Modifying the reactivity of copper (II) by its encapsulation into polydimethylsiloxane: A selective sensor for ephedrine-like compounds.

This paper demonstrates that the reactivity of copper (II) can be modified through its entrappment in a polymeric matrix of polydimethylsiloxane (PDMS), which makes possible the reaction into the support instead of in solution. Amino-containing compounds such as amino acids, proteins and sugars, which react with Cu (II) in solution, do not react inside the polymer. As a prove of concept, a highly specific Cu (II) PDMS-based sensor for ephedrines has been developed in this work. When the sensors are put into contact with solutions of these drugs under basic conditions, a change in their color from pale green to purple is observed. This change enables the visual identification of ephedrine (Eph) in a few min, as well as its quantification using both reflectance diffuse measurements of the sensors and color intensities of their digitalized images. The sensors show suitable analytical performance for Eph-like compounds, and provide limits of detection (LODs) of 0.3-1.0 mg, and relative standard deviations (RDSs) < 10%. The method has been applied to both the qualitative and quantitative analysis of different types of liquid and solid samples (intravenous injection solution of Eph, dietary supplements and illicit drug-street samples) without the need of any special sample treatment.