Impact of spherical diffusion on labile trace metal speciation by electrochemical stripping techniques

The impact of the spherical diffusion contribution in labile trace metal speciation by stripping techniques was studied. It was shown that the relative error in the calculation of the stability constants caused by assuming linear diffusion varies with the efficiency of stirring, the diffusion coefficient of the complex and the value of the stability constant itself. A model system (lead/carboxyl modified latex nanospheres) was studied to quantify the effect of these parameters in the error. The results showed that under the usual experimental conditions the relative error in the calculation of the stability constant is never smaller than 10% when using a Metrohm 663VA stand. A new equation, considering spherical diffusion, was applied to the model system under study and successfully calculated the correct stability constants. Therefore, it is clear that in trace metal speciation determinations using stripping techniques at spherical electrodes the linear approximation should not be used.