Natural Indicators in Quantitative Analysis: A Review with Special Reference to Acidimetry and Alkalimetry

Abstract

Acid–base titrimetry remains a cornerstone of quantitative chemical analysis in teaching, industrial quality control, and routine laboratory practice. Conventional endpoint detection in acidimetry and alkalimetry has long relied on synthetic halochromic indicators; however, growing emphasis on safer reagents, greener analytical practices, and wider accessibility has stimulated renewed interest in natural indicators derived from plants and other renewable sources. Natural indicators—most commonly anthocyanins, curcuminoids, and betalains—offer visually distinct and often broad pH-responsive colour transitions that can rival standard indicators for many neutralisation systems when appropriately extracted, stabilised, and validated. This review synthesises evidence from the modern literature on the chemical basis of natural indicator behaviour, extraction and standardisation strategies, analytical performance in common titration classes, and practical challenges such as stability, matrix effects, and observer variability. Particular attention is given to suitability in strong acid–strong base, weak acid–strong base, strong acid–weak base, and polyprotic titrations, alongside emerging approaches that immobilise natural dyes in solid supports to improve handling and reproducibility. The review also positions natural indicators within contemporary green analytical chemistry frameworks and highlights research directions for improving metrological robustness and broadening adoption in quantitative laboratories.