Fluoride, analytical determination

Analytical determinations with the fluoride ion-selective electrode These are based either on direct potentiometry of fluorides [37, 84, 85, 88, 430] or on titration determinations of either fluorides or of other ions and also on titrations with fluoride ions as indicator. The advantages of potentiometry with an ISE over other analytical methods for determining fluorides were pointed out by Crosby etai [67], Further comparison studies [42, 56, 191, 433] came to the same conclusions, confirmed also by a study of 16 methods [365]. Fluoride ions are titrated either with La (for concentrations greater than 1 mM) or Th (in the concentration range 0.2-1 mM F ) [13, 102, 103, 113,233, 234]. Titration with fluoride ions can be used for the determination of Al with formation of the AIF4 complex up to nanomolar concentrations, especially in ethanol-water mixtures [25] (see also [267,384]). Precipitation titrations can also be used to determine La, Th and UOJ [241, 384] as well as Li in... 

Quentin. K E. et at. "Analytical Determination of Small Amounts of Fluorine in Foods and Waters. 4. Fluoride Studies in Foods" (in German i, Chem. Abstr. 54. 6, 5967. I960. 

NIOBIC ACID. Any hydrated form of Nb Os. It forms as a white, insoluble precipitate when a potassium hydrogen sulfate fusion of a niobium compound is leached with hot water or when niobium fluoride solutions are treated widi ammonium hydroxide. Soluble in concentrated sulfuric acid, concentrated hydrochloric acid, hydrogen fluoride, and bases. Important in analytical determination of niobium. See also Niobium. 

The aim of the present work is to estimate the linear voltammetry possibilities in oxide-ion analytical determination in FLINAK melt with and without addition of tantalum and boron complex fluorides. Sodium oxide was used as a source of oxygen in the melts. 

Schubert, F. et al.. Plant tissue hybrid electrode for determination of phosphate and fluoride. Analytical Chemistry 56,1677,1984. 

Ion-selective electrodes can be used for analytical determinations over an extremely wide range of solution concentrations (from 10" to 10 M to saturation) and are therefore applicable to trace as well as to major-constituent analysis. There are presently about two dozen ion-selective electrodes commercially available for cations, including the heavy metals for anions such as fluoride, sulfide, and the halides and for gases such as oxygen, carbon dioxide, and ammonia. ... 

Analytical Procedures. Oxygen difluoride may be determined conveniently by quantitative appHcation of k, nmr, and mass spectroscopy. Purity may also be assessed by vapor pressure measurements. Wet-chemical analyses can be conducted either by digestion with excess NaOH, followed by measurement of the excess base (2) and the fluoride ion (48,49), or by reaction with acidified KI solution, followed by measurement of the Hberated I2 (4). 

Okabayasi et al. used two identical columns containing Alizarin-Fluorine Blue sulphonate-lanthanum complex in an alternate fashion in order to increase the sample throughput in the preconcentration/separation of fluoride prior to its determination by use of an ISE (Fig. 4.14.B). By switching valve SV, the analyte in a sample was measured and eluted while that in the next sample was retained in the odier column [129]. 

F.N. Hattab, Analytical methods for the determination of various forms of fluoride in toothpastes, J. Dent. 17 (1989) 77-83. 

Reliable analytical techniques are a prerequisite for accurate and precise determination of human exposure to fluoride. The goal is to monitor the intake of fluoride and maintain it at adequate levels so that optimal protection against dental caries is achieved, without excessive intake resulting in the appearance of dental or, in the worst case, skeletal fluorosis. 

The aim of this section is to present a concise overview of separation, concentration and decomposition methods for sample pre-treatment and an overview of the analytical methods available for determining free inorganic fluoride and total fluorine in the environment (natural and drinking water, air and soil), biological and related materials, and fluoride supplements and dental products. 

The concentration of fluoride in water can usually be determined directly without pre-treatment. Among the numerous published analytical techniques, potentiome-try with fluoride ISE, ion chromatography, and spectrophotometry are commonly used. If the amount of fluoride present in water is very low, pre-concentration may be required. 

There have been some unsuccessful attempts to prepare a volatile hexafluoride from fluorine and polonium-210 26, 104), but recently such a fluoride has been prepared in this way from polonium-208 plated on platinum 132). The product appears to be stable while in the vapor phase, but on cooling a nonvolatile compound is formed, probably polonium tetrafluoride resulting from radiation decomposition of the hexafluoride. Analytical data are not recorded for any polonium fluoride, largely owing to the difficulty of determining fluoride ion accurately at the microgram level. 

Another analytical procedure for sample preparation including analyte separation and enrichment is the coprecipitation of the trace elements to be determined. The co-precipitation behaviour of Ti, Mo, Sn and Sb under two different fluoride forming conditions (at < 70 °C in an ultrasonic bath and at 245 °C using a Teflon bomb) has been studied to improve the accuracy of the trace analysis of these elements in Ca-Al-Mg fluorides, by ICP-MS.14 The applicability of this analytical method (including isotope dilution technique) was demonstrated for four carbonaceous chondrites and silicate reference materials of basalt or andesite.14... 

Analysis of major elements (except Si) and total phosphorus on bomb-digested samples was accomplished by inductively coupled plasma emission spectrometry (ICP, ARL model 34,000). Silicon was analyzed colorimetrically (14). Phosphorus in total digests was also determined colorimetrically by the method of Murphy and Riley (15), as modified by Erickson (16). To avoid interference from fluoride ion used in the digestion technique, sample volumes were restricted to <1.5 mL in the standard P analytical protocol. 

The determination of the nitrogen content in different cereal grains represents a nice example 66,67). The flour of the grain was mixed with 10% of lithium fluoride. The relative integrals Fn and Ff obtained are now plotted against the nitrogen content CN determined by classical analytical techniques (Fig. 11). The bent slope of the curve can be easily explained even with a crude picture. The integral F is proportional to the intensity of the photoelectron beam / ... 

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... 

Lamb, J. D., Eatough, D. J., and Smith, R. G. (1993) Determination of Fluoride in Atmospheric Samples Using Macrocycle-based Ion Chromatography, Int. J. Ertvir. Analyt. Chem. 56, 317-325. 

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