Simple and affordable colorimetric sensing strips for quantitative determination of total manganese in porewater samples

Simple and economical colorimetric strips for measuring manganese (Mn) in natural waters are described. For their construction, leucomalachite green (LMG) embedded in a Nafion (R) polymeric matrix was immobilized on a polyvinylchloride surface. Upon immersing the strips in the sample, any soluble manganese(II/III) present catalyzed the oxidation of the LMG base to malachite green by adding sodium periodate. The observed color change is related to the manganese concentration and can be quantified using a field device constructed using commercial red-green-blue sensors and an Arduino (R) board. A linear response from 0.1 to 0.6 mu mol L-1 manganese (limit of detection: 0.1 mu mol L-1) was observed. The signal for strips prepared on 7 d gave a relative standard deviation equal to 13%. The strips showed good agreement with results obtained by ICP-MS in porewater collected on Spiekeroog Island (North Sea). Therefore, the method is a tool for rapid measurements of manganese in porewater samples offering new possibilities in understanding biogeochemistry for high temporal and spatial resolution manganese surveys and providing an analytical technique that provides field results comparable to laboratory systems.