Fluorometric determination of fluoride ion by reagent tablets containing 3-hydroxy-2'-sulfoflavone and zirconium(IV) ethylenediamine tetraacetate

A reagent tablet for determination of fluoride ion has been prepared using ethylenediamine-N,N,N′,N′-tetraacetate complex of zirconium (Zr-EDTA), 3-hydroxy-2′-flavone (FS) and an appropriate pH buffer. Dissolving of the tablet into water exhibits an intense blue fluorescence (λ_max = 460 nm) upon excitation at 377 nm and the fluorescence intensity decreases with the presence of fluoride ion. Hence, a simple fluorescent detection procedure for fluoride ion in aqueous media was successfully constructed with this tablet. The principle of this detection system is the ligand exchange reaction of FS bound to Zr-EDTA with fluoride ion. The present system provides an easy, rapid and selective determination method of fluoride ion ranging from 5 × 10⁻⁶ to 1 × 10⁻³ mol dm⁻³. The measurement of real samples with this tablet showed the similar results as those by the common method with the Alfusone reagent.     

Development of a flow manifold for Fe(III) ion determination with a fluoride ion-selective electrode

Continuous-flow (CF) and flow-injection (FI) analysis using the fluoride ion-selective electrode (FISE) as detector have been investigated. The measurements were performed in a home-made cell under appropriate flow conditions (2.86 or 3.45 ml min⁻¹, 0.2 ml samples, 10⁻⁶ M sodium fluoride). The calibration graph was obtained by plotting the signal height versus concentration of iron in the range of Fe(III) concentration from 10⁻⁵ to 10⁻¹ M in acetate buffer (pH 2.8 or 3.4). In all described procedures, the range of linear response extends to the Fe(III) concentration from 1×10⁻³ to 1×10⁻¹ M, with detection limit 9×10⁻⁵ M. The effect of double-line, two-line flow manifold and CF was investigated and discussed.     

Preparation and properties of a new solid state borate ion selective electrode and its application

A new borate ion selective electrode using solid salts of Ag₃BO₃, Ag₂S and Cu₂S has been developed. Detailed information is provided concerning the composition, working pH and conditioning of the electrode. An analytically useful potential change occurred from 1 × 10⁻⁶ to 1 × 10⁻¹ M borate ion. The slope of the linear portion was 31 ± 2 mV/10-fold changes in borate concentration. The measurements were made at constant ionic strength (0.1 M NaNO₃) and at room temperature. The effect of Cl⁻, Br⁻, NO₃⁻, SO⁼₄, H₂PO₄⁻ anions and K⁺, Na⁺, Cu²⁺, Ag⁺, Ca²⁺ cations on borate response is evaluated and it was found that only Ag⁺ had a small interference effect. The lifetime of the electrode was more than two years, when used at least 4-5 times a day, and the response time was about 20-30 s. Borate content in waste water of borax factory, tap water of a town situated near to the borax factory and city tap water far from these mines were also determined. The validation was made with differential pulse polarography for the same water sample, and high consistency was obtained.     

Lanthanum-selective membrane electrode based on 2,2′-dithiodipyridine

In this study, a new poly(vinyl chloride) (PVC) membrane sensor for La³⁺ ion based on 2,2′-dithiodipyridine as an ion carrier was prepared. This electrode revealed good selectivity for La³⁺ over a wide variety of other metal ions. Effects of experimental parameters such as membrane composition, nature and amount of plasticizer, the amount of additive and concentration of internal solution on the potential response of La³⁺ sensor were investigated. The electrode exhibited a Nernstian slope of 20.0 ± 1.0 mV per decade of La³⁺ over a concentration range of 7.1 × 10⁻⁶ to 2.2 × 10⁻² M of La³⁺ in the pH range 3.3-8.0. The response time was about 7 s and the detection limit was 3.1 × 10⁻⁶ M. The electrode can be used for at least 2 months without a considerable divergence in potential. The proposed electrode was used as an indicator electrode in potentiometric titration of oxalate and fluoride ions and was applied for determination of F⁻ ion in mouthwash solution.     

Organotin compounds: an ionophore system for fluoride ion recognition

Ion-selective properties were established for membrane electrodes prepared by using organotin compounds of type (L^CNRSnF₂)_n, (R = n-Bu (I), = Ph (II)) and (L^CNSnF₃)_n (III) (L^CN = C₆H₄(CH₂NMe₂)-2). Electrodes formulated with the optimized membranes containing the organotin compounds I-III as ionophores and sodium tetraphenylborate (10-30%) exhibited high selectivity for fluoride over other anions. An electrode prepared with ionophore II using dibutyl phthalate as the plasticizer and 15% sodium tetraphenylborate (NaTPB) as anion additive, possesses the best potentiometric response characteristics. It shows a detection limit of 7.9 × 10⁻⁷ M with a slope of 62.7 mV decade⁻¹ of activity in buffer solutions of pH 5.5. The interference from other anions is suppressed under this optimized measurement conditions. An entirely non-Hofmeister selectivity sequence (F⁻ > CH₃COO⁻ > Cl⁻ > I⁻ ∼ Br⁻ >ClO₄⁻ > NO₂⁻ > NO₃⁻ > SCN⁻) with remarkable preference towards fluoride is obtained. The influence on the electrode performances by anion additive was studied, and the possible response mechanism was investigated by UV-vis spectra. The electrode has been used for direct determination of fluoride in drinking mineral water with satisfactory results.     

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.     

Determination of fluoride and oxalate using the indicator reaction of Zr(IV) with methylthymol blue adsorbed on silica gel

Solid-phase spectrophotometric and visual test-methods of fluoride and oxalate determination are proposed. The methods are based on the competitive reactions of ZrOCl₂ with methylthymol blue immobilized on silica gel and fluoride or oxalate in solution. Absorbance of the solid-phase reagent at 590 nm decreases with the growth of fluoride and oxalate contents in solution. The developed methods demonstrate high selectivity. The interference of Bi(III) and SO₄²⁻, PO₄³⁻ is eliminated by the addition of 0.01 mol L⁻¹ solution of ascorbic acid and 0.01 mol L⁻¹ of BaCl₂, respectively. To eliminate the fluoride interference with oxalate determination 1 × 10⁻³ mol L⁻¹ solution of Ca(NO₃)₂ at pH 1.5 was added. The anions of the organic acids were destructed prior to F⁻ determination by ultrasonic exposition (44 kHz, intensity of ≤10 W cm⁻² for 3 min). The proposed methods were applied to the analysis of mineral water, toothpaste and biological fluids.     

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.     

A selective modified carbon paste electrode for determination of cyanide using tetra-3,4-pyridinoporphyrazinatocobalt(II)

A chemically modified carbon paste electrode with 3,4-tetra pyridinoporphirazinatocobalt(II) (Co(3,4 tppa) was applied to the determination of free cyanide ion. The electrode has a linear range between 1.5 × 10⁻⁵ M and 1.0 × 10⁻² M with a Nernstian slope of 60 ± 1.5 mV/decade and its detection limit is 9 × 10⁻⁶ M. The response time of electrode is 5 min. The proposed electrode was applied successfully for the determination of cyanide in commercially available spring water. Some anions, such as SCN⁻, I⁻, Cl⁻, Br⁻ and oxalate that are usually serious interfering species for most of cyanide selective electrodes, did not have any interfering effect for this proposed electrode.     

Colorimetric detection of fluoride in an aqueous solution using Zr(IV)-EDTA complex and a novel hemicyanine dye

A new highly sensitive and selective colorimetric method for fluoride determination in water is described. The novel reagent used is a hemicyanine dye (HC), which forms a stable complex with Zr-EDTA, the fluoride-binding site, through the hydroxyl groups. The hemicyanine-chelating Zr-EDTA complex (HC-Zr-EDTA) is ready to react with fluoride ion to release HC. This result in remarkable color change of the sensing solutions from red (λ_max = 513 nm) to yellow (λ_max = 427 nm) at pH 4.40. When applied to the colorimetric determination of fluoride ions, a linear range from 3.0 × 10⁻⁶ to 5.0 × 10⁻⁵ mol/L and a detection limit of 2.8 × 10⁻⁶ mol/L with a correlation coefficient of 0.9993 can be achieved under the optimized conditions. Because of the specific affinity of fluorides for the [Zr-EDTA], there is little interference by other ions. This method has been successfully applied to the determination of fluorides in toothpaste samples.     

Sensitive fluorimetric flow injection analysis for fluoride ion with a novel reagent, 2',7'-dichlorofluorescein di-tert-butyldimethylsilyl ether

A novel reagent, 2′,7′-dichlorofluorescein di-tert-butyldimethylsilyl ether (FCl₂TBS), was synthesized for fluoride ion and used for a sensitive fluorimetric flow injection analysis by detecting the recovery of fluorescence due to cleavage of Si-O bond. Four kinds of fluorescein di-tert-butyldimethylsilyl ether (FTBS) analogues were synthesized and FCl₂TBS was the best. By introducing chlorine to FTBS, stability of the reagent, reactivity and the baseline signals were improved. The FIA system was three lines. The sample solution (aqua medium) was injected in the carrier solution (water) and merged with the reagent solution (2.0 × 10⁻⁵ M FCl₂TBS acetone solution), then mixed with phosphate buffer solution (pH 7.5). The fluorescence intensities were measured at λ_ex 503 nm and λ_em 527 nm. The calibration graph had linear relationship between (1.0-50.0) × 10⁻⁶ M and the determinable limit was 1.0 × 10⁻⁶ M. The relative standard deviation of 12 measurements with 1.0 × 10⁻⁵ M F⁻ solution was 1.0% and the sample throughput was 13 h⁻¹. The developed method was successfully applied to river and tap water samples.     

Construction of a new Cu2+ coated wire ion selective electrode based on 2-((2-(2-(2-(2-hydroxy-5-methoxybenzylidene amino)phenyl)disufanyl)phenylimino)methyl)-4-methoxyphenol Schiff base

In this article a new coated platinum Cu²⁺ ion selective electrode based on 2-((2-(2-(2-(2-hydroxy-5-methoxybenzylideneamino)phenyl)disufanyl)phenylimino) methyl)-4-methoxyphenol Schiff base (L₁) as a new ionophore is described. This sensor has a wide linear range of concentration (1.2 × 10⁻⁷-1.0 × 10⁻¹ mol L⁻¹) and a low detection limit of 9.8 × 10⁻⁸ mol L⁻¹of Cu(NO₃)₂. It has a Nernstian response with slope of 29.54 ± 1.62 mV decade⁻¹ and it is applicable in the pH range of 4.0-6.0 without any divergence in potentioal. The coated electrode has a short response time of approximately 9 s and is stable at least for 3.5 months. The electrode shows a good selectivity for Cu²⁺ ion toward a wide variety of metal ions. The proposed sensor was successfully applied for the determination of Cu²⁺ ion in different real and environmental samples and as indicator electrode for potentiometric titration of Cu²⁺ ion with EDTA.     

Improved potentiometric response of solid-contact lanthanum (III) selective electrode

For the first time, the analytical application of integrate ionophore-transducer material based on magnetic graphene hybrids and 2,2-dithiodipyridine (DTDP) in solid-contact lanthanum (III) selective electrode is reported. The attachment of Fe₃O₄ nanoparticles (NPs) to graphene oxide (GO) for magnetic graphene hybrid is achieved by covalent bonding, and the universal problem, Fe₃O₄ NPs may easily leach out from the graphene during application, is successfully solved by the method above. The proposed electrode exhibits an excellent near-Nernstian response to lanthanum (III) ranging from 1.0 × 10⁻⁹ to 1.0 × 10⁻³ M with a slope of 17.81 mV/dec. Moreover, the excellent performance on fairly good selectivity, wide applicable pH range (3.0^_8.0), fast response time (10 s) and long life time (2 months) reveal the superiority of the electrode. Most importantly, we have made a great improvement in the detection limit (2.75 × 10⁻¹⁰ M), which brings new dawn to the real-time detection of lanthanum (III) using ion selective electrode.     

Solid phase extraction-spectrophotometric determination of fluoride in water samples using magnetic iron oxide nanoparticles

A new, sensitive, fast and simple method using magnetic iron oxide nanoparticles (MIONs), as an adsorbent has been developed for extraction, preconcentration and determination of traces of fluoride ions. The determination method is based on the discoloration of Fe(III)-SCN complex with extracted fluoride ions which was subsequently monitored spectrophotometrically at λ_max = 458 nm. Various parameters affecting the adsorption of fluoride by the MIONs have been investigated, such as pH of the solution, type, volume and concentration of desorbing reagent, amount of adsorbent and interference effects. A linear response for the determination of fluoride was achieved in the concentration range of 0.040-1.250 μg mL⁻¹. The limit of detection (LOD) and limit of quantification (LOQ) for fluoride based on 3 times and 10 times the standard deviation of the blank (3S_b, 10S_b) were 0.015 and 0.042 μg mL⁻¹ (n = 20) for fluoride ion, respectively. A preconcentration factor of 50 was achieved in this method. The proposed procedure has been applied for determination of fluoride concentration in various water samples. The results obtained from this method were successfully compared with those provided by standard SPADNS method.     

Ion imprinted polymer based ion-selective electrode for the trace determination of dysprosium(III) ions

Ion-selective electrode (ISE) was designed by dispersing the dysprosium(III) IIP particles in 2-nitrophenyloctyl ether plasticizer and then embedded in polyvinyl chloride matrix. The ISE shows a Nernstian response for dysprosium(III) over a wide concentration range (8.0 × 10⁻⁶ to 1.0 × 10⁻¹ M) with a slope of 21.7 mV per decade. The limit of detection was 2 × 10⁻⁶ M. This sensor has a very fast response time (∼10 s) and offers high selectivity compared to conventional chemical sensors towards dysprosium(III) with respect to several alkali, alkaline earth and transition metal ions as the selectivity is 10-100-fold better. The sensor was used for determination of dysprosium(III) ions by potentiometric (EDTA) titration and has been successfully demonstrated for the determination of fluoride in mouth wash solution.     

Glucose and urea biosensors based on all solid-state PVC-NH2 membrane electrodes

Miniaturized urea and glucose sensors prepared by immobilization of glucose oxidase or urease directly onto all solid-state contact PVC-NH₂ membrane ammonium and hydrogen ion selective electrodes are described. The resulting biosensing membranes function equivalently to normal PVC membranes in terms of potentiometric response properties. The most important features of the glucose and urea sensors were high sensitivity, long life-time, easily built at a low cost, micro-construction and short response time. The characteristics of the glucose and urea sensors were examined in several buffer solutions at different concentrations and pH values. The influence of immobilization conditions on the dynamic response properties and life-time of the electrodes was studied. Under optimal conditions, the urea electrode showed a linear response between 5×10⁻² and 5×10⁻⁴ M urea, while the glucose electrode showed a linear response between 5×10⁻² and 1×10⁻⁴ M glucose.     

An all-solid-state monohydrogen phosphate sensor based on a macrocyclic ionophore

An all-solid-state electrode, containing a synthesized chiral A₂B₂ macrocyclic compound namely (4R,5R,15R,16R)-4,5,15,16-tetraphenyl-3,6,14,17-tetraazatricyclo [13.3.1.18,12] tetracosa-1(23),8,10,12(24)19,21-hexaene-2,7,13,18-tetrone as an ionophore in polyvinyl chloride (PVC)/polyurethane (PU) membrane matrix, has been developed for the selective quantification of monohydrogen phosphate ions. The best performing membrane contained PVC, PU, ionophore, and nitrophenyl octyl ether as a plasticizer in the ratio 32.2:2.6:65.1 (w/w, %). It exhibited a near-Nernstian slope of 31.0 ± 1.0 mV/decade of activity for HPO₄²⁻ ions in the concentration range of 1.0 × 10⁻⁶ to 1.0 × 10⁻² M at pH 7.4. The detection limit of the electrode was 8.4 × 10⁻⁷ M and the life time was six weeks. The electrode displayed excellent selectivity for monohydrogen phosphate over other anions and the selectivity sequence was determined as HPO₄²⁻ > SO₄²⁻ > Ac⁻ > NO₃⁻ > ClO₄⁻ > Cl⁻ > I⁻. The selective electrode for the monohydrogen phosphate ions was evaluated with a standard reference material (SRM 1548) and the titration of the sample solution.     

Novel platinum(II) selective membrane electrode based on 1,3-bis(2-cyanobenzene)triazene

A plasticized poly (vinyl chloride) membrane electrode based on 1,3-bis(2-cyanobenzene)triazene (CBT) for highly selective determination of platinum(II) (in PtCl₄²⁻ form) is developed. The electrode showed a good Nernstian response (29.8 ± 0.3 mV decade⁻¹) over a wide concentration range (1.0 × 10⁻⁶ to 1.0 × 10⁻² mol L⁻¹). The limit of detection was 5.0 × 10⁻⁷ mol L⁻¹. The electrode has a response time of about 40 s, and it can be used for at least 1 month without observing any considerable deviation from Nernstian response. The proposed electrode revealed an excellent selectivity toward platinum(II) ion over a wide variety of alkali, alkaline earth, transition, and heavy metal ions, and it could be used in the pH range of 3.2-5.1. The practical utility of the electrode has been demonstrated by its use in determination of platinum ion in, alloy, tap, mineral and river water samples.     

Calix[2]furano[2]pyrrole and related compounds as the neutral carrier in silver ion-selective electrode

The performance of calix[2]furano[2]pyrrole and related compounds used as neutral carriers for silver selective polymeric membrane electrode was investigated. The silver ion-selective electrode based on calix[2]furano[2]pyrroles gave a good Nernstian response of 57.1 mV per decade for silver ion in the activity range 1×10⁻⁶ to 1×10⁻² M. The present silver ion-selective electrode displayed very good selectivity for Ag⁺ ion against alkali and alkaline earth metal ions, NH₄⁺, and H⁺. In particular, the present Ag⁺-selective electrode exhibited very low responses towards Hg²⁺ and Pb²⁺ ions. The potentiometric selectivity coefficients of the silver ion-selective electrode exhibited a strong dependence on the solution pH. In particular, the response of the electrode to the Hg²⁺ activity was greatly diminished at pH 2.5 compared to that at pH 5.0. Overall, the performance of the present silver ion-selective electrode based on the ionophore, calix[2]furano[2]pyrrole, is very comparable to that of the electrode prepared with the commercially available neutral carrier in terms of slope, linear range, and detection limits.     

Characterization of home-made silver sulphide based iodide selective electrode

Polycrystalline silver sulphide/silver iodide ion selective electrodes (ISEs) with four different compositions, 9:1, 2:1, 1:1, 1:9 Ag₂S-AgI mole ratios, have been fabricated in the laboratory and characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), and electrochemical impedance spectroscopy (EIS). X-ray diffraction studies show the presence of Ag₃SI, Ag₂S and AgI crystalline phases in the electrode material. The electrode surfaces have been found to become smoother and lustrous with increasing percentage of silver sulphide in silver iodide. ISE 1:1, ISE 2:1 and ISE 9:1 all responded in Nernstian manner with slopes of about 60 mV/decade change in iodide ion concentration in the linear range of 1 × 10⁻¹ to 1 × 10⁻⁶ M while ISE 1:9 showed sub-Nernstian behavior with slope of about 45 mV up to the concentration 1 × 10⁻⁵ M. Two capacitive loops, one corresponding to the charge transfer process at metal electrode and the back contact and a second loop corresponding to the charge transfer process at membrane-electrolyte interface have been observed at high and low frequency ranges, respectively. Mott-Schottky analysis shows that the materials are n-type semiconductors with donor defect concentrations in the range of 5.1 × 10¹⁴ to 2.4 × 10¹⁹/cm³.