Potentiometric determination of iron using a fluoride ion-selective electrode-the application of the Apple II-ISE intelligent ion analyzer

A new method for determining iron is based on both nonlinear regression calibration plots and parabolic interpolation using a fluoride ion-selective electrode (ISE) and the Apple II-ISE intelligent ion Analyzer developed by ourselves. The experimental conditions for determining iron are discussed. The appropriate acidity of the experimental solution is pH 3, controlled by total ionic strength adjustment buffer (TISAB) that is composed of glycine (aminoacetic acid), nitric acid and sodium nitrate. The suitable total concentration of fluoride is equal to the highest concentration of iron in the standard series. Because the mathematical model of the method coincides with the experimental data the Apple II-ISE intelligent ion Analyzer can perform data acquisition and data processing, and the performance of fluoride electrode is excellent, the new method for determination of iron is fast and accurate. This method has been used successfully in the determination of iron in mineral samples.     

The petentiometric determination of peroxide hydrogen and glucose on the glassy electrode modified by the calix[4]arene

A new petentiometric method to determine peroxide hydrogen and glucose had been studied. This method had been applied on the petentiometric determination of peroxide hydrogen and glucose in the total ionic strength adjustment buffer (TISAB) (pH 7.5) solution with the glassy electrode modified by the calix[4]arene. The glassy carbon electrode covered with the calix[4]arene depended on the H₂O₂ concentration in the range of log[H₂O₂] from −3.3 to −1.2 in the solution of TISAB (pH 7.5) with nearly Nernstian slope of about 65.6 ± 3 mV and the detection limit of peroxide hydrogen was 4.0 × 10⁻⁵ mol L⁻¹. The glassy carbon electrode covered with the calix[4]arene depended on the glucose concentration in the range of log[glucose] from −3.6 to −2.8 in the solution of TISAB (pH 7.5) with nearly Nernstian slope of about 50.2 ± 2 mV and the detection limit of glucose was 2.0 × 10⁻⁵ mol L⁻¹. The electrode had the good selectivity, sensitivity, stability and repeatability.     

The fluoride ion-selective electrode in flow injection analysis : Part 3. Applications

Flow-injection potentiometry with a combination fluoride-selective electrode is used to determine fluoride in tap water, beverages and urine. Excellent sensitivity (down to 1 μg l^?1) and long-term stability are obtained, with a sample throughput of 30–40 h^?1, based on triplicate injections at 120 h^?1. The commonly used buffer TISAB-III is unsuitable for the analysis of undiluted tea and urine samples. The application of a modified citrate-containing TISAB overcomes interferences caused by high natural ionic strength and avoids complexation of fluoride. Recoveries after spiking tap water, tea and urine with fluoride concentration ranging from 0.01 to 1 mg l^?1 are in the range 91–106%. The equipment used provides a flexible system allowing fast changes between different buffers and carrier streams depending on the samples presented.     

Simultaneous flow injection determination of calcium and fluoride in natural and borehole water with conventional ion-selective electrodes in series

An on-line automated system for the simultaneous flow injection determination of calcium and fluoride in natural and borehole water with conventional calcium-selective and fluoride-selective membrane electrodes as sensors in series is described. Samples (30 μl) are injected into a TISAB II (pH=5.50) carrier solution as an ionic strength adjustment buffer. The sample-buffer zone formed is first channeled to a fluoride-selective membrane electrode and then via the calcium-selective membrane electrode to the reference electrodes. The system is suitable for the simultaneous on-site monitoring of calcium (linear range 10⁻⁵–10⁻² mol l⁻¹ detection limit 1.94×10⁻⁶ mol l⁻¹ recovery 99.22%, RSD<0.5%) and fluoride (linear range 10⁻⁵–10⁻² mol l⁻¹ detection limit 4.83×10⁻⁶ mol l⁻¹ recovery 98.63%, RSD=0.3%) at a sampling rate of 60 samples h⁻¹.     

A new TISAB with Aluminon for fluoride determination in water with ion-selective electrode

The application of a new TISAB solution with Aluminon as a complexing agent for the determination of fluoride with a fluoride ion-selective electrode in various water samples has been studied. The proposed TISAB has been compared to some of the well-known TISABs in the literature, since it concerns the linear response and equilibrium time of the electrode, as well as the effectiveness on complexation of Al³⁺, Fe³⁺, Mg²⁺, and Ca²⁺. The experimental results showed that the use of TISAB-Aluminon results in high sensitivity of the electrode in low fluoride concentrations, short equilibrium time, and equal or better ability to eliminate the interferences of the cations mentioned.     

Simultaneous direct determination of aluminum, calcium and iron in silicon carbide and silicon nitride powders by slurry-sampling graphite furnace AAS.

A fast and accurate analytical method was established for the simultaneous direct determination of aluminum, calcium and iron in silicon carbide and silicon nitride powders by graphite furnace atomic absorption spectrometry using a slurry sampling technique and a Hitachi Model Z-9000 atomic absorption spectrometer. The slurry samples were prepared by the ultrasonication of silicon carbide or silicon nitride powders with 0.1 M nitric acid. Calibration curves were prepared by using a mixed standard solution containing aluminum, calcium, iron and 0.1 M nitric acid. The analytical results of the proposed method for aluminum, calcium and iron in silicon carbide and silicon nitride reference materials were in good agreement with the reference values. The detection limits for aluminum, calcium and iron were 0.6 microg/g, 0.15 microg/g and 2.5 microg/g, respectively, in solid samples, when 200 mg of powdered samples were suspended in 20 ml of 0.1 M nitric acid and a 10 microl portion of the slurry sample was then measured. The relative standard deviation of the determination of aluminum, calcium and iron was 5 - 33%.     

Calcium binding by fulvic acids studied by an ion selective electrode an ultrafiltration method

The interaction between Ca(2+) and two well-characterized fulvic acids (Armadale and Laurentide FA) has been studied at 0.100 and 0.010M sodium nitrate using a fixed concentration of fulvic acid (100 ppm) and varying amounts of calcium (0.005-0.020 mmoles). Free calcium concentration was determined by in situ measurements employing a calcium electrode. For Armadale FA, free calcium was additionally determined via an ultrafiltration technique followed by atomic absorption measurements. For both fulvic acids, Ca(2+) binding was observed to be decreased by an increase in the ionic strength of the system. At the lower ionic strength the tendency for binding is dependent on the fulvic acid-to-metal ratio while at the higher ionic strength, the binding is insensitive to changes in the fulvic acid-to-metal ratio (an observation corroborating the contention that calcium binding to humic substances is primarily electrostatic). Comparison of the computed overall complex formation functions shows that values obtained from the ultrafiltration method were higher than those obtained using the calcium electrode. The binding of calcium was similar for the two fulvic acids.     

Reliable electrophoretic mobilities free from Joule heating effects using CE

Ionic electrophoretic mobilities determined by means of CE experiments are sometimes different when compared to generally accepted values based on limiting ionic conductance measurements. While the effect of ionic strength on electrophoretic mobility has been long understood, the increase in the mobility that results from Joule heating (the resistive heating that occurs when a current passes through an electrolyte) has been largely overlooked. In this work, a simple method for obtaining reliable and reproducible values of electrophoretic mobility is described. The electrophoretic mobility is measured over a range of driving powers and the extrapolation to zero power dissipation is employed to eliminate the effect of Joule heating. These extrapolated values of electrophoretic mobility can then be used to calculate limiting ionic mobilities by making a correction for ionic strength; this somewhat complicated calculation is conveniently performed by using the freeware program PeakMaster 5. These straightforward procedures improve the agreement between experimentally determined and literature values of limiting ionic mobility by at least one order of magnitude. Using Tris-chromate BGE with a value of conductivity 0.34 S/m and ionic strength 59 mM at a modest dissipated power per unit length of 2.0 W/m, values of mobility for inorganic anions were increased by an average of 12.6% relative to their values free from the effects of Joule heating. These increases were accompanied by a reduction in mobilities due to the ionic strength effect, which was 11% for univalent and 28% for divalent inorganic ions compared to their limiting ionic mobilities. Additionally, it was possible to determine the limiting ionic mobility for a number of aromatic anions by using PeakMaster 5 to perform an ionic strength correction. A major significance of this work is in being able to use CE to obtain reliable and accurate values of electrophoretic mobilities with all its benefits, including understanding and interpretation of physicochemical phenomena and the ability to model and simulate such phenomena accurately.     

Determination of the second ionization constant of 3,5-dinitrosalicylic acid (DNSH2) and the instability constant of [DNSFe]+ and titrimetric determination of thiourea with a 3,5-dinitrosalicylate-selective electrode

Measurements made with a combination of glass and 3,5-dinitrosalicylate-selective membrane electrode in DNSHNa solutions varying in pH and ionic strength have been used to determine the second ionization constant of 3,5-dinitrosalicylic acid. Also the instability constant of the complex [DNSFe]⁺ has been determined by titrating known amounts of iron(III) with standard DNSHNa solution. A method has been developed for the semiautomatic potentiometric titration of thiourea with silver nitrate in the presence of 3,5-dinitrosalicylate ions, using the aforementioned selective electrode. Thiourea in the range 1.5–15 mg was determined with average relative error and relative standard deviation of about 1%.     

Kinetic and equilibrium study of the reaction of nitroprusside and hydroxide ions: Influence of ionic strength using Pitzer model

A kinetic and equilibrium study of the addition reaction of hydroxide ions to nitroprusside has been carried out in this paper. Rate and equilibrium constants at different salt concentrations (up to 4 mol kg^?1) were obtained, and the influence of ionic strength was studied by means of Pitzer equations. This model is of special interest because it is able to explain the experimental behavior at high ionic strength, when Debye–Huckel limiting law is no longer valid. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 650–660, 2004     

Diffusion coefficients at rotated microelectrodes

The limiting current for several electrode reactions at a rotated microelectrode is observed to vary with the two-thirds power of the diffusion coefficient at infinite dilution in accordance with the theories of TACHI, EISBNBERG, LIN, and others. However, the uncertainties involved in estimating diffusion coefficients at given ionic strength require, that for accurate work, the limiting currents for different electrode reactions be compared on the basis of electrode sensivity, k_ion= i₁/C, and without regard to the role of diffusion in the transport process. The method of LAITINEN AND KOLTHOFF using an electrode reaction with only linear diffusion is recommended for measuring diffusion coefficients at given ionic strength under conditions similar to those extant in voltammetry.     

The impact of ionic strength and background electrolyte on pH measurements in metal ion adsorption experiments

Our understanding of metal ion adsorption to clay minerals has progressed significantly over the past several decades, and theories have been promulgated to describe and predict the impacts of pH, ionic strength, and background solution composition on the extent of adsorption. Studies evaluating the effects of ionic strength on adsorption typically employ a broad range of background electrolyte concentrations. Measurement of pH in these systems can be inaccurate when pH values are measured with liquid junction pH probes calibrated with standard buffers due to changes in the liquid junction potential between standard, low ionic strength (0.05 M) buffers and high ionic strength solutions (>0.1 M). The objective of this research is to determine the extent of the error in pH values measured at high ionic strength, and to develop an approach for accurately measuring pH over a range of ionic strengths using a combined pH electrode. To achieve this objective, the adsorption of cobalt (10(-5) M) onto gibbsite (10 g/L) from various electrolyte solutions (0.01-1 M) was studied. The pH measurements were determined from calibrations with standard buffers and ionic strength corrected buffer calibrations. The results show a significant effect of the aqueous solution background electrolyte anion and ionic strength on pH measurement. The 0.5 and 1 M ionic strength metal ion adsorption edges shifted to lower pH with increasing ionic strength when pH was calibrated with standard buffers whereas no shift in the adsorption edges was observed when calibrated with ionic strength corrected buffers. Therefore, to obtain an accurate pH measurement, pH calibration should contain the same electrolyte and ionic strength as the samples.     

Acetylcholinesterase Immobilization on 3‐Mercaptopropionic Acid Self Assembled Monolayer for Determination of Pesticides

Studies on the immobilization of acetylcholinesterase onto a SAM gold electrode and the use of the fabricated biosensor for the determination of carbaryl and parathion are presented. The influence of pH, ionic strength, enzyme loading and concentration of glutaraldehyde on the response of the biosensor was investigated . The amperometric biosensor developed in this study provided linearity to parathion and carbaryl in the 2.0 a 30.0×10^?6 mol L^?1 concentration range. The detection limits under the optimum working conditions were found to be 9.3 μg L^?1 for parathion and 9.0 μg L^?1 for carbaryl. The enzyme electrode was found to be stable for 7 days.     

Flow injection potentiometry by a new coated graphite ion-selective electrode for the determination of Pb(2+)

A new graphite coated electrode for the determination of Pb²⁺ based on a recently synthesized ionophore 1-hydroxy-2-{2-[2-(2-hydroxy-ethoxy)-ethoxy]-ethoxy methyl}-anthracene-9,10-dione (L) has been developed. The electrode was used in flow injection potentiometry by a home-made flow cell. Under both the batch and flow conditions, the electrode revealed a near Nernstian response over a wide lead ion concentration range (10⁻⁶ to 10⁻¹ M) and very low limit of detection. In flow injection potentiometry, excellent reproducibility (RSD%=0.49%), very high sampling rate (170 injections h⁻¹) and stable baseline was observed in the presence of 10⁻³ M KCl as ionic strength adjuster. The electrode showed high sensitivity and good selectivity for Pb²⁺ over a wide variety of alkali, alkali earth and transition metal ions and the electrode can be used for at least 3 months without any considerable change in potential response. The proposed sensor was successfully applied to the direct determination of lead in real samples and also used for the titrimetric determination of phosphate ions by both batch and flow injection potentiometry.     

Bipolar pulse conductometric monitoring of ion-selective electrodes: Part 1. Method development with a calcium-selective electrode and elucidation of the basic principles involved

The potential generated by a plastic-membrane calcium ion-selective electrode (i.s.e.) is shown to be indirectly measurable by a non-zero current method based on bipolar pulse conductance. Linear current—voltage curves are obtained using 0–5-V pulses; the current axis intercept is related to the i.s.e. potential. A simple electrical contact (e.g., platinum or stainless steel) can be used instead of a poised reference electrode as the counter electrode in this two-electrode system. Long-term exposure of the i.s.e. to calcium solutions causes an upward drift in the measured current. This drift is minimized by avoiding long exposure times to solution, rinsing the electrode between measurements, and constructing current—voltage curves for determination of the current axis intercepts. Voltage pulses lasting 100 μs are optimum for this method. Shorter pulses are subject to error from capacitive charging currents, and longer pulses yield poorer precision, and degrade the electrode through faradaic reactions. The measured signal is dependent upon Ca²⁺ concentration (rather than activity), making ionic strength adjustment unnecessary. The concentration dependence is induced by application of voltage pulses greater than ~ 15 mV in amplitude. Selectivities of the potentiometric and conductometric methods are shown to be comparable for a variety of interfering monovalent and divalent cations. The conductometric method yields a fast i.s.e. response because of induced migration of Ca²⁺ into the membrane. Response time decreases as the pulse height increases. Pulses greater than 2 V in magnitude yield response times limited by the solution mixing time rather than by the electrode.     

Determination of Total and Fluoride Bound Aluminium in Tea Infusions by Ion Selective Electrode and Flame Atomic Absorption Spectrometry

ABSTRACT

Speciation of metallic compunds is important especially for their bioavailability. In this present study fluoride bound aluminium species were determined in tea infusion. Total aluminium was measured using flame atomic absorption spectrometry (FAAS). Free fluoride and total fluoride were measured by fluoride selective ion electrode (FISE) with the assistance of TISAB buffer solution used for adjustment of pH and total ionic strength, and ALCOA buffer solution which decomposes all of the Al-fluoride complexes in solution.

During the studies, the effects of pH and time on the formation of Al-F complexes and interference of some metal ions found in tea infusion such as Al³⁺, Mg²⁺, Fe²⁺, Fe³⁺ and Mn²⁺ on the concentration of free fluoride were investigated. The concentration of each Al-fluoride complexes in tea fusion were determined indirectly by calculation using pF-Mole Fraction Diagram. It was found that 1.13±0.15 mg 1^? of 12.00±0.86 mg 1^? total aluminium is fluoride bound aluminium, which means that appoximately 10% of total aluminium in tea infusion is complexed with fluoride.     

Flow-injection determination of phosphate species in detergents with a calciumion-selective electrode

A calcium ion-selective electrode is applied for the determination of ligands which complex calcium ions. The response of the electrode is measured when ligand solutions are injected into a buffered carrier stream containing calcium. Injections of EDTA, citrate, tripolyphosphate and pyrophosphate provide peaks with heights dependent on both the ligand and calcium concentrations. Ligand concentrations down to. 2 × 10^?5 M can be detected. Tripolyphosphate in detergents is easily determined. Use of the electrode has advantages over spectrophotometric methods for phosphates in flow systems.     

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     

铁(Ⅲ)的滴定计算分析法测定

在Fe^2 存在的条件下，以铂电极为指示电极、Ce^4 标准溶液为滴定剂，对氧化还原滴定计算分析法测定Fe^3 进行了研究。结果表明，电极的系统误差是影响结果准确度的主要因素。     

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.