Fluoride selective electrode
- Fluoride selective electrode
A fluoride electrode is a kind of electrode sensitive to the concentration of fluoride ion, as used in potentiometric analysis. A common example is the LaF3 electrode, which is one of the simplest kinds of solid state electrode.
Lanthanum Fluoride Electrode
In the lanthanum fluoride electrode, the sensing element is a crystal of LaF3, doped with EuF2 to create lattice vacancies. Such a crystal is an ionic conductor by virtue of the mobility of fluoride ions which jump between lattice vacancies. An electrochemical cell may be constructed using such a crystal as a membrane separating two fluoride solutions. This cell acts as a concentration cell with transference where the fluoride transport number is 1. As transference of charge through the crystal is almost exclusively due to fluoride, the electrode is highly specific to fluoride. The only ion which significantly interferes is hydroxide (OH-). Generally such "alkaline error" can be avoided by buffering the sample to a pH below 7.
The cell diagram of a typical experimental arrangement is
Cu' | Ag,AgCl | KCl || solution | LaF3 | KF,KCl | AgCl,Ag | Cu
where Cu' | Ag, AgCl | KCl is an external reference electrode and the KF,KCl/AgCl,Ag/Cu is an internal reference inside the fluoride selective electrode.
Some commercially available reference electrodes have an internal junction which minimizes the liquid junction potential between the sample solution and the electrolyte in the reference electrode (KCl). The internal electrolyte is at fixed composition and the electrode response is given by the Nernst equation:
E=E0- RT/F ln aF-
where
*E is the measured cell potential
*E0 is the standard cell potential
*R is the ideal gas constant
*T is the temperature in Kelvin
*F is the Faraday constant (9.6485309×104 C mol-1), and
*aF- is the activity of the fluoride ion.
References
Wikimedia Foundation.
2010.
Look at other dictionaries:
Ion selective electrode — An ion selective electrode (ISE), also known as a specific ion electrode (SIE), is a transducer (or sensor) that converts the activity of a specific ion dissolved in a solution into an electrical potential, which can be measured by a voltmeter or … Wikipedia
Cobalt(II) fluoride — Cobalt(II) fluoride … Wikipedia
Electroanalytical method — Electroanalytical methods are a class of techniques in analytical chemistry which study an analyte by measuring the potential (Volts) and/or current (Amps) in an electrochemical cell containing the analyte. [Bard, A.J.; Faulkner, L.R.… … Wikipedia
pH — For other uses, see PH (disambiguation). Acids and Bases Acid dissociation constant Acid base extraction Acid–base reaction Acid–base titration Dissociation c … Wikipedia
Thermometric titration — titration systems have pre dominated in this area since the 1970 s. With the advent of cheap computers able to handle the powerful thermometric titration software, development has now reached the stage where easy to use automated thermometric… … Wikipedia
Fast ion conductor — Fast ion conductors, also known as solid electrolytes and superionic conductors, are solid state electrical conductors which conduct due to the movement of ions through voids (or empty crystallographic positions)in their crystal lattice. One… … Wikipedia
Total ionic strength adjustment buffer — A Total Ionic Strength Adjustment Buffer ( TISAB ) is a buffer solution which increases the ionic strength of a solution to a relatively high level. This is important for potentiometric measurements, including ion selective electrodes, because… … Wikipedia
Equivalence point — or stoichiometric point occurs during a chemical titration when the amount of titrant added is equivalent, or equal, to the amount of analyte present in the sample. In some cases there are multiple equivalence points which are multiples of the… … Wikipedia
metallurgy — metallurgic, metallurgical, adj. metallurgically, adv. metallurgist /met l err jist/ or, esp. Brit., /meuh tal euhr jist/, n. /met l err jee/ or, esp. Brit., /meuh tal euhr jee/, n. 1. the technique or science of working or heating metals so as… … Universalium
environmental works — ▪ civil engineering Introduction infrastructure that provides cities and towns with water supply, waste disposal, and pollution control services. They include extensive networks of reservoirs, pipelines, treatment systems, pumping stations … Universalium
