A color reaction for the determination of Cu2+ in distilled beverages employing digital imaging

Abstract

In this work, we describe for the first time the synthesis of a thiocarbazone for the selective determination of Cu2+ in distilled beverages. The method was based on the complexation reaction of Cu2+ with the thiocarbazone, and the colored product was analyzed using a smartphone application. The thiocarbazone reacts with Cu2+ to form a 1:1 (metal:ligand) complex. The Cu2+ 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 Cu2+ concentrations ranging between 0.25 and 6.75 mg L−1; 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−1. 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%.