For example, catechol and its derivatives can be electrooxidized
to form o-quinones which can be attacked by a
variety of nucleophiles and were converted to the corresponding
addition adducts [1–7]. Spectrophotometric
determination of o-quinone (5–100 lM) in the presence of
dimethylamine has been proposed [8]. Cyclic voltammetric
determination of analytes, using various redox indicators
and the concept of 1,4-Michael addition reactions, has
been assessed [4–7]. The increased oxidation current of
the redox indicators can be used to determine cysteine
(12–50 lM) [4] and sulfide (10–300 lM) [5]. Square wave
voltammetric detection of penicillamine (0.1–2.5 lM) and
cysteine (0.1–1 lM) using dopamine (DA) as an indicator
has been reported [6].