Extraction and Evaluation of a New Acid-Base Indicator From Black Gram Husk (Vigna Mungo)

Abstract

There are several indicators used in different titration procedures for the determination of acids and bases in solutions. Out of these, a widely preferred method is the rapid volumetric analysis because of its simplicity, reliability, and cost-effectiveness. In the present work, the indicator evaluated is extracted from a food waste category, namely black gram (Vigna mungo) husk of India. The new indicator has been characterized as a mixture of three isomeric forms of quercitin-3-O-pentoside, which is a flavonol, using LC/MS/UV data. The indicator color change is pH dependent, pH < 7 (pale pink), pH > 7 (yellow), and pH 7 (colorless), which imparts a sharp color change at the endpoint. The novelty of the method is that the permutations and combinations of different indicators used for the analyses of strong-weak acids/bases can be avoided by adopting this procedure. The efficiency of the indicator is cross-checked by comparing the titration results with those of standard indicators and conductometry. The importance of this approach is that the indicator functions around the neutral pH thus minimizing the possible errors.

Keywords:

• acid
• acid-base titration
• base
• black gram husk
• color change
• endpoint
• indicator
• quercitin-3-O-pentoside
• Vigna mungo