Improved Calcium Ion-Selective Electrode Based on a Neutral Carrier

Abstract

The performance of a liquid-membrane electrode using a synthetic, neutral carrier in o-nitro-phenyl-n-octyl-ether as membrane component in a PVC matrix, in the presence of sodium tetra-phenyl-borate, is described. Selectivities, working range, lifetime and anion interference are discussed. The electrode makes possible the measurement of calcium ion activities in the range 10^?1M to 10^?6M in unbuffered and in the range 10^?1M to 10^?8M in calcium buffered systems respectively. The selectivities of calcium over protons, magnesium, sodium and zinc are 25,000, 26,000, 2,800 and 7,100, respectively, and are far superior than those reported for other calcium sensors.     

A Calcium Ion-Selective Electrode Based on a Neutral Carrier

Abstract

The performance of a liquid-membrane electrode using a synthesized ligand in p-nitroethylbenzene as membrane component is described. Selectivities, working range, lifetime, pH-dependence, and dependence on the dielectric constant of the membrane solvent are discussed. The electrode makes possible the measurement of calcium ion activities in the range of 10^?1 M to 10^?5 M In unbuffered systems with a selectivity of calcium over sodium and magnesium of 175 and 33,000 respectively. The selectivity constants of the cell discussed are heavily influenced by the dielectric constant of the membrane solvent.     

A Neutral Carrier Membrane Calcium-Sensitive Electrode with Wide Working pH Range

Abstract

A poly(vinyl chloride) (PVC) membrane calcium-sensitive electrode based on a new type of synthetic carrier 1,7-di[2-(1-phenylazo)naphtyl]-1,4,7-trioxaheptan is introduced. This electrode exhibited Nernstian response over the concentration range 1.0×10^?1 - 3.0×10^?8 mol/L Ca²⁺ with a slope of 28.8 mV/pCa in calcium ion buffer solutions. The detection limit for calcium ion was 1.0X10^?8 mol/L. The response time varied from 10 to 30 seconds. The working pH range for the electrode was 3.5 - 12.3 when the concentration of Ca²⁺ was 10^?3 mol/L. The lifetime of the electrode was proved to exceed 8 months. It was applied successfully in the determination of calcium ion in river water, mineral water and cosmetic. A method for the determination of total calcium in urine was developed.     

Voltammetric determination of nitrate,perchlorate and iodide at a hanging electrolyte drop electrode

The use of a hanging electrolyte drop electrode is examined for the determination of nitrate, perchlorate and iodide. A three-electrode system was used with a polarographic analyzer. Crystal violet dicarbollylcobaltate(III) electrolyte in the nitrobenzene phase and magnesium sulphate in the aqueous phase with a Pb/PbSO₄ reference electrode made it possible to increase the viable potential range. For nitrate, the peak current/concentration relation was linear over the range 0–5 × 10^?5 M, and nitrate in potable water was easily determined.     

Simultaneous spectrophotometric determination of calcium and magnesium with chlorphosphonazo-III by flow injection analysis

In this flow-injection method, the total concentration of calcium and magnesium is determined by using triethanolamine/hydrochloric acid buffer (pH 7.0) and chlorphosphonazo-III (CPA-III) in the flow streams, and the concentration of calcium alone is determined by using 1.6×10^?3 M hydrochloric acid and CPA-III in the flow treams. At pH 7.0, medium, the linear calibration ranges were 0–2.00 mg l^?1 for both calcium and magnesium and the detection limits were each 0.02 mg l^?1; at pH 2.2, the linear calibration range for calcium and the detection limit were 0.20–2.00 mg l^?1 and 0.1 mg l^?1, respectively. Injection rates are 200 h. The method is suitable for analyzing natural waters.     

Preconcentration and determination of calcium and magnesium in brine with flow-injection systems

On-line preconcentration on a chelating resin (Dowex A-1) and elution with 0.1 M hydorchloric acid is followed by spectrophotometry based on the metal complexes formed with 1- (2-hydroxy-4-diethylamino-1-phenylazo)-2-hydroxynaphthalene-3,6-disulfonic acid. The total concentration of calcium and magnesium is determined; in a second sample, calcium is masked with a ligand buffer containing excess of barium(II) and EGTA, and magnesium is determined. The calcium concentration is measured by difference. Magnesium (1–30 μg l^?1 and calcium (8– 10 μg l^?1) in 2.5 M sodium chloride can be determined. Calcium and magnesium in analytical reagent-grade sodium chloride and potassium chloride and primary standard sodium chloride are aslo determined. The method based on the exchange between calcium ions and Mg(EDTA) is proposed to enchance the sensitivity for calcium.     

Synthesis of o,o′-dihydroxyazo compounds and their application to the determination of magnesium and calcium by flow injection analysis

Seven _o,o′-dihydroxyazo dyes were synthesized and examined as spectrophotometric reagents for magnesium and calcium. These reagents are highly sensitive for magnesium (? = 47 000) and calcium (? = 39 000 l mol^?1 cm^?1). Of the reagents synthesized, 2-(2-hydroxy-3,6-disulfo-1-naphthylazo)-5-(N,N-diethylamino)phenol was the best because of its ease of preparation and purification, and its stability in alkaline solution. This dye was applied in the determination of magnesium and calcium by flow injection analysis. The total concentration of magnesium (0.1–1.2 mg 1^?1) and calcium (0.4–4.0 mg 1^?1) was determined by masking iron(III), aluminium(III), copper(II), zinc(II), manganese(II) and cadmium(II) with 2,3-dimercapto-1-propanol (DMP) and triethanolamine (TEA). Magnesium was determined by masking calcium and the other metal ions with a ligand buffer containing barium(II)—EGTA, DMP and TEA. The amount of calcium was obtained as the difference between the two peak heights. Results for the determination of magnesium and calcium in potable water and serum are presented.     

Preparation and examination of calcium ion-selective electrodes for flow analysis

The preparation of calcium ion-selective electrodes based on known alkylphenylphosphate exchangers or on the ETH 1001 ionophore, and their use in a flow-through cell in a flow-injection system for the determination of calcium are described. The response and lifetime of the electrodes and the effects of magnesium and sodium ions on the determination of 10^?3?10^?5 M calcium are examined in detail. The ionophore electrode is shown to be most satisfactory.     

Photocured polymers in ion-selective electrode membranes

A fast and convenient method is reported for preparing ion-selective electrode membrane based on bisphenol. A epoxyacrylate, 1,6-hexanedioldiacrylate and benzophenone photoinitiator. A calcium-selective electrode is used as example; responses are Nernstian in the range 10^?1–10^?5 M with the calcium salt of bis-[4-(1′,1′,3′,3′-tetramethylbutyl)phenyl]phosphoric acid as the active substance.     

Preparation of a solid-state ion-selective electrode based on polypyrrole conducting polymer for magnesium ion

In this study, a potentiometric sensor based on a pencil graphite electrode (PGE) coated with polypyrrole doped with Titan yellow dye (PPy/TY) was prepared for potentiometric determination of magnesium ion in aqueous solutions. The structural characteristics of magnesium sensor electrode (PGE/PPy/TYMg) were studied using scanning electron microscopy and Fourier transform infrared along with energy-dispersive spectroscopy. Under the optimal conditions, the electrode reveals a good Nernstian behavior with slope of 28.27 ± 0.40 mV per decade over the concentration range of 1.0 × 10^?5–5.0 × 10^?2 M and a detection limit of 6.28 × 10^?6 M. The potentiometric response of fabricated electrode toward magnesium ion was found to be independent of the pH of the test solution in the pH range of 4.5–8.0. The electrode showed fast response time (<10 s) and good shelf lifetime (>2 months). The prepared magnesium sensor electrode can also be used as an indicator electrode in potentiometric titration of Mg²⁺ with EDTA with distinguished end point. The electrode revealed good selectivity with respect to many cations including alkali, alkaline earth, transition and heavy metal ions. The introduced magnesium electrode was used for measurement of Mg²⁺ ion in real samples without any serious interferences from other ions.     

Interaction of calcium ion with sodium triphosphate determined by potentiometric and calorimetric techniques

The stoichiometry of the interaction of Ca²⁺ with sodium triphosphate was determined using a Ca²⁺ sensitive electrode, divalent ion sensitive electrode, a glass electrode and by titration calorimetry, A 2:1 and 1:1 complex of Ca²⁺ and P₃O^5?₁₀ is found when titrating calcium chloride with sodium triphosphate by the calcium ion sensitive electrode and tritation calorimetry. However, only by titration calorimetry is the 2:1 and 1:1 complex found when titrating sodium triphosphate with calcium chloride. Thermodynamic value (log K, ΔH and ΔS) are reported for the formation of CaP(in3)O^?3₁₀ and Ca₂P₃O^?₁₀ in aqueous solution.     

Analytical Study of New Creatininium and Tetramethyl-ammonium Cation Selective Membrane Electrodes

Abstract

Two new liquid membrane electrodes which respond to creatininium and tetramethylammonium cations are described. The creatininium cation electrode exhibits rapid and near Nernstian response to creatininium cation activity, at pH 3, in the 10^?3?10^?1 mol/L range. The useful concentration range extends to 10^?4 mol/L. The tetramethyl-ammonium cation electrode exhibits rapid and near Nernstian response to tetramethylammonium cation activity, at pH 2–11.5, in the 2x10^?5? 10^?1 mol/L range. Major interferences for the creatininium electrode are Na⁺, K⁺, NH⁺ ₄ and creatine. The pK_a of the creatininium cation was calculated. A method is described for the potentiometric precipitation titration of tetramethylammonium cation with sodium tetraphenylboron. Amounts of tetramethylammonium in the range 20–200 μol have been determined using Gran's plots, with an average error of about 0.6%.     

Solid contact Zn2+ -selective electrode with low detection limit and stable and reversible potential

A new solid contact Zn²⁺ polyvinylchloride membrane sensor with 2-(2-Hydroxy-1-naphthylazo)-1,3,4 -thiadiazole as an ionophore has been prepared. For the electrode construction, ionic liquids, alkylmethylimidazolium chlorides are used as transducer media and as a lipophilic ionic membrane component. The addition of ionic liquid to the membrane phase was found to reduce membrane resistance and determine the potential of an internal reference Ag/AgCl electrode. The electrode with the membrane composition: ionophore: PVC: o-NPOE: ionic liquid in the percentage ratio of (wt.) 1:30:66:3, respectively, exhibited the best performance, having a slope of 29.8 mV decade^?1 in the concentration range 3×10^?7–1×10^?1 M. The detection limit is 6.9×10^?8 M. It has a fast response time of 5–7 s and exhibits stable and reproducible potential. It has a fast response time of 5–7 s and exhibits stable and reproducible potential, which does not depend on pH in the range 3.8–8.0. The proposed sensor shows a good and satisfactory selectivity towards Zn²⁺ ion in comparison with other cations including alkali, alkaline earth, transition and heavy metal ions. It was successfully applied for direct determination of zinc ions in tap water and as an indicator electrode in potentiometric titration of Zn²⁺ ions with EDTA.      

Determination of lead (II) ion by highly selective and sensitive lead (II) membrane electrode based on 2-(((E)-2-((E)-1-(2-hydroxyphenyl) methyliden)hydrazono)metyl)phenol

A PVC (poly vinyl chloride) membrane electrode for lead ion based on 2-(((E)-2-((E)-1-(2-hydroxyphenyl)methyliden)hydrazono)metyl)phenol (HMHMP) as a membrane carrier was prepared. This electrode exhibited linear response with Nernstian slope of 29.2?±?0.2?mV per decade within the concentration range of 2.0?×?10^?7–1.0?×?10^?1?M lead ion. The limit of detection, as determined from the intersection of the extrapolated linear segments of the calibration plot, was 8.0?×?10^?8 M. The electrode exhibited high selectivity for Pb (II). The response time of the electrode was about 5–10?s for different concentrations. The electrode is suitable for use in aqueous solutions in a pH range of 5.0–7.5. It was used as an indicator electrode in a titration of Pb (II) with chromate at constant pH. This electrode was used for the determination of lead in ore samples, and the results were in agreement with those obtained with an atomic absorption spectroscopy (AAS) method. Also lead selective electrode was used for monitoring of lead in spiked samples of the Zayanderud River and waste water by the potentiometry technique.     

Renewable Ceramic (TiN) Ring Electrode in Stripping Voltammetry. Determination of Pb(II) Without Removal of Oxygen

Characteristic features of the process of Pb(II) reduction and oxidation at a renewable ceramic ring electrode (RCRE) were studied by stripping voltammetry. The main constituents of the RCRE are: a specially constructed TiN ring electrode, a silver sheet used as silver counter/quasi‐reference electrode and a silicon O‐ring are fastened together in a polypropylene body. The renovation of this electrode is carried out through mechanical removal of solid contaminants and electrochemical activation in the electrolyte which fills the RCRE body. The optimal measurement conditions, composition of supporting electrolyte and procedures of the electrode activation were selected. The measurements were carried out from nondeaerated solutions. As shown on selected examples, RCRE exhibits good performance in underpotential deposition stripping voltammetry (UPD‐SV) applied for the determination of lead(II) in synthetic solutions with and without surfactants and in certified reference materials. The peak current is proportional to the concentration of lead(II) over the range 2×10^?9–1×10^?7 mol L^?1, with a 3σ detection limit of 1×10^?9 mol L^?1 with an accumulation time of 30 s. The obtained results showed good reproducibility, (RSD=2–5%; n=5) and reliability.     

Disopyramide-Selective Membrane Electrode∗

Abstract

A liquid membrane electrode based on disopyramide - dipicrylamine ion - pair complex, dissolved in nitrobenzene as solvent was proposed for the determination of disopyramide - an antiarrhythmic drug. The linear response covers the range from 10^?2 - 5 × 10^?6 M disopyramide solution, with a slope of 51.0 mV/decade (pH range 3.0 to 7.0). The detection limit is 4.7 × 10^?8 M. The electrode shows a good stability, reproducibility and fast response. The selectivity of the electrode is good. The strong interfering ion is thiamine (Vitamin B₁). These characteristics of the electrode made it to be used for the determination of disopyramide through direct and indirect potentiometric methods. Through indirect potentiometric method, disopyramide - as active substance can be determined with an average recovery of 99.98% and a relative standard deviation of 0.24%, and also this method can be used for its determination in pharmaceutical formulations such as capsules and ampoules with a relative standard deviation less than 1%. The electrode can be used at the dissolution tests of disopyramide capsules. The physical processes are numerically simulated by typical equations. The apparent first - order rate constants for disintegration and dissolution processes were calculated.

     

Investigations on adsorption potentiometry Part I. Derivative adsorption chronopotentiometry of the iron(III)-2-(5′-bromo-2′-pyridylazo)-5-diethylaminophenol system

An electroanalytical method, based on derivative chronopotentiometry of the iron complex with 2-(5′-bromo-2′- pyridylazo)-5-diethylaminophenol (5-Br-PADAP) accumulated adsorptively on the surface of a hanging mercury drop electrode, for determining trace iron in food has been developed. The dependences of the peak height on the dt/dE vs. E curve on the preconcentration time, preconcentration potential and electrode area are discussed. Optimum experimental conditions include 0.005 mol 1^?1 NH₃NH₄Cl, 2 × 10^?7 mol 1^?1 5-Br-PADAP and a preconcentration potential of ?0.40 V (vs. SCE). Under these conditions, the detection limit and the linear range are 2 × 10^?9 and 6.7 × 10^?9?1.7 × 10^?7 mol 1^?1, respectively. The relative standard error of the method is 1.5% for 6.7 × 10^?8 mol 1^?1 Fe(III). The method was applied to samples of microwave digested food.     

Flow-through tubular PVC matrix membrane electrode without inner reference solution for flow injection analysis

A simply constructed tubular PVC matrix membrane electrode without inner reference solution suitable for flow injection analysis is described. The nitrate-selective electrode developed allows simple replacement of an exhausted membrane, or change of function with a new sensor membrane. The compact design ensures mechanical stability and the tubular configuration minimizes distortion of the hydrodynamic flow in the detector. Nitrate can be determined in the range 10^?1–10^?5 M, under different flow conditions, with a sampling frequency of about 120 h^?1.     

Cyclic voltammetry of Tifluadom at a C18-modified carbon-paste electrode

Tifluadom, N-[5-(2-fluorophenyl)-2,3-dihydro-methyl-1H-1,4-benzodiazepine]-2-4-methyl-3-thiophene carboxamide, was determined by using a carbon-paste electrode modified with C₁₈ μBondapak. Adsorption on the electrode served as a preconcentration step which improved the limit of detection. Preconcentration for 5 min (open circuit) gave a linear range of 2.2×10^?7 M?4.5×10^?6 M with a detection limit of 1.3×10^?7 M (%C₁₈=25, w/w) for Tifluadom in Britton-Robinson buffer pH 6. The determination of Tifluadom added to urine required no preliminary treatment; the detection limit was 1.3×10^?6 M.