REAL-TIME CONTINUOUS MN(II) MONITORING IN LAKES USING A NOVEL VOLTAMMETRIC IN-SITU PROFILING SYSTEM

The application of a novel voltammetric in situ profiling system (VIP System) for real-time continuous monitoring of Mn(ll) in anoxic lake w aters is described. The heart of the submersible voltammetric probe is a gel-integrated microsensor including either a single or an array mi croelectrode. The integration of a microelectrode in a gel is a novelt y which protects its surface from fouling and allows its application f or direct measurements in complex media. The main features of this kin d of microsensors for in situ measurements in natural waters are discu ssed. Reliability and validity of concentration profiles obtained usin g the VIP System have been demonstrated by comparing in situ and on-fi eld voltammetric data with those obtained using classical techniques. The advantages of combining the VIP System with classical techniques f or environmental study are also illustrated. In particular, (i) specif ic measurements of the mobile forms (i.e., hydrated Mn2+ and small com plexes with size smaller than a few nanometers), the colloidal forms ( a few nanometers to 1 mu m) and the particulate forms (>1 mu m), which are three key fractions for understanding Mn biogeochemical cycles as well as (ii) the discrimination between seasonal and temporal variati ons can be performed with minimum sample handling and analysis time.