A novel potentiometric hydrogen peroxide sensor based on pKa changes of vinylphenylboronic acid membranes

A potentiometric hydrogen peroxide (H₂O₂) sensing scheme was developed using arylboronic acid as the electrode modifier. It is well-known that both aliphatic and aryl boronic acid undergo electrophilic displacement reaction with H₂O₂. This reaction involves replacement of boronic acid by the hydroxyl group of peroxide resulting in a change in pK_a value that can be exploited for sensing of H₂O₂. Vinylphenylboronic acid (VPBA) ink was prepared using Nafion as the binder and it was drop cast on an electrode surface. Morphology of the modified electrode was analysed using scanning electron microscopy (SEM). The present modifier exhibited a linear relationship between the difference in electrode potential (?Ep) vs. [H₂O₂] with a Nernstian slope of 26 ± 2 mV in the concentration range of 10^? 1–10^? 5 M. Application of the VPBA modified electrode for hydrogen peroxide sensing was studied in an industrial dye-bleach effluent.     

Highly selective fluorometric determination of polyamines based on intramolecular excimer-forming derivatization with a pyrene-labeling reagent

We introduce a novel approach in highly selective and sensitive fluorescence derivatization of polyamines. This method is based on an intramolecular excimer-forming fluorescence derivatization with a pyrene reagent, 4-(1-pyrene)butyric acid N-hydroxysuccinimide ester (PSE), followed by reversed-phase high-performance liquid chromatography (HPLC). Polyamines, having two to four amino moieties in a molecule, were converted to the corresponding dipyrene- to tetrapyrene-labeled derivatives by reaction (100 degrees C, 20 min) with PSE. The derivatives afforded intramolecular excimer fluorescence (450-520 nm), which can clearly be discriminated from the monomer (normal) fluorescence (360-420 nm) emitted from PSE, its hydrolysate and monopyrene-labeled derivatives of monoamines. The structures of the derivatives were confirmed by HPLC with mass spectrometry, and the emission of excimer fluorescence could be proved by spectrofluorometry and time-resolved fluorometry. The PSE derivatives of four polyamines [putrescine (Put), cadaverine (Cad), spermidine (Spd), and spermine (Spm)] could be separated by reversed-phase HPLC on a C8 column with linear gradient elution. The detection limits (signal-to-noise ratio of 3) for the polyamines were 1 (Put), 1 (Cad), 5 (Spd), and 8 (Spm) fmol on the column. Furthermore, the present method was so selective that biogenic monoamines gave no peak in the chromatogram.     

New potentiometric sensor for the determination of iodine species

The characteristics, performance and application of novel triiodide potentiometric sensor based on ion-pair of Rhodamine B triiodide as a membrane carrier are described. The electrode has a linear dynamic range between 1 × 10^? 6 and 1 × 10^? 1 M, with a Nernstian slope of 68 ± 1 mV pC^? 1 and detection limit of 3.9 × 10^? 7 M. Fast and stable response, good reproducibility, long-term stability, very good selectivity over a large number of common organic and inorganic anions, applicability over a pH range of 2–10 are demonstrated. The proposed sensor has been applied for potentiometric determination of some iodine species.     

Highly sensitive and selective ethanol sensor based on micron-sized zinc oxide porous-shell hollow spheres

Zinc oxide (ZnO) porous-shell hollow spheres (PHS) were prepared by thermally oxidizing high-purity zinc powder in an oxygen-containing atmosphere, and its ethanol gas sensing properties were measured in the concentration range of 10–400 ppm. At the optimum operating temperature of 350 °C, a sensitivity of 0.25/ppm was obtained and the response–concentration curve was of high linearity. The response and recovery times were measured to be ～5–12 s and 8–13 s, respectively. The sensor was proved to be highly selective to ethanol. Our results indicate that ZnO PHS might be a promising material for fabricating practical ethanol sensors.     

Determination of zinc(II) ions in waste water samples by a novel zinc sensor based on a new synthesized Schiff's base

A highly selective and sensitive zinc ion-selective membrane electrode based on N,N′-phenylenebis (salicylideaminato) (L) as a new carrier is reported. The membrane is composed of poly (vinyl chloride) (PVC), o-nitrophenyl octyl ether (NPOE) as plasticizer, potassium tetrakis(p-chlorophenyl) borate (KTpClPB) as lipophilic ionic additive, and L as sensing material. The proposed electrode displays a Nernstian response to Zn²⁺ ions over a wide concentration range of 5.0 × 10^? 7–1.0 × 10^? 1 M with the slope of 29.4 ± 0.2 mV per decade and a detection limit of 2.6 × 10^? 7 M. The sensor has a relatively fast response time of < 10 s and it can be used in the pH range of 3.0–7.0 for at least 2 months without any significant divergency in potential. The selectivity coefficients for mono-, di-, and trivalent cations indicate the good selectivity of sensor for Zn²⁺ ions over a large number of interfering cations. As a result the proposed electrode was applied to Zn²⁺ ions determination in mixture solutions and wastewater samples.     

PVC membrane potentiometric sensor based on 5-pyridino-2,8-dithia[9](2,9)-1,10-phenanthroline-phane for selective determination of neodymium(III)

Spectrofluorometric studies on the binding properties of 5-pyridino-2,8-dithia[9](2,9)-1,10-phenanthrolinephane (L) toward La3+, Sm3+, Gd3+, Yb3+, and Nd3+ in methanol solution revealed the occurrence of both 1:1 and 2:1 (ligand/metal) complexation with a stability order of Nd3+ > Yb3+ > Gd3+ > Sm3+ > La3+. Consequently, L was used as a suitable neutral ionophore for the preparation of a novel polymeric membrane-selective electrode for Nd3+ ion. The electrode exhibited a Nernstian response over a wide concentration range (1.0 x 10(-6)-1.0 x 10(-2) M) with a low limit of detection of 7.9 x 10(-7) M. The electrode possesses a fast response time of <5 s and can be used for at least 9 weeks without observing any considerable deviation. The proposed electrode revealed a very good selectivity for Nd3+ over a wide variety of alkali, alkaline earth, transition, and heavy metal ions, including members of the lanthanide family other than Nd3+. The potentiometric response of the electrode is independent of the pH of test solution in the pH range 4.0-6.5. The proposed electrode was successfully applied to the recovery of Nd3+ ion from tap water samples and, also, as an indicator electrode, in potentiometric titration of neodymium(III) ions.     

Amperometric sensor based on a graphene/copper hexacyanoferrate nano-composite for highly sensitive electrocatalytic determination of captopril

In this work, a bi-layer modified glassy carbon electrode (GCE) was prepared by depositing appropriate amounts of multilayered graphene (GR) on the surface of GCE, followed by electrodepositing copper hexacyanoferrate (CuHCF) nano-particles on the graphene layer. The combination of graphene and CuHCF considerably improved the current response of the GCE towards the oxidation of captopril. Studies showed that the best response of the modified electrode could be achieved within neutral pHs. At a fixed potential under hydrodynamic conditions (stirred solutions), the oxidation current is proportional to the captopril concentration and the calibration plots were linear over the concentration ranges of 0.2 to 5.8 μM and 5.8 to 480 μM. The detection limit of the method was 0.09 μM. The modified electrode was used for electrocatalytic determination of captopril in some real samples.     

Highly selective and sensitive voltammetric sensor based on modified multiwall carbon nanotube paste electrode for simultaneous determination of ascorbic acid,acetaminophen and tryptophan

A carbon-paste electrode modified with multiwall carbon nanotubes (MWCNTs) was used for the sensitive and selective voltammetric determination of ascorbic acid (AA) in the presence of 3,4-dihydroxycinnamic acid (3,4-DHCA) as mediator. The mediated oxidation of AA at the modified electrode was investigated by cyclic voltammetry (CV), chronoamperommetry and electrochemical impedance spectroscopy (EIS). Also, the values of catalytic rate constant (k), and diffusion coefficient (D) for AA were calculated. Using square wave voltammetry (SWV), a highly selective and simultaneous determination of AA, acetaminophen (AC) and tryptophan (Trp) has been explored at the modified electrode. The modified electrode displayed strong function for resolving the overlapping voltammetric responses of AA, AC and Trp into three well-defined voltammetric peaks. In the mixture containing AA, AC and Trp, the three compounds can well separate from each other with potential differences of 200, 330 and 530 mV between AA and AC, AC and Trp and AA and Trp, respectively, which was large enough to determine AA, AC and Trp individually and simultaneously.     

Highly selective and sensitive magnetic silica nanoparticles based fluorescent sensor for detection of Zn ions

In this work, quinoline group modified multifunctional silica nanoparticles having high magnetization and excellent Zn²⁺ selectivity have been successfully prepared. These multifunctional nanoparticles were characterized by high resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy (FT-IR), thermal gravimetric analysis (TGA), X-ray powder diffraction (XRD) and vibrating sample magnetometer (VSM). The characterization data indicated that the organic ligand was successfully grafted on the surface of the magnetic silica nanoparticles. The fluorescent properties of the nanosensor were characterized and employed to detect Zn²⁺ with excellent selectivity and sensitivity (0.1 μM) toward Zn²⁺ over other cations even in trace amount.     

High-sensitivity humidity sensor based on SnO2 nanoparticles synthesized by microwave irradiation method

Tin oxide hexagonal-shaped nanodiscs (SnO) and spherical nanoparticles (SnO₂) have been prepared by using a simple household microwave irradiation method with an operating frequency of 2.45 GHz. This technique permits us to produce gram quantity of homogeneous nanoparticles in just 10 min. The crystallite size was evaluated from powder X-ray diffraction (XRD) studies and was in the 20 to 25 nm range. Transmission electron microscopy (TEM) analysis showed that the as prepared SnO form as hexagonal-shaped nanodiscs and upon subsequent annealing at 500 °C for 5 h in air, the SnO gets converted to spherical-shaped nanoparticles of SnO₂. The SnO₂ sample shows good sensitivity towards the relative humidity. The calculated response and recovery time were found to be 32 s and 25 s respectively. These results indicate promising applications of SnO₂ nanoparticles in a highly sensitive environmental monitoring and humidity controlled electronic devices. The samples were further subjected to thermal analyses (TG–DTA) and UV–VIS diffusion reflectance spectroscopy (DRS) studies.     

Development of a specific and highly sensitive optical chemical sensor for determination of Hg(II) based on a new synthesized ionophore

A novel optode for determination of Hg(II) ions is developed based on immobilization of a recently synthesized ionophore, 7-(1H-imidazol-1-ylmethyl)-5,6,7,8,9,10-hexahydro-2H-1,13,4,7,10 benzodioxatriaza cyclopentadecine-3,11(4H,12H)-dione, in a PVC membrane. Dioctyl sebacate was used as a plasticizer, sodium tetraphenylborate as an anionic additive and ETH5294 as a chromoionophore. The response of the optode was based on the complexation of Hg(II) with the ionophore in the membrane phase, resulting an ion exchange process between Hg(II) in the sample solution and H⁺ in the membrane. The effects of pH and amounts of the ionophore, chromoionophore, ionic additive and type of plasticizer on the optode response were investigated. The selectivity of the optode was studied in the present of several cations. The optode has a linear response to Hg(II) in the range of 7.2 × 10^? 13–4.7 × 10^? 4 mol L^? 1 with detection limit of 0.18 pmol L^? 1. The optode was successfully applied to the determination of Hg(II) in real samples.     

PVC membrane and coated graphite potentiometric sensors based on Et4todit for selective determination of samarium(III)

Solution studies on the binding properties of 4,5,6,7-tetrathiocino[1,2-b:3,4-b']diimidazolyl-1,3,8,10-tetraethyl-2,9-dithione (Et(4)todit) toward a number of cationic species including some lanthanide ions revealed the occurrence of a selective 1:1 complexation of the ligand with Sm(3+) ion. Consequently, Et(4)todit was used as a suitable neutral ionophore for the preparation of novel polymeric membrane (PME) and coated graphite (CGE) Sm(3+)-selective electrodes. The electrodes exhibit a Nernstian behavior for Sm(3+) ions over wide concentration ranges (1.0 x 10(-5)-1.0 x 10(-1) M for PME and 1.0 x 10(-7)-1.0 x 10(-1) M for CGE) and very low limits of detection (8.0 x 10(-6) M for PME and 1.6 x 10(-8) M for CGE). The proposed potentiometric sensors manifest advantages of relatively fast response, and, most importantly, good selectivities relative to wide variety of other cations, including other lanthanide ions. The selectivity behavior of the proposed Sm(3+)-selective electrodes revealed a great improvement compared to the best previously reported electrode for samarium(III) ion. The potentiometric responses of the electrodes are independent of the pH of the test solution in the pH range 4.0-6.5. The electrodes were successfully applied to the recovery of Sm(3+) ion from tap water samples and also, as an indicator electrode, in potentiometric titration of samarium(III) ions.     

A smart LPG sensor based on chemo-bio synthesized MgO nanostructure

The present work reports the synthesis of magnesium oxide nanoparticles (MgO NP’s) using A. barbadensis Mill (aloe vera) as the stabilizer by green synthesis approach as well as solution-combustion method. The morphological, structural and optical properties of synthesized MgO NP’s were characterized by transmission electron microscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, and X-ray diffraction. The characterization results show the fibrous shaped porous structure of synthesized MgO NP’s with size range of 2–25 nm. The as-synthesized MgO NP’s were subjected to sensing of liquefied petroleum gas (LPG) having different concentration ranges (400–1000 ppm) and different operating temperatures along with dynamic characteristics. The sensor exhibits high selectivity and sensitivity towards LPG.     

An electrochemical sensing platform based on a new copper complex for the determination of hydrogen peroxide and nitrite

Abstract

A new copper(II) complex [Cu(C₁₂H₂₃N₃)₄Br₂·2H₂O] was synthesized and its structure was characterized by x-ray crystallography and elemental analysis. The copper atom had a distorted octahedron coordination involving two bromide anions and four nitrogen atoms from the 1-decyl-1H-[1,2,4]triazole ligands. Moreover, the electrochemical behavior and electrocatalysis of the carbon paste electrode (Cu-CPE) bulk-modified by the complex have been studied in detail. The Cu-CPE showed excellent electrocatalytic activities toward the reduction of hydrogen peroxide and nitrite, and the detection limit was much lower than that mentioned in earlier reports. This bulk-modified CPE has good reproducibility, long-term stability and surface renewability, which appear promising for constructing chemical sensors.     

Low cost selective sensor for carbonyl compounds in air based on a novel conductive poly(p-xylylene) derivative

A novel poly(p-xylylene), PPX, derivative bearing phenyl side groups was electrochemically synthesized in 85% yield. The polymer, poly(2-phenyl-p-xylylene) (PPPX), presented a major fraction (88%) soluble in common organic solvents. It showed to be thermally resistant up to 140 °C. UV–VIS analysis revealed an Egap of ~ 3.0 eV. Gas sensors made from thin films of CSA doped PPPX deposited on interdigitated electrodes exhibited significant changes in electrical conductance upon exposure to five carbonyl compounds: acetaldehyde, propionaldehyde, benzaldehyde, acetone and butanone. Three-dimensional plots of relative response vs. time of half-response vs. time of half-recovery showed good discrimination between the five carbonyl compounds tested.     

Lanthanide recognition: A Ho3+ potentiometric membrane sensor as a probe for determination of terazosin

In this study, complexation of N′-(1-pyridin-2-ylmethylene)-2-furohydrazide (NFH) with some metal ions was investigated by conductometry and spectroscopy. Then, a Ho³⁺ potentiometric membrane sensor was prepared based on the highly selective complexation between this ionophore and Ho³⁺. These new ionophores are more selective than the previously reported ones. In this work, for the first time, the proposed sensor was applied in indirect determination of the terazocine in its pharmaceutical formulation. The interest in constructing lanthanide sensors arises because they have similar ionic radii to calcium, but a higher charge density, which allows them to be used as probes to find the interactions between Ca²⁺ and biologically important molecules.     

Gadolinium(III) ion selective sensor using a new synthesized Schiff's base as a sensing material

According to a solution study which showed a selective complexation between N,N′-bis(methylsalicylidene)-2-aminobenzylamine (MSAB) and gadolinium ions, MSAB was used as a sensing element in construction of a gadolinium(III) ion selective electrode. Acetophenon (AP) was used as solvent mediator and sodium tetraphenyl borate (NaTPB) as an anion excluder. The electrode showed a good selectivity towards Gd(III) ions over a wide variety of cations tested. The constructed sensor displayed a Nernstian behavior (19.7 ± 0.3 mV/decade) in the concentration range of 1.0 × 10^? 6 to 1.0 × 10^? 2 mol L^? 1 with detection limit of 5.0 × 10^? 7 mol L^? 1 and a short response time (< 10 s). The working pH range of the electrode was 3.5–10.1 and lifetime of the sensor was at least 10 weeks. Analysis of certified reference materials confirmed the accuracy of the proposed sensor. The electrode was successfully applied as an indicator electrode in gadolinium titration with EDTA.     

A selective optical sensor for beryllium determination based on incorporating of 1,8-dihydroxyanthrone in a poly (vinyl chloride) membrane

A new optical sensor was fabricated for determination of beryllium ions. The optode membrane was prepared by incorporation of 1,8-dihydroxyanthrone and sodium tetraphenylborate (NaTPB) in a plasticized poly (vinyl chloride) membrane containing ortho-nitrophenyl octyl ether (o-NPOE) as a plasticizer. Color of the sensing membrane in contact with Be(2+) ions at pH 10.5, was changed from orange to red. The different variables affecting uptake efficiency were evaluated and optimized. Under the optimum conditions (i.e. 28.0% PVC, 60.0% o-NPOE, 8.0% 1,8-dihydroxyanthrone, 4.0% NaTPB and response time of 6 min), the proposed sensor displayed a linear range of 0.1-5 μg mL(-1) with a detection limit of 0.03 μg mL(-1). Also the precision (RSD%) was better than 2.9% for 7 replicate determinations of 1 μg mL(-1) Be in various membranes. The selectivity of the probe was studied for some cations and anions. Experimental results showed that the sensor was high selective in the presence of ethylenediaminetetraacetic acid (EDTA) as a masking agent and could be used as an effective tool in analyzing the beryllium content of water samples.     

Highly selective NH3 gas sensor based on polypyrrole/Ti3C2Tx nanocomposites operating at room temperature

Journal of Materials Science: Materials in Electronics - Semiconducting nanomaterials with different sizes and shapes have wide applications in the field of electronics, and one of the key pathway...     

Ultrasensitive Pb(II) potentiometric sensor based on copolyaniline nanoparticles in a plasticizer-free membrane with a long lifetime

A newly designed Pb(II) potentiometric sensor based on intrinsically conducting nanoparticles of solid poly(aniline-co-2-hydroxy-5-sulfonic aniline) possessing many ligating functional groups like -NH-, -N=, -OH, -SO(3)H, -NH(2) as ionophores in plasticizer-free vinyl resin solid membranes has been fabricated. A linear Nernstian response is obtained within a wide Pb(II) activity range from 1.0 × 10(-3) to 1.0 × 10(-10) M with a detection limit as low as 2.2 × 10(-11) M. The pH independent plateau ranges between 3.5 and 7.0. After 15 months' usage, the sensor maintains 95% performance parameters. Its anti-interference ability to Cu(II), Cd(II), Ag(I), and Hg(II) is much stronger than other sensors with a detection limit at (sub)nanomolar level. Electrochemical impedance spectroscopy reveals that the solid sensing membrane has a diffusion coefficient of around 5 × 10(-14) to 1 × 10(-13) cm(2) s(-1). The much lower diffusion coefficient for Pb(II) is highly beneficial for the elimination of Pb(II) flux across the membrane. The wide detection concentration range, low detection limit, high selectivity, extensive pH window, and long lifetime make for a robust sensor giving reliable measurement of Pb(II) content with potential application in real-world samples at trace levels.