Tetraethylammonium

Tetraethylammonium (TEA) is a quaternary ammonium cation consisting of four ethyl groups attached to a central nitrogen atom. Like other members of its class, it can be used to alter a compound's solubility by displacing hard acids with this comparatively softer acid. For example, addition of tetraethylammonium bromide to an aqueous solution of a sodium salt may cause it to precipitate from water as the tetraethylammonium salt. The tetraethylammonium salt may also be more lipophilic, dissolving in organic solvents such as chloroform.

An example of the tetraethylammonium cation is found in [NEt4]2[ReBr3(CO)3], a common precursor to rhenium compounds having the tricarbonyl fragment. It is synthesized from bromopentacarbonylrhenium(I) by heating it with tetraethylammonium bromide in diglyme.

Biology
In biology, the tetraethylammonium cation is a potassium-selective ion channel blocker. It is used in neurophysiology experiments to block the voltage activated potassium channels involved in the trailing part of the transmission of an action potential along a neuron. TEA is also known to reverse the action of drugs such as tubocurarine, a non-depolarizing blocker. TEA evokes more release of the neurotransmitter, and thus it will reverse the competitive antagonistic block of any drugs belonging to the curare family. TEA salts are used in supercapacitors as electrochemically active species.

Tetrodotoxin (TTX) is another toxin used to elucidate the ionic currents involved in action potentials of neurons because it complements TEA by blocking relevant sodium channels.