Efficacy of plant extracts as green indicators in acid-base titrimetric analysis: Perspective towards green chemistry

Modern analytical techniques are predominantly developed for compound identification, a shift from earlier focus on gravimetry and titrimetric analysis. In acid-base titrimetric analysis, usually synthetic pH indicators are employed to detect the end point. However, synthetic pH indicators are fraught with significant challenges such as potential toxicity, carcinogenic and non-biodegradable nature, contributing to environmental and public health concerns. Herein, we discussed natural pigments, sourced from various plants (vegetables as well as fruits), serving as eco-friendly acid-base (pH) indicators. These natural indicators extracted via divergent extraction techniques such as, maceration, cold distillation, electrolyte based extraction, alcoholic extraction and ultrasonic bath sonication, are the focused concerns, discussed here. These extracts manifest different phytochemical constituents, most specifically anthocyanins that exhibit red color in acidic but yellow color in basic medium and have been elucidated by phytochemical screening in addition to FT-IR and UV–Vis spectroscopy. So, this review mentions the potential use of natural pigments as green indicators in place of synthetic pH indicators in acid-base titrations, highlighting the need for more safer, sustained and green alternatives while maintaining environmental sustainability.