sensors for flucarbazone herbicide anion. However, aliquat S 336 was also studied as a charged carrier in the fabrication of Aliquat/PANI/ISEs for flucarbazone monitoring. The polyaniline (PANI) film was inserted between the ion-sensing membrane (ISM) and the electronic conductor glassy carbon substrate (GC). The sensors showed a noticeable response towards flucarbazone anions with slopes of −45.5 ± 1.3 (r² = 0.9998) and −56.3 ± 1.5 (r² = 0.9977) mV/decade over the range of 10⁻²–10⁻⁵, 10⁻²–10⁻⁴ M and detection limits of 5.8 × 10⁻⁶ and 8.5 × 10⁻⁶ M for MIP/PANI/ISE and Aliguat/PANI/ISE, respectively. The selectivity and long-term potential stability of all presented ISEs were investigated. The short-term potential and electrode capacitances were studied and evaluated using chronopotentiometry and electrochemical impedance spectrometry (EIS). The proposed ISEs were introduced for the direct measurement of flucarbazone herbicide in different soil samples sprayed with flucarbazone herbicide. The results agree well with the results obtained using the standard liquid chromatographic method (HPLC).

Potentiometric PVC-Membrane-Based Sensor for Dimethylamine Assessment Using A Molecularly Imprinted Polymer as A Sensory Recognition Element

A new simple potentiometric sensor is developed and presented for sensitive and selective monitoring of dimethylamine (DMA). The sensor incorporates a molecularly imprinted polymer, with a pre-defined specific cavity suitable to accommodate DMA. The molecularly imprinted polymer (MIP) particles were dispersed in an aplasticized poly(vinyl chloride) matrix. The MIP is synthesized by using a template molecule (DMA), a functional monomer (acrylamide, AM), cross-linker (ethylene glycol dimethacrylate, EGDMA) and initiating reagent (benzoylperoxide, BPO). Using Trizma buffer solution (5 mmol L^-1, pH 7.1), the sensor exhibits a rapid, stable and linear response for 1.0 × 10^-5 to 1.0 × 10^-2 mol L^-1 DMA⁺ with a calibration slope of 51.3 ± 0.3 mV decade^-1, and a detection limit of 4.6 × 10^-6 mol L^-1 (0.37 µg mL^-1). The electrode exhibited a short response time (10 s) and stable potential readings (± 0.5 mV) for more than 2 months. Potentiometric selectivity measurements of the sensor reveal negligible interferences from most common aliphatic and aromatic amines. High concentration levels (100-fold excess) of many inorganic cations do not interfere. The sensor is successfully used for quantification of low levels of DMA down to 0.5 µg mL^-1. Verification of the presented method was carried out after measuring the detection limit, working linearity range, ruggedness of the method, accuracy, precision, repeatability and reproducibility. Under flow-through conditions, the proposed sensor in its tubular form is prepared and introduced in a two-channel flow injection setup for hydrodynamic determination of DMA. The sampling rate is 50-55 samples h^-1. The sensor is used to determine DMA in different soil samples with an accuracy range of 97.0-102.8%.

Novel Aminoacridine Sensors Based on Molecularly Imprinted Hybrid Polymeric Membranes for Static and Hydrodynamic Drug Quality Control Monitoring

Novel biomimetic potentiometric ion-selective electrodes (ISEs) were fabricated and designed for the assessment of aminoacridine (ACR) based on newly synthesized imprinted polymer (MIP) membranes. Thermal polymerization of methacrylic acid (MAA) or acrylamide (AM) as function monomer, aminoacridine as a template and ethylene glycol dimethacrylate (EGDMA) as across-linker, were utilizedto give the molecular recognition part. The membranes of sensors I andII consist of MIP based MAA and AM, respectively, dispersed in a poly(vinyl chloride) membrane plasticized with dioctyl phthalate (DOP) in the ratio of 3.0 wt%, 32.2 wt% and 64.8 wt%, respectively. Sensors III and IV were similarly prepared with added 1.0 wt% tetraphenyl borate (TPB⁻) as an anionic discriminator. Sensors I and II exhibited near-Nernstian potential response to ACR⁺ with slopes of 51.2 ± 1.3 and 50.5 ± 1.4 mV/decade in a 0.01 M phosphate buffer of pH 6.0. The linear response coversthe concentration range of 5.2 × 10⁻⁶ to 1.0 × 10⁻³ M with a detection limit of 0.05 and 0.17 μg/mL for sensors I and II, respectively. The performance characteristics of these sensors were evaluated under static and hydrodynamic mode of operations. They were used for quality control assessment of aminoacridine in some pharmaceutical preparations and biological samples.

Tailor-Made Specific Recognition of Cyromazine Pesticide Integrated in a Potentiometric Strip Cell for Environmental and Food Analysis

Screen-printed ion-selective electrodes were designed and characterized for the assessment of cyromazine (CYR) pesticide. A novel approach is to design tailor-made specific recognition sites in polymeric membranes using molecularly imprinted polymers for cyromazine (CR) determination (sensor I). Another sensor (sensor II) is the plasticized PVC membrane incorporating cyromazine/tetraphenyl borate ion association complex. The charge-transfer resistance and water layer reached its minimal by incorporating Polyaniline (PANI) solid-contact ISE. The designed electrodes demonstrated Nernstain response over a linear range 1.0 × 10-2-5.2 × 10-6 and 1.0 × 10-2-5.7 × 10-5 M with a detection limit 2.2 × 10-6 and 8.1 × 10-6 M for sensors I and II, respectively. The obtained slopes were 28.1 ± 2.1 (r2 = 0.9999) and 36.4 ± 1.6 (r2 = 0.9991) mV/decade, respectively. The results showed that the proposed electrodes have a fast and stable response, good reproducibility, and applicability for direct measurement of CYR content in commercial pesticide preparations and soil samples sprayed with CYR pesticide. The results obtained from the proposed method are fairly in accordance with those using the standard official method.

Single-Piece All-Solid-State Potential Ion-Selective Electrodes Integrated with Molecularly Imprinted Polymers (MIPs) for Neutral 2,4-Dichlorophenol Assessment

A novel single-piece all-solid-state ion-selective electrode (SC/ISE) based on carbon-screen printed is introduced. Polyaniline (PANI) is dissolved in a membrane cocktail that contains the same components used for making a conventional ion-selective polyvinyl chloride (PVC) matrix membrane. The membrane, having the PANI, is directly drop-casted on a carbon substrate (screen-printed-carbon electrode). PANI was added to act as an intermediary between the substrate and the membrane for the charge transfer process. Under non-equilibrium sensing mechanism, the sensors revealed high sensitivity towards 2,4-dichlorophenol (DCP) over the linearity range 0.47 to 13 µM and a detection limit 0.13 µm. The selectivity was measured by the modified separate solution method (MSSM) and showed good selectivity towards 2,4-DCP over the most commonly studied ions. All measurements were done in 30 mm Tris buffer solution at a pH 5.0. Using constant-current chronopotentiometry, the potential drift for the proposed electrodes was checked. Improvement in the potential stability of the SPE was observed after the addition of PANI in the sensing membrane as compared to the corresponding coated-wire electrode (membrane without PANI). The applicability of the sensor has been checked by measuring 2,4-DCP in different water samples and the results were compared with the standard HPLC method.

Improved Solid-Contact Nitrate Ion Selective Electrodes Based on Multi-Walled Carbon Nanotubes (MWCNTs) as an Ion-to-Electron Transducer

Possible improvement of the performance characteristics, reliability and selectivity of solid-contact nitrate ion-selective electrodes (ISE) (SC/NO3--ISE) is attained by the application of a nitron-nitrate (Nit+/NO3-) ion association complex and inserting multi-walled carbon nanotubes (MWCNTs) as an ion-to-electron transducer between the ion sensing membrane (ISM) and the electronic conductor glassy carbon (GC) substrate. The potentiometric performance of the proposed electrode revealed a Nernstian slope -55.1 ± 2.1 (r² = 0.997) mV/decade in the range from 8.0 × 10-8-1 × 10-2 M with a detection limit of 2.8 × 10-8 (1.7 ng/mL). Selectivity, repeatability and reproducibility of the proposed sensors were considerably improved as compared to the coated disc electrode (GC/NO3--ISE) without insertion of a MWCNT layer. Short-term potential stability and capacitance of the proposed sensors were tested using a current-reversal chronopotentiometric technique. The potential drift in presence of a MWCNT layer decreased from 167 μVs-1 (i.e., in absence of MWCNTs) to 16.6 μVs-1. In addition, the capacitance was enhanced from 5.99 μF (in absence of MWCNTs) to 60.3 μF (in the presence of MWCNTs). The presented electrodes were successfully applied for nitrate determination in real samples with good accuracy.

Gold Plate Electrodes Functionalized by Multiwall Carbon Nanotube Film for Potentiometric Thallium(I) Detection

Solid-contact potentiometric ion-selective electrodes (SC-ISEs) for thallium determination have been designed using multiwall carbon nanotubes (MWCNTs) as the ion-to-electron transducer. Dispersed MWCNTs were drop-casted over a gold plate electrode. Two different crown ethers were used in the sensing membrane for the recognition of thallium (I). Sensorsbased on dibenzo-18-crown-6 (DB18C6) as a neutral carrier and NaTPB as an anionic additive exhibited a near Nernstian response of 57.3 mV/decade towards Tl+ ions over the activity range 4.5 × 10-6-7.0 × 10-4 M, with a limit of detection of 3.2 × 10-7 M. The time required to achieve 95% of the steadyequilibrium potential was <10 s. The complex formation constant (log βML) between dibenzo-18-crown-6 and thallium (I) (i.e., 5.99) was measured using the sandwich membrane technique. The potential response was pH independent over the range 3.0-9.5. The introduction of MWCNTs as an electron-ion-transducer layer between gold plate and the sensing membrane lead to a smaller membrane resistance and a large double layer capacitance, which was proven using impedance spectra and chronopotentiometry (i.e., 114.9 ± 12 kΩ, 52.1 ± 3.3 pF, 200 ± 13.2 kΩ, and 50 ± 4.2 µF). Additionally, reduction ofthe water layer between the sensing membrane and the underlying conductor wastested. Thus, it is clear that MWCNTs can be used as a transducing layer in SC-ISEs. The proposed sensor was introduced as an indicator electrode for potentiometric titration of single and ternary mixtures of I-, Br-, and S2- anions.

Non-Equilibrium Potential Responses towards Neutral Orcinol Using All-Solid-State Potentiometric Sensors Integrated with Molecularly Imprinted Polymers

Molecularly imprinted polymer (MIP) receptors have been synthesized, characterized, and applied as new selective receptors in solid-contact ion selective electrodes (ISEs) towards non-dissociated 3,5-dihydroxytoluene (orcinol). Two monomers, namely methacrylic acid (MAA) and acrylamide (AA), were used in the preparation of MIP receptors. Graphene (Gr) was used as the solid contact material between the sensing membrane and the electrical contact substrate. Based on non-equilibrium sensing mechanism, the proposed sensors reveal observably enhanced detection sensitivity towards orcinol with detection limits 1.7 × 10⁻⁵ and 3.3 × 10⁻⁶ M for sensors based on MIP/MAA and MIP/AA, respectively. The selectivity coefficients measured by the modified separate solution method (MSSM) for the proposed sensors showed good selectivity towards orcinol over most common other phenols and inorganic anions. All measurements were made in the presence of 30 mM phosphate buffer solution (PBS) with a pH of 7.0. Potential stability for the proposed sensors was tested by constant-current chronopotentiometry. No water films were formed between the sensing membrane and the electron conductor substrate. The applicability of MIP/MAA incorporated ISE has been checked by recovery test of orcinol in the presence of soil matrix and by standard addition method.

Single-Piece Solid Contact Cu2+-Selective Electrodes Based on a Synthesized Macrocyclic Calix[4]arene Derivative as a Neutral Carrier Ionophore

Herein, a facile route leading to good single-walled carbon nanotubes (SWCNT) dispersion or poly (3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS) based single-piece nanocomposite membrane is proposed for trace determination of Cu²⁺ ions. The single-piece solid contact Cu²⁺-selective electrodes were prepared after drop casting the membrane mixture on the glassy-carbon substrates. The prepared potentiometric sensors revealed a Nernstian response slope of 27.8 ± 0.3 and 28.1 ± 0.4 mV/decade over the linearity range 1.0 × 10^-3 to 2.0 × 10^-9 and 1.0 × 10^-3 to 1.0 × 10^-9 M with detection limits of 5.4 × 10^-10 and 5.0 × 10^-10 M for sensors based on SWCNTs and PEDOT/PSS, respectively. Excellent long-term potential stability and high hydrophobicity of the nanocomposite membrane are recorded for the prepared sensors due to the inherent high capacitance of SWCNT used as a solid contact material. The sensors exhibited high selectivity for Cu²⁺ ions at pH 4.5 over other common ions. The sensors were applied for Cu²⁺ assessment in tap water and different tea samples. The proposed sensors were robust, reliable and considered as appealing sensors for copper (II) detection in different complex matrices.

All Solid-State Poly (Vinyl Chloride) Membrane Potentiometric Sensor Integrated with Nano-Beads Imprinted Polymers for Sensitive and Rapid Detection of Bispyribac Herbicide as Organic Pollutant

All-solid-state potentiometric sensors were prepared by using polyaniline (PANI) as the solid contact material. A film of PANI (thickness approximately being 0.25 µm) was deposited on a solid substrate (carbon screen printed platform). The PANI layer was subsequently coated with an ion-selective membrane (ISM) containing uniform-sized molecularly imprinted nanoparticles to produce a solid-contact ion-selective electrode (SC/ISE) for bispyribac herbicide (sensor I). In addition, aliquat 336 was also used as an ion exchanger in plasticized PVC membrane (sensor II). The proposed sensors revealed a remarkably improved sensitivity towards bispyribac ions with anionic slopes of −47.8 ± 1.1 (r² = 0.9995) and −44.4 ± 1.4 (r² = 0.9997) mV/decade over a linear range 1.0 × 10⁻²–8.6 × 10⁻⁶ M, 1.0 × 10⁻²–9.0 × 10⁻⁶ M and detection limits of 1.33 and 1.81 µg/mL for sensors I and II, respectively.Selectivity of both sensors is significantly high for different common pesticides and inorganic anions. The potential stability of the SC/ISEs was studied using chronopotentiometry. Electrochemical impedance spectrometry was used to understand the charge-transfer mechanisms of the different types of ion-selective electrodes studied. The impedance response of the electrodes was modelled by using equivalent electrical circuits. The sensors were used for a direct measurement of the bispyribac content in commercial herbicide formulations and soil samples collected from agricultural lands planted with rice and sprayed with bispyribac herbicide. The results agree fairly well with data obtained using HPLC method.