A color reaction for the determination of Cu2+ 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 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%.

A digital image method of spot tests for determination of copper in sugar cane spirits.

In this work the development and validation of analytical methodology for determination of copper in sugarcane spirit samples is carried out. The digital image based (DIB) method was applied along with spot test from the colorimetric reaction employing the RGB color model. For the determination of copper concentration, it was used the cuprizone - a bidentate organic reagent - which forms with copper a blue chelate in an alkaline medium. A linear calibration curve over the concentration range from 0.75 to 5.00mgL-1 (r2=0.9988) was obtained and limits of detection and quantification of 0.078mgL-1 and 0.26mgL-1 were acquired, respectively. For the accuracy studies, recovery percentages ranged from 98 to 104% were obtained. The comparison of cooper concentration results in sugar cane spirits using the DIB method and Flame Atomic Absorption Spectrometry as reference method showed no significant differences between both methods, which were performed using the paired t-test in 95% of confidence level. Thus, the spot test method associated with DIB allows the use of devices as digital cameras and smartphones to evaluate colorimetric reaction with low waste generation, practicality, quickness, accuracy, precision, high portability and low-cost.