Padronização de Soluções de NaOH Utilizando Repolho Roxo e Imagens Digitais

Resumo

The standardization of sodium hydroxide (NaOH) solutions by titration is widely used but can be labor-intensive, require relatively large reagent volumes, and rely on the analyst’s visual perception, which may introduce experimental uncertainties. This study proposes an alternative methodology based on the use of red cabbage extract as a natural acid–base indicator combined with smartphone-based digital image analysis to determine NaOH concentration. Since the pH of NaOH solutions is directly related to their concentration, the chromatic response of the indicator was quantitatively correlated with this parameter. RGB color channel histograms extracted from the images were modeled using partial least squares (PLS) regression. The model exhibited excellent predictive performance, with a validation coefficient of determination (R² = 0.981), RMSEP of 0.71 mmol L–1, and RPD of 8.79. Although a statistical difference was observed for one sample when applying an independent t-test, the results obtained by the proposed method were generally consistent with those from conventional titration and suitable for routine analytical applications. In addition, the approach reduced the required sample volume by approximately 80%, minimized waste generation, and employed a biodegradable indicator, providing a sustainable, accessible, and rapid alternative for NaOH solution standardization.