Application of electrodeposition to elemental separation in atomic spectrometry

Jan Knápek

Two systems for preconcentration of cadmium were studied, one with electrochemical microcell and
graphite rod electrodes, the second with large surface area electrode from reticulated vitreous
carbon (RVC), an open-pore foam material of honeycomb structure. Cadmium electrolytic deposited on
the carbon electrode was dissolved in 100 ml of 0.1 mol l^-1 HNO[3] and transported by nebuliser
capillary to air – acetylene flame. Although deposition of cadmium in first microcell was increased
by coating graphite rod electrode with bismuth film, thus higher sensitivity of determination was
achieved by application of RVC electrode. The optimal conditions of electrolysis, such as pH of
solution, deposition current and flow-rate of sample solution, were evaluated by using method of
artificial neural network. The arrangement with RVC electrode was employed for determination of
cadmium in waters with high content of salts. Using this arrangement detection limit of 10 mg l^-1
Cd was attained.

A novel method for determination of heavy metals in high saline matrix is presented.  The method is
based on the electrodeposition of metals and subsequent laser ablation coupled to inductively
coupled plasma optical emission spectrometry (ICP-OES). Three arrangements for electrodeposition,
two with stationary working electrode with placement of the electrodes in the cell face-to-face or
with position of working electrode at the bottom of electrochemical cell and one with rotating
working electrode; the use of different working electrode materials and suitable conditions for
electrodeposition of Cd, Cr and Cu (pH, deposition current, time of electrolysis) from high salt
matrices were studied. Nickel was chosen as the optimal electrode material. The current 10 mA, pH =
4.8, the speed of stirring 300 rpm for stationary or 196 rpm for rotating electrode arrangement and
10 min deposition time were selected as optimum. After electrodeposition the metal accumulated on
the surface of electrode was evaporated/ablated by Nd:YAG laser into ICP-OES spectrometer. The
detection limits were 0.13 mg L^-1 Cd, 0.15 mg L^-1 Cu and 1.9 mg L^-1 Cr for arrangement with
stationary bottom working electrode and 0.25 mg L^-1 Cd, 0.05 mg L^-1 Cu, 0.8 mg L^-1 Cr for
arrangement with rotating electrode. The precision expressed as RSD was in range 3.8-10.3%.
Analysis of waste water was performed by standard addition method.