Fluoride ion-selective electrod

The titration of AF+ with E in a water-acetonitrile mixture is followed potentiometrically using a fluoride ion-selective electrode. The cumulative formation constant for AlEs is determined from the titration curve. 

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

Describe the response mechanism of the fluoride ion-selective electrode. Explain clearly why the OH- is the major interfering ion in F ISE measurements. 

The fluoride ion is the only inorganic ligand to form a complete substitution series, Be(H20)4 flFJ(2 1 (n = 1-4), though there is considerable variation in the equilibrium constants that have been reported. The most reliable values are probably those of Anttila et al. (117) who used both glass and fluoride-ion selective electrodes and also took account of the competing hydrolysis reactions. They did not, however, make measurements in the conditions where BeF2 would have been formed. A speciation diagram based on reported equilibrium constants is shown in Fig. 12. It can be seen that the fluoride ion competed effectively with hydroxide at pH values up to 8, when Be(OH)2 precipitates. 

Characteristics of the fluoride ion-selective electrode The LaFj ISE exhibits Nernstian response to the activity of fluoride ions in the concentration range 1 M to 10" M [31, 53,325]. When the solution is buffered for fluoride ions using ZiO and Th " salts, Baumann [28] has demonstrated that Nernstian response can be obtained down to a free fluoride ion concentration of 10" ° moldm". In solutions with an ionic strength of 2 moldm", the detection limit is 0.2 ppm, i.e. about 10" moldm", while in pure NaF solutions it may be as low as 10" moldm ... 

The analytical properties of the fluoride ion-selective electrode At present, practically only ISEs constructed from a LaFj single crystal doped with EuFj and with internal metal contacts are used (see p. 65). A microelectrode for 2iLd of sample has also been constructed [85]. The standard type of LaFj ISE... 

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... 

Elemental composition F 51.30%, H 10.88%, N 37.82%. A measured amount is dissolved in water and the aqueous solution diluted appropriately and analyzed for fluoride by fluoride ion-selective electrode, or by ion chromatography. Ammonium ion (or hberated ammonia) is analyzed by titration or by ammonium ion-specific electrode (see Ammonia). 

Elemental composition Cd 74.74%, F 25.26%. The metal may be analyzed by various instrumental techniques (see Cadmium). Fluoride may be determined by ion chromatography or by using a fluoride ion—selective electrode. 

Elemental composition Co 60.80%, F 39.20%. Cobalt(II) fluoride is dissolved in hot nitric acid, the solution is appropriately diluted with water and analyzed for cobalt by AA or ICP spectrophotometry (see Cohalt). A small amount of salt dissolved in cold water (hot water may partially decompose forming oxyfluoride, C0F2 CoO H2O) may he analyzed for fluoride ion by fluoride ion-selective electrode or ion chromatography. 

Elemental composition Cu 62.58%, F 37.42%. Copper(ll) fluoride acid extract is analyzed for copper by instrumental methods. Powder may be analyzed by tbe x-ray diffraction method. Aqueous solution (in cold water) may be analyzed for fluoride ion using a fluoride ion-selective electrode or by ion chromatography. 

Elemental composition H 5.04%, F 94.96%. The total acidity of an aqueous HF solution may be measured by titration with a standard solution of base using phenolphthalein or another suitable color indicator. Alternatively, the end point may be determined by potentiometric titration. The fluoride ion may be analyzed using a fluoride ion-selective electrode or by ion chromatography. The HF gas may be analyzed by GC/MS using a GC column having... 

Elemental composition I 57.19%, F 42.81%. The compound may be hydrolyzed with water slowly and cautiously (a violent reaction occurs), lodate anion may be measured by redox titration and the fluoride ion by using a fluoride ion-selective electrode. Alternatively, these anions in their aqueous solution may be determined by ion chromatography after appropriate dilution. 

Elemental composition Pb 84.50%, F 15.50%. The compound can be identified from its physical properties and x-ray measurement. Lead may be analyzed by various instrumental techniques (See Lead). Fluoride ion may be determined by dissolving a minute quantity of the compound in water (the compound is slightly soluble in water) and analyzing the solution by ion chromatography or hy fluoride-ion selective electrode. 

Elemental composition Li 26.75%, F 73.25%. An aqueous solution prepared by dissolving 100 mg in a liter of water may be analyzed for lithium by AA or ICP spectrophotometry and for fluoride by ion chromatography or by using a fluoride ion selective electrode. 

Elemental composition K 67.30%, F 32.70%. The aqueous solution may be analyzed for potassium by various methods (see Potassium.) and for fluoride by fluoride ion selective electrodes or ion chromatography. 

Elemental composition Na 54.75%, F 45.25%. The salt is dissolved in water and analyzed for sodium and fluoride anion. The anion can be measured effectively with a fluoride ion-selective electrode or by ion chromatography. 

Elemental fluorine, which is a member of the halogen family, is a pale yellow-green, irritating gas with a sharp odour and atomic mass of 18.998. Fluorine is chemically most reactive of all the elements and does not therefore occur naturally in the free state. In combination it comprises 0.065% of the earth s crust, being the 13th element in abundance [1], and is an inevitable part of the biosphere and human life. The term fluorine is, in this report, used to denote the element in any of its forms and fluoride to denote free inorganic fluoride to which a fluoride ion-selective electrode (ISE) responds. 

M. Ponikvar, V. Stibiij, B. Zemva, Daiiy dietary intake of fluoride by Siovenian Military based on analysis of total fluorine in total diet samples using fluoride ion selective electrode. Food Chem. 103(2007) 369-374. 

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. 

K. Chiba, K. Tsunoda, Y. Umezawa, H. Haraguchi, S. Fujiwara, K. Fuwa, Plateshaped silver/silver halide reference electrode for determination of fluoride ion in microliter solution with fluoride ion selective electrode. Anal. Chem. 52 (1980) 596-598. 

The main methods for determining fluoride ion in solution are acidimetry, colorimetry, titrimetry and potentiometry using the fluoride ion selective electrode, and ion chromatography. 

The fluoride ion selective electrode is the most popular means of fluoride ion determination after sample destruction by any method but it does have limitations. It can be used either directly to measure the fluoride potential6 or as an end-point detector in a potentiometric titration with a lanthanum(l II) reagent as titrant.4,7 Problems can be experienced with potential drift in direct potentiometry, especially at low fluoride ion concentrations. Titration methods often yield sluggish end points unless water miscible solvents are used to decrease solubilities and increase potentia 1 breaks and sulfate and phosphate can interfere. End-point determination can be facilitated by using a computerized Gran plotting procedure.4... 

Warning This is a long problem, best done by five people, each completing one line of the table.) A fluoride ion-selective electrode responds to fluoride activity above JAF = 10 6 in the following manner at 25°C ... 

Figure 15-18 Calibration curve for fluoride ion-selective electrode. [Data from M. S. Front and J. W. Ross, Jr., Electrode tor Sensing Fluoride Ion Activity in Solution," Science 1966, 154, 1553.]...

C. A solid-state fluoride ion-selective electrode responds to F, but not to HF. It also responds to hydroxide ion at high concentration when [OH J [F ]/10. Suppose that such an electrode gave a potential of +100 mV (versus S.C.E.) in 10 5 M NaF and +41 mV in 10 4 M NaF. Sketch qualitatively how the potential would vary if the electrode were immersed in I0-5 M NaF and the pH ranged from 1 to 13. 

There are five major methods for the determination of fluoride ions m aqueous solution (1) volumetric, (2) gravimetric, (3) null pointpotentiometry, (4) fluoride ion-selective electrode (also known as specific ion electrode), and (5) ion chromatography... 

The availability of ion-selective electrodes has revolutionized the field of analytical chemistry The fluoride ion-selective electrode has greatly assisted in the task of... 

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