A phosphate-selective electrode based on immobilized alkaline phosphatase and glucose oxidase.

An enzyme electrode which senses oxygen consumption for the assay of phosphate ion (10^-3-10^-4M), was constructed by using two enzymes together:

The competitive inhibition by phosphate ion added caused a smaller and slower oxygen consumption which could be detected by a platinum disc electrode at -0.6 V vs. SCE amperometrically. This dual enzyme electrode was also found useful for the assay of oxyacids other than phosphate, such as arsenate, tungstate, molybdate and borate.     

Chemically Modified Carbon Paste Electrode for Determination of Sulfate Ion by Potentiometric Method

Four Schiff base complexes of different metal ions, M=Cr(III), Mn(III), Fe(III), and Co(III), were studied to characterize their ability as sulfate ion carriers in carbon paste electrode (CPE). The modified CPE electrode with Schiff base complex of Cr(III), N,N′‐ethylenebis(5‐hydroxysalicylideneiminato) chromium(III) Chloride, showed good response characteristics to SO₄^2? ion. The proposed electrode exhibits a Nernstian slope of 28.9±0.4 mV per decade for SO₄^2? ion over a wide concentration range from 1.5×10^?6?4.8×10^?2 M, with a detection limit of 9.0×10^?7 M. The CPE electrode manifested advantages of relatively fast response time, suitable reproducibility and life time and, most important, good potentiometric selectivity relative to a wide variety of other common inorganic anions. The potentiometric response of the electrode is independent of the pH of the test solution in the pH range 4.0–9.0. The proposed electrode was used as an indicator electrode in potentiometric titration of sulfate with Ba²⁺ ion, the determination of zinc in zinc sulfate tablet and also determination of sulfate content of a mineral water sample.     

Viskosimetrische Bestimmung der Hemmkonstante (K I) von β-1,4-Glucan-4-glucanohydrolase (EC 3.2.1.4)—[C x -Cellulasen-Enzyme] in Anwesenheit eines kompetitiven Hemmstoffs Lactose

Zusammenfassung Nach der entwickelten Theorie⁵ bestimmt man viskosimetrisch die HemmkonstanteK _I=2,78·10^–2 mMol/ml der hydrolytischen Reaktion der Natriumcarboxymethylcellulose (Na-CMC) unter der katalytischen Wirkung vonC _x-Cellulasenenzym [(EC 3.2.1.4), (-1,4-Glucan-4-glucanohydrolase)], aus Aspergillus oryzae isoliert, und unter der Hemmwirkung des kompetitiven Hemmstoffs Lactose.

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Viscosimetric determination of the inhibition constant (K _I ) of -1,4-glucan-4-glucano hydrolase (EC 3.2.1.4)-[C_x-cellulase enzyme] in presence of a competitive inhibitor (Lactose)

According to a recently developed theory⁵, an inhibition constantK _I=2,78·10^–2 mMol/ml was determined viscosimetrically for the hydrolase reaction of sodium carboxymethyl cellulose (Na-CMC) withC _x-cellulase enzyme (EC 3.2.1.4, -1,4-glucan-4-glucanohydrolase), isolated from Aspergillus oryzae. Lactose was used as a competitive inhibitor.

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Potentiometric study of the kinetics and equilibria of formation of chloroglycinate palladium(II) complexes from bis-glycinato palladium(II) complexes

The equilibria and kinetics of the reaction of Pd(gly)₂ complexes with hydrogen ions and chloride ions has been studied by a potentiometric method. The underlying idea of the method is the measurement of solution pH as a function of reaction time t using a glass electrode. The solutions used had the following initial compositions: xM Pd(gly)₂, xM Hgly, and 1 M NaCl with x = 1 × 10^?4, 5 × 10^?4, and 1 × 10^?3; initial pH₀ was from ～3.5 to ～4.4. The experimentally determined pH versus t dependences and the rate equation for a pseudo-second-order reaction were used to determine the equilibrium constant of formation of Pd(gly)(Hgly)Cl complexes from Pd(gly)₂ complexes and the observed rate constant for this reaction, k _obs. The dependence of k _obs on the pH of the acid solutions studied was assigned to a change in the sequence of the reactions of addition of a hydrogen ion and a chloride ion to the complex Pd(gly)₂.     

Radiation induced electron exchange reaction of thallium/I/-thallium/III/ at low sulfate ion concentration in perchloric acid solution

To understand the behaviour of Tl/II/ and the bridging group SO ₄ ^2– in radiation induced electron exchange reactions we have investigated the rate constants and mechanisms of reaction of Tl/II/ with Tl/I/ and Tl/III/ in perchloric acid solutions. The results indicated that Tl/II/ is an intermediate in the -ray induced electron exchange process of T1/I/–T1/III/. Sulfate ions at [SO ₄ ^2– ]>-0.02M serve as bridging groups and play an important role in accelerating the T1/II/–T1/I/ reaction. A cooperative effect was found between hydrogen peroxide and sulfate ion at low sulfate ion concentration, [SO ₄ ^2– ]0.02M in perchloric acid solution.     

Kinetic investigation of the bromate–ascorbic acid–malonic acid system

According to our experiments the bromide ion concentration exhibits in the bromate–ascorbic acid–malonic acid–perchloric acid system three extrema as a function of time. To describe this peculiar phenomenon, the kinetics of four component reactions have been studied separately. The following rate equations were obtained: Bromate–ascorbic acid reaction: Bromate–bromide ion reaction: Bromide–ascorbic acid reaction: Bromine–malonic acid reaction: k₄ = 6 × 10^?3 s^?1, k_-4 ≥ 1.7 × 10³ s^?1, k₅ ≥ 1 × 10⁷M^?1 · s^?1 Taking into account the stoichiometry of the component reactions and using these rate equations, the concentration versus time curves of the composite system were calculated. Although the agreement is not as good as in the case of the component reactions, it is remarkable that this kinetic structure exhibits the three extrema found.     

An Ion-Selective Electrode for Dibasic Phosphate Ion

Abstract

A phosphate-selective electrode is developed based on a silver coordination reaction. The electrode responds linearly toward HPO₄ ⁼ in the concentration range of 10^?4 to 10^?1 M (slope = 27 mV/dec.). The electrode also shows good selectivity over sulfate, nitrate, perchlorate and acetate.     

Enzyme electrode system for oxalate determination utilizing oxalate decarboxylase immobilized on a carbon dioxide sensor

A highly selective enzyme electrode system for oxalate is described in which the enzyme oxalate decarboxylase is immobilized on a carbon dioxide gas-sensing electrode. The response of the system is linear with the logarithm of the oxalate concentration between 2 × 10^-4 and I × 10^-2 M with a slope of 57–60 mV/decade. The oxalate detection limit is 4 × 10^-5 M. Electrodes used with chemically immobilized enzyme are not affected by phosphate and sulfate at levels normally found in urine and are very stable showing no decrease in response after one month of operation. The enzyme electrode system functions well in urine, requiring minimal sample pretreatment. The recovery of oxalate added to five aliquots of a human control urine sample averaged 97.7% with an average relative standard deviation of 4.5%.     

Kinetics and mechanism of the oxidation of iron(II) ion by chlorine dioxide in aqueous solution

The mechanism by which an excess of iron(II) ion reacts with aqueous chlorine dioxide to produce iron(III) ion and chloride ion has been determined. The reaction proceeds via the formation of chlorite ion, which in turn reacts with additional iron(II) to produce the observed products. The first step of the process, the reduction of chlorine dioxide to chlorite ion, is fast compared to the subsequent reduction of chlorite by iron(II). The overall stoichiometry is The rate is independent of pH over the range from 3.5 to 7.5, but the reaction is assisted by the presence of acetate ion. Thus the rate law is given by At an ionic strength of 2.0 M and at 25°C, k_u = (3.9 ± 0.1) × 10³ L mol^?1 s^?1 and k_c = (6 ± 1) × 10⁴ L mol^?1 s^?1. The formation constant for the acetatoiron(II) complex, K_f, at an ionic strength of 2.0 M and 25°C was found to be (4.8 ± 0.8) × 10^?2 L mol^?1. The activation parameters for the reaction were determined and compared to those for iron(II) ion reacting directly with chlorite ion. At 0.1 M ionic strength, the activation parameters for the two reactions were found to be identical within experimental error. The values of ΔH? and ΔS? are 64 ± 3 kJ mol^?1 and + 40 ± 10 J K^?1 mol^?1 respectively. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 554–565, 2004     

Arginine Determination with Ion-Selective Membrane Electrodes

Abstract

A new method for the determination of the amino acid arginine utilizes a dual enzyme catalyzed reaction monitored with an ammonium ion selective membrane electrode of the antibiotic type. The technique gives a linear correlation between arginine concentration and electrode response over the 3 × 10^?3 M to 3 × 10^?5 M range and a useful, but non-linear, response over a wider range. Major interferences are urea, K⁺, and NH₄ ⁺, but Na⁺ does not interfere in the physiological concentration range.     

Amperometric determination of As(III) and Cd(II) using a platinum electrode modified with acetylcholinesterase,ruthenium(II)-tris(bipyridine) and graphene oxide

The authors describe an amperometric biosensor for the determination As(III) and Cd(II) based on the inhibition of the enzyme acetylcholineesterase (AChE). A platinum electrode was modified with ruthenium(II)-tris(bipyridyl), graphene oxide and AChE and then showed redox peaks at 0.06 and 0.2 V vs Ag/AgCl in the presence of acetylthiocholine chloride (ATChCl). Amperometry unveiled a steady-state turnover rate with the release of thiocholine. In the presence of arsenic(III) and cadmium(II), AChE showed an inhibitive response at 0.214 and 0.233 V vs Ag/AgCl, respectively. The electrode exhibits a detection limit and linear range of 0.03 μM and 0.05–0.8 μM for As(III) and 0.07 μM and 0.02–0.7 μM for Cd(II), respectively. Type of inhibition and inhibition constants induced by As(III) and Cd(II) on the catalytic sites of AChE were determined from Dixon and Lineweaver-Burk plots. The modified electrode was applied to the determination of As³⁺ and Cd²⁺ in river, tap and waste water, and the results proved that the method is sensitive and can be an alternative to chromatographic and spectroscopic techniques.

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Graphical abstract Schematic presentation of Pt/Ru(II)-tris(bipy)-GO/AChE electrode in absence and presence of metal ions (As³⁺/Cd²⁺).

     

Cobalt(II) complexes with pentadentate Schiff bases 2,6-diacetylpyridine hydrazones: Syntheses and structures

Seven new cobalt(II) complexes based on the Schiff bases, 2,6-diacetylpyridine bis(isonicotinoylhydrazone) (H₂L¹) and 2,6-diacetylpyridine bis(nicotinoylhydrazone) (H₂L²), are synthesized and studied by X-ray diffraction analysis: [Co(H₂L¹)(NCS)₂] · 2.25H₂O (I), [Co(H₂L²)(NCS)₂] · CH₃OH (II), [Co(H₂L²)(NCS)(H₂O)]NCS (III), [Co(H₄L¹)(NCS)₂](NO₃)₂ · 2H₂O (IV), [Co(H₄L¹)(NCS)₂][Co(NCS)₄] · 0.75H₂O (V), [Co(H₄L²)(NCS)₂][Co(NCS)₄] · 1.75H₂O (VI), and [Co(H₂L²)(NCS)(CH₃OH)]₂[Co(NCS)₄] · 2CH₃OH (VII) (CIF files CCDC 941186 (I), 1457906 (Ia), 1457905 (II), 941187 (III), 1457907 (IV), 1457908 (V), 1457909 (VI), and 941188 (VII)). The organic ligands in the complexes act as pentadentate neutral H₂L or doubly protonated (H₄L)²⁺ coordinated through the same set of donor atoms N₃O₂. In all compounds I–VII, the coordination polyhedron of the Co²⁺ ion in a complex with the Schiff bases has a shape of a pentagonal bipyramid. The hydrazones are arranged in the equatorial plane of the bipyramid. Its axial vertices are occupied by the nitrogen atoms of the NCS￣ anions in compounds I, II, and IV–VI and by the nitrogen atoms of NCS￣ and oxygen of the water molecule in compound III or methanol in compound VII. The NO ₃ ^- anions or [Co(NCS)₄]^2￣ complex anions obtained by the reactions are involved along with the NCS￣ anions in the formation of compounds IV–VII.     

Potentiometric investigation of NaSO 4 − ion pair formation in NaClO4 medium

The ion pair formation of NaSO ₄ ⁻ has been investigated potentiometrically in 1M NaClO ₄ medium at 25°C using two different sodium-selective indicator electrodes and a perchlorate reference electrode. The stability constant of NaSO ₄ ⁻ obtained in this study was . Although is small, it lowers the free sulfate concentration drastically in 1M NaClO ₄ medium and is a factor which should be considered in the use of NaClO ₄ as inert supporting electrolyte.     

Kinetics of silver dissolution in sulfide containing thiocarbamide electrolytes

Effective values of reaction order with respect to ligand P, transfer coefficient α, and exchange current i ₀ at constant silver surface coverages θ by sulfide ions are measured. The employed solutions contained from 0.4 to 0.05 M thiocarbamide, 0.5 M HClO₄, 10^?4 M AgNO₃, and from 10^?5 to 10^?4 M Na₂S. It is shown that the exchange current grows approximately linearly from 10^?5 to 1.5 × 10^?4 A/cm² at θ increase in the range from zero to 0.8, while α and P values grow negligibly in the ranges of 0.4–0.45 and 0.9–1.1, accordingly. The obtained results are compared with the data of similar studies of the gold behavior in acidic thiocarbamide solutions. The possible reasons for the different effects of sulfide ion chemisorption on the anodic dissolution of gold and silver in the studied solutions are discussed.     

A study of metal chelation of dinucleotide analogs in the gas phase by fast-atom bombardment mass spectrometry

Fast-atom bombardment (FAB) mass spectrometry was used to investigate the interaction of proton and alkali metal ions with dinucleotide analogs such as T-n-T (T = thymine moiety, n = polyether chain, e.g., triethylene, tetraethylene, pentaethylene, and hexaethylene ether 1–4), A-n-T (A = adenine unit 5–8), and T-n-OMe (9–12) in 3-nitrobenzyl alcohol matrix. The [M + H]⁺ ion is the most abundant ion for the A-n-T series, whereas in 1–4 and 9–12 the (TC₂H₄)⁺ ion is the most abundant. Formation of [M + H -C₂H₄O]⁺ ions, a characteristic fragmentation of crown ethers under electron ionization, is observed for compounds 1–12 and is more pronounced in 6 and 7. An abundant [M ? H]^? ion is observed for all the compounds studied under negative ion FAB due to the presence of the (-CO-NH-CO-) group of thymine, an indication of existence of intramolecular H bonding. The FAB mass spectra of 1–12 with alkali metal ions (Li⁺, Na⁺, K⁺, Rb⁺, and Cs⁺) showed formation of abundant metal-coordinated ions ([M + Met]⁺ and [TC₂H₄ + Met]⁺). Compounds 3, 4, 6, 7, and 10–12 showed ions due to the substitution of the thymine moiety by a hydroxyl group ([M + Met ? 108]⁺, Met = metal ion). For compound 3 alone, substitution of two thymine groups ([M + Met - 216]⁺) was observed. Metastable ion studies were used to elucidate the structures of these potentially significant ions, and the ion formule were confirmed with high resolution measurements. Selectivity toward metal complexation with ligand size was seen in the T-n-T and A-n-T series and was even more pronounced in A-n-T series. These dinucleotide analogs fall in the following order of chelation of alkali metal ions, acyclic glymes < dinucleotide analogs (acyclic glymes substituted with nitrogen bases) < crown ethers, which places them in perspective as receptor models.     

Polymeric membrane and coated graphite electrode based on newly synthesized tetraazamacrocyclic ligand for trace level determination of nickel ion in fruit juices and wine samples

Novel polymeric membrane electrode (PME) and coated graphite electrode (CGE) for nickel ion were prepared based on 2,9-(2-methoxyaniline)₂-4,11-Me₂-[14]-1,4,8,11-tetraene-1,5,8,12-N₄ as a suitable neutral ionophore. The addition of lipophilic anion excluder (NaTPB) and various plasticizers viz o-nitrophenyloctylether (o-NPOE), dioctylphthalate (DOP), dibutylphthalate (DBP), 1-chloronaphthalene (CN) and tri-n-butylphosphate (TBP) have found to improve the performance of the sensors. The best performance was obtained for the membrane sensor having a composition of I:NaTPB:TBP:PVC in the ratio 6:4:100:90 (w/w; mg). The electrodes exhibit Nernstian slopes for Ni²⁺ ions over wide concentration ranges of 4.6 × 10^?7–1.0 × 10^?1 M for PME and 7.7 × 10^?8–1.0 × 10^?1 M for CGE with limits of detection of 2.7 × 10^?7 M for PME and 3.7 × 10^?8 M for CGE. The response time for PME and CGE was found to be 10 and 8 s respectively. The potentiometric responses are independent of the pH of the test solution in the pH range 3.0–8.0. The proposed electrodes revealed good selectivities over a wide variety of other cations including alkali, alkaline earth, transition and heavy metal ions. The coated graphite electrode was used as an indicator electrode in the potentiometric titration of nickel ion with EDTA and in direct determination in different fruit juices and wine samples.     

Amperometric determination of sulfide ion by glassy carbon electrode modified with multiwall carbon nanotubes and copper (II) phenanthroline complex

Electrocatalytic oxidation of sulfide ion on a glassy carbon electrode (GCE) modified with multiwall carbon nanotubes (MWCNTs) and a copper (II) complex was investigated. The Cu(II) complex was used due to the reversibility of the Cu(II)/Cu(III) redox couple. The MWCNTs are evaluated as a transducer, stabilizer and immobilization matrix for the construction of amperometric sensor based on Cu(II) complex adsorbed on MWCNTs immobilized on the surface of GCE. The modified GCE was applied to the selective amperometric detection of sulfide at a potential of 0.47 V (vs. Ag/AgCl) at pH 8.0. The calibration graph was linear in the concentration range of 5 µM–400 µM; while the limit of detection was 1.2 µM, the sensitivity was 34 nA µM^?1. The interference effects of SO₃ ^2?, SO₄ ^2?, S₂O₃ ^2?, S₄O₆ ^2?, Cysteine, and Cystein were negligible at the concentration ratios more than 40 times. The modified electrode is more stable with time and more easily restorable than unmodified electrode surface. Also, modified electrode permits detection of sulfide ion by its oxidation at lower anodic potentials.      

Stabilization of [Sc(NCS)<Subscript>6</Subscript>]<Superscript>3−</Superscript> anion by [M(18C6)]<Superscript>+</Superscript> complexes in solvation systems

The [M(18C6)]₄[Sc(NCS)₆]Cl · nH₂O complexes were established to form in the solutions ScCl _x -Solv-MNCS-18C6, where Solv is ethanol, THF, acetonitrile, or isopropyl alcohol; M = Na, K; 18C6 is 1,4,7,10,13,16-hexaoxocyclooctadecane. X-ray diffraction analysis of [K(18K6)]₄[Sc(NCS)₆]Cl · 3.33H₂O showed that the thiocyanate ion was coordinated by Sc through the N atom. The structure consists of octahedral Sc(NCS) ₆ ^3? that are united via nonvalent K-S interaction with macrocyclic dimers [M(18C6)]₂ into chains. Each 18C6 molecule coordinates one K atom.     

Single-Walled Carbon Nanotubes Functionalized with N-(6-aminohexyl) Carboxamide as Ionophore for Sensing Silver Ions

In this work; we constructed a silver ion-selective electrode based on N-(6-aminohexyl) carboxamide functionalized single-walled carbon nanotubes (NAHAFSWCN) as an ionophore. The selectivity constant of a number of cations was measured using silver ion selective electrode. Optimal pH was between 3 and 6 and the upper and lower detection limits of the designed electrode were 1.2 × 10^–2 and 8 × 10^–7 M. The electrode showed a Nernstian response over a silver ion concentration range of 1 × 10^–6 to 1 × 10^–2 M with a slope of 59.1 ± 0.5 mV/decade. The response time of the electrode was less than 18 s and its effective lifetime was 3 months. The isothermal temperature coefficient of the electrode dE°/dT was determined as 0.00011 V/grad. Thermodynamic functions such as ΔS°, ΔH° and ΔG° were obtained by calculating the thermal coefficient of the electrode.     

Electrochemical sensor for lead(II) ion using a carbon ionic-liquid electrode modified with a composite consisting of mesoporous carbon, an ionic liquid, and chitosan

A novel electrode was prepared that enables sensing of lead(II) ion. A suspension composed of ordered mesoporous carbon (OMC), an ionic liquid (IL), and chitosan was deposited on the highly conductive surface of a carbon ionic-liquid electrode (CILE). The surface of the sensing electrode was characterized by scanning electron microscopy and cyclic voltammetry. The new electrode can be used to determine lead(II) ion because the hydrophobic ionic liquid of the CILE can extract Pb(II), while the OMC accelerates the electron transfer rate between the electrode and Pb(II) and also strongly adsorbs Pb(II). The resulting electrode displays excellent and synergistic response to Pb(II) which is linear in the range from 0.05 to 1.4?μM, with a correlation coefficient of 0.997 and a detection limit of 25 nM.