Competitive enzyme-linked immunosorbent assay for the determination of catecholamine, dopamine in serum

A competitive enzyme-linked immunosorbent assay for dopamine (DA) has been optimized and characterized. DA is sensitive to oxygen and light according to a function of the pH on the DA oxidation process. The phenolic groups in DA are readily oxidisable to a quinoid form and thus, free DA deteriorates in alkaline media. Thus, effect of factors such as pH, enzyme-label with substrate, ionic strength and reaction time was considered on performance of ELISA. Assay was performed with 5 μg mL⁻¹ of BSA-DA and 1/7500 dilution of anti-DA antibody. A dose-response curve was constructed, and a limit of detection and a dynamic range for DA were accomplished to 1.0 × 10⁻⁹ M (0.19 μg L⁻¹) and five orders (3.2 × 10⁻⁸ M to 3.2 × 10⁻³ M) of magnitude, respectively. The correlation diagram of the absorbance obtained both in buffer and in serum has shown good agreement with correlation coefficient (R² = 0.9947): Abs. (in serum) = 0.6128 × Abs. (in buffer) + 0.2926. The cross-reactivity was examined with the structurally similar compounds. And the results demonstrated that epinephrine and 3-methoxytyramine showed cross-reactivity (18.9% each), whereas 3,4-dihydroxyphenylacetic acid and homovanillic acid showed low cross-reactivity (<1%). And percent recoveries of DA in serum were quite satisfactory. This provides usefulness of the present assay to monitor DA in serum.     

Highly sensitive detection of human thrombin in serum by affinity capillary electrophoresis/laser-induced fluorescence polarization using aptamers as probes

The detection and quantification of disease-related proteins play critical roles in clinical practice and diagnostic assays. We present an affinity probe capillary electrophoresis/laser-induced fluorescence polarization (APCE/LIFP) assay for detection of human thrombin using a specific aptamer as probe. In the APCE/LIFP assay, the mobility and fluorescence polarization of complex are measured simultaneously during CE analysis. The affinity complex of human thrombin can be well separated from unbound aptamer on CE and clearly identified on the basis of its fluorescence polarization and migration. Because of the binding favorable G-quartet conformation potentially involved in the specific aptamer, it was assumed that monovalent and bivalent cations promoting the formation of a stable G quadruplex conformation in the aptamer may enhance the binding of the aptamer and thrombin. Therefore, we investigated the effects of various metal cations on the binding of human thrombin and the aptamer. Our results show that cations like K⁺ and Mg²⁺ could not stabilize the affinity complex. Without the use of typical cations, a highly sensitive assay of human thrombin was developed with the corresponding detection limits of 4.38 × 10⁻¹⁹ and 2.94 × 10⁻¹⁹ mol in mass for standard solution and human serum, respectively.     

Quantum dot-enhanced chemiluminescence detection for simultaneous determination of dopamine and epinephrine by capillary electrophoresis

A sensitive method based on quantum dot (QD)-enhanced capillary electrophoresis-chemiluminescence (CE-CL) detection was developed for simultaneous determination of dopamine (DA) and epinephrine (E). In this work, CdTe QD was added into the running buffer of CE to catalyze the post-column CL reaction between luminol and hydrogen peroxide, achieving higher CL emission. Negative peaks were produced due to the inhibitory effects on CL emission from DA and E eluted from the electrophoretic capillary. The decrease in CL intensity was proportional to the concentration of DA and E in the range of 8.0 × 10⁻⁸-5.0 × 10⁻⁶ M and 4.0 × 10⁻⁸-5.0 × 10⁻⁶ M, respectively. Detection limits for DA and E were 2.3 × 10⁻⁸ M and 9.3 × 10⁻⁹ M, respectively. Using this method, the levels of DA and E in human urine from healthy donors were determined.     

Cu nanoparticles incorporated polypyrrole modified GCE for sensitive simultaneous determination of dopamine and uric acid

Cu nanoparticles have been electrochemically incorporated polypyrrole film that was used for modification of the glassy carbon electrode surface. The performance of the electrode has been characterized by cyclic voltammetry and atomic force microscopy. The electrode has shown high electrocatalytic activity towards the oxidation of dopamine (DA) and uric acid (UA) simultaneously in a phosphate buffer solution (pH 7.00). The electrocatalytic oxidation currents of UA and DA were found linearly related to concentration over the range 1 × 10⁻⁹ to 1 × 10⁻⁵ M for UA and 1 × 10⁻⁹ to 1 × 10⁻⁷ M for DA using DPVs method. The detection limits were determined as 8 × 10⁻¹⁰ M (s/n = 3) for UA and 8.5 × 10⁻¹⁰ M (s/n = 3) for DA at a signal-to-noise ratio of 3.     

Electrochemiluminescence biosensor for the assay of small molecule and protein based on bifunctional aptamer and chemiluminescent functionalized gold nanoparticles

An electrochemiluminescence (ECL) biosensor for simultaneous detection of adenosine and thrombin in one sample based on bifunctional aptamer and N-(aminobutyl)-N-(ethylisoluminol) functionalized gold nanoparticles (ABEI-AuNPs) was developed. A streptavidin coated gold nanoparticles modified electrode was utilized to immobilize biotinylated bifunctional aptamer (ATA), which consisted of adenosine and thrombin aptamer. The ATA performed as recognition element of capture probe. For adenosine detection, ABEI-AuNPs labeled hybridization probe with a partial complementary sequence of ATA reacted with ATA, leading to a strong ECL response of N-(aminobutyl)-N-(ethylisoluminol) enriched on ABEI-AuNPs. After recognition of adenosine, the hybridization probe was displaced by adenosine and ECL signal declined. The decrease of ECL signal was in proportion to the concentration of adenosine over the range of 5.0 × 10⁻¹²–5.0 × 10⁻⁹ M with a detection limit of 2.2 × 10⁻¹² M. For thrombin detection, thrombin was assembled on ATA modified electrode via aptamer–target recognition, another aptamer of thrombin tagged with ABEI-AuNPs was bounded to another reactive site of thrombin, producing ECL signals. The ECL intensity was linearly with the concentration of thrombin from 5 × 10⁻¹⁴ M to 5 × 10⁻¹⁰ M with a detection limit of 1.2 × 10⁻¹⁴ M. In the ECL biosensor, adenosine and thrombin can be detected when they coexisted in one sample and a multi-analytes assay was established. The sensitivity of the present biosensor is superior to most available aptasensors for adenosine and thrombin. The biosensor also showed good selectivity towards the targets. Being challenged in real plasma sample, the biosensor was confirmed to be a good prospect for multi-analytes assay of small molecules and proteins in biological samples.     

Label-free aptamer-based chemiluminescence detection of adenosine

We have developed a novel sensitive chemiluminescence (CL) aptasensor for the target assay as exemplified by using adenosine as a model target. In this work, we have demonstrated the signaling mechanism to make detection based on magnetic separation and 3,4,5-trimethoxyl-phenylglyoxal (TMPG), a special CL reagent as the signaling molecule, which reacts instantaneously with guanine nucleobases (G) of adenosine-binding aptamer strands. Briefly, amino-functioned capture DNA sequences are immobilized on the surface of carboxyl-modified magnetic beads, and then hybridized with label-free G-rich (including 15 guanine nucleobases) adenosine-binding aptamer strands to form our CL aptasensor. Upon the introduction of adenosine, the aptamer on the surface of magnetic beads is triggered to make structure switching to the formation of the adenosine/aptamer complex. Consequently, G-rich aptamer strands are forced to dissociate from magnetic beads sensing interface, resulting in a decrease of CL signal. The decrement of peak signal is proportional to the amount of adenosine. The effects of the amounts of capture DNA, aptamer, magnetic beads are investigated and optimized. It was found that the CL intensity had a linear dependency on the concentration of adenosine in the range of 4 × 10⁻⁷ to 1 × 10⁻⁵ M. With a low detection limit of 8 × 10⁻⁸ M and simplicity in CL detection, this novel technique will offer a great promise for future target/aptamer analysis.     

Selective detection of dopamine in the presence of ascorbic acid and uric acid by a carbon nanotubes-ionic liquid gel modified electrode

The electrochemistry of dopamine (DA) was studied by cyclic voltammetry at a glassy carbon electrode modified by a gel containing multi-walled carbon nanotubes (MWNTs) and room-temperature ionic liquid of 1-octyl-3-methylimidazolium hexafluorophosphate (OMIMPF₆). The thickness of gel on the surface of the electrode has to be controlled carefully because the charging currents increase with the modified layer being thicker. The anodic peaks of DA, ascorbic acid (AA) and uric acid (UA) in their mixture can be well separated since the peak potential of AA is shifted to more negative values, while that of UA is shifted to more positive values due to the modified electrode. At pH 7.08 the three peaks are separated ca. 0.20 and 0.15 V, respectively; hence DA can be determined in the presence of UA and more than 100 times excess of AA. Under optimum conditions linear calibration graphs were obtained over the DA concentration range 1.0 × 10⁻⁶ to 1.0 × 10⁻⁴ M. The detection limit of the current technique was found to be 1.0 × 10⁻⁷ M based on the signal-to-noise ratio of 3. The modified electrode has been successfully applied for the assay of DA in human blood serum. This work provides a simple and easy approach to selectively detect dopamine in the presence of ascorbic acid and uric acid.     

Quantification of biogenic amines by microchip electrophoresis with chemiluminescence detection

A highly sensitive microchip electrophoresis (MCE) method with chemiluminescence (CL) detection was developed for the determination of biogenic amines including agmatine (Agm), epinephrine (E), dopamine (DA), tyramine, and histamine in human urine samples. To achieve a high assay sensitivity, the targeted analytes were pre-column labeled by a CL tagging reagent, N-(4-aminobutyl)-N-ethylisoluminol (ABEI). ABEI-tagged biogenic amines after MCE separation reacted with hydrogen peroxide in the presence of horseradish peroxidase (HRP), producing CL emission. Since no CL reagent was added to the running buffer, the background of the CL detection was extremely low, resulting in a significant improvement in detection sensitivity. Detection limits (S/N = 3) were in the range from 5.9 × 10⁻⁸ to 7.7 × 10⁻⁸ M for the biogenic amines tested, which were at least 10 times lower than those of the MCE–CL methods previously reported. Separation of a urine sample on a 7 cm glass/poly(dimethylsiloxane) (PDMS) microchip channel was completed within 3 min. Analysis of human urine samples found that the levels of Agm, E and DA were in the ranges of 2.61 × 10⁻⁷ to 4.30 × 10⁻⁷ M, 0.81 × 10⁻⁷ to 1.12 × 10⁻⁷ M, and 8.76 × 10⁻⁷ to 11.21 × 10⁻⁷ M (n = 4), respectively.     

Assay of anti-coagulant drug warfarin sodium in pharmaceutical formulation and human biological fluids by square-wave adsorptive cathodic stripping voltammetry

The cyclic voltammogram of the anti-coagulant drug warfarin sodium at the hanging mercury drop electrode exhibited a well-defined single two-electron irreversible peak over the pH range 4-7, which may be attributed to the reduction of the CO double bond of the drug molecule. Based on the interfacial adsorptive character of the drug onto the mercury electrode surface, a square-wave cathodic stripping procedure was optimized for its trace determination. The calibration plot was linear over the concentration range of 5×10⁻⁹ to 4×10⁻⁷ M warfarin sodium in Britton-Robinson (B-R) buffer of pH 5, with limits of detection and quantitation of 6.5×10⁻¹⁰ and 2.1×10⁻⁹ M warfarin sodium, respectively. The proposed procedure was successfully applied for assay of warfarin sodium in its pharmaceutical formulation “hemofarin tablets”, human serum and urine without the necessity for sample pretreatment or time-consuming extraction or evaporation steps, prior to assay of the drug. Limits of detection of 1.1×10⁻⁹ and 1.3×10⁻⁸ M warfarin sodium were achieved, while limits of quanitation of 3.7×10⁻⁹ and 4.3×10⁻⁸ M warfarin sodium were estimated in human serum and urine, respectively. The pharmacokinetic profiles of the drug were studied and the estimated pharmacokinetic parameters were favorably compared with those reported in literature.     

Exonuclease I aided enzyme-linked aptamer assay for small-molecule detection

A novel enzyme-linked aptamer assay (ELAA) with the aid of Exonuclease I (Exo I) for colorimetric detection of small molecules was developed. The fluorescein isothiocyanate (FITC)-labeled aptamer was integrated into a double-stranded DNA (dsDNA). In the presence of target, the binding of aptamer with target protected the aptamer from Exo I degradation, which resulted in the FITC tag remaining on the aptamer. Then, the anti-FITC-HRP conjugate was used to produce an optically observable signal. By monitoring the color change, we were able to detect two model molecules, ATP and L-argininamide, with high selectivity and high sensitivity even in the serum matrix. It is expected to be a simple and general ELAA method with wide applicability.

Anodic voltammetric behavior and determination of cefixime in pharmaceutical dosage forms and biological fluids

The voltammetric behavior of cefixime was studied using cyclic, linear sweep, differential pulse and square wave voltammetric techniques. The oxidation of cefixime was irreversible and exhibited diffusion controlled process depending on pH. The oxidation mechanism was proposed and discussed. Different parameters were tested to optimize the conditions for the determination of cefixime. The dependence of current intensities and potentials on pH, concentration, scan rate, nature of the buffer was investigated. According to the linear relationship between the peak current and the concentration, differential pulse (DPV) and square wave (SWV) voltammetric methods for cefixime assay in pharmaceutical dosage forms and biological fluids were developed. For the determination of cefixime were proposed in acetate buffer at pH 4.5, which allows quantitation over the 6 × 10⁻⁶-2 × 10⁻⁴ M range in supporting electrolyte and spiked serum sample; 8 × 10⁻⁶-2 × 10⁻⁴ M range in urine sample; 6 × 10⁻⁶-1 × 10⁻⁴ M range in breast milk samples for both techniques. The repeatability, reproducibility, precision and accuracy of the methods in all media were investigated. No electroactive interferences from the excipients and endogenous substances were found in the pharmaceutical dosage forms and in the biological samples, respectively.     

Selective detection of dopamine in the presence of uric acid using a gold nanoparticles-poly(luminol) hybrid film and multi-walled carbon nanotubes with incorporated β-cyclodextrin modified glassy carbon electrode

Gold nanoparticles-poly(luminol) (Plu-AuNPs) hybrid film and multi-walled carbon nanotubes with incorporated β-cyclodextrin modified glassy carbon electrode (β-CD-MWCNTs/Plu-AuNPs/GCE) was successfully prepared for simultaneous determination of dopamine (DA) and uric acid (UA). The surface of the modified electrode has been characterized by X-ray photo-electron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDS), field-emission scanning electron microscope (SEM) and transmission electron microscope (TEM). Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV) have been used to investigate the β-CD-MWCNTs/Plu-AuNPs composite film. Gold nanoparticles anchored into poly(luminol) film exhibited catalytic activity for DA. MWCNTs with incorporated β-CD can greatly promote the direct electron transfer. In 0.10 M phosphate buffer solution (PBS, pH 7.0), the DPV response of the β-CD-MWCNTs/Plu-AuNPs/GCE sensor to DA is about 8-fold as compared with the Plu-AuNPs/GCE sensor, and the detection limit for DA is about one order of magnitude lower than the Plu-AuNPs/GCE sensor. The steady-state current response increases linearly with DA concentration from 1.0 × 10⁻⁶ to 5.6 × 10⁻⁵ M with a low detection limit (S/N = 3) of 1.9 × 10⁻⁷ M. Moreover, the interferences of ascorbic acid (AA) and uric acid (UA) are effectively diminished. The applicability of the prepared electrode has been demonstrated by measuring DA contents in dopamine hydrochloride injection.     

An electrochemical sensor prepared by sonochemical one-pot synthesis of multi-walled carbon nanotube-supported cobalt nanoparticles for the simultaneous determination of paracetamol and dopamine

Multi-walled carbon nanotubes (MWCNTs) functionalized by cobalt nanoparticles were obtained using a single step chemical deposition method in an ultrasonic bath. The composite material was characterized using scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). The electroactivity of the cobalt-functionalized MWCNTs was assessed in respect to the electrooxidation of paracetamol (PAR) and dopamine (DA). It was found that the carbon nanotube supported cobalt nanoparticles have significantly higher catalytic properties. The proposed electrode has been applied for the simultaneous determination of PAR and DA. The modified electrode could resolve the overlapped voltammetric waves of PAR and DA into two well-defined voltammetric peaks with peak to peak separation of about 203 mV. On the other hand, the presence of potential drug interfering compounds AA and UA did not affect the voltammetric responses of PAR and DA. The current of oxidation peaks showed a linear dependent on the concentrations of PAR and DA in the range of 5.2 × 10⁻⁹–4.5 × 10⁻⁷ M (R² = 0.9987) and 5.0 × 10⁻⁸–3.0 × 10⁻⁶ M (R² = 0.9999), respectively. The detection limits of 1.0 × 10⁻⁹ M and 1.5 × 10⁻⁸ M were obtained for PAR and DA, respectively. The proposed electrode showed good stability (peak current change: 4.9% with and RSD of 2.6% for PAR; 5.5% with and RSD of 3.0% for DA over 3 weeks), reproducibility (RSD 2.3% for PAR and RSD 1.5% for DA), repeatability (RSD 2.25% for PAR and RSD 2.50% for DA) and high recovery (99.7% with an RSD of 1.3% for PAR; 100.8% with an RSD of 1.8% for DA). The proposed method was successfully applied to the determination of PAR and DA in pharmaceuticals.     

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).     

Zeolite A functionalized with copper nanoparticles and graphene oxide for simultaneous electrochemical determination of dopamine and ascorbic acid

A novel Cu-zeolite A/graphene modified glassy carbon electrode for the simultaneous electrochemical determination of dopamine (DA) and ascorbic acid (AA) has been described. The Cu-zeolite A/graphene composites were prepared using Cu²⁺ functionalized zeolite A and graphene oxide as the precursor, and subsequently reduced by chemical agents. The composites were characterized by X-ray diffraction, Fourier transform infrared spectra and scanning electron microscopy. Based on the Cu-zeolite A/graphene-modified electrode, the potential difference between the oxidation peaks of DA and AA was over 200 mV, which was adequate for the simultaneous electrochemical determination of DA and AA. Also the proposed Cu-zeolite/graphene-modified electrode showed higher electrocatalytic performance than zeolite/graphene electrode or graphene-modified electrode. The electrocatalytic oxidation currents of DA and AA were linearly related to the corresponding concentration in the range of 1.0 × 10⁻⁷–1.9 × 10⁻⁵ M for DA and 2.0 × 10⁻⁵–2.0 × 10⁻⁴ M for AA. Detection limits (<!-- no-mfc -->S/N<!-- /no-mfc --> = 3) were estimated to be 4.1 × 10⁻⁸ M for DA and 1.1 × 10⁻⁵ M for AA, respectively.     

Poly(3,4-ethylenedioxythiophene-co-(5-amino-2-naphthalenesulfonic acid)) (PEDOT-PANS) film modified glassy carbon electrode for selective detection of dopamine in the presence of ascorbic acid and uric acid

Poly(3,4-ethylenedioxythiophene-co-(5-amino-2-naphthalenesulfonic acid)) (PEDOT-PANS) film modified glassy carbon electrode was prepared by electrochemical polymerization technique. The properties of modified electrode was studied. It was found that the electrochemical properties of modified electrode was very much dependent on the experimental conditions, such as monomer oxidation potential and pH. The modified electrode surface was characterized by scanning electron microscopy (SEM). The PEDOT-PANS film modified electrode shows electrocatalytic activity toward oxidation of dopamine (DA) in acetate buffer solution (pH 5.0) and results in a marked enhancement of the current response. The linear sweep voltammetric (LSV) peak heights are linear with DA concentration from 2 × 10⁻⁶ to 1 × 10⁻⁵ M. The detection limit is 5 × 10⁻⁷ M. More over, the interferences of ascorbic acid (AA) and uric acid (UA) were effectively diminished. This work provides a simple and easy approach for selective determination of dopamine in the presence of ascorbic acid and uric acid.     

Design and evaluation of a thorium (IV) selective optode

A novel optical sensor has been proposed for sensitive determination of thorium (IV) ion in aqueous solutions. The thorium sensing membrane was prepared by incorporating 4-(p-nitrophenyl azo)-pyrocatechol (NAP) as ionophore in the plasticized PVC membrane containing tributyl phosphate (TBP) as plasticizer. The membrane responds to thorium ion by changing color reversibly from yellow to red-brown in glycine buffer solution at pH 3.5. The proposed sensor displays a linear range of 8.66 × 10⁻⁶-2.00 × 10⁻⁴ M with a limit of detection of 6 × 10⁻⁶ M. The response time of the optode was about 8.8-12.5 min, depending on the concentration of Th (IV) ions. The selectivity of optode to Th (IV) ions in glycine buffer is good. The sensor can readily be regenerated by exposure to a solution mixture of sodium fluoride and 5-sulfosalicylic acid (dihydrate) (0.01 M each). The optode is fully reversible. The proposed optode was applied to the determination of thorium (IV) in environmental water samples.     

Determination of amlodipine besylate by adsorptive square-wave anodic stripping voltammetry on glassy carbon electrode in tablets and biological fluids

The adsorptive and electrochemical behavior of amlodipine besylate on a glassy carbon electrode were explored in Britton-Robinson buffer solution by using cyclic and square-wave voltammetry. Cyclic voltammetric studies indicated the oxidation of amlodipine besylate at the electrode surface through a single two-electron irreversible step and fundamentally controlled by adsorption. The solution conditions and instrumental parameters were optimized for the determination of the authentic drug by adsorptive square-wave stripping voltammetry. Amlodipine besylate gave a sensitive adsorptive oxidation peak at 0.510 V (versus Ag/AgCl). The oxidation peak was used to determine amlodipine besylate in range 4.0×10⁻⁸ to 2.0×10⁻⁶ with a detection limit of 1.4×10⁻⁸ M. The procedure was successfully applied for the assay of amlodipine besylate in tablets (Norvasc)^®. The percentage recoveries were in agreement with those obtained by the reference method. Applicability to assay the drug in urine and serum samples was illustrated. The mean percentage recoveries were 96.31±1.18 and 96.98±1.17, respectively. The proposd method used for monotoring clinically relevant concntrations of drug in human urine and serum.     

Selective response of dopamine in the presence of ascorbic acid on carbon paste electrode modified with titanium phosphated silica gel

Titanium phosphate grafted on the surface of silica gel (devoted briefly as Si-TiPH) was synthesized and used as bulk modifier to fabricate a renewable three-dimensional chemically modified electrode. The Si-TiPH bulk modified carbon paste electrode was used for the selective determination of dopamine (DA) in the presence of ascorbic acid (AA). The modified electrode offers an excellent and stable response for the determination of DA in the presence of AA. The differential pulse voltammetry peak current was found to be linear with the DA concentration in the range 2 × 10⁻⁷ to 1 × 10⁻⁶ and 2 × 10⁻⁶ to 6 × 10⁻⁵ mol L⁻¹. The detection limit of the proposed method in the presence of 2.0 × 10⁻⁵ M of AA was found to be 4.3 × 10⁻⁸ mol L⁻¹ for DA determination. The proposed method was successfully applied for the determination of DA in injections.     

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.