Remote stripping analysis of lead and copper by a mercury-coated platinum microelectrode

The performance of a remote stripping sensor based on mercury microelectrodes (MM-RS) for the in situ detection of trace metals in aquatic systems, was investigated. The submersible device employed here consists of a single mercurycoated platinum disk microelectrode assembled in a two-electrode cell configuration, and connected remotely by a 30 m long shielded cable. First, the MM-RS device is characterized in Ru(NH3)3 6 and Pb2 synthetic aqueous solutions by applying cyclic voltammetry and anodic stripping voltammetry (ASV), respectively. The results obtained show that the small electrode dimensions and the related low currents involved, the long remote connection cable or the use of a two-electrode system do not cause noise effects or uncompensated resistance problems in the measurements. Using square-wave voltammetry in the stripping step, linear calibration graphs for Pb2 ions over the concentration range 11095107 M were obtained, and a detection limit, DL, of 0.15 nM was found. The relative standard deviation (RSD), at 5108M Pb2 level, was within 5%. The effect of humic acid and of sodium dodecylsulfate surfactants on the stripping responses was also investigated. The performance of the submersible MMRS system was tested for the in situ monitoring of the labile fraction of lead and copper on a site of the Lagoon of Venice. In situ Pb2 and Cu2 concentrations were monitored for about 8 hours, by leaving the sensor immersed in the lagoon waters (2 m depth) and recording the response every hour. Under these field conditions, reliable in situ data for the labile fraction of these metal ions with a satisfactory precision, the RSD being within 7 and 9 % for lead and copper, respectively, were obtained.