Potentiometric evaluation of calix[4]arene anion receptors in membrane electrodes: Phosphate detection

Pyrazine Functionalization in Eu-MOF for Exclusive Ratiometric Luminescence Sensing of PO43

Single-emission luminescence sensors are less than satisfactory for complex systems due to their susceptibility to environmental disturbances. Lanthanum-based metal-organic frameworks (Ln-MOFs) with highly stable ratiometric dual-emission are regarded as promising luminescence probes owing to their fascinating ligand-to-metal energy transfer behaviors (also known as the antenna effect). Herein, we report the synthesis of a pair of isostructural europium-based MOFs (termed JNU-219 and JNU-220) by utilizing two X-shaped tetracarboxylate linkers, 4,4',4″,4‴-benzene-2,3,5,6-tetrayl-tetrabenzoate (BTEB) and 4,4',4″,4‴-pyrazine-2,3,5,6-tetrayl-tetrabenzoate (BTTB). Both JNU-219 and JNU-220 present the characteristic red luminescence of Eu3+, yet the pyrazine functionalization of the BTTB linker renders JNU-220 with significantly increased luminescence emission, almost 30 times that of JNU-219. As a result, the detection limit of JNU-220 for the ratiometric luminescence sensing of PO43- was determined to be as low as 0.22 μM, which is far superior to those of other reported MOF materials. Additionally, we demonstrate the excellent stability and reusability of JNU-220, further verifying its potential as a robust ratiometric luminescence probe.

Ion-Selective Electrode Based on a Novel Biomimetic Nicotinamide Compound for Phosphate Ion Sensor

Phosphorus is not only an import nutrient to aquatic habitats, but it also acts as a growth inhibitor in aquatic ecosystems; however, it also aggravates environmental issues, such as eutrophication. There is a growing interest in rapid phosphorus detection to manage and protect water resources. Due to the large molecular structure and high hydration energy of phosphate ions, ion-selective electrodes (ISEs) remain in their infancy for real-time measurements in terms of practical application. In this study, a newly developed ionophore based on a biomimetic nicotinamide functional group was used to detect phosphate selectively, displaying efficient binding through charge interactions and hydrogen bonds. The ISE membrane containing silicone rubber demonstrated an effective detection performance over a long period of time. With a dynamic range between 10-6 and 10-2 M and a limit of detection of 0.85 × 10-6 M (26 μg/L), the newly synthesized ISE membranes demonstrated selectivity for phosphate ions over other ions, including acetate, sulfate, and chloride.

Electrochemical Devices to Monitor Ionic Analytes for Healthcare and Industrial Applications

Recent advances in electrochemical devices have sparked exciting opportunities in the healthcare, environment, and food industries. These devices can be fabricated at low costs and are capable of multiplex monitoring. This overcomes challenges presnted in traditional sensors for biomolecules and provides us a unique gateway toward comprehensive analyses. The advantages of electrochemical sensors are derived from their direct integration with electronics and their high selectivity along with sensitivity to sense a wide range of ionic analytes at an economical cost. This review paper aims to summarize recent innovations of a wide variety of electrochemical sensors for ionic analytes for health care and industrial applications. Many of these ionic analytes are important biomarkers to target for new diagnostic tools for medicine, food quality monitoring, and pollution detection. In this paper, we will examine various fabrication techniques, sensing mechanisms, and will also discuss various future opportunities in this research direction.

A Cobalt-Nickel Metal-Alloy Thin-Film Sensor for Hydrogen-Phosphate Ion

Cobalt-nickel alloy thin-films were prepared by electrodepositing on Au-coated Al₂O₃ substrate from aqueous solutions of metal-salts, and applied as a potentiometric hydrogen-phosphate ion sensor. A doping of 20 mol% nickel in cobalt contributed to enhancing hydrogen-phosphate ion sensing performances, i.e., the sensing range and response time were drastically improved. The Co₈₀Ni₂₀ thin-film electrode showed good potentiometric response to hydrogen-phosphate ion between 1.0 × 10^-5 and 1.0 × 10^-3 M with a slope of -59 mV/decade and high anion selectivity. The 90% response time to 1 mM H₂PO₄^- was as short as 15 s at pH 5.0, 30°C. A mixed potential sensing mechanism could be proposed on the basis of the results.

t-Butyl calixarene/Fe2O3@MWCNTs composite-based potentiometric sensor for determination of ivabradine hydrochloride in pharmaceutical formulations

Ivabradine hydrochloride (IVB) has shown high medical importance as it is a medication for lowering the heart rate for the symptomatic chronic heart failure and symptomatic management of stable angina pectoralis. The high dose of IVB may cause severe and prolonged bradycardia, uncontrolled blood pressure, headache, and blurred vision. In this study, a highly sensitive carbon-paste electrode (CPEs) was constructed for the potentiometric determination of IVB in pharmaceutical formulations. t-Butyl calixarene (t-BCX) was used as an ionophore due to its ability to mask IVB in the cavity via multiple H-bonding at the lower rim, as estimated quantitatively by the sandwich membrane method (Log β_ILn = 8.62). Besides, the use of multi-walled carbon nanotubes decorated with Fe₂O₃ nanoparticles (Fe₂O₃@MWCNTs) as an additive for the paste electrode significantly improved the detection limit of the sensor up to 36 nM, with Nernstian response of 58.9 mV decade^-1 in the IVB linear dynamic range of 10^-3-10^-7 M in aqueous solutions. The constructed sensors showed high selectivity against interfering species that may exist in physiological fluids or pharmaceutical formulations (e.g. Na⁺, K⁺, NH₄⁺, Ca²⁺, Mg²⁺, Ba²⁺, Fe³⁺, Co²⁺, Cr³⁺, Sr²⁺, glucose, lactose, maltose, glycine, dopamine, and ascorbic acid). The sensors were successfully employed for IVB determination in the pharmaceutical formulations (Savapran®).

Using the interfacial barrier effects of p-n junction on electrochemistry for detection of phosphate

A novel type of electrochemical sensor for detection of phosphate in water environment was developed by combining the interfacial barrier of p-n junction with the adsorption of phosphate. The electrochemical response was produced by the induced change of the barrier height, which was only caused by the specific adsorption of phosphate. Two linear concentration ranges (0-0.045 mg L^-1 and 0.045-0.090 mg L^-1) with two sensitivities (4.98 μA (μg L^-1)^-1 and 1.28 μA (μg L^-1)^-1) were found. The good performance made the sensor meet the requirements of the World Health Organization for drinking water (1 mg L^-1 of phosphate). It is an approach to develop electrochemical sensors by employing the interfacial barrier effects on electrochemistry.

An incisive optical recognition of monohydrogen phosphate by a fluorescein-based chemodosimeter

We herein devised an incisive chromofluorogenic chemodosimeter (FLH) for detecting HPO₄²⁻ over other phosphates, viz. H₂PO₄⁻, PO₄³⁻, and PPi.

Indigo Carmine-Cu complex probe exhibiting dual colorimetric/fluorimetric sensing for selective determination of mono hydrogen phosphate ion and its logic behavior

A new selective probe based on copper complex of Indigo Carmine (IC-Cu₂) for colorimetric, naked-eye, and fluorimetric recognition of mono hydrogen phosphate (MHP) ion in H₂O/DMSO (4:1v/v, 1.0mmolL^-1 HEPES buffer solution pH7.5) was developed. Detection limit of HPO₄^2- determination, achieved by fluorimetric and ₃lorimetric method, are 0.071 and 1.46μmolL^-1, respectively. Potential, therefore is clearly available in IC-Cu₂ complex to detect HPO₄^2- in micromolar range via dual visible color change and fluorescence response. Present method shows high selectivity toward HPO₄^2- over other phosphate species and other anions and was successfully utilized for analysis of P₂O₅ content of a fertilizer sample. The results obtained by proposed chemosensor presented good agreement with those obtained the colorimetric reference method. INHIBIT and IMPLICATION logic gates operating at molecular level have been achieved using Cu²⁺and HPO₄^2- as chemical inputs and UV-Vis absorbance signal as output.

Triphosphate Ion-Selective Electrode Based on Zr-Porphyrin Complex

Ion-selective electrode using zirconium(IV) complex with octaethylporphin (H₂oep) as a carrier showed high selectivity to triphosphate (TP, H₅tp) against other hydrophilic anions including diphosphate and phosphate. The electroactive species was identified to be [(Zr₄(oep)₄(Htp)₂] (TP/Zr ratio of 0.5) of the unique structure; triphosphates are recognized by one Zr atom through three O atoms on three different P atoms and by another Zr atom through two O atoms on two terminal P atoms and are also involved in complementary intermolecular hydrogen bonding to be surrounded by four porphyrin complexes. In contrast, Zr(IV) in the other complex with tetraphenylporphin has the higher Lewis acidity, due to the electron-withdrawing property of phenyl rings and, at the higher TP concentration, forms a species having a TP/Zr ratio of unity, which precipitates to lose the electroactivity. The electrode was successfully applied to monitor hydrolysis of TP that provides diphosphate and phosphate.

Solution and structural binding studies of phosphate with thiophene-based azamacrocycles

Two thiophene-based monocyclic receptors L1 and L2 have been studied for phosphate binding in solutions (D2O and DMSO-d6 ) by 1H NMR and 31P NMR titrations, and in the solid state by single crystal X-ray analysis. Results from 1H NMR titrations suggest that the ligands bind phosphate anions in a 1:2 binding mode in DMSO-d6 , with the binding constants of 5.25 and 4.20 (in log K), respectively. The binding of phosphate to L1 and L2 was further supported by 31P NMR in D2O at pH = 5.2. The crystal structure of the phosphate complex of L1 reveals unambiguous proof for the formation of a ditopic complex via multiple hydrogen bonds from NH···O and CH···O interactions.

Reverse osmosis integrity monitoring in water reuse: The challenge to verify virus removal - A review

A reverse osmosis (RO) process is often included in the treatment train to produce high quality reuse water from treated effluent for potable purposes because of its high removal efficiency for salinity and many inorganic and organic contaminants, and importantly, it also provides an excellent barrier for pathogens. In order to ensure the continued protection of public health from pathogen contamination, monitoring RO process integrity is necessary. Due to their small sizes, viruses are the most difficult class of pathogens to be removed in physical separation processes and therefore often considered the most challenging pathogen to monitor. To-date, there is a gap between the current log credit assigned to this process (determined by integrity testing approved by regulators) and its actual log removal capability as proven in a variety of laboratory and pilot studies. Hence, there is a challenge to establish a methodology that more closely links to the theoretical performance. In this review, after introducing the notion of risk management in water reuse, we provide an overview of existing and potentially new RO integrity monitoring techniques, highlight their strengths and drawbacks, and debate their applicability to full-scale treatment plants, which open to future research opportunities.

Electroanalytical Opportunities Derived from Ion Transfer at Interfaces between Immiscible Electrolyte Solutions

This review presents an introduction to electrochemistry at interfaces between immiscible electrolyte solutions and surveys recent studies of this form of electrochemistry in electroanalytical strategies. Simple ion and facilitated ion transfers across interfaces varying from millimetre scale to nanometre scales are considered. Target detection strategies for a range of ions, inorganic, organic, and biological, including macromolecules, are discussed.

Amperometric Ion Sensing Approaches at Liquid/Liquid Interfaces for Inorganic, Organic and Biological Ions

Electrochemistry at the interface between two immiscible electrolyte solutions (ITIES) has become an invaluable tool for the selective and sensitive detection of cationic and anionic species, including charged drug molecules and proteins. In addition, neutral molecules can also be detected at the ITIES via enzymatic reactions. This chapter highlights recent developments towards creating a wide spectrum of sensing platforms involving ion transfer across the ITIES. As well as outlining the basic principles needed for performing these sensing applications, the development of ITIES-based detection strategies for inorganic, organic, and biological ions is discussed.

Electrochemical study of ivabradine hydrochloride ion selective electrodes using different ionophores

Development of novel sensors for the determination of ivabradine hydrochloride using sulphonated calix-8-arene and cyclodextrin derivatives as neutral ionophores.

Separation of amino acids by high performance liquid chromatography based on calixarene-bonded stationary phases

In this work, we present a new method for synthesis of silica gel stationary phases based on calix[4]arene derivatives. In order to achieve it, 25,27-dipropoxy-26,28-bis-[3-propyloxydimethylsililoxy]calix[4]arene has been synthesized in six steps and immobilized on silica via chlorotrimethylsilane. Stationary phases were characterized by elemental analysis, infrared spectroscopy and thermal analysis and used for the separation of amino acid derivatives by high performance liquid chromatography. The effect of isocratic and gradient elution, pH and column temperature on retention and selectivity of the Fmoc-protected amino acids were studied. The retention mechanism was also discussed. The results indicated that the stationary phase behaves like a reverse phase packing. Size exclusion, electron-π, π-π and hydrophobic interactions seem to be involved in the separation process.

An excellent copper selective chemosensor based on calix[4]arene framework

The article depicts a detailed study regarding copper selective chemosensing and complexation nature of 5,11,17,23-tetrakis[(N,N-diphenylamino)methyl]-25,26,27,28-tetrahydroxycalix[4]arene (PAC4). Its photophysical characteristics in various solvents of different polarities along with the influence of acid and base on its spectral properties in these solvents are also discussed. The complexation affinity of PAC4 with regard to its latent applications as Cu(II) selective colorimetric and fluorescent sensor among the selected series of various cations such as Li(I), Na(I), K(I), Rb(I), Ba(II), Sr(II), Al(III), Fe(III), Cd(II), Co(II), Hg(II), Mn(II), Ni(II), Pb(II) and Zn(II) was examined by UV-visible and fluorescence emission spectroscopy in dichloromethane:acetonitrile (DCM:MeCN) solvent system. In addition, the process of complexation has been investigated through Job's plot and it has been observed that the complex between PAC4 and Cu(II) is formed in 1:1 stoichiometric ratio. The complex formation between PAC4 and Cu(II) has also been confirmed by FT-IR spectroscopy and thermal gravimetric analysis (TGA).

Corrole-based ion-selective electrodes

Different corrole derivatives have been exploited as ionophores for the development of ion-selective electrodes (ISEs). The compounds used are free-base 5,10,15-triphenylcorrole, the corresponding Mn and Fe chloride complexes, the Cu complex of 5,10,15-tris(4-tert-butylphenyl)-corrole and the Fe chloride complex of 2,3,17,18-tetraethyl,7,8,12,13-tetramethylcorrole. Corroles have been dispersed in the polyvinyl chloride polymeric matrix and different plasticizers have been used for the preparation of selective membranes. The developed ISEs have been tested for the detection of model analytes and the working mechanism has been investigated in detail. In the case of free-base corrole, the results showed that it is difficult to obtain high selective ISEs, due to the macrocycle high sensitivity to the background solution pH. On the other hand, Mn derivative are shown to be highly selective for chloride ion detection, with performances superior to the corresponding Mn porphyrin-based ISEs. Finally both Cu and Fe derivatives are very promising ionophores for the detection of hydrophilic anions, such as carbonate and monohydrogen phosphate ion.

Electrochemical Determination of Inorganic Phosphate

An electrochemical phosphate sensor based on the precipitation of molybdophosphate on electrode surface was developed for the determination of inorganic phosphate. The condition for the formation of the molybdophosphate was studied and cyclic voltammetry and differential pulse voltammetry were utilized for the determination. A detection limit of 10 ppm was obtained and the sensor response was approximate liner in the range between 10-100 ppm.