Construction of a peptide with an electroactive daunomycin like a pendant arm to detect ovalbumin

In this study, a peptide-1 (RNRCKGTDVQAW) constructing lysozyme was conjugated with an electroactive daunomycin in order to voltammetrically detect ovalbumin (OVA). Hetero-bifunctional cross-linking agents with four kinds of ethylene chains in differing lengths were used to bind the peptide-1 and daunomycin. After a cross-linking agent had reacted with an amino group of daunomycin, the compound was introduced into the peptide to the cysteine residue in the peptide using a pendant arm. The OVA was sensed via a change in the electrode response of the daunomycin moiety, based on the binding between the peptide and the OVA. The adsorption of the peptide probe on the electrode increased with increases in the ethylene chain. The binding constants between the peptide probes and the OVA, however, did not depend on the length of the chain. This was because the ethylene chain influenced the binding. When the peptide and the daunomycin were bound using N-(6-maleimidocaproyloxy) sulfosuccinimide, the electrode response of the peptide probe was the most sensitive from among the four cross-linking agents. The calibration curve of the OVA using the peptide probe was linear and ranged from 1.5 × 10⁻¹¹ to 3.0 × 10⁻¹⁰ M. Furthermore, this method could be applied to the electrochemical sensing of the OVA in egg whites and in fetal bovine serum.     

Electrochemical Sensing of Ovalbumin Based on the Interaction between Lysozyme Origin/Tyrosine‐rich Peptides Modified on Magnetic Beads and Oligothreonine/Ovalbumin‐origin Peptide

We developed a highly sensitive electrochemical system for the sensing of ovalbumin (OVA). Lysozyme origin/tyrosine‐rich peptides (RNRCKGTDVQAWY₄C) were immobilized on magnetic beads, and the competitive reaction between OVA and oligothreonine/OVA origin peptide probe (T₈VLLPDEVSG) could then be measured. In a previous study, the detection of OVA at the 10^?13 M level was achieved using RNRCKGTDVQAWY₄C‐modified beads via a cross‐linker. To improve the sensitivity to OVA, this system uses T₈VLLPDEVSG peptide probe to measure the interaction to RNRCKGTDVQAWY₄C immobilized on magnetic beads. The peak of Y₄C actually was an electron‐transfer peptide, which represented the oxidation of a phenolic hydroxyl group. First, we confirmed that the oxidation response of Y₄C was increased based on an improvement in the electron transfer accessibility by oligothreonine. Next, T₈VLLPDEVSG peptide probe was used for the electrochemical sensing of OVA in solutions that contained consistent amounts of RNRCKGTDVQAWY₄C on magnetic beads. As a result, the peak current decreased as the concentration of OVA increased. The sensitivity to OVA was improved compared with the use of only RNRCKGTDVQAWY₄C on magnetic beads. The OVA detection level was 10^?14 M, which approximates the results from antibody‐antigen reactions. Consequently, the proposed system is a powerful new concept in protein sensing.     

Construction of Protein Probe with a His-tag and an Electron-transfer Peptide for a Target Protein Sensing

A protein probe with an electron-transfer peptide and a His-tag was designed to electrochemically sense a target protein. We selected tyrosine-rich (Y₄C) and tryptophan-rich (W₄C) peptides for use as electron-transfer agents. The peak for oxidation was based on the oxidations of the phenolic hydroxy groups in Y₄C and on the indole rings in W₄C. Asialofetuin (ASF) with galactose residues was the protein probe, and a galactose recognition protein, soybean agglutinin (SBA), was the target protein. A protein probe composed of an amino acid and carbohydrate residue was expected to be biocompatible. When voltammetric measurements were performed using a glassy carbon electrode, the oxidation peaks of H₆Y₄C and ASF-H₆Y₄C appeared at the same potential. The peak current of ASF-H₆Y₄C was 4-fold that of H₆Y₄C because of the stronger adsorption of ASF-H₆Y₄C onto the electrode. The electrode response of ASF-H₆Y₄C with SBA was half that of ASF-H₆Y₄C alone. By contrast, the peak current of ASF-Y₄CH₆ was higher than that of ASF-H₆Y₄C, which was the result of a greater degree of contact between the Y₄C moieties and an electrode. On the other hand, the voltammetric behaviors of ASF with W₄C and a His-tag were similar to those with Y₄C and a His-tag. The sensitivity of SBA using ASF-Y₄CH₆ was at the 10⁻¹³ M level. To confirm the function of the sensing system, measurements were performed in human serum with SBA and ASF-Y₄CH₆. When SBA was added, the serum had a concentration that ranged between 5.0×10⁻¹³ and 4.0×10⁻¹² M, and the amount of SBA that could be recovered ranged from 97 to 101%. Consequently, this system could be applied to the detection of SBA in serum.     

Simultaneous determination of tyrosine and tryptophan by mesoporous silica nanoparticles modified carbon paste electrode using H-point standard addition method

A simple, selective and sensitive sensor based on mesoporous silica nanoparticles modified carbon paste electrode (MSNs/CPE) is introduced for electrochemical determination of tyrosine (Tyr) and tryptophan (Trp). Compared with the unmodified electrode and commercial SiO₂ modified electrode (SiO₂/CPE), the oxidation peak current significantly improved for both amino acids. Under optimized experimental conditions, the oxidation peak current of Trp was linear over a concentration range of 5.0 × 10⁻⁸ to 4.0 × 10⁻⁴ M with a detection limit of 3.4 × 10⁻⁸ M. The oxidation peak current of Tyr was linear over a concentration range from 5.0 × 10⁻⁷ to 6.0 × 10⁻⁴ M with a detection limit of 1.5 × 10⁻⁷ M. For simultaneous determination Trp and Tyr, H-point standard addition method was applied to resolve the overlapping of differential pulse voltammetric peaks of Trp and Tyr. The results showed that the method was successfully applied to the simultaneous determination of Trp and Tyr in some synthetic samples. Moreover, the applicability of the method was demonstrated by the recovery tests of Trp and Tyr in artificial urine.     

Electrochemically monitoring the binding of concanavalin A and ovalbumin

To evaluate protein-protein interactions, a new voltammetric method was developed using a protein labeled with an electroactive compound. Concanavalin A (ConA), which is a lectin, recognizes α-mannose residues. Because the ConA was to be bound to ovalbumin (OVA), which has a high-mannose sugar chain, ConA labeled with daunomycin was prepared as the probe to monitor the binding. The binding to OVA was caused by the label modification of the ConA. As a result, the electrode response of the labeled ConA decreased as the OVA concentration increased. The electrode response of the labeled ConA was linearly over the range of 1.5 × 10⁻¹⁰ and 1.5 × 10⁻⁹ M OVA. The relative standard deviation of 1.5 × 10⁻⁸ M labeled ConA and 1.5 × 10⁻¹⁰ M OVA was 6.9% (n = 5). The labeled ConA-OVA binding could then be conveniently monitored based on the change in response. In contrast, interactions between the labeled ConA and a protein with no specific sugar chain also were investigated. Incubation scarcely influenced the peak current of the labeled ConA. When several concentrations of OVA were added to a serum, good recovery determined it. Consequently, this method could be applied to the measurement of protein-protein interactions.     

Fabrication of an electrochemical sensor based on spiropyran for sensitive and selective detection of fluoride ion

In the past decades, numerous electrochemical sensors based on exogenous electroactive substance have been reported. Due to non-specific interaction between the redox mediator and the target, the instability caused by false signal may not be avoided. To address this issue, in this paper, a new electrochemical sensor based on spiropyran skeleton, namely SPOSi, was designed for specific electrochemical response to fluoride ions (F⁻). The breakage of Si–O induced by F⁻ based on the specific nucleophilic substitution reaction between F⁻ and silica would directly produce a hydroquinone structure for electrochemical signal generation. To improve the sensitivity, SPOSi probe was assembled on the single-walled carbon nanotubes (SWCNTs) modified glassy carbon electrode (GCE) through the π–π conjugating interaction. This electrode was successfully applied to monitor F⁻ with a detection limit of 8.3 × 10⁻⁸ M. Compared with the conventional F⁻ ion selected electrode (ISE) which utilized noncovalent interaction, this method displays higher stability and a comparable sensitivity in the urine samples.     

Voltammetric Sensing of Soybean Agglutinin Using an Electrode Modified with Electron-transfer,Carbohydrate-mimetic/Cross-linker-peptide-collagen Film

We constructed an electrochemical sensor based on an electrode modified with electron-transfer, carbohydrate-mimetic peptides on collagen film. The peptide consisted of Ac-Y₄C combined with soybean agglutinin (SBA). To evaluate the binding between SBA and the peptide, we prepared Ac-Y₄CA_n (3-6) containing oligoalanine as a cross-linker. When SBA and Y₄C on the electrode were incubated, the peak was decreased by the SBA uptake of the peptide. The change in the peak current using Ac-Y₄CA₆ was the greatest of the four peptides. The calibration curve was linear and ranged from 4.0×10⁻¹⁴ to 1.2×10⁻¹² M with a detection limit of 1.3×10⁻¹⁴ M.     

Preparation and characterization of Prussian blue nanowire array and bioapplication for glucose biosensing

Prussian blue nanowire array (PBNWA) was prepared via electrochemical deposition with polycarbonate membrane template for effective modification of glassy carbon electrode. The PBNWA electrode thus obtained was demonstrated to have high-catalytic activity for the electrochemical reduction of hydrogen peroxide in neutral media. This enabled the PBNWA electrode to show rapid response to H₂O₂ at a low potential of −0.1 V over a wide range of concentrations from 1 × 10⁻⁷ M to 5 × 10⁻² M with a high sensitivity of 183 μA mM⁻¹ cm⁻². Such a low-working potential also substantially improved the selectivity of the PBNWA electrode against most electroactive species such as ascorbic acid and uric acid in physiological media. A detection limit of 5 × 10⁻⁸ M was obtained using the PBNWA electrode for H₂O₂, which compared favorably with most electroanalysis procedures for H₂O₂. A biosensor toward glucose was then constructed with the PBNWA electrode as the basic electrode by crosslinking glucose oxidase (GOx). The glucose biosensor allowed rapid, selective and sensitive determination of glucose at −0.1 V. The amperometric response exhibited a linear correlation to glucose concentration through an expanded range from 2 × 10⁻⁶ M to 1 × 10⁻² M, and the response time and detection limit were determined to be 3 s and 1 μM, respectively.     

Electrochemical sensing platform based on covalent immobilization of thionine onto gold electrode surface via diazotization-coupling reaction

A novel electrochemical sensing platform by modification of electroactive thionine (Th) onto gold electrode surface was constructed, which was realized by diazotization of 4-aminothiophenol (ATP) self-assembled monolayer, followed by coupling of Th with the diazonium group to form a covalent diazo bond. A pair of well-defined redox peaks of Th was observed in the cyclic voltammetric measurement. The resulting diazo-ATP monolayer displayed superior electrical conductivity, which contributed to the sensitive detection of hydrogen peroxide (H₂O₂). The immobilized Th also showed a remarkable stability, which may benefit from the π-π stacking force and the covalent diazo bond between diazo-ATP and Th molecules. Under the optimized experimental conditions, the current fabricated non-enzyme and reagentless sensor could show a rapid response to H₂O₂ within 3 s and a linear calibration plot ranged from 1.0 × 10⁻⁶ to 6.38 × 10⁻³ M with a detection limit of 6.7 × 10⁻⁷ M. The current fabrication strategy of electroactive interface is expected to be used as a versatile route for the immobilization of more electroactive molecules and offer more opportunities for the applications in electrochemical sensor, biosensor, electrocatalysis, etc.     

Electrochemical detection of DNA hybridization based on polypyrrole/ss-DNA/multi-wall carbon nanotubes paste electrode

A sensitive electrochemical detection of DNA hybridization using a paste electrode assembled by multi-wall carbon nanotubes (MWNT) and immobilizing DNA probe within electropolymerized polypyrrole (ppy) was developed. The detection approach relied on entrapping of DNA probe within electropolymerized ppy film on the MWNT paste electrode and monitoring the current change generated from an electroactive intercalator of ethidium bromide (EB) after DNA hybridization. As a consequence of DNA hybridization, significant changes in the current of EB intercalated with double-stranded DNA (ds-DNA) on the MWNT paste electrode were observed. Based on the response of EB, only the complementary DNA sequence gave an obvious current signal compared with the five-point mismatched and non-complementary sequences. The oxidation peak current was linearly related to the logarithm of the concentration of the complementary DNA sequence from 1.0 × 10⁻¹⁰ to 1.0 × 10⁻⁸ M with a detection limit of 8.5 × 10⁻¹¹ M. This work demonstrates that the incorporation of MWNT paste electrode with electropolymerization is a promising strategy of functional interfaces for the immobilization of biological recognition elements.     

Selective recognition of ovalbumin using a molecularly imprinted polymer

Micro-contact imprinting has been used to form thin-film molecular imprints of ovalbumin (OVA) in polymers supported on glass slides. Thermocalorimetric data was used to optimise the choice of functional monomer and cross-linker to maximise selectivity and minimise non-specific recognition.A polymer comprising polyethyleneglycol 400 dimethacrylate (95 vol.%) and methacrylic acid (5 vol.%) showed both maximum recognition for OVA when made as a molecularly imprinted polymer (MIP), and minimal recognition when made as a non-imprinted, i.e. control polymer. OVA rebinding to the molecularly imprinted polymer, from a buffered 2 µM OVA solution, was 1.55 × 10^{− 11} mol cm^{− 2}, while the control polymer showed 10-fold less re-binding, i.e. 0.154 × 10^{− 11} mol cm^{− 2}.Experiments in which human serum albumin (HSA), conalbumin, ovomucoid or lysozyme, were re-bound to the polymers, either as single proteins or in competition with OVA, showed them to have low affinity for the polymer formulation used. Of the competing proteins examined, in non-competitive binding experiments, HSA showed the greatest affinity 0.45 × 10^{− 11} mol cm^{− 2} for the OVA imprinted polymer. In two protein competition experiments, i.e. with OVA and a competing protein present at equal concentrations (2 µM), OVA binding to the OVA imprinted polymer was in all cases significantly greater than that of the competitor.     

Electrochemistry and scanning electron microscopy of polyaniline/peroxidase-based biosensor

An amperometric biosensor was prepared by in situ deposition of horseradish peroxidase (HRP) enzyme on a polyaniline (PANI)-doped platinum disk electrode. The PANI film was electrochemically deposited on the electrode at 100 mV s⁻¹/Ag-AgCl. Cyclic voltammetric characterization of the PANI film in 1 M HCl showed two distinct redox peaks, which prove that the PANI film was electroactive and exhibited fast reversible electrochemistry. The surface concentration and film thickness of the adsorbed electroactive species was estimated to be 1.85×10⁻⁷ mol cm⁻² and approximately 16 nm, respectively. HRP was electrostatically immobilized onto the surface of the PANI film, and voltammetry was used to monitor the electrocatalytic reduction of hydrogen peroxide under diffusion-controlled conditions. Linear responses over the concentration range 2.5×10⁻⁴ to 5×10⁻³ M were observed. Spectroelectrochemistry was used to monitor the changes in UV-vis properties of HRP, before and after the catalysis of H₂O₂. The biosensor surface morphology was characterized by scanning electron microscopy (SEM) using PANI-doped screen-printed carbon electrodes (SPCEs) in the presence and absence of (i) peroxidase and (ii) peroxide. The SEM images showed clear modifications of the conducting film surface structure when doped with HRP, as well as the effect of hydrogen peroxide on the morphology of biosensor.     

Detection of nicotine based on molecularly imprinted TiO2-modified electrodes

Amperometric detection of nicotine (NIC) was carried out on a titanium dioxide (TiO₂)/poly(3,4-ethylenedioxythiophene) (PEDOT)-modified electrode by a molecular imprinting technique. In order to improve the conductivity of the substrate, PEDOT was coated onto the sintered electrode by in situ electrochemical polymerization of the monomer. The sensing potential of the NIC-imprinted TiO₂ electrode (ITO/TiO₂[NIC]/PEDOT) in a phosphate-buffered saline (PBS) solution (pH 7.4) containing 0.1 M KCl was determined to be 0.88 V (vs. Ag/AgCl/saturated KCl). The linear detection range for NIC oxidation on the so-called ITO/TiO₂[NIC]/PEDOT electrode was 0-5 mM, with a sensitivity and limit of detection of 31.35 μA mM⁻¹ cm⁻² and 4.9 μM, respectively. When comparing with the performance of the non-imprinted one, the sensitivity ratio was about 1.24. The sensitivity enhancement was attributed to the increase in the electroactive area of the imprinted electrode. The at-rest stability of the ITO/TiO₂[NIC]/PEDOT electrode was tested over a period of 3 days. The current response remained about 85% of its initial value at the end of 2 days. The ITO/TiO₂[NIC]/PEDOT electrode showed reasonably good selectivity in distinguishing NIC from its major interferent, (−)-cotinine (COT). Moreover, scanning electrochemical microscopy (SECM) was employed to elucidate the surface morphology of the imprinted and non-imprinted electrodes using Fe(CN)₆³⁻/Fe(CN)₆⁴⁻ as a redox probe on a platinum tip. The imprinted electrode was further characterized by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR).     

Sensing lymphoma cells based on a cell-penetrating/apoptosis-inducing/electron-transfer peptide probe

To electrochemically sense lymphoma cells (U937), we fabricated a multifunctional peptide probe that consists of cell-penetrating/apoptosis-inducing/electron-transfer peptides. Electron-transfer peptides derive from cysteine residue combined with the C-terminals of four tyrosine residues (Y₄). A peptide whereby Y₄C is bound to the C-terminals of protegrin 1 (RGGRLCYCRRRFCVCVGR-NH₂) is known to be an apoptosis-inducing agent against U937 cells, and is referred to as a peptide-1 probe. An oxidation response of the peptide-1 probe has been observed due to a phenolic hydroxyl group, and this response is decreased by the uptake of the peptide probe into the cells. To improve the cell membrane permeability against U937 cells, the RGGR at the N-terminals of the peptide-1 probe was replaced by RRRR (peptide-2 probe). In contrast, RNRCKGTDVQAWY₄C (peptide-3 probe), which recognizes ovalbumin, was constructed as a control. Compared with the other probes, the change in the peak current of the peptide-2 probe was the greatest at low concentrations and occurred in a short amount of time. Therefore, the cell membrane permeability of the peptide-2 probe was increased based on the arginine residues and the apoptosis-inducing peptides. The peak current was linear and ranged from 100 to 1000 cells/ml. The relative standard deviation of 600 cells/ml was 5.0% (n = 5). Furthermore, the membrane permeability of the peptide probes was confirmed using fluorescent dye.     

Application of a new potentiometric method for determination of phosphate based on a surfactant-modified zeolite carbon-paste electrode (SMZ-CPE)

A phosphate-selective electrode based on surfactant-modified zeolite (SMZ) particles into carbon-paste has been proposed (SMZ-CPE). The electrode was fully characterized in terms of composition, response time, ionic strength, thermal stability and usable pH range. The electrode containing 20% SMZ exhibited linear response range to phosphate species in the range of 1.58 × 10⁻⁵ to 1.00 × 10⁻² M with a detection limit of 1.28 × 10⁻⁵ M and a Nernstian slope of 29.9 ± 0.9 mV per decade of phosphate concentration. The electrode response to phosphate remains constant in the pH range of 4-12 and in the presence of 1 × 10⁻⁴ to 4 × 10⁻³ M NaNO₃. The response of the electrode reaches equilibrium within several seconds after immersing the electrode in phosphate solution. Common anions such as Cl⁻, Br⁻, I⁻, NO₃⁻, SO₄²⁻ and Cr₂O₇²⁻ have little effect on the determination of phosphate but AsO₄³⁻ shows some interference. A successful application of the electrode for determination of phosphate in a fertilizer, using direct potentiometry, is presented. The electrode was also used for the potentiometric titration of phosphate. The validation of the obtained results in each case was proved by statistical methods.     

Coated wire chromium(III) ion-selective electrode based on azamacrocycles

Tetraazacyclotetradecane, tetratosyltetraaza 12C4, and tritosyltriaza 9C3 have been explored as electroactive materials for preparing coated wire ion-selective electrodes (CWISEs) for Cr(III) ions. The best performance was observed for the membrane comprising electroactive material (tetratosyltetraaza 12C4), plasticizer (dibutyl phthalate), and poly(vinyl chloride) in the optimum ratio 5:60:35 (w/w). Linear Nernstian response for this electrode was obtained over the total Cr(III) concentration range of 1×10^–1 to 1×10^–7 M in 0.05 M NH₄NO₃ medium, with a slope of 20±1 mV per decade change. The working pH range of the electrode was 1.8–5.5. Selectivity coefficients of some mono, divalent, and trivalent metal ions were determined. Analyses of electroplating bath solutions, chromating, and effluent samples have been carried out using this CWISE and the results are found to be comparable with those obtained by using conventional methods or by AAS.     

基于碳纳米管修饰电极的胆碱电化学发光生物传感器研制

在碳纳米管(CNTs)和K3Fe(CN)6修饰的铂电极上吸附固定胆碱氧化酶,以鲁米诺为发光试剂,研制了胆碱电化学发光(ECL)生物传感器.CNTs可有效提高电极表面的电荷传输能力、提高电极表面的生物相容性和对酶分子的固载能力;K3Fe(CN)6对酶活性具有激活作用,同时对H2O2增敏的鲁米诺ECL有增强作用,均有利于提...     

Direct electrochemistry and electrocatalysis of myoglobin-based nanocomposite membrane electrode

The direct electron transfer of myoglobin (Mb) was achieved based on the immobilization of Mb/Silver nanoparticles (AgNPs) on glassy carbon electrode by multi-wall carbon nanotubes (MWNTs)-chitosan(Chit) film. The immobilized Mb displayed a pair of well-defined and reversible redox peaks with a formal potential (E^θ′) of − 24 mV (vs. Ag/AgCl) in 0.1 M pH 7.0 phosphate buffer solution. The apparent heterogeneous electron transfer rate constants (k_s) of Mb confined to Chit-MWNTs film was evaluated as 5.47 s^{− 1} according to Laviron's equation. The surface concentration (Γ^?) of the electroactive Mb in the Chit-MWNTs film was estimated to be (4.16 ± 0.35) × 10^{− 9} mol cm^{− 2}. Meanwhile, the catalytic ability of Mb toward the reduction of H₂O₂ was studied. Its apparent Michaelis–Menten constant for H₂O₂ was 0.024 mM, showing a good affinity. The linear range for H₂O₂ determination was from 2.5 × 10^{− 5} M to 2.0 × 10^{− 4} M with a detection limit of 1.02 × 10^{− 6} M (S/N = 3). Moreover, the biosensor displays rapid response to H₂O₂ and good stability and reproducibility.     

A novel method for determination of magnesium in urine and water samples with mercury film-plated carbon paste electrode

A square wave adsorptive stripping voltammetric (SWAdSV) method for the indirect determination of trace amounts of magnesium with thiopentone sodium (TPS) as an electroactive ligand, at carbon paste mercury film electrode (CP-MFE) is proposed. It is observed that the increase of the square wave voltammetric cathodic peak current of TPS, under alkaline conditions, is linear with the increase of Mg concentration. Under optimum experimental conditions viz.; pH 10.75, 3×10⁻⁵ M TPS and 0.05 M phosphate buffer (Na₂HPO₄-NaH₂PO₄), a linear relation in the range 6×10⁻⁹ to 9×10⁻⁸ M Mg²⁺ (0.14-2.16 ppb), at 60 s deposition time, is obtained. The detection limit of Mg²⁺ is 0.14 ppb for 60 s deposition time with the relative standard deviation is 0.5% (n=5). The proposed method was successfully applied to the determination of magnesium in urine and tap water samples with satisfactory results. The data obtained are compared with the standard flame atomic absorption spectrophotometric method (FAAS).     

Preparation of a new solid state fluoride ion selective electrode and application

A new solid state fluoride ion selective electrode composed of 70% Ag₂S, 10% Cu₂S and 20% CaF₂ has been developed. An analytically useful potential change occurred, from 1 × 10⁻⁶ to 1 × 10⁻¹ M fluoride ion. The slope of the linear portion (1 × 10⁻¹-1 × 10⁻⁵ M) was about 26 ± 2 mV/10-fold concentration changes in fluoride. It was found that pH change between 1 and 8 had no effect on the potential of the electrode. There was no interference of most common cations such as K^+, Na⁺, Ca²⁺ and Mg²⁺ and anions such as Cl⁻, NO₃⁻, SO₄²⁻ and PO₄³⁻. The lifetime of the electrode was more than 2 years, when used at least 4-5 times a day, and the response time was about 60 s.The measurements were made at constant ionic strength (0.1 M NaNO₃) and at room temperature. This electrode has been used for the determination of fluoride ion in Ankara city tap water and in bottled spring water using standard addition method. The validation of the electrode has been made with a commercial fluoride ion selective electrode (Orion) and high consistency was obtained.