Surface Characterizations of Mercury-Based Electrodes with the Resulting Micro and Nano Amalgam Wires and Spheres Formations May Reveal Both Gained Sensitivity and Faced Nonstability in Heavy Metal Detection

Surface characterizations of mercury-coated screen-printed electrodes with interest for electrochemical stripping analysis of heavy metals detection are presented. SEM images and microanalysis data of the working electrode surface show a homogeneous distribution of mercury film prior to sensor application in heavy metals detection in seawater. The response stability during the 16 days measuring period in terms of RSD (relative standard deviation) was 33%, 24%, and 7.7% for Cd2+, Pb2+, and Cu2+, respectively. Detection limits lower than 7.0 mu g L-1 in a seawater matrix modified with HCl arc achieved for the three metals. The microscopic and microanalysis studies revealed some damages of the mercury film after a long period of use (continuous measuring) of the SPE. The decrease of the sensitivity as well as splitting of the peaks is related to the deposition and stripping of heavy metals in mixed mercury and "mercury free" areas. The application of this sensor for a longer period would need the use of a less acidic medium so as to avoid the damage of the working electrode. This would need further optimizations so as to find a compromise between sensitivity and stability. The frequency of measurements with interest for application in an automatic control system where the sensor may be integrated and applied in the future should also be considered. Moreover, the deposition of metals into the surface of the electrode was evaluated. Surface characterizations of mercury-based electrodes with the resulting micro and nano amalgam wires and spheres formations may in addition reveal both gained sensitivity and faced nonstability while being applied in real water samples.