Ion selective electrode potentiometry

Extract

[...] The ion selective electrode, although sensitive to specific ions, are not completely selective. Depending on the varying quantities of these compounds and the properties of the system, (temperature, pressure, etc) these ions can interact with the electrode in a manner similar to the analyte.(Rundle, 2007) In order to compensate for this undesirable interaction, a selectivity coefficient is utilized. This relation is used as a means to determine the relative interactions of these ions and account for their presence. In this particular analysis, the inclusion of interfering ions is relatively minimal. [...]

[...] (Rundle, 2007) A slight drift within the experimental values was also observed throughout the investigation. Between each subsequent measurement of equivalent samples, the potentials displayed tended to increase. This increase within the data would indicate a gradual reduction in the concentration of the sample. Although this effect could potentially be cause by mechanical discrepancies, it is most likely the consequence of potential drift. Potential drift can occur between subsequent measures of equivalent solutions. As the electrodes are immersed within the sample solutions, they require rinsing between measurements. [...]

[...] (Harris, 2007) As previously stated, several ion selective electrodes exist with regards to their specific functions. In general, there are four categories of ISE. A solid state electrode employs the use of a specialized crystal lattice which allows only specific ions to travel through it. (Fluoride ion selective electrodes) Several potentiometric operations utilize the use of pH sensing electrodes. These glass electrodes are primarily permeable to ions, making them ideal for the determination of pH levels. The exterior regions of a glass electrode is composed of a hydrated gel, in which several metal ions are transferred into solution, allowing ions to replace them in their absence. [...]

[...] Ion selective electrodes function by the quantification of ionic concentrations at equilibrium, on the surface of the selective membrane. At relatively low concentrations, the total quantity of ions is related directly to the state of equilibrium. At higher concentrations, molecular interactions cause a reduction within the mobility of the ions, thereby expressing results lower than the actual concentration. (Rundle, 2007) The ionic strength of a solution is directly related the ionic activity. This variable has been accounted for within the Nernst relation, although the relatively low experimental results indicate very little inter ionic relations. [...]

[...] High concentrations of fluoride ions 4.0 mg/L) within drinking water can result in various harmful effects, potentially increasing an individuals risk to cancer.(Government of Canada) This analysis aims to determine the quantities of fluoride within an unknown sample of tap water by means of ion selective electrode potentiometry. Theory Potentiometry is collectively known as a group of techniques, which utilize electrodes to measure electronic voltages and subsequently the concentrations of various ions. Ion selective electrodes are designed to respond exclusively to one ion, and under ideal conditions bind only to selected analytes. [...]