Adsorptive Stripping Voltammetric Behavior of Probucole. Experimental and Theoretical Treatment

Adsorptive stripping voltammetric behav-
ior of probucole has been studied by means of cyclic
staircase and square-wave voltammetry. It was found
that the redox reaction of probucole in an aqueous
medium exhibits properties of a surface process involv-
ing signi®cant repulsion interactions between ad-
sorbed molecules. A theoretical model was developed
to explain the experimentally observed phenom-
ena. Analytical application of the adsorptive stripping
square-wave voltammetry for quantitative determina-
tion of probucole has been discussed.
Key words: Probucole; square-wave voltammetry; cyclic voltam-
metry; surface redox reaction.
The demands for the detection of traces of substances
with environmental, clinical and forensic signi®cance
increase continuously. The electroanalytical techni-
ques such as differential pulse voltammetry 1DPP),
cyclic staircase voltammetry 1CV) and particularly
square-wave voltammetry 1SWV) have become indis-
pensable tools in modern analytical chemistry [1, 2].
The unique advantages of square-wave voltam-
metry such as fast scan rate, large frequency and
amplitude, as well as the speci®c approach in the
current sampling procedure ranks SWV as one of the
most advanced methods among the family of pulse
voltammetric techniques. This voltammetric method
is particularly appealing for studying the processes in
which the reactant and=or the product of the redox
reaction adsorbs to the electrode surface [3±11].
The compound studied in this paper is known in the
pharmacy as probucole [4,40-[11-methylethylidene)-
bisthio)] bis[2,6-bis11,1-dimethyl]phenole] propion-
amide 1Fig. 1). Probucole is an important drug ex-
tensively used as a cholesterol lowering agent [12].
We have recently observed that the redox reaction of
probucole at the hanging mercury drop electrode
1HMDE) in an aqueous solution exhibits properties of
an electrode process coupled by adsorption of the
redox couple [11]. It was demonstrated that under
suitable experimental conditions the SWV response
of probucole splits in two peaks. Utilizing the prop-
erties of ``split SW peaks'' [10] together with the
``quasireversible maximum'' [3, 5±7], the kinetic
parameters of the redox reaction of probucole such as
the standard rate constant 1ks � 1400 s�1
), the electron
transfer coef®cient 1 � 0.55) as well as the number
of electrons exchanged 1n � 1) were estimated [11]. In
addition it should be noted that the redox properties of
probucole under oxidation mode in a non-aqueous
medium have been also recently studied [13].
This paper is concerned with further study of the
adsorptive voltammetric behavior of probucole in
aqueous medium in order to elucidate some speci®c
properties of its electrode reaction. The objective of
this work is also to develop an adsorptive stripping
voltammetric method for quantitative determination
of probucole.