Eliminating the interfering signals of different metals could lead to better analysis of heavy metals in drinking water.

Electrochemical analysis is used to measure trace amounts of heavy metals, such as arsenic and copper, in drinking water.  But real water samples typically contain a range of different metals. This can lead to interference and unwanted signals. 

To tackle this problem, Richard Compton's team at Oxford University, UK, working with researchers at the Autonomous University of Barcelona, Spain, modified an electrode surface with a regular coating of droplets.  The droplets contain a ligand that binds the interfering metal, in this case arsenic, but doesn't bind copper, which is the metal to be detected.  The arsenic is effectively captured in the droplet, while the copper is free to diffuse to the electrode surface, to be measured.

Compton's team deposited droplets onto an electrode surface patterned with silicon oxinitride blocks. The droplets preferentially form on the blocks, allowing the size and spacing of the droplets to be carefully and reproducibly positioned on the electrode surface.

Team member Andrew Simm from Oxford University said that choosing the right material for the droplets is very important. 'Careful selection of appropriate ligands is required that are able to remove the interference metal whilst allowing the metal of interest to diffuse to the electrode surface in the optimum conditions for trace detection of that metal.' 

Anastasios Economou, an expert in the field of electroanalysis at the Aristotle University of Thessaloniki, Greece, welcomed the work. 'This approach could potentially extend the scope and applicability of electroanalysis, especially in complex matrices,' said Economou.

Simm agreed that there is huge scope for developing electroanalytical methods free of interferences. 'We have illustrated the principle in respect to the detection of copper and arsenic where there is significant mutual interference, but with suitable ligands placed over part but not all of an electrode surface the scope is almost limitless,' he said.

Stephen Wilkes