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KeywordsOctanol-modified glassy carbon electrode, anodic oxidative treatment, cyclic voltammetry, electrochemical detection, alkylammonium ion sensor, calcium ion sensorWe have recently found that a potential sweep treatment of a glassy carbon electrode at between 0 -+2.0 V vs. Ag wire in an alkanol containing 1 M H2SO4 can modify the electrode surface with the alkanol probably via an ether linkage.' A glassy carbon electrode anodized in 1-octanol (C8-GCE) acquired a hydrophobic membrane on its surface similar to a selfassembled monolayer of 1-octanethiol formed on a gold electrode. However, the surface condition was suggested to be totally different from that of a glassy carbon electrode anodized in H2O (W-GCE) by essentially the same procedure. In order to elucidate the nature of the C8-GCE surface in more detail, the electrochemical performance of C8-and W-GCEs was compared further. In this paper we report on the effects of CaC12, butylamine hydrochloride, and hexylamine hydrochloride upon the voltammetric response of Fe(CN)63-at C8-and W-GCEs, which is expected to introduce a new concept in designing a modified electrode as an ionsensor.A C8-GCE and a W-GCE were prepared as follows. A mechanically polished GCE (3 mm4) was anodized in 1-octanol or H2O containing H2SO4 (0.1 M) by controlled potential electrolysis at +2.0 V vs. Ag wire, instead of the potential sweep method', in order to precisely control the amount of electricity consumed during the treatment. After 5 mC electricity was consumed the electrode was successively washed with McOH and deionized water, and then cathodically treated by sweeping the potential five times from 0--0 .5 V vs. SCE in 0.1 M aqueous KCI.