The analytical performances of the developed sensor were evaluated in laboratory for the semicontinuous monitoring of Cd and Pb in water samples at mg L À1 level. The effects of oxygen, pH, and stirring on the voltammetric response of these metals were investigated. The O 2 removal did not allow to improve the peak current. In return, stirring appeared indispensable to avoid the impoverishment of metals in the diffusion layer. The necessity to control the pH and the solution evolution in laboratory experiments was also clearly established. The semicontinuous monitoring of Cd and Pb was then performed for 42 h in tap water and demonstrated that sensor is a promised tool for semicontinuous environmental analyses.

A microwell has been deposited on the working surface of a screen-printed electrode in order to reduce the sample volume from 10 mL to 200 mL for trace metal analysis in square wave anodic stripping voltammetry. It has been shown that the sample volume reduction did not affect the sensitivity. A detection limit of 2 Â 10 À9 mol L À1 of Cd was established with these modified sensors for a preconcentration time of 60 s without stirring. Also it has been shown that pH ranging from 4 to 7 did not affect the sensor sensitivity. These modified sensors were able to run at neutral pH in real samples, such as soil solutions, containing higher organic carbon concentration and thus offered a first and rapid approach of Cd speciation.

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