A color reaction for the determination of Cu in distilled beverages employing digital imaging.

In this work, we describe for the first time the synthesis of a thiocarbazone for the selective determination of Cu in distilled beverages. The method was based on the complexation reaction of Cu with the thiocarbazone, and the colored product was analyzed using a smartphone application. The thiocarbazone reacts with Cu to form a 1:1 (metal:ligand) complex. The Cu complex was characterized by UV, IR and NMR spectral analyses. The proposed reaction yields a yellow color, and therefore, channel B of the RGB system was used in the analysis. After optimizing the reaction conditions, an analytical curve was obtained to determine Cu concentrations ranging between 0.25 and 6.75 mg L; the use of 400 μL sample volumes led to a relative standard deviation (n = 5) of 3.2% and a detection limit of 0.18 mg L. Recovery experiments were performed with sugar cane spirits, whiskies and tequilas to evaluate the accuracy of the method, and the recovery obtained ranged from 80.5 to 112.2%.