Evaporative concentration of analytes and sensing using a super hydrophobic surface

Sensitivity of heavy metal detection could be improved by concentrating a droplet of sample solution using a super hydrophobic surface surrounding the sensitive area. A bismuth working electrode and a Ag/AgCl reference electrode were formed in a concentric configuration. The super hydrophobic area was formed by placing polytetrafluoroethylene (PTFE) beads. A droplet of an aqueous solution was placed on the electrode area and was concentrated by evaporation. During the evaporative concentration, heavy metal ions were deposited on the working electrode. Square wave anodic stripping voltammetry was conducted to detect Cd²⁺ and Pb²⁺ ions. Irrespective of the increase in the sample volume, the droplet shrank to the sensitive area. As a result, the peak height increased in proportion to the sample volume. The sensitivity could be improved further by replacing the Ag/AgCl electrode with an Ag/AgI electrode.