Fluoride-selective electrode

Anfalt and Jagner [57] measured total fluoride ion concentration by means of a single-crystal fluoride selective electrode (Orion, model 94-09). Samples of seawater were adjusted to pH 6.6 with hydrochloric acid and were titrated with 0.01 M sodium fluoride with use of the semi-automatic titrator described by Jagner [28]. Equations for the graphical or computer treatment of the results are given. Calibration of the electrode for single-point potentiometric measurements at different seawater salinities is discussed. 

Ke and Regier [71] have described a direct potentiometric determination of fluoride in seawater after extraction with 8-hydroxyquinoline. This procedure was applied to samples of seawater, fluoridated tap-water, well-water, and effluent from a phosphate reduction plant. Interfering metals, e.g., calcium, magnesium, iron, and aluminium were removed by extraction into a solution of 8-hydroxyquinoline in 2-butoxyethanol-chloroform after addition of glycine-sodium hydroxide buffer solution (pH 10.5 to 10.8). A buffer solution (sodium nitrate-l,2-diamino-cyclohexane-N,N,N. AT-tetra-acetic acid-acetic acid pH 5.5) was then added to adjust the total ionic strength and the fluoride ions were determined by means of a solid membrane fluoride-selective electrode (Orion, model 94-09). Results were in close agreement with and more reproducible than those obtained after distillation [72]. Omission of the extraction led to lower results. Four determinations can be made in one hour. 

A recent study has revisited the reactivity of oximate nucleophiles toward detoxification of sarin, soman and DFP, using a fluoride-selective electrode to kinetically monitor decomposition of the neurotoxin . Results are shown in Table 1. 

Elemental composition Cr 47.71%, F 52.29%. A nitric or hydrochloric acid solution of the compound may be analyzed for chromium by various instrumental techniques (see Chromium). The solution may be diluted appropriately and measured for fluoride ion by using a fluoride-selective electrode or by ion chromatography. 

Oxygen difluoride may be analyzed by GC, GC/MS, IR, and NMR methods. The compound may be identified by GC/MS, the characteristic mass ions are 54, 38 and 35. The compound can be measured quantitatively by wet methods based on its strong oxidizing ability (see Reactions). It liberates I2 from an acidified solution of potassium iodide and the liberated I2 can be measured by iodometric titration using Na2S20s titrant and starch indicator. Alternatively, the compound may he treated with a measured amount of excess NaOH and the unreacted excess NaOH measured hy titrating against a standard solution of HCl. Also, the fluoride ion, F, may he measured by fluoride selective electrode. 

Elemental composition Si 26.97%, F 73.03%. The gas is bubbled slowly through water to decompose into silicic acid and hydrofluoric acid. HE is analyzed for fluoride ion by fluoride-selective electrode or by ion chromatography. Silicon in the aqueous solution can be measured by AA or ICP. 

A kinetic flow injection analytical method was also described for isoxsuprine, which was based on the use of a fluoride-selective electrode for detection after reaction with l-fluoro-2,4-dinitrobenzene [38]. 

Methanol and Water. Methanol and water mixtures have been a popular choice for workers interested in free energies of transfer of ions from water into a mixed solvent. Such mixtures exhibit a drop in dielectric constant with increasing methanol content. Hence the electrical term must be estimated in order to compare spectroscopic and thermodynamic quantities. Feakins and Voice (28) have presented new data and revised earlier data for the alkali metal chlorides. In advance of carefully determined and extrapolated emf data for fluorides, using the solid state fluoride selective electrode based on lanthanum fluoride, some data of moderate accuracy have been presented (27). On the... 

A great number of anionic complexes containing four, five or six halide ions have been characterized. However, in aqueous solutions containing V111 ions and F-, the potentiometric technique using a fluoride selective electrode has shown no indication of any complex other than VF2+ (stability constant log / = 5.00 0.03 at 25 °C in 1.0 M NaC104 solution).295... 

For example, the aluminium ion, for which there is no selective electrode, can be determined in the following way. Sodium fluoride can be added as a reagent to lead to insoluble AIF3. The end point of the reaction can be determined by the presence of an excess of fluoride ions in solution, easily measured with a fluoride selective electrode. 

The glass electrode is so important that it deserves a special section in this book. However, there are other solid-state ISEs that have excellent performance, and one of them is the fluoride-selective electrode. There are only few analytical methods that allow simple and selective determination of fluoride ion. For this reason, the ion-selective electrode is one of the most important analytical tools. Although it was... 

Vickery and Vickery [9] have investigated the interference by aluminium and iron in the ion-selective electrode method for the determination of fluoride in plant extracts. They demonstrated that plant ashes may contain sufficient of these two elements to seriously interfere in the determination of fluoride when using the fluoride-selective electrode. In the presence of these metals, the known additions method gives erroneous results, as did that involving the attempted formation of complexes with ethylene diamine tetraacetic acid (disodium salt) or 1,2-cyclohexylenedinitrilotetraacetic acid. 

Solid-state fluoride selective electrode Frant and Ross Jr.3... 

Eor example, to calculate the concentration of aluminium in solution, an ion for which no selective electrode exists, this analyte is transformed into insoluble aluminium fluoride AIE3 by adding sodium fluoride. The end point of this reaction is determined by the presence of an excess of sodium fluoride ions in solution, easily detected by a fluoride selective electrode. 

P7.24 (a) The Nemst equation appropriate to the fluoride selective electrode is... 

The majority of data in Table V-8 were obtained in NaC104 solutions using a fluoride selective electrode, but some pH-metric [56AHR/ROS], kinetic [69FUN/TAN] and polarographic [71 BON] results are included, too. The SIT analysis of the experimental stability constants is depicted in Figure V-20. 

The fluoride complexes of the divalent ions from Mn(II) to Zn(Il) have been studied by potentiometric titration, using a fluoride selective electrode at 298.15 K and I = 1.0 M NaC104. Under the experimental conditions employed (25 cm 0.05 M metal(II) perchlorate solution was titrated by 10 cm 0.004 M NaF solution), only monofluoride complexes are formed but in rather low concentrations (at the end of titrations [NiF ] 2.2x10 M can be calculated). This yielded only a moderate effect (1-2 mV) in the measured electrode potential, therefore we estimate higher uncertainty in K ((2.2 1.0) for NiF in the present review, than suggested by the authors. The authors reported an anomalous stability sequence in the Mn(II)-Zn(II) series which does not fit an Irving-Williams type trend. This behaviour was later confirmed by several authors (see e.g., [83SOL/BON]). 

The authors have reported the formation and thermodynamic parameters (K, A H, A S ) of fluoride complexes of the Mn(II) - Zn(II) series in three papers [76KUL/BLO], [81KUL/BLO], [83AVR/BLO]. In the first paper [76KUL/BLO] they reported the stability constants and thermodynamic functions of complex formation determined at 298.15 K and at 7 = 3 M NaC104, by means of a fluoride-selective electrode and a differential double calorimeter. The experiments were performed in the presence of an excess of metal ions (0.1 M Me(C104)2) to assure the formation of only monofluoro complexes. 

In the third paper [83AVR/BLO], the stability constant values for NiF have been reported for 0-60 vol. % HzO/EtOH mixture (7 = 0.25, 0.5 and 1.0 M NaC104), using a fluoride-selective electrode. In contrast with the earlier conclusions, the authors suggest inner-sphere association for NiF. This assumption was based on the determination of the so called complete equilibrium constant, in which the water is also taken into consideration in the equilibrium process ... 

P. van den Winkel, G. de Backer, M. Vandeputte, N. Mertens, L. Dryon, and D. L. Massart, Performance and Characteristics of the Fluoride-Selective Electrode in a Flow Injection System. Anal. Chim. Acta, 145 (1983) 201. 

The authors have studied the complex formation between Th(lV) and fluoride using the redox couple Fe(ni)/Fe(ll) as indicator electrode. In a separate experiment they determined the fluoride complexes formed by Fe (the fluoride complex formation of Fe is negligible under the conditions nsed). From the known equilibrium data for the iron system they then calculated the free fluoride concentration from the measured redox potential in test solutions that in addition to Fe(lll)/Fe(ll) also contained Th(lV) the indicator system acts as a fluoride selective electrode. 

The author has used liquid-liquid extraction with thenoyltrifluoroacetone (TTA) and potentiometry using a fluoride selective electrode to determine the stoichiometiy and equihbrium constants of the fluoride complexes of Th(lV) and U(1V) only the Th(IV) data will be discussed here as the U(1V) data have been reviewed previously in [1992GRE/FUG]. The experiments have been made in a 4 M HCIO4 ionic medium at 20°C. The experimental data are described in detail and this study provides very useful information on the quality of the two experimental approaches used. The same author has previously studied the Zr(lV) and Hf(lV) systems using the same experimental approach. The slope of the ion selective electrode was determined experimentally and equilibrium was assumed to be attained when the emf changed by less than 0.1 mV/h. The experiments were made at three different total concentrations of Th(lV), 0.90, 1.79 and 4.48 mM and with the total concentration of HF varying from 0.406 to 225 mM. This corresponds to a concentration of free fluoride, 8 x 10 < [F ] < 5 x 10 M. The analysis of the experimental emf data is straightforward and the conditional equilibrium constants for the two reactions ... 

Fignre A-24 Observed ([1970BAU]) and predicted F activities at 25°C for fluoride-selective electrode studies in 0.01 M NH4NO3 solutions. Predictions based on NONLINT-SIT calculations nsing the thermodynamic data summarised in Tables VIII-8 and VIII-9. 

Figure A-33 Observed ([1990SAW/CHA2]) and predicted activities at (23 + 2)°C for potentiometric titrations using fluoride-selective electrode in 1 M (H,Na)C104 solutions. Predictions based on NONLINT-SIT calculations using the thermodynamic model summarised in Tables Vlll-8 and Vlll-9.

The fluoride selective electrode is routinely used for flie determination of fluoride in drinking water, industrial effluents, sea water, air, aerosols, flue gases, soils and minerals, urine, serum, plasma, plants, and other biological materials. The following discussion focuses on flie development of analogous techniques for flie determination of fluorine in hydrocarbons. 

The determination of fluoride in air is very important in areas near aluminium industry. We have constructed an instrument using potentiometry with a fluoride selective electrode for continuous measurement of hydrogen fluoride in stack gases by absorbing them in a suitable... 

Fluoride-selective electrode cell (single-probe measuring cell recommended)... 

Nicholson E and Duff EJ (1981) Fluoride determination in water - an optimum buffer system for use with fluoride-selective electrode. Analytical Letters 14 887-912. 

Solid-state sensors for chloride, iodide, and fluoride are based on the solubility product of silver chloride or silver iodide particles in silicone rubber and a doped lanthanum fluoride single crystal, respectively. The fluoride-selective electrode was applied for the analysis of urine and bone tissue of people exposed to industrial sources as well as for control of therapeutic fluoride application for osteoporosis, whereas the chloride-selective sensor was applied to the analysis of sweat for the diagnosis of cystic fibrosis. In solid-state contact electrodes the solvent polymeric membrane is directly contacted to the solid field transducing element, although the reference electrode is separated from the ion-selective sensing pad. 

Aluminum Complex formation with F " Stopped-flow technique, fluoride-selective electrode... 

X-i-F Fluoro complexes Fe lll)-Zr(IV) Use of a fluoride-selective electrode. Kalman filter algorithm... 

Primary and secondary amines Reaction with 1-fluoro-2,4-dinitrobenzene Reaction with 1,2-naphthoquinone-4-sulfonate lO- -iQ- moir A fluoride-selective electrode is used. Measurement of color formation in the presence of Triton X-100... 

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