Separation of microamounts of fluoride coexisting with large amounts of aluminium and silica by improved trimethylsilylating distillation

The previously reported distillation method for the separation of fluoride as trimethyl- fluorosilane is much improved. When hexamethyldisilazane serves as the silylating agent, interference of silica can be avoided and distillation is rapid at room temperature. Aluminum is effectively masked by pyrophosphoric acid. Almost all ions tested can be tolerated in 1000-fold molar amounts to fluoride. Over 98% recovery is obtained for 49 μg of fluoride in the presence of 80 mg of aluminum plus 200 mg of silica. Concentration of fluoride from very dilute (μg l^-1) solutions is easily achieved. Satisfactory results were obtained for standard rocks.     

Phosphate rock treatment with citric acid for the rapid potentiometric determination of fluoride with ion-selective electrode

A fast method for sample treatment of phosphate rock has been developed for the purpose of quantitative leaching (98-100%) of fluoride but less of the interfering cations such as iron and aluminum. Citric acid (0.5 M) was used to extract fluoride in 15-45 min. Leaching of iron and aluminum is minimal, and these ions are complexed with citric acid. The leaching method was optimized with respect to sample size, citric acid concentration, leaching time and temperature. The analysis was completed by the rapid determination of fluoride with ion-selective electrode. The proposed treatment method was applied to phosphate rock samples from Jordan and Morocco and yielded accurate results as compared to the standard steam distillation from strong acid solution followed by thorium nitrate titration.     

Voltammetric,potentiometric and amperometric studies with a rotated aluminum wire electrode: Amperometric determination of fluoride with the raie

A simple and rapid amperometric method is described for the determination of traces of fluoride by measuring the anodic current at the RAIE at —0.75 V vs. SCE. In order to be independent of varying sensitivity of the RAIE, use is made of the standard addition technique. Proportionality between current and concentration is found between 0.2 and 6 p.p.m. of fluoride. Chloride, sulfate, nitrate, alkali and earth alkali ions do not interfere. Phosphate decreases the sensitivity but does not interfere. Aluminum ions interfere but can be made harmless by EDTA. Oxidising agents (including oxygen) must be removed. The method gives excellent results in potable and natural waters.     

Fast migration of fluoride ions in growing anodic titanium oxide

The rapid inward migration of fluoride ions in growing anodic titanium oxide under a high electric field has been elucidated by anodizing a Ti–12 at% silicon alloy, where film growth proceeds at nearly 100% efficiency in selected electrolytes. Further, incorporated silicon species in the anodic film are immobile, acting as marker species. The migration rate of fluoride ions is determined precisely by three-stage anodizing, consisting of initial anodic film formation at a constant current density to 50 V in ammonium pentaborate electrolyte, subsequent incorporation of fluoride ions by reanodizing to 55 V in ammonium fluoride electrolyte and, finally, anodizing again in ammonium pentaborate electrolyte at high current efficiency. The resultant films were analyzed by glow discharge optical emission spectroscopy to reveal the depth distribution of fluoride ions and the location of the silicon marker species. The fluoride ions migrate inward at twice the rate of O²⁻ ions. Consequently, anodizing of titanium in fluoride-containing electrolytes develops a fluoride-rich layer that separates the alloy substrate from the anodic oxide, with eventual detachment of the film from the substrate.     

Rapid titrimetric determination of microgram amounts of fluoride ion with spadns -thorium lake

A rapid titrimetric method has been developed for the determination of microgram amounts of fluoride ion in the range from Img-Ioomg, in 50 ml final volume. It involves the adjustment of pH, addition of 1 ml of 0.02% SPADNS indicator, dilution to volume and titration with standard 0.004M Th(NO₃)₄ until the colour obtained matches a blank containing the buffered solution of the indicator with a. trace of thorium nitrate solution. Interference by various ions was also studied. The method described for the determination of fluoride ion is very rapid and the colour change at the end point being sharp, the detection of the end point is very easy. The method is applicable to pure solutions of fluondes.     

Adsorption of fluoride, phosphate, and arsenate ions on a new type of ion exchange fiber

A new type of ion exchange fiber for the removal of fluoride, phosphate, and arsenate ions has been developed. A batch adsorption technique for investigating adsorption kinetic and equilibrium parameters and determining pH adsorption edges is applied. It is shown that the adsorption properties of the ion exchange fiber for fluoride, phosphate, and arsenate ions depend on the pH value and anion concentration. The adsorption of arsenate on the sorbent reaches a maximum of 97.9% in the pH value range of 3.5 to 7.0. The adsorption percentage of phosphate is more than 99% in the pH range of 3.0 to 5.5. The adsorption of fluoride on the ion exchange fiber is found to be 90.4% at pH 3.0. The Freundlich model can describe the adsorption equilibrium data of fluoride, arsenate, and phosphate anions. The sorption of the three anions on the ion exchange fiber is a rapid process, and the adsorption kinetic data can be simulated very well by the pseudo-second-order rate equation. The column performance is carried out to assess the applicability of the ion exchange fiber for the removal of fluoride, phosphate, and arsenate ions from synthetic wastewaters with satisfactory removal efficiency. The desorption experiment shows that fluoride ion sorbed by the fiber column can be quantitatively desorbed with 5 mL of 0.50 mol/L NaOH at elution rate of 1 mL/min, and 30 mL of NaOH is necessary for the quantitative recovery of phosphate and arsenate ions.     

Azeotropic drying-free aliphatic radiofluorination to produce PET radiotracers in a mixed organic solvent system

Efficient aliphatic radiofluorination in a mixed organic solvent system was investigated. This method obviates the time-consuming [¹⁸F]fluoride drying step routinely required in the preparation of most fluorine-18 positron emission tomography (PET) radiotracers. The [¹⁸F]fluoride ions eluted from a QMA (quaternary ammonium anion exchange) cartridge with phase transfer agents were directly mixed in various organic solvents for subsequent radiofluorination. Herein, we report the azeotropic drying-free radiofluorination of aliphatic substrates and demonstrate the viability of hydrated [¹⁸F]fluoride ions in a mixed organic solvent system for obtaining useful radiochemical yields (RCYs). This practical and simple method has demonstrated general applicability to the production of established PET tracers as well as to the rapid assessment and chemical optimization of early-stage potential radiotracers.     

An Extractive‐Spectrophotometric Method for Determination of Fluoride Ions in Natural Waters Based on its Bleaching Effect on the Iron (III)‐Thiocyanate Complex

An extractive‐spectrophotometric method based on the bleaching effect of F^? ions on the iron (III)‐thiocyanate complex extracted into methyl iso‐butyl keton (MIBK) is proposed for the determination of fluoride ions in natural waters. This method is a simple and rapid method and there is no need for special and expensive reagents. The experimental conditions such as SCN^? concentration, pH and kind of solvent were optimized, and we found that 0.15 M SCN^?, pH = 5 and MIBK are the best selections. Limit of detection is 0.1 mg F^?/L with a linear dynamic range 0.5–7 mg/L which covers optimum concentration of F^? ions in drinking water (0.7–1.2 mg/L). Interference of Fe³⁺ and Al³⁺ ions was easily eliminated by the extractive procedure using a solution of oxine in chloroform. Finally, the proposed method was used in determination of fluoride content of some real water samples and the obtained results compared with those obtained from the standard method. No significant differences were observed between them.     

Voltammetric determination of lead,cadmium and copper traces in ammonium fluoride

A rapid and precise voltammetric method for the determination of traces of Pb, Cd and Cu in NH(4)F has been developed based on the capability of boric acid to mask fluoride ions and on the measurement of the analyte signals of the blank and the sample in the same solution.     

A colorimetric method of determination of Borax

A method is described for the rapid and accurate determination of borax. The principle of this method is to cause the boron of the borax under analysis to form a complex by the addition of an excess of a fluoride , the excess of fluorine ions causes decolourization of the violet compound Fe(III) - sulphosalicylic acid by forming the colourless complex (FeF₆)^-3.The extinction coefficient of the solution, measured in the Pulfrich photometer, decreases with increasing content of this excess of fluorine ions, and consequently can be used as an indirect measure of the borax to be determined.     

A novel chemosensor based on Fe(III)-complexation for selective recognition and rapid detection of fluoride anions in aqueous media

A novel fluorogenic receptor 1 was prepared by the reaction of thiosemicarbazide with 1-naphthaldehyde. Based on in situ-formed 1-Fe(III) complexes having the specific binding affinity for F⁻ anions, this sensory system allows rapid recognition and quantitative detection of fluoride in neutral aqueous media in an ‘off-on’ fashion. The fluoride measurement method not only exhibits a low detection limit but also has strong anti-interference ability to common coexisting ions, as evidenced by competitive experiments.     

Voltammetric determination of lead, cadmium and copper traces in ammonium fluoride

A rapid and precise voltammetric method for the determination of traces of Pb, Cd and Cu in NH₄F has been developed based on the capability of boric acid to mask fluoride ions and on the measurement of the analyte signals of the blank and the sample in the same solution.     

A molecular receptor based on the 2,3,7,8,12,13,17,18-octaethyl-21,23-dimethylporphyrin for detection of fluoride ions: Synthesis, spectral and complexation properties

2,3,7,8,12,13,17,18-Octaethyl-21-methylporphyrin and 2,3,7,8,12,13,17,18-octaethyl-22,23-dimethylporphyrin monotriflate based on the former were synthesized. Basic and complexing properties of these compounds were studied by the method of spectrophotometric titration in acetonitrile-perchloric acid and acetonitrile-tetrabutylammonium fluoride systems at 298 K. It was established that in the system of acetonitrile-perchloric acid the cationic forms of 2,3,7,8,12,13,17,18-octaethyl-21-methylporphyrin do not form complexes with fluoride ions, whereas 2,3,7, 8,12,13,17,18-octaethyl-22,23-dimethylporphyrin monotriflate forms complexes of 1:1 composition with the fluoride ions. The protonation constant of 2,3,7,8,12,13,17,18-octaethyl-21-methylporphyrin and the stability constant of the complex of 2,3,7,8,12,13,17,18-octaethyl-22,23-dimethylporphyrin with fluoride ions in acetonitrile at the standard temperature were determined.     

The determination of microgram quantities of fluoride : The use of the aluminium-haematoxylin complex

This paper describes a method for the spectrophotometric determination of fluoride. The fluoride is separated from interfering ions by the standard method of distillation as hydrofluosilicic acid. The fluoride in this distillate is determined by its destruction of the aluminium-haematoxylin complex; the amount of complex destroyed which is directly proportional to the concentration of fluoride is measured spectrophotometrically using radiation of 5700 A. The method will detect down to 0.05 p.p.m. of fluoride on a 10 gram sample with precision of rather better than ± 10% with larger amounts of fluoride. references p. 368.     

Extraction and spectrophotometric determination of cobalt(II) with thiobenzoylacetone and simultaneous determination of cobalt and nickel

Thiobenzoylacetone in benzene is used for the extraction and spectrophotometric determination of cobalt at pH 8.4-9.1. The orange-yellow complex is measured at 460 nm. The system conforms to Beer's law over the range 0.20-4.58 microg ml of extract. The colour of the complex is stable for at least 144 hr. Cobalt(II) is quantitatively extracted and determined in the presence of 200:1 (w w ratios) of various ions. The method is made selective by using common sequestering agents such as thiourea or fluoride or by selective extraction with mesityl oxide, tributylphosphate and acetylacetone. It is possible to determine cobalt in the presence of nickel by simultaneous spectrophotometry. The method is rapid, simple, selective and sensitive.     

The determination of microgram quantities of fluoride: The use of the aluminium-chromeazurol-s complex

A spectrophotometric method for determining fluoride using the aluminium chromeazurol complex is described. Fluoride in solution free from interfering ions or obtained by distillation as hydrofluosilicic acid is determined by destruction of the complex, the amount destroyed being directly proportional to the fluoride present. The method will detect as little as 0.02 μg/ml of fluoride and with 0–20 μg in the final solution fluoride can be determined with an accuracy of ± 0.6 μg.     

Rapid volumetric method for the estimation of iron in presence of interfering ions

Summary It has been shown that in the photochemical reduction method for the volumetric estimation of iron, there is no interference by chromium, titanium, tungsten, molybdenum, manganese, cobalt, nickel and fluoride. This method is therefore recommended for a rapid determination of iron in alloys and ores without the elimination of these interfering ions. Vanadium, however, was found to give slightly higher values for iron.Our thanks are due to Prof. G.Gopala Rao for his kind interest in the work.     

Fluorimetric determination of sulphate by ternary complex formation with zirconium and biacetylmonoxime nicotinylhydrazone

A fluorimetric procedure for the determination of sulphate (0.5-6 mug ml ) based on the formation of a ternary complex with biacetylmonoxime nicotinylhydrazone and zirconium(IV) is described. The excitation and fluorescence maxima are at 415 and 505 nm, respectively. The method is rapid and the procedure reproducible. The precision is +/- 2% near to the middle range of the calibration curves. There is no interference from most common ions. Phosphate and fluoride are tolerated at 100-fold molar ratio to sulphate. The method has been applied to the determination of sulphate in a variety of water samples.     

Resolving the different dynamics of the fluorine sublattices in the anionic conductor BaSnF(4) by using high-resolution MAS NMR techniques

19F and (119)Sn MAS NMR spectroscopy have been used to investigate the fluoride ion conductor, BaSnF(4), a member of the MSnF(4) family of fluorite-related anionic conductors containing double layers of Sn(2+) and M(2+) cations. Two fluorine sublattices were observed by (19)F MAS NMR, which could be assigned to specific sites in the lattice. The first sublattice is due to fluorine atoms located in Ba(2+) double layers and is rigid on the MAS NMR time scale at room temperature. The second sublattice comprises the fluoride ions between the Ba(2+) and Sn(2+) layers, and the few fluorine atoms that inhabit the Sn(2+)-Sn(2+) double layers. These ions are in rapid exchange with each other, and an extremely short correlation time tau(C) for the motion of these ions of <3 x 10(-)(5) s is obtained at -100 degrees C. T(1) measurements indicate that tau(C) approaches 10(-)(8) s at room temperature. (19)F-to-(119)Sn cross-polarization (CP) experiments confirmed the assignments of the resonances, and that the fluorine atoms located next to the tin atoms are extremely mobile at room temperature (and thus do not contribute to the CP process). Two-dimensional (19)F exchange experiments showed that exchange between the rigid and mobile lattice does occur, but at a much slower rate (tau(C) approximately 10 ms at 250 degrees C). Low-temperature (19)F MAS and (19)F-to-(119)Sn CP NMR spectra demonstrate that the motion of the fluoride ions has almost completely frozen out by -150 degrees C. The results are consistent with rapid two-dimensional (anisotropic) conductivity involving the fluoride ions between the Ba and Sn layers. Conductivity in three dimensions requires hops between the ions in the BaF(2)-like layers and the mobile ions. This process does occur, but with exchange rates that are at least 6-7 orders of magnitude slower.     

The determination of fluoride by titration with calcium chloride

A new method for the determination of fluoride ions is described. Precipitation is effected with an excess of standard calcium chloride and, after standing overnight, the unconsumed calcium ions are back-titrated with ethylenediamine tetra-acetic acid (EDTA) using Eriochrome Black T as indicator. Halides, sulphate, phosphate and arsenate do not interfere under the recommended conditions. The method is applicable over the range 5-65 mg of fluoride ion.