Potassium selective electrode
Encyclopedia
Potassium selective electrodes are a type of ion selective electrode
used in biochemical
and biophysical
research, where measurements of potassium
concentration
in an aqueous solution
are required, usually on a real time basis.
These electrodes are typical ion exchange resin membrane electrodes, using valinomycin
, a potassium ionophore
, as the ion carrier in the membrane to provide the potassium specificity.
This type of ion-selective electrode is subject to interference from (in declining order of magnitude) rubidium
, caesium
, ammonium
, sodium
, calcium
, magnesium
, and lithium
. The most significant interference with measurement of potassium concentration is from the ammonium ion, which in practice is a problem where the ammonium concentration is approximately equal to or greater than the potassium concentration. Although sodium is usually present in high concentrations in biological preparations, the degree of interference is low enough to represent an error on the order of only 0.05 parts per million for the normal range of sodium concentration, requiring reduction of sodium only for measurements of very low potassium concentrations. Although the interference from rubidium or caesium is strong enough to require that these ions be present in much lower concentration than the potassium to be measured, this is not usually a problem in most experiments. Interference from calcium, magnesium, or lithium, on the other hand, is weak enough that their presence in normal concentrations is also usually not a problem.
Ion selective electrode
An ion-selective electrode , also known as a specific ion electrode , is a transducer that converts the activity of a specific ion dissolved in a solution into an electrical potential, which can be measured by a voltmeter or pH meter. The voltage is theoretically dependent on the logarithm of the...
used in biochemical
Biochemistry
Biochemistry, sometimes called biological chemistry, is the study of chemical processes in living organisms, including, but not limited to, living matter. Biochemistry governs all living organisms and living processes...
and biophysical
Biophysics
Biophysics is an interdisciplinary science that uses the methods of physical science to study biological systems. Studies included under the branches of biophysics span all levels of biological organization, from the molecular scale to whole organisms and ecosystems...
research, where measurements of potassium
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
concentration
Concentration
In chemistry, concentration is defined as the abundance of a constituent divided by the total volume of a mixture. Four types can be distinguished: mass concentration, molar concentration, number concentration, and volume concentration...
in an aqueous solution
Aqueous solution
An aqueous solution is a solution in which the solvent is water. It is usually shown in chemical equations by appending aq to the relevant formula, such as NaCl. The word aqueous means pertaining to, related to, similar to, or dissolved in water...
are required, usually on a real time basis.
These electrodes are typical ion exchange resin membrane electrodes, using valinomycin
Valinomycin
Valinomycin is a dodecadepsipeptide antibiotic.Valinomycin is obtained from the cells of several Streptomyces strains, among which "S. tsusimaensis" and S. fulvissimus....
, a potassium ionophore
Ionophore
An ionophore is a lipid-soluble molecule usually synthesized by microorganisms to transport ions across the lipid bilayer of the cell membrane...
, as the ion carrier in the membrane to provide the potassium specificity.
This type of ion-selective electrode is subject to interference from (in declining order of magnitude) rubidium
Rubidium
Rubidium is a chemical element with the symbol Rb and atomic number 37. Rubidium is a soft, silvery-white metallic element of the alkali metal group. Its atomic mass is 85.4678. Elemental rubidium is highly reactive, with properties similar to those of other elements in group 1, such as very rapid...
, caesium
Caesium
Caesium or cesium is the chemical element with the symbol Cs and atomic number 55. It is a soft, silvery-gold alkali metal with a melting point of 28 °C , which makes it one of only five elemental metals that are liquid at room temperature...
, ammonium
Ammonium
The ammonium cation is a positively charged polyatomic cation with the chemical formula NH. It is formed by the protonation of ammonia...
, sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
, calcium
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
, magnesium
Magnesium
Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...
, and lithium
Lithium
Lithium is a soft, silver-white metal that belongs to the alkali metal group of chemical elements. It is represented by the symbol Li, and it has the atomic number 3. Under standard conditions it is the lightest metal and the least dense solid element. Like all alkali metals, lithium is highly...
. The most significant interference with measurement of potassium concentration is from the ammonium ion, which in practice is a problem where the ammonium concentration is approximately equal to or greater than the potassium concentration. Although sodium is usually present in high concentrations in biological preparations, the degree of interference is low enough to represent an error on the order of only 0.05 parts per million for the normal range of sodium concentration, requiring reduction of sodium only for measurements of very low potassium concentrations. Although the interference from rubidium or caesium is strong enough to require that these ions be present in much lower concentration than the potassium to be measured, this is not usually a problem in most experiments. Interference from calcium, magnesium, or lithium, on the other hand, is weak enough that their presence in normal concentrations is also usually not a problem.