Utilization of electrodeposition for electrothermal atomic absorption spectrometry determination
of  elements

Marie Konečná


   Electrothermal atomic absorption spectrometry (ET-AAS) is one of the most frequently used
technique for the determination of elements which occur on the Earth in very low contents. Direct
determination of these elements by ET-AAS in samples with a complex matrix, e.g. seawater or
biological materials, is affected by different types of interferences. The use of matrix modifiers,
Zeeman-effect background correction and isothermal conditions during atomization from a platform or
a probe are required for the elimination of interferences. For the determination of analytes
concentration at the ng l^-1 levels the precontration stage is required prior to analysis. This
step is realized by electrochemical deposition.

   Gold was determined by ET-AAS after electrochemical preconcentration on the graphite ridge probe
used as a working electrode and sample support. The probe surface was electrochemically modified
with Pd, Re and the mixture of both. The electrolysis of Au was performed under galvanostatic
control. The sensitivity of Au determination was reproducible for 300 electrodeposition and
atomization cycles. When the probe surface was modified with a mixture of Pd and Re the detection
limit was 31 ng l^−1 for 2 min electrodeposition, 3.7 ng l^−1 for 30 min, 1.5 ng l^−1 for 1 h and
0.4 ng l^−1 for 4 h electrodeposition, respectively. The procedure was applied to the determination
of Au in river and sea water samples.

   Traces of cadmium were determined by ET-AAS after electrochemical preconcentration on the
commercial graphite ridge probe modified with Pd. Cd was electrodeposited at a controlled potential
(vs. saturated calomel electrode) using the Pd-modified graphite probe as a working electrode. The
sensitivity of Cd determination remained unchanged for 300 electrodeposition and atomization
cycles.

   Noble metals (Pd, Re and the mixture of both) electrodeposited on the probe surface prior to
analyte electrodeposition were used not only for thermal stabilization of  volatile analytes (Au or
Cd) but also protected the graphite surface. The lifetime of the modified probes was prolonged in
comparison with unmodified probes, especially in the presence of the high salt content matrix of
the real sample.