4-tert-Butylcalix[4]arene-tetraacetic acid tetraethyl ester (CAS# 97600-39-0) is a calix[n]arene and chelating agent, able to complex with alkali metal cations in water in the presence of counterions and a buffer solution. 4-tert-Butylcalix[4]arene-tetraacetic acid tetraethyl ester has also been used in wearable technology, such as skin-mounted microfluidic potentiometric device for electrochemical monitoring of sodium and potassium in sweat.