Lipophilic ionophore for Ca²⁺ selective electrodes with detection limit in the sub-nanomolar range.

Extremely efficient carrier of Ca²⁺ -ions; induces a selectivity in membranes for Ca²⁺ over Mg²⁺ by a factor of about 10⁴. Calcium ionophore II (ETH 129) was used in preparing calcium selective minielectrodes which are used in determination of dissociation constant (K_d).