Indicator Electrode Research Articles

A novel copper selective sensor based on ion imprinted 2-vinylpyridine polymer

A novel potentiometric Cu2+-selective microsensor has been developed that is based upon ion imprinted 2-vinylpyridine polymer. The polymer was synthesized using Cu(II) ions, 2-vinylpyridine, methacrylic acid, and ethylene glycol dimethacrylate as a template, functional monomer, and cross-linker, respectively. The resultant polymer was used as ionophore to obtain a selective potentiometric response towards Cu(II) ions in the structure of the PVC membrane. The detection limit of the microsensor was determined to be 8.4 × 10−7mol/L, and its response time was considerably short (less than 15 s). The prepared microsensor exhibited a near-Nernstian response for Cu(II) ions over the concentration range of 10−1to 10−6mol/L, with a slope of 28.5 mV per decade over 2 months, and without any considerable divergence in potentials. The microsensor was effectively performed in a pH range between 4.0 and 7.0 and used as an indicator electrode in the potentiometric titration of Cu(II) ions with EDTA. The proposed microsensor has been successfully demonstrated for the determination of copper in a number of environmental water samples. The obtained potentiometric results were in good harmony with the results obtained by the AAS method.

Synthesis of Urea Sensors using Potentiometric Methods with Modification of Electrode Membranes Indicators of ISE from PVA-Enzymes Coating PVC-KTpClPB

Potentiometric sensors provide an opportunity to perform biomedical, environmental analysis, and industry analysis, these sensors are generally easy to use, portable, simple, and inexpensive. The potentiometric method is a method of measuring the potential difference of the balance between the indicator electrode and the reference electrode. Chemical sensors are a device that can convert chemical quantities into electrical quantities. Chemical sensors sensitive to one analyte involve a combination of molecular recognition elements PVA-enzyme PVC-KTpClPB and transducer to detect an analytical bond through a voltage signal. The urease enzyme is used for the determination of urea, the urea sensor means an accurate determination of urea essential with respect to renal function and biomedical applications. ISE is a good approach to build chemical sensors in detecting urea analyte. The immobilized product as a molecular recognition element of PVC-enzyme PVC-KTpClPB has a sensitivity of 19,069 mV/decade R2 = 0.94 with a range of 1.10-5 - 5.10-4 M in electrolyte solution consisting of buffer KH2PO4 0.001 M and KCl 0.001 M.

Synthesis and characterization of cation exchange membrane based on Polyaniline Bi(III)tungstophosphate nanocomposite: its application as Ni(II) selective electrode

In the present study an organic-inorganic nanocomposite ion exchanger Polyaniline Bi(III)tungstophosphate was synthesized via sol-gel process showing excellent ion exchange capacity (IEC–3.2 meqg−1). It showed high DC electrical conductivity (3.35 S cm−1) with good retention capability up to 120 °C under isothermal and cyclic ageing experiments. This nanocomposite was utilized in preparation of heterogeneous ion exchange membrane (IEC–1.2 meqg−1) by solution casting method. The materials were characterized by SEM with EDX, TEM, XRD, FTIR, and TGA-DTA. A Ni2+ selective membrane electrode was fabricated, and its various parameters like detection limit (6.3 × 10−8 M), linear response range (6.3 × 10−8 M to 1.0 × 10−1 M), response time (35 s) and working pH range (4–8) were calculated. It was employed as an indicator electrode in the potentiometric titration of Ni2+.

Application of 1,4-Diaminoanthraquinone as a New Sensing Material for Fabrication of a Iron(III)-Selective Modified Carbon Paste Electrode

In the present work, a novel sensitive electrochemical potentiometric sensor for sensing Fe3+ ions based on 1,4-diaminoanthraquinone (DAQ) as a hydrophobic selector element was prepared to implement as an ion selective carbon paste electrode in the aqueous solutions. The adequate amounts of ionophore (5%), paraffin oil (25%) as a binder, Nanosilica (NS: 0.5%) multi-wall carbon nanotubes (MWCNTs: 1%) as a modifier, and graphite powder (68.5%) as an inert matrix was occupied to form the paste. This new FeCP sensor demonstrated a Nernstian slope of 19.7 ± 0.7 mV per decade over widish linear range between 1.0 × 10–8 to 1.0 × 10–2 mol L–1 at working pH range of 1.9–5.0 in the optimized conditions. The average elapsed time to response of electrode was about ~6 s for concentrations from lower (1.0 × 10−8 mol L–1) to higher (1.0 × 10−2 mol L–1) of Fe3+ ion solution. The selectivity of electrode toward Fe3+ ions in comparison with other cations was studied by matched potential method. The making FeCP sensor has been put to use successfully as an indicator electrode in analytical applications such as the potentiometric titration and determination of iron(III) ion in blend of different ions.

New chemically modified carbon paste sensor for nanomolar concentration measurement of rifampicin in biological and pharmaceutical media

A new carbon paste electrode for rifampicin (RIF) drug was prepared and fully characterized in terms of composition, usable pH range and temperature. The sensor is based on 2-hydroxypropyl β-cyclodextrin as a good ionophore in the carbon paste matrix. The modified electrode showed a Nernstian slope of 59.2 mV/decade over the concentration range of 3.2 × 10−8 to 2.2 × 10−4 M with a limit of detection 2.3 × 10−8 M. The electrode has a short and stable response time of 4 s. The sensor manifested advantages of simple design, low cost, wide concentration range, excellent selectivity to rifampicin, applicable as an indicator electrode and renewability. The sensor was successfully used for determination of rifampicin in tablet and blood serum samples. Temperature dependence of the sensor potential response was examined in the temperature range of 15–55 °C. The sensor showed a very low thermal coefficient within the studied temperature range.

A Novel Modified Carbon Paste Electrode for the Determination of Chromium(III) in Water

Two kinds of modified carbon paste electrodes for chromium(III) ion based on zeolite as ionophore were prepared. 3-Methylpyrazol-5-one was used as modifier in sensor 1. Sensor 1 exhibits a Nernstian response for Cr(III) ions over a wide concentration range from 1 × 10–6 to 1 × 10–2 M with a slope of 19.8 ± 0.1 mV/decade. Sensor 2 was modified by using chlorinated multiwalled carbon nanotubes. This sensor shows a Nernstian response for Cr(III) ions over a concentration range from 1 × 10–7 to 1 × 10–2 M with a slope of 19.74 ± 0.1 mV/decade. Some parameters were optimized for the two sensors, such as pH of solution, composition of membrane and response time of electrode. The sensors were successfully applied to direct determination of chromium(III) in water samples and as an indicator electrodes in potentiometric titration of Cr(III) with EDTA.

Determination of Cu2+ in aqueous solution using a polyindole–tin(IV) molybdophosphate conductive nanocomposite ion-selective membrane electrode

Polyindole–tin (IV) molybdophosphate (PIn-SMP), an organic-inorganic nanocomposite ion exchanger, was synthesized by a sol-gel process and exhibited excellent ion exchange capacity (2.1 meq g−1). A heterogeneous ion exchange membrane of PIn-SMP (ion exchange capacity 0.95 meq g−1) was also prepared by a solution casting method. The materials were characterized by various instrumental methods, such as scanning electron microscopy, transmission electron microscopy, Fourier transform IR spectroscopy, and thermogravimetric analysis. PIn-SMP exhibits high electrical conductivity (6.1 × 10−2 S/cm) and is stable up to 120 °C under ambient conditions. A Cu2+-selective membrane electrode was fabricated, and its linear working range (1.8 × 10−7–1.0 × 10−1 M), response time (20 s), Nernstian slope (24.07 mV dec−1), and working pH range (4–7) were calculated. Moreover, it was used as an indicator electrode in the potentiometric titration of Cu2+.

Preparation of new and novel wave like poly(2-anisidine) zirconium tungstate nanocomposite: Thermal, electrical and ion-selective studies

Abstract It is necessary to synthesize new material for the advancements of the technology. In this study, new and novel poly(2-anisidine)@zirconium tungstate (P2A/ZrW2O8) was synthesized by simple so-gel method. Physicochemical characterization of P2A/ZrW2O8 was done by thermogravimetric analysis (TGA), scanning electron microscopy (SEM), X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), ion exchange and simultaneous four probe dc conductivity studies. The conductivity study revealed its highly semiconducting nature, in the range of 10− 1–10− 2 S·cm− 1. Ion-exchange capabilities of the composite make it applicable for cation-exchange studies. The result of distribution studies (Kd) revealed its selectivity towards Cd2 + compared to other metal ions. This property of the composite was utilized for designing Cd2 + selective membrane electrode. Several important physical parameters of the ion-selective electrode were determined, such as Nernstian slope (32.32 mV·decade− 1), working pH range was 2.0–4.0 and response time was found ~ 17 s. The analytical utility of this wave like composite membrane electrode was as, indicator electrode in various potentiometric titrations.

Electrochemical Determination of Copper(II) in Water Samples Using a Novel Ion-Selective Electrode Based on a Graphite Oxide–Imprinted Polymer Composite

ABSTRACTA novel copper(II)-selective electrode based on graphite oxide/imprinted polymer composite was developed for the electrochemical monitoring of copper(II) (Cu2+) ions. The electrode exhibited highly selective potentiometric response to Cu2+ with respect to common alkaline, alkaline earth and heavy metal cations. The composite composition studies indicated that the most suitable composite composition performing the most promising potentiometric properties was 20.0% ionophore (Cu2+-ion imprinted polymer), 10.0% paraffin oil, 5.0% multiwalled carbon nanotubes, and 65.0% graphite oxide. The fabricated electrode exhibited a linear response to Cu2+ over the concentration range of 1.0 × 10− 6–1.0 × 10− 1 M (correlation coefficient of 0.9998) with a sensitivity of 26.1 ± 0.9 mV decade− 1. The detection limit of the fabricated electrode was determined to be 4.0 × 10− 7 M. The electrode worked well in the pH range of 4.0–8.0. The electrode had stable, reversible and fast potentiometric response (3 s). In addition, the electrode had a lifetime of more than 1 year. The analytical applications of the proposed electrode were performed using as an indicator electrode for the potentiometric titration of Cu2+ with ethylene diamine tetraacetic acid solution and for the determination of Cu2+ of spiked river, dam, and tap water samples. The obtained results for potentiometric titration and water samples were satisfactory.

All‐solid‐State Potentiometric Cu(II)‐selective Sensor Based on Ion Imprinted Methacrylamide Polymer

AbstractIn this study; a novel all‐solid‐state type potentiometric microsensor based on ion‐imprinted polymer (IIP) has been developed for Cu(II) sensing. The IIP was synthesized by suspension polymerization by using Cu(II) ion, methacrylamide, methacrylic acid and ethylene glycol dimethacrylate as template, functional monomers and cross‐linker respectively. The resultant Cu(II)‐imprinted polymer was used as ionophore in the structure of the PVC membrane to obtain a selective potentiometric response towards Cu(II) ions. The fabricated microsensor exhibited a highly selective Nernstian response (28.6±2.2 mV per decade) over the concentration range of 10−1 to 10−6 mol L−1 of Cu2+ ion for 2 months without any considerable divergence in potentials. The response time of the microsensor was considerably short (less than 15 s) and its detection limit was determined as 7.6×10−7 mol L−1. The microsensor was effectively performed in the pH range of 4–7. The microsensor was successfully used as an indicator electrode in the potentiometric titration of Cu(II) ions with EDTA. The proposed microsensor was also used for the determination of Cu(II) contents of some environmental water samples. The obtained potentiometric results were in good harmony with the results obtained by the AAS method.

Potentiometric Graphite Coated Electrode Based on Ditertbutyl-cyclohexano18crown6 for Detection of Strontium (II) Ions

In this work, a highly sensitive strontium ion selective polymer membrane coated on a graphite electrode based on ditertbutylcyclohexano18crown6 as ionophore is described. The sensor responds to strontium ions in a linear concentration range of 10-5 - 10-1 M with a Nernstian slope of 29.1 ± 0.3 mV/decade and a detection limit of 4.0×10-6 M in the pH range of 3.0 - 10.6. It has a fast response time of less than 10 s and can be used for at least 5 months without any considerable divergence in its potentials. The proposed sensor revealed good selectivity for strontium ions with respect to other cations and was used as an indicator electrode in the potentiometric titration of strontium ions with EDTA and also in the determination of strontium ions in binary mixtures and different real samples.

A New Highly Selective Neodymium(III) Polyvinylchloride Membrane Electrode Based on 4-Hydroxypyrrolidine-2-Carboxylic Acid as an Active Material

The present paper describes the fabrication of a new polyvinylchloride (PVC) membrane electrode for the determination of Nd(III) ion based on 4-hydroxypyrrolidine-2-carboxylic acid (LHP) as an active material along with sodium tetraphenyl borate (NaTPB) as an anionic additive and acetophenone (AP) as solvent mediator. The optimum composition (%, w/w) of the best performing membrane contained 66 AP, 30 PVC, 2 NaTPB and 3 LHP. The basic analytical parameters of this electrode such as slope characteristics, detection limit, response time, selectivity and pH effect were assessed. The electrode displayed a Nernstian response in terms of slope (20.5 ± 0.4 mV per decade) and response time (~8 ± 1 s) over a wide neodymium ion concentration range of 10–6 to 10–2 M with a detection limit of 7.5 × 10−7 M. The potentiometric response of the electrode was constant in the pH range of 3.2‒8.9. According to the selectivity coefficients determined by the matched potential method, the interference of many common alkaline, alkaline earth, transition, heavy metals and specially lanthanide ions in determination of Nd(III) ion was very low. The proposed electrode has been successfully used as an indicator electrode in the potentiometric titration of Nd(III) ion with EDTA and applied for determination of Nd(III) ion in mixtures of different ions.

Fabrication of Pb(II) Selective Polymeric Membrane Electrode Based on 2,2’[Propane-1,3-Diylbis(Oxy)]Dibenzaldehyde as an Ionophore. J Anal Bioanal Tech

2,2'-[propane-1,3-diylbis(oxy)]dibenzaldehyde has been explored as an ionophore and fabricated in a polyvinylchloride (PVC)-based membrane. The electrode shows excellent potentiometric response characteristics and displays a linear log [Pb(II)] versus emf response over a wide concentration range of 1.2 × 10-7 M to 1.0 × 10-1 M with detection limit 3.3 × 10-8 M and having nernstian slope of 29.06 mV/decade. Potential response remains almost unchanged at pH range of 3.0-8.0. The electrode shows fast response time of <10 s and a lifetime of four months. It shows good selectivity for Pb(II) ions over the other cations. The complexation 2,2'-[propane-1,3- diylbis(oxy)]dibenzaldehyde and Pb(II) cation was studied spectrophotometrically in 1:1 DMF:H2 O mixed solvents. Spectra shows the strong interaction between Ionophore and Pb(II) ion. The electrode can also be used as an indicator electrode in potentiometric titration of Pb(II) ions with standard chromate solution and its determination in real samples.

Ionophore Properties of Schiff Base Compounds as Ion Sensing Molecules for Fabricating Cu(II) Ion-Selective Electrodes

Bis(2-hydroxybenzaldehyde)-1,2-diaminoethane (LI), bis(2-hydroxybenzaldehyde)-1,3-diaminopropane (LII) and bis(2-hydroxybenzaldehyde)-4,4'-methylendianiline (LIII) were examined as ionophores for fabrication of polyvinylchloride (PVC) membrane Cu(II) ion-selective potentiometric sensors. The optimum composition (%) for the sensors was: 5 LI, 30 PVC, 6 sodium tetraphenylborate (NaTPB), 59 ortho-nitrophenyloctyl ether (NPOE); 4 LII, 30 PVC, 5 NaTPB, 61 dibutyl phthalate; 6 LIII, 30 PVC, 5 NaTPB, 59 NPOE. The linear response range of the electrodes was 5 × 10–4–0.05 (LI), 5 × 10–4–0.1 (LII) and 1 × 10–6–0.01 M (LIII), and the corresponding detection limits were 4 × 10–4, 4 × 10–4 and 2 × 10–7 M, respectively. The sensors were showed rapid response time (≈10 s). Their responses were independent on pH in the range 2.5–5.0 (LI), 3.2–4.7 (LII) and 4.0–5.0 (LIII). The selectivity of the prepared electrodes towards copper ions over some mono-, di- and trivalent metal ions was evaluated. The sensors were used as indicator electrode in potentiometric titration of copper ions in aqueous solutions.

Pyrite/pyrrhotite mineral based electrochemical sensor for redox determination in aqueous media

The characterization, construction and performance characteristics of a novel sensor have been carried out. With this purpose, an accurate characterization of the mineral has been performed using scanning electron microscopy (SEM/EDX), X-ray spectrometer and potentiometry. The elemental composition of the sample has been obtained by X-ray microanalysis. The main compounds of the mineral are a pyrite and a pyrrhotite. The potentiometric analysis has allowed investigating some properties of the pyrite/pyrrhotite mineral as a potential sensor material. This technique has also been useful to investigate possibility of using this mineral as indicator electrode for redox determination in aqueous solution. The sensor based on pyrite/pyrrhotite mineral as an electroactive material, displays a stable, reproducible and linear response for iron(III) over concentration range of 10-6-10-1 mol/L with non-Nernstian slope of 38.7 ± 0.6 mV per decade. The response time was 10 s. The proposed sensor was applied to determine cobalt(II) and the results were compared with that of a platinum electrode. The determination of 2 mg of cobalt(II) shows an average recovery of 100.9%. The relative standard deviation of this method was 0.5%.

Highly Selective Lead(II) Coated Graphite Sensor Based on 4,13-Didecyl-1,7,10,16-tetraoxa-4,13- diazacyclooctadecane as a Neutral Ionophore

4,13-Didecyl-1,7,10,16-tetraoxa-4,13-diazacyclooctadecane (kryptofix22DD) has been explored as a neutral ionophore for preparing polyvinyl chloride (PVC)-based membrane sensor selective to lead(II). The optimized membrane incorporating kryptofix22DD as the active material, nitrobenzene as plasticizer and sodium tetraphenylborate as an anion excluder and membrane modifier in PVC (in the weight ratio of 5.0: 63.0: 2.0: 30.0, respectively) was directly coated on the surface of graphite rod. The sensor exhibits a Nernstian slope (29.4 mV/decade) in the concentration range of 1.0 × 10–5 to 1.0 × 10–1 M Pb2+. The detection limit of the sensor is 6.5 × 10–6 M. The proposed sensor has a fast response time (~10 s), a satisfactory reproducibility and relatively long lifetime. The electrode shows high selectivity toward Pb2+ ion in comparison to other common cations. The proposed sensor is suitable for use in aqueous solutions in a wide pH range of 2.0–10.0. It was used as an indicator electrode for the end point detection in the potentiometric titration of Pb2+ ion with ethylenediaminetetraacetic acid (EDTA) and sodium iodide (NaI) solutions. The proposed sensor was successfully applied for the recovery of Pb2+ ions spiked in real water samples.

Evaluation of Serum Electrolytes among Psoriasis Patients: A Prospective Case-Control Study from Telangana, South India

Background: Psoriasis is a non-contagious autoimmune skin disorder. Patients present with symptoms of abnormal patches on the skin, joints and nails, which are dry and itchy. There are many factors responsible for this disease which initiates an inflammatory response leading to abnormal keratinization of the skin. Electrolytes play a significant role in maintaining the cell function and fluid balance both within and surrounding the cell. Any disturbance in the electrolyte balance could cause fluid loss and cell death/damage.Objective: None of the previous research studies have evaluated the role of electrolytes in the management and progression of psoriasis. The present study is aimed to assess the levels of electrolytes (sodium and potassium) among patients diagnosed with psoriasis.Methods: A prospective case-control study was conducted, which included 25 patients diagnosed with psoriasis and equal number of age and sex matched control group without psoriasis. The study was carried out at the Chalmeda Anandrao institute of medical sciences, a tertiary care teaching hospital located at Karimnagar, Telangana, India. Blood samples were collected from all the subjects included in the study and serum electrolyte (sodium and potassium) levels were measured using an indicator electrode of standard potential.Results: The mean levels of serum electrolytes (sodium and potassium) and the ratio of sodium to potassium among the psoriasis patients and the control subjects. The results demonstrated an increase of electrolyte levels of sodium (151.04 ± 3.79; p<0.0001), sodium to potassium ratio (44.999 ± 5.37; p<0.0001) and a decrease in the levels of potassium (3.352 ± 0.28; p<0.0001) as compared to the controls. Conclusion: There is an evidence of electrolyte imbalance among psoriasis patients. The levels of sodium and sodium to potassium ratio increased and the potassium levels were reduced. Further studies including a larger group of psoriasis patients and a regular follow-up of serum electrolytes may improve the understanding of the role of electrolytes in psoriasis disease and its progression.

Development of a potentiometric sensor for europium(III) based on N, N, N′, N′-tetraoctyldiglycolamide (TODGA) as the ionophore

A polymer inclusion membrane (PIM) with N,N,N′,N′-tetraoctyl diglycolamide (TODGA) as the ionophore and polyvinyl chloride (PVC) as the base polymers was synthesized and evaluated for potentiometric membrane sensing of Eu3+ ions. Effects of membrane composition, inner filling solution and pH on the electrode performance were investigated and it was found that the membrane with a composition of 30.3% TODGA, 9.1% NaTPB and 60.6% PVC showed a wide linear dynamic range (1.5×10−6M to 1.2×10−2M) with a slope of 17.3±0.1mV per decade with 1.2×10−6M as the limit of detection for Eu3+. Interference from mono-, di-, tri-, tetra- and hexa-valent ions was investigated by matched potential method. The sensor was also tested as an indicator electrode in the titration of Eu3+ with standard EDTA solution. The response time of the proposed sensor was found to be <10s. The life time of the sensor electrode was found to be one month under optimized storage conditions. The potentiometric sensor as developed was employed in the determination of Eu3+ in the synthetic mixture of uranyl nitrate and europium nitrate, after the removal of major matrix using 30% TBP-n-dodecane. The analytical results, compared with those obtained from inductively coupled plasma - atomic emission spectroscopy (ICP-AES), showed good agreement between the two methods.

Platinum electrode regeneration and quality control method for chronopotentiometric and chronoamperometric determination of antioxidant activity of biological fluids

The state of the indicator electrode surface, its quality control and regeneration methods play a major role in electroanalysis results. It is especially important in in the analysis of biological fluids and tissue, because the adsorption of biological matrix components may distort analytical signals and results of the analysis. This article describes an integrated approach to resolving the problem, which includes the selection of regeneration and quality control methods evaluation of availability of platinum screen-printed electrodes for chronopotentiometric and chronoamperometric analysis, as well as their use for determining antioxidant activity of blood serum and ejaculate. The electrodes are treated with solvents (acetone or ethanol) or subjected to annealing. Sources of information about the availability of electrodes for measurements are chronopotentiograms, chronoamperograms and cyclic voltammograms. For chronopotentiometric and chronoamperometric analyses, the most effective regeneration method is annealing at 750°C for 1h. Satisfactory regenerated platinum screen-printed electrodes are used as indicator electrodes for evaluating antioxidant activity of blood serum and ejaculate with the use of chronopotentiometry and chronoamperometry. The role of indifferent electrolyte in analytical signal formation is considered. Composition of solution used for different biological fluids (blood serum/plasma, ejaculate) was optimized and unified. The obtained results demonstrate a strong correlation: r=0.91 for blood serum and r=0.80 for the ejaculate.

Rapid Monitoring of Copper Over a Wide Concentration range by High-Sensitive Potentiometric Membrane Electrode Based on 1-cyano-1-piperidino-2(N- piperidino methyl)-cyclo hexane

n this paper, 1-cyano-1-piperidino-2(N- piperidino meth-yl)-cyclohexane was synthesized. The lowest-energy conformer of this molecule (Ligand) with axial and equatorial forms of cyanide toward cyclohexane and local minima corresponding to their complexes with various ions were obtained using Monte Carlo procedure by Molecular Mechanics with MMFF94 method. The calculated results of the Gibbs free energy of the reaction using density functional theory (DFT) show that the thermodynamic reactivity of complexation of copper ion with studied ligand is the best. Finally, a selective and sensitive copper-ion selective liquid membrane electrode for potentiometric monitoring of ultra-trace amounts of Cu2+ was prepared by using 1-cyano-1-piperid-ino-2(N- piperidino methyl)-cyclohexane as an excellent ionophore. This electrode exhibits a Nernstian response for Cu2+ ions over a con-centration range (1.5 × 10-2 to 1.0 × 10-8 mol L-1) with a slope of 28.4±0.4 mV per decade. The limit of detection of the sensor is 6.3 × 10-9 mol L-1. The sensor has a relatively fast response time (&lt;10 s) and a useful working pH range of 5.0–8.5. Interference of some cations was also evaluated. The practical utility of the Cu2+ ion sensor has been demonstrated by using it as an indicator electrode in potentiomet-ric titration of Cu2+ with EDTA and for direct determination of Cu2+ in well water samples.