Development of a new passive sampler based on diffusive milligel beads for copper analysis in water

A new device of a passive sampler was developed. Composed with hydrogel, the Diffusive Milli-Gel (DMG) differs from classic samplers by their unique geometry as a result of the manufacturing technique. A droplet-flow millifluidic process allowed precise control of the size and the geometry of each DMG. The synthesis by this process provided a system composed of several spherical DMG of around 1 millimeter diameter. The main advantage of this device is the increase of the exchange surface improving the analysis of the targeted chemical element.
Based on the same principle as diffusive gradient in thin-film (DGT), DMG are composed of a polyacrylamide gel crosslinked in which a cation exchange resin is incorporated. Yields close to 100% demonstrated a complete synthesis. The inclusion of the resin in the gel was an important step in the process which was essential to master. A set of experiments highlighted two important parameters for the control of the resin inclusion: the particle size of the resin and the flow rates used for the synthesis by the millifluidic technique. A preliminary step of resin is embedding in hydrogel is essential. An analysis by microscopy has set a threshold particle size (above 30 microns) that must not be exceeded for an efficient incorporation.
DMG passive samplers were performed in natural freshwater and soil, and compared with different other technique. The results obtained highlight the ability of DMG to uptake copper and particularly the labile fraction. DMG open a lot of perspectives and opportunities in environmental monitoring as in situ technique for dynamic trace metal speciation.