Six kinds of lipopholic 16-crown-5 derivatives possessing double side-chains were synthesized. The Na-selectivities were examined with poly(vinyl chloride) (PVC) matrix-membrane electrodes using these crown compounds. It is an effective way for obtaining high Na-selectivity by introducing a bulky side-chain such as a benzyloxymethyl group into the 16-crown-5. The electrodes based on 16-crown-5 derivatives having both a methyl or ethyl group and a benzyloxymethyl group at the pivot carbon (C-15) (3 or see 4, Figure 1) exhibited excellent Na-selectivity over K (log KNa.x= -2.65and -2.75 for 3 and 4, respectively).
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