The construction and performance characteristics of a coated graphite phenylephrine-selective electrode based on incorporation of the ion-association complex of phenylephrine-tetraphenylborate in plasticized PVC matrix was studied. The electrode exhibited a Nernstian slope of 59.0 mV/decade to phenylephrine over a wide concentration range from 3.0 10 À6 to 5.6 10 À2 M with a low detection limit of 1.5 10 À6 M. The proposed electrode manifested advantages of fast response, long life time and, most important, good selectivities for phenylephrine relative to a wide variety of common foreign inorganic cations, anions and also organic species. The electrode was successfully applied to determine phenylephrine in adult cold tablets, phenylephrine eye-drops and also blood serum samples. The inclusion complex formation between a-and b-cyclodextrine and phenylephrine was studied potentiometrically by the proposed electrode.