Immobilization of anthocyanin in polymeric film to obtain a colorimetric sensor for detection of copper in cachaça

Abstract

Cachaça is a uniquely Brazilian product, being the most popular distilled spirit in Brazil and the fourth most consumed worldwide. Its production using copper stills can result in the leaching of the metal, contaminating the product. Then, techniques that are simple, inexpensive, and fast are required for the quantification of copper in cachaça. Here, films composed of starch, with or without enrichment of amylopectin, and polyvinyl alcohol were produced for use as supports to immobilize anthocyanin, with the aim of obtaining a sensor for detection of Cu2+ in cachaça. FTIR showed that the incorporation of anthocyanin in the films was according to a non-covalent mechanism. An increase in the amylopectin content altered the morphology of the material, as shown by MEV. The most homogeneous film, with low solubilization in cachaça, was applied as a sensor to detect Cu2+. The Cu2+ presence in the film, after its contact with cachaça samples containing Cu2+ at pH 7.0, was confirmed by XEDS, with the metal being homogeneously distributed over the film. Detection ofCu2+ in the cachaça was achieved by a change of the sensor color from red to green. The LOD and LOQ of the method were 1.39 and 2.00 mg/L, respectively. The method was accurate to determine Cu2+ in real samples of cachaça, with percentual relative error, in modulus, in the range of 3.02–9.54% in comparison with the standard spectrophotometric method using 2,2′-diquinolyn. At pH 7.00 and 5.0 mg/L Cu2+ (the maximum concentration permitted according to Brazilian legislation), the response time of the sensor was 3.16 h, with the sensor being selective towards Cu2+. The characteristics of the sensor evidenced the commercial applicability of the film as a colorimetric sensor for the simple, inexpensive, and selective identification of copper in cachaça.