Natural macrocvclic compounds, such as valinomycin, are attractive to analysts who have interest in the high selectivity of potassium ion as compared to sodium ion. This selectivity in alkali metal ions was not found in other ligands. Pedersen synthesized many crown ethers [1] and published his result that dibenzo-18-crown-6 (DB18C6) had a larger affinity to potassium than other alkali metals. Since then, these ligands and related compounds have held great interest for physical, inorganic and biochemists.