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

ABSTRACT

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

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

Direkte potentiometrische st?rungsfreie Fluoridbestimmung in Mineral-, Trink- und Brauchw?ssern

Zusammenfassung Das von Chang et al. [5] kürzlich entdeckte Verfahren, Fluorid neben großen Aluminiummengen durch Dekomplexierung mit Hilfe von Tiron zu bestimmen, wurde von uns überprüft und dessen Brauchbarkeit in bezug auf Störelemente und Mengenbereich erweitert.Theoretisch wie praktisch konnte bewiesen werden, daß Tiron (Dinatrium-brenzcatechin-3,5-disulfonat) tatsächlich in der Lage ist, Fluoridionen aus allen seinen Komplexen, wie z. B. aus denen mit Al³⁺, Fe³⁺, TiO²⁺, Mg²⁺, SiO₂, H₃BO₃, freizusetzen und somit die direkte potentiometrische Bestimmung der Fluoridionen auch in Lösungen unbekannter Zusammensetzung zu ermöglichen. Im Gegensatz zu den in herkömmlichen TISABs (total ionic strength adjustment buffers) enthaltenen Komplexbildnern [6, 9, 15] komplexiert das Tiron Lanthanionen kaum, wodurch gegenüber der Messung mit TISAB der Leerwert erniedrigt und der Lanthanfluorideinkristall der Elektrode geschont wird. Gleichzeitig werden auch pH und Ionenstärke durch Tiron geregelt.Der Fluoridgehalt natürlicher Wässer wurde direkt nach Zugabe von 0,06 M Tironlösung bei pH 6,5 bestimmt. In akratischen und hypotonischen Wässern können bis zu 0,2 mg F^–/l mit ±3 % und mit geringerer Genauigkeit noch bis zu 0,01 mg erfaßt werden. Für hypertonische Wässer wird die Erstellung einer entsprechenden Eichkurve empfohlen. Bei Säuerlingen und künstlich mit CO₂ versetzten Wässern nimmt der Fluoridgehalt der Wasserproben in der Originalflasche mit der Zeit der Lagerung ständig ab.

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Direct potentiometric determination of fluoride in mineral, drinking and industrial waters without interferences

Summary The method recently discovered by Chang et al. [5] to determine fluoride in presence of huge amounts of aluminium by means of decomplexation with the aid of tiron, was checked by us; the determination limits were extended and the method was also investigated concerning other substances.Theoretical calculations and practical measuring could prove the reagent tiron (pyrocatechol 3,5-disodium disulphonate) to be able to liberate fluoride from several complexes, e.g. from Al³⁺, Fe³⁺, TiO²⁺, Mg²⁺, SiO₂, H₃BO₃ etc.; so the direct determination of fluoride in solutions of unknown composition becomes possible by means of tiron.In contrast to those complexing agents present in common TISABs [6, 9, 15] (total ionic strength adjustment buffers) tiron hardly complexes lanthanum-ions; therefore the value of the reagent blank is lowered compared with the measured value in presence of TISAB, and the LaF₃ single-crystal of the electrode is saved. Simultaneously pH and ionic-strength are regulated by the reagent.The determination of fluorine is recommended in 0.03 M solutions of tiron at pH 6.5. In akratic and hypertonic waters down to 0.2 mg of F^–/l can be determined. In the linear region of the calibration graph the accuracy is ±3 %.It has been shown that the fluoride content of originally bottled water samples declines steadily with the time of storage, particularly if the sample is acidic or CO₂ is added artificially.

     

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.     

Fluoride ion-selective electrode in flow injection analysis : Part 2. Interference Studies

The influence of the sample composition on the response characteristics of the fluoride ion-selective electrode in flow injection analysis is described. Sample parameters such as ionic strength, viscosity and pH affect the response time of the electrode and cause transient signals when limiting values are exceeded. The respective limiting values depend on the total ionic-strength adjustment buffer (TISAB) used and these interferences can be minimized by proper choice of the TISAB. The complex formation of fluoride by several elements in the presence of TISAB containing CDTA is discussed. Aluminium and magnesium were found to interfere when present at levels above 1 and 100 mg l^?1, respectively. The signal decrease in the presence of iron, calcium and silicon can be attributed to ionic strength effects rather than complexation. Provided that the ionic strength is taken into account and corrected for, no influence occurs even in the presence of 0.5, 2 and 5% of iron, calcium and silicon, respectively.     

Trace fluoride determination with specific ion electrode

A method is described for determining 10^-5–10^-4M fluoride in a variety of solutions potentiometrically with a fluoridc-specific electrode, by a standard addition method. Any change of ionic strength or the nature of the solution that might alter activity coefficients or junction potentials is minimized. The relationship between potential and fluoride concentration thus follows the Nernst equation, and the unknown concentration can be calculated. Experimental data are given for solutions of sodium choride, sodium nitrate, acidified sodium silicate and sodium hydroxide, lithium chloride, and phosphoric acid. Metal ions (e.g., Al³⁺, UO₂²⁺, Fe³⁺, Th⁴⁺) that interfere by forming complexes with fluoride can be precomplexed with phosphoric acid. The relative error is estimated at 10%, and the relative standard deviation is less than 5% over the concentration range 10^-5–10^-4M fluoride.     

Microdetermination of fluoride using Gran's plots

Summary The known addition method has been used in combination with Gran's plots for the determination of 0.08 to 3 ppm (4.0 · 10^–6 to 3.2 · 10^–4 M) fluoride. The effectiveness of the total ionic strength adjustment buffers (TISAB) recommended by Frant and Ross, Liberti and Mascini, and Peters and Ladd has been investigated. For complexation of Al³⁺, that used by Peters and Ladd was found most effective, while for Fe³⁺ and Si⁴⁺, that used by Liberti and Mascini was most effective. The original TISAB recommended by Frant and Ross was found adequate in the presence of large amounts of Mg²⁺, Ca²⁺, chloride, nitrate, sulfate, and phosphate.

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Zusammenfassung Das Verfahren mit bekannten Zusätzen wurde mit der von Gran angegebenen Methode der Äquivalenzpunktbestimmung kombiniert und für die Bestimmung von 0,08–3 ppm Fluorid (4,0 · 10^–6 bis 3,2 · 10^–4 Mol) herangezogen. Die Eignung von Pufferlösungen zur Einstellung der Gesamtionen-stärke, wie sie von Frant und Ross, Liberti und Marcini sowie von Peters und Ladd empfohlen wurden, wurde untersucht. Für die Komplexierung von Al³⁺ eignet sich am besten die von Peters und Ladd angegebene Lösung, während für Fe³⁺ und Si⁴⁺ die Lösung nach den Angaben von Liberti und Marsini am besten entspricht. Das ursprünglich von Frant und Ross empfohlene Gemisch ist bei Gegenwart großer Mengen Mg²⁺, Ca²⁺, Cl^–, NO₂ ^–, SO₄ ^2– und PO₄ ^3– angebracht.

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Work performed under the auspices of the U. S. Atomic Energy Commission. Reference to a company or product name does not imply approval or recommendation of the product by the University of California or the U. S. Atomic Energy Commission to the exclusion of others that may be suitable.     

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

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

Determination of fluoride by use of a fluoride-selective cell

A concentration cell with a lanthanum fluoride membrane as the junction (fluoride-selective cell) was applied to the determination of fluoride in the concentration range 0.2–100 mg 1^?1. Fluoride was determined by direct potentiometry and/or by standard additions. Background fluoride levels in TISAB solutions were determined by means of standard additions. It is shown that the fluoride-selective cell makes possible the elimination of interferences in fluoride determination. Equations are give for the e.m.f. of the fluoride-selective cell and for standard additions. The advantages of the fluoride-selective cell over the conventional fluoride-selective electrode are summarized.     

Potentiometric Study of Aluminium-Fluoride Complexation Equilibria and Definition of the Thermodynamic Model

Complexation constants of the Al³⁺/F⁻ system were determined at different ionic strengths in a NaClO₄ (1.0, 2.0 and 3.0 mol⋅dm⁻³) ionic medium by means of a potentiometry using two electrode systems: an ion fluoride selective electrode as well as a glass electrode. All the experimentation was performed at 25 °C. The main species in the complexation equilibria were determined as AlF²⁺, AlF₂⁺, AlF₃⁰, AlF₄⁻, AlF₅²⁻ and AlF₆³⁻. The differences found in the complexation constants for the ionic strength considered were explained by the different behavior of the interaction parameters for the AlF _n ³⁻ⁿ species. These parameters were calculated using the Modified Bromley’s Methodology (MBM). The corresponding thermodynamic quantities were also determined. From all the results obtained, it can be concluded that pH, fluoride concentration and ionic strength influenced the distribution of the fluoride-aluminium complexes.     

Potentiometric behaviour of lanthanum polyalkoxylate complexes in PVC membrane electrodes: effect of plasticizers and applications

Tetraphenylborate salts of lanthanum complexes of nonylphenoxypolyethyleneoxyethanol (Antarox CO-880) and polypropylene glycol-425 (PPG-425) have been prepared and examined for their applicability as sensing species for lanthanum ions by incorporating them in a poly (vinyl chloride) membrane system in the presence of 2-nitrophenyl phenyl ether (NPPE), dioctylphenyl phosphonate or a mixture of both as plasticizers. Almost all of the systems studied showed an excellent response for lanthanum ions in pure solutions with a near Nernstian response of 18–20 mV per decade between 10^?5 and 10^?1 M lanthanum and a static response time of less than 1 min. Among the systems studied, lanthanum(Antarox CO-880)TPB/100% NPPE (TPB=tetraphenylborate) was the best in terms of tolerance to interfering ions. K⁺, Ba²⁺, Pb²⁺ and Al³⁺ were serious interferents, but most other interferents investigated were tolerable at [La³⁺] > 10^?4 M. Plasticizers were found to be decisive in determining the sensor selectivity towards the different metal ions. A lanthanum(Antarox CO-880)TPB/100% NPPE PVC membrane electrode was utilized for the potentiometric titration of fluoride, in sodium fluoride, against lanthanum nitrate solutions. It proved to be successful for fluoride concentrations of ? 10^?3 M.     

A Coated Graphite Thorium‐Ion Selective Potentiometric Sensor Based on a Calix[4]arene Bearing Phosphoryl Groups

5,11,17,23‐Tetra‐tert‐butyl‐25,26,27,28‐tetrakis(diphenylphosphinoylmethoxy)calix[4]arene ( 1 )has been used for the preparation of a graphite coated thorium ion‐selective electrode (Th⁴⁺‐ISE). The plasticized PVC membrane containing 30% PVC, 58% ortho‐nitrophenyloctylether (NPOE), 4% sodium tetraphenylborate (NaTPB) and 8% ionophore was directly coated on a graphite rod. This sensor gave good Nernstian responses with a slope of 15.5 ± 0.1 mV/decade over a concentration range of 1 × 10^?5 ?1 × 10^?3 M of thorium ions with a limit of detection of 7.9 × 10^?6 M. The dynamic response time of the electrode to achieve a steady potential was found to be about 15 seconds. The potential of the prepared sensor was independent of the pH variation in the range 2.3–4.0. The selectivity relative to several mono‐, di‐ and tri‐valent metal ions, i.e. Li⁺, Na⁺, K⁺, Ag⁺, NH₄⁺, Sr²⁺, Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, La³⁺, Sm³⁺, Dy³⁺, Er³⁺ and Y³⁺ was examined. This electrode can be used for 6 months without any considerable divergences in the potential response. The sensor was successfully used as an indicator electrode for the potentiometric titration of a thorium solution using a standard solution of EDTA.     

Eine Grlaselektrode zur Indizierung der direkten potentiometrischen Kaliumtitration mit Hexafluorosilicat

Zusammenfassung Aus einem Natriumaluminiumsilicat-Glas mit der Synthese-Zusammensetzung (Mol-%) 27% Na₂O, 8% Al₂O₃ und 65% SiO₂ (NAS 27-8) wurden Glaselektroden hergestellt, deren Eignung zur Indizierung der Kaliumtitration mit Zn[SiF₆] in methanoliseher Lösung untersucht wurde. In reinen, schwach sauren Kaliumsalzlösungen erhält man gut auswertbare Titrationskurven. Die Glaselektrode versagt in stark saurer Lösung. Außer den Ionen, die mit Hexafluorosilicat schwerlösliche Salze bilden, stören auch Ca²⁺, Mg²⁺ und Al³⁺, die mit den im Gleichgewicht vorliegenden Fluoridionen reagieren.

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Summary Glass electrodes have been prepared from a sodium-alumina-silica glass of the synthesis composition (mole %) of 27% Na₂O, 8% Al₂O₃, 65% SiO₂ (NAS 27-8) and their suitability for the indication of the potassium titration by means of Zn[SiF₆] in methanolic solution has been studied. With pure potassium salt solutions of low acidity it is possible to obtain well definable titration curves. With strongly acid solutions the glass electrode fails. Apart from ions forming sparingly soluble salts with hexafluorosilicate also Ca²⁺, Mg²⁺, and Al³⁺ are interfering by reaction with the fluoride ions present in equilibrium.

     

The formation of flouride complexes of titanium(IV)

The complex formation equilibria between titanium(IV) and fluoride ions have been studied at 25°C in 3 M(Na)Cl ionic medium by measuring, with an ion selective electrode for F^?, the free HF concentration in acid Ti(IV) solutions. The [H⁺] was kept within 0.25 and I M where the predominant form of uncomplexed metal is the dihydroxotitanium(IV) ion, Ti(OH)²⁺₂. The potentiometric data have been explained by assuming Ti(OH)₂F⁺, TiF₄ and HTiF^?₆, with equilibrium constants given in Table 3. Within the accuracy of the present e.m.f. study, ±0.2 mV, no evidence for intermediate complexes bearing 2, 3 and 5 F^? was found.From a special series of measurements, carried out by replacing a large part of the Cl^? with ClO^?₄, it is concluded that no appreciable amount of Ti(IV)Cl complexes is formed at the 3 M level employed as ionic medium.     

A Bis‐Oxime Derivative of Diaza‐18‐Crown‐6 as an Ionophore for Silver Ion

A new pendant‐arm derivative of diaza‐18‐crown‐6, containing two oxime donor groups, has been synthesized and incorporated into a polyvinyl chloride (PVC) membrane ion‐selective electrode. The electrode shows selectivity for Ag⁺ ion, with a near Nernstian response. Pb²⁺, Cu²⁺, Hg²⁺, and Tl⁺ are major interfering ions, with Cd²⁺ having minor interference. The electrode shows no potentiometric response for the ions Mg²⁺, Al³⁺, K⁺, Ca²⁺, Ni²⁺, Fe³⁺, and La³⁺, and is responsive to H⁺ at pH<6.     

Single‐Piece Solid‐Contact Pb2+‐Selective Electrodes Based on Thiophene Oligomer

A single‐piece solid‐contact Pb²⁺‐selective electrode was prepared by adding a thiophene oligomer into the ion‐selective cocktail directly. The one‐step fabrication yielded an electrode with Nernstian response spanning a wide concentration range of 10^?3–10^?8 mol L^?1, and detection limit as low as 5.6×10^?9 mol L^?1. The electrode had a quick response time of approximately 10–15 s and showed excellent selectivity over the most common univalent and divalent cations. The practical application of the proposed electrode has been tested by determining Pb²⁺ in real water samples.     

The determination of fluoride in environmentally relevant matrices

This report covers analytical methods for the determination of total fluoride in gaseous emissions, rain water and aqueous effluents, vegetation, human urine, factory air and environmental air. All the methods are based on final measurement of fluoride by means of the fluoride ion-selective electrode. Interferences which cannot be eliminated by the masking power of the TISAB buffer solution are avoided by separation of fluoride by steam distillation. Decomposition methods are used for vegetation and for samples which may contain insolubles such as stack gases or aqueous effluents. Sampling of fluoride from air is done by alkaline absorption for the high concentration range (stack gases) and by filter methods for low fluoride concentrations, e.g., in factory and environmental air. Detection limits as low as 0.3 μg m^?3 fluoride can thus be achieved. The methods were established after the individual analytical procedures, common in the various member countries of CTEF, had been compared. Thus, the most practicable method was selected or an optimized version was designed for full testing. The accuracy of the different methods was verified by comparative tests.     

A New Silver(I) Potentiometric Sensor Based on a Calix[4]arene Substituted at the Narrow Rim by Amide/Phosphoryl Groups

A coated‐wire type silver ion‐selective electrode has been constructed using a modified p‐tert‐butyl‐calix[4]arene by amide‐phosphoryl groups, named 5, 11, 17, 23‐tetra‐tert‐butyl‐25, 27‐bis(diethylcarbamoylmethoxy)‐26,28‐bis(diphenylphosphinoylmethoxy)calix[4]arene (Calix), as neutral carrier. A plasticized PVC membrane containing 30% PVC, 60% ortho‐nitrophenyloctylether (NPOE), 2% sodium tetraphenylborate (NaTPB) and 8% “Calix” was coated on a graphite rod. The prepared electrode exhibited a linear Nernstian response over the range 1 × 10^?6 to 1 × 10^?2 M with a slope 58.4 (±0.2) mV per decade change and a detection limit of 6.3 × 10^?7 M. The working pH range of the sensor is 4‐6.7. It is found that the dynamic response time of the electrode to achieve a steady potential was very fast (～11 s). The selectivity of the sensor relative to NH₄⁺, Li⁺, Na⁺, K⁺, Ca²⁺, Sr²⁺, Ba²⁺, Mn²⁺, Pb²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Fe³⁺, La³⁺, Sm³⁺ and Th⁴⁺ was examined. The prepared electrode exhibits adequate stability with good reproducibility (57.6 ± 0.5 mV per decade change for 10 weeks). It was successfully used as an indicator electrode in potentiometric titration of silver ions with standard solution of EDTA. The sensor was also used for silver ion measurements in various synthetic samples.     

Chemical processing for inorganic fluoride and oxyfluoride materials having optical functions

Chemical processing such as a sol–gel method can offer interesting and useful routes for designing and synthesizing inorganic metal fluoride and oxyfluoride materials for applications in optics and photonics. In our series of studies during the last decade, a variety of fluoride materials including alkaline earth fluorides (MgF₂, CaF₂, SrF₂ and BaF₂), rare-earth fluorides (LaF₃, NdF₃, GdF₃, etc.), rare-earth oxyfluorides (LaOF, EuOF, GdOF, Sm₄O₃F₆, Er₄O₃F₆, etc.) and complex fluorides (SrAlF₅, BaMgF₄, BaLiF₃, LiGdF₄, etc.) have been prepared, using trifluoroacetic acid as a fluorine source, in the form of nanoparticles, thin films and oxide/fluoride nanocomposites. They can be utilized as anti-reflective coatings, luminescent materials, VUV materials, IR materials, and so forth. This article summarizes fundamentals and possible applications of optically useful inorganic fluoride and oxyfluoride materials, with emphasis on porous single-layer anti-reflective coatings and visible photoluminescence of doped Eu³⁺ or Eu²⁺ ions. Furthermore, our recent results on LaF₃:Ce³⁺ and LaOF:Ce³⁺ are originally reported here.     

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

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

A novel ion selective membrane potentiometric sensor for direct determination of Fe(III) in the presence of Fe(II)

A new PVC membrane potentiometric sensor that is highly selective to Fe(III) ions was prepared by using 2-[(2-hydroxy-1-propenyl-buta-1,3-dienylimino)-methyl]-4-p-tolylazo-phenol [HPDTP] as a suitable carrier. The electrode exhibits a linear response for iron(III) ions over a wide concentration range (3.5 × 10⁻⁶ to 4.0 × 10⁻²) with a super Nernstian slope of 28.5 (±0.5) per decade. The electrode can be used in the pH range from 4.5 to 6.5. The proposed sensor shows fairly a good discriminating ability towards Fe³⁺ ion in comparison to some hard and soft metals such as Fe²⁺, Cd²⁺, Cu²⁺, Al³⁺ and Ca²⁺. It has a response time of <15 s and can be used for at least 2 months without any measurable divergence in response characteristics. The electrode was used in the direct determination of Fe³⁺ in aqueous samples and as an indicator electrode in potentiometric titration of Fe(III) ions.