Electrochemical Micropipette-Tip for Low-Cost Environmental Applications: Determination of Anionic Surfactants through their Interaction with Methylene Blue

Abstract Miniaturization is one of the main requirements of the design of portable devices that allow in-field analysis. This is especially interesting in environmental monitoring, where the time of the sample-to-result process could be decreased considerably by approaching the analytical platforms to the sampling point. We employed traditional mass-produced and low-cost elements (micropipette tips and pins) in an out-of-box application to generate an innovative and cost-effective platform for analytical purposes. We have designed simple and easy-to-use electrochemical cells inside polypropylene micropipette tips with three stainless-steel pins acting as the working, reference and counter electrodes of a potentiostatic system. The pin acting as working electrode was previously coated with carbon ink, meanwhile the rest were used unmodified. In this way, electrochemical measurements were done directly in-the-tip using low volumes (μL) of sample. The devices showed good reproducibility, with a relative standard deviation of 7% (n=5) for five different tip-based complete electrochemical cells. As a proof-of-concept, its utility has been probed by the determination of an anionic surfactant (sodium dodecyl sulphate, SDS) in water through its interaction with methylene blue (MB). Two different alternatives were presented: 1) electrochemical determination of the MB remaining in the aqueous phase after extraction of the pair SDS-MB to an organic medium.