Rhodanine and its derivatives are used for the quantitative analysis of
silver, gold (III), palladium (II), copper (1) and (II), rhodium (III), mercury
and other ions / I/.
p-dimethylaminobenzylidene rhodanine (p-DABR) was first proposed as
an analytical reagent by Feigl. It is widely used for separation and spectrophotometric determination of Ag and Pd. It is also used as a reagent for Au,
Hg and Pt, for indirect determination of CI" and CN", as an acid-base indicator
in acetic acid medium, and in selective resins /2,3/. Gelatin or gum Arabic is
utilized to stabilize the formed complexes. Drawbacks of these methods are
the limited solubility of the reagent and instability of the reaction products
/4/. On the other hand, surfactants and micellar systems are currently used to
improve the sensitivity and/or selectivity of the spectrophotometric methods
for metal ion determination. Such systems manipulate the solubility and micro environment of reagents and analytes, and control the reactivity,
equilibrium and pathway of chemical or photochemical processes /5,6/.
In the present paper, the reactions of Au (III) and Rh (III) with p-DABR
in the presence of cationic [cetyltrimethylammonium bromide, CTAB]
surfactant have been studied. Simultaneous photometric determination of Au
(III) and Rh (III) is hampered due to spectral overlap of their complexes. In
such cases spectrophotometry coupled with derivative techniques is useful in
analysis of such mixtures Π-91. In this work derivative spectrophotometry
was also used to improve the sensitivity and selectivity /ΙΟ,II/. As the
proposed methods are practically free from interferences, they have been
applied to Rh (III) and Au (III) determination in synthetic samples.