Determination of fluoride

As an alternative to plotting a calibration curve, the method of standard addition may be used. The appropriate ion-selective electrode is first set up, together with a suitable reference electrode in a known volume (Ft) of the test solution, and then the resultant e.m.f. ( t) is measured. Applying the usual Nernst equation, we can say 

Provided that the first and second solutions are of similar ionic strength, the activity coefficients will be the same in each solution, and the difference between the two e.m.f. values can be expressed as 

Hence provided the value of the slope constant k is known, the unknown concentration Ct can be calculated. 

Procedure. Set up the ion activity meter in accordance with the manual supplied with the instrument. 

The electrodes required are a fluoride ion selective electrode and a calomel reference electrode of the type supplied for use with pH meters. 

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DETERMINATION OF FLUORIDE PRECIPITATION AS LEAD CHL0R0FLU0RIDE COUPLED WITH VOLHARD TITRATION... 

The addition of sodium dodecyl sulfate improves the conventional spectro-photometric method for the determination of fluoride/lanthanum/alizarine flour-ine blue tertiary complex [172]. 

Ion selective electrodes are emerging as a method of preference for the determination of fluoride in seawater [53-58]. 

Table2.2. Determination of fluoride in seawater under a variety of conditions to demonstrate the reliability of the method [58] ...

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. 

Evaluation of Methods for the Determination of Fluoride in Water Samples. 2 Analysis of a Competitive Product. 3 The Assessment of the Heavy Metal Pollution in a River Estuary. 4 The Analysis of Hydrocarbon Products in a Catalytic Reforming Study. 

Evaluation of Methods for the Determination of Fluoride in Water Samples... 

After the treatment with sodium, the reaction mixture was washed with water into a beaker and brought to the correct pH for the determination of fluoride. 

When substances adsorbed on aerosol particles are to be determined, the gas is passed through a membrane or other filter and the filter is dissolved in or extracted with a suitable solution. An interesting method is used for determination of fluoride adsorbed on atmospheric aerosols [87]. The particles are trapped on a filter impregnated with citric acid and heated to 80 °C, while the fluorides pass through and are absorbed in a thin layer of sodium carbonate in a spiral absorber. The sodium carbonate is periodically washed with a sodium citrate solution, in which solution the fluoride is then determined, and the absorption layer regenerated. 

The determination of fluoride ions has always been difficult, so the discovery of the lanthanum trifluoride electrode by Frant and Ross in 1966 was a great step forward. Until recently, this was the most important sensor in the ISE field, except for the glass electrode sensitive to hydrogen ions. The extraordinary specificity of this electrode made the greatest contribution to its usefulness. The only important interferent is the hydroxide ion. 

The first such sensor, developed for the determination of fluoride ion, relies on the formation of the zirconium(IV)-Calcein Blue-fluoride complex... 

This approach may not account for all the fluoride released by glass-ionomers [252], A recent study has used two methods of decomplexation of fluoride, using the same solutions for both methods, by dividing a given storage volume into two and treating each aliquot differently. One aliquot was diluted with an equal volume of TISAB, as is usual in the determination of fluoride by ion-selective electrode. The other solution was treated with a small volume of 4 M hydrochloric acid, allowed to stand for 3 h, then neutralised with an equal amount of 4 M sodium hydroxide. A volume of TISAB equal to the initial volume of the aliquot was added. This technique is known to liberate fluoride from monofluorophosphate as well as from aluminofluoride complexes [253],... 

Methods for determining gaseous fluorides are generally based on the absorption of gaseous fluorides into a train of absorbing solutions, or collection on a filter with a treated pad and subsequent determination of fluoride. 

Total fluorine in fluoride supplements and dental products could be determined with minimal samples pre-treatment as for example by direct acid extraction or heating in TISAB buffer solution and subsequent determination of fluoride using fluoride ISE for the reason that entire fluorine, in these products, should be, by definition, available as free inorganic fluoride. 

M. Haidimann, B. Zimmerii, Evaiuation of ashing procedures for the gas chromatographic determination of fluoride in bioiogicai materiais, Anai. Chim. Acta 282 (1993) 589-601. 

R.W. Dabeka, A.D. McKenzie, H.B.S. Conacher, B.S. Kirkpatrick, Determination of fluoride in Canadian infant foods and calculation of fluoride intake by infants. Can. J. Public Health 73 (1982) 188-191. 

L. Singer, W.D. Armstrong, Determination of fluoride. Procedure based upon diffusion of hydrogen fluoride. Anal. Chem. 26 (1954) 904-906. 

R. Ikenishi, M. Kanai, M. Ishida, A. Harihara, S. Matsui, I. Yahara, T. Kitagawa, Determination of fluoride ion in animal bone by microdiffusion analysis. Anal. Chem. 62 (1990) 2636-2639. 

M. Ponikvar, B. Sedej, B. Pihlar, B. Zemva, Determination of fluoride in M(SbF6)x compounds. Anal. Chim. Acta 418 (2000) 113-118. 

B. Eyde, Determination of fluoride in plant material with a ion-selective electrode, Fresenius Z. Anal. Chem. 311 (1982) 19-22. 

M. Kjellevold Malde, K. Bjorvatn, K. Julshamn, Determination of fluoride in food by the use of alkali fusion and fluoride ion-selective electrode, Food Chem. 73 (2001) 373-379. 

I. Inkielewicz, W. Czarnowski, J. Krechniak, Determination of fluoride in soft tissues. Fluoride 36 (2003) 16-20. 

V.L. Dressier, D. Pozebon, E.L.M. Flores, J.N.G. Paniz, E.M.M. Flores, Potentiomet-ric determination of fluoride in geological and biological samples following pyrohy-drolytic decomposition. Anal. Chim. Acta 466 (2002) 117-123. 

L. forma, Collaborative study of ion selective electrode method for the direct determination of fluoride in feeds, J. AOAC 58 (1975) 477-481. 

H.B. Li, F. Chen, A highly sensitive fluorimetric method for the determination of fluoride in biological material with AP -calcein complex, Fresenius J. Anal. Chem. 368 (2000) 501-504. 

J. Ekstrand, A micromethod for the determination of fluoride in blood plasma and saliva, Calcif. Tissue Res. 23 (1977) 225-228. 

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