Electrochemical behaviour of mono- and oligonucleotides: Part VII. Comparative studies on the adsorption of cytidine at the mercury-aqueous solution interface by pulse polarography and ac polarography

Abstract

Cytidine has been investigated in order to explore the potentialities of normal pulse polarography and phase-sensitive ac polarography (out-of-phase mode) in connection with the DME for the study of the adsorption and interfacial behaviour of nucleotides. The results are compared with those of a previous study [8] by single-sweep and phase-sensitive ac voltammetry at the HMDE. While the joint application of these latter approaches yields more comprehensive and also more reliable information on the adsorption parameters, normal pulse polarography is also able to provide, with good approximation, the values of certain adsorption parameters for the dilute layer (adsorption coefficient b, free adsorption enthalpy − G 0, interaction coefficient a) provided the span of the drop life before the application of the pulse is adjusted to a period sufficiently long to attain adsorption equilibrium. Normal pulse polarography is particularly valuable for estimation of the kinetic parameters of the electrode process of non-adsorbed cytidine provided that the electrode surface is incompletely covered. Phase-sensitive ac polarography at the DME yields — for the adsorption parameters b, − G 0 and a — data of equivalent reliability to the more laborious approach by phase-sensitive ac voltammetry at the HMDE provided the drop time of the DME has been adjusted to a period sufficiently long to attain adsorption equilibrium.