Paper-based analytical device for colorimetric detection of Cu2+ in Brazilian sugarcane spirits by digital image treatment

The presence of copper ions in sugarcane spirits is harmful due to the high toxicity to humans and its maximum allowed concentration is defined as 5 mg L-1, according to the Brazilian agency of agricultural e food (ANVISA). In order to monitor the product quality, the recommended analytical method for quantification of Cu(II) employs Flame Atomic Absorption Spectroscopy (FAAS) providing accurate and sensitive results, although the instrument bulkiness makes the method less attractive for routine and screening analysis. In this study, we have described a simple analytical method for the determination of Cu(II) based on the colorimetric reaction between Cu(II) and diethyldithiocarbamate (DDTC) performed onto a paper-based spot test. The yellow-brownish product was formed and the measurement of the analytical signal was performed directly on the paper-based device with no needing of previous extraction steps. Digital images were obtained using an ordinary flatbed scanner and parameters derived from the RGB color space were used for quantification. Under optimized conditions, a linear relation (R-2 > 0,99) from 3 to 25 mg L-1 of Cu(II) was obtained using 20 mu L of the sample solution and 40 mu L of the reagent. The developed paper-based analytical device was therefore applied for copper quantification in sugarcane spirits. It represents an interesting alternative for a fast, simple, portable, and low-cost method for evaluating sugarcane spirit quality according to the current legislation.