Application of Natural Reagent from Orchid Flower as Indicator for Volumetric Acid-base Titration
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Abstract
A green analytical chemistry method employing crude aqueous extracted from the orchid flower Dendrobium Sonia ‘Earsakul’ as an acid-base indicator for acid-base titration was reported. In the orchid extract, there are many anthocyanin compounds which are red in acidic solution, purple in neutral solution and greenish-yellow in alkaline solution. When the orchid extract was utilized as indicators in acid-base titrations, sharp color changes at the equivalence point were observed. Titration curves of a strong acid, and weak acid to strong base were demonstrated. Moreover, the equivalence points obtained by the orchid extract were coincided with those of standard indicators and potentiometric titration. Additionally, this method was successfully applied for the determination of the total acidity in cooking vinegar samples and the measured values were reported as the percentage of acetic acid content. Our results were not significantly different from the standard AOAC method as well as potentiometric titration at a 95 % confidence level (ANOVA test). This indicated that orchid extract was acceptable to be used as a natural acid – base indicator, which was also economical, simple, accurate and reliable.
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