Exploring Purple Sweet Potato Pigment as An Eco-Friendly Titration Indicator for Acid Determination
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Abstract
Ipomea batatas L., or purple sweet potato (PSP) tubers, are sources of anthocyanin, a pigment that can show colour changes at different pH values. The aims of this study are to explore the phytochemical content, colour characteristics, stability, precision, and accuracy of PSP pigment (PSPP) as a titration indicator. Further, PSPP was applied as a titration indicator for acid (H+) determination. PSPP was extracted with medical-grade ethanol (PSPP-MG) and analysis-grade ethanol (PSPP-AG). This study showed PSPP-MG and PSPP-AG contain alkaloids, flavonoids, saponins, tannins, and steroids. They showed red colour at pH 1-2, pink at pH 3-6, and purple at pH 7. At pH 8–9, they were blue, turned to green at pH 10–11, and yellow at pH 12–14. These pigments were stable for 90 days at room temperature in tropical areas (25–30 0C) and showed clear colour changes at the endpoint of titrations with good precision and accuracy. Furthermore, PSPP-MG and PSPP-AG are used as titration indicators for H+ determination. The results of this study highlight the performance of PSPP-MG and PSPP-AG for H+ determination in HCl samples. Both of these pigments were able to show clear colour changes at the endpoint of the HCl sample titration. They were able to show a similar value of H+ concentration as determined using phenolphthalein. Thus, PSPP can be used as titration indicator replacing phenolphthalein. Using this pigment as a titration indicator is cheaper, easier to obtain, easier to prepare, and environmentally friendly.
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