An automated flow-injection thin-layer electrochemical platform for online silicate monitoring in marine environments.

Silicate is an essential nutrient in marine ecosystems, exhibiting a dynamic concentration due to complex biogeochemical processes. Accurate and high-frequency monitoring of silicate in marine environments is therefore highly desirable. In this study, a fully automated electrochemical system was developed for online determination of silicate in natural seawater and in diatom incubation experiments. This system integrates flow injection analysis with thin-layer electrochemistry (TLE), using square wave voltammetry (SWV) for silicate measurement. The optimized system achieved a low detection limit of 0.4 μM and demonstrated excellent long-term stability, with a relative standard deviation (RSD) of 7.4% over 90 days of operation. The method was validated using coastal seawater collected from 10 sites spanning a range of salinities, showing good agreement with a reference spectrophotometric method. Moreover, continuous monitoring over 7 days in a Phaeodactylum tricornutum culture captured significant changes in the silicate concentration during its growth cycle. Overall, the system provides sensitive, long-term online monitoring of silicate in laboratory-controlled seawater systems and provides a technical basis for future field-deployable applications.