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Indicators

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Certain organic substances change color in dilute solution when the hydronium ion concentration reaches a particular value. For example, phenolphthalein is a colorless substance in any aqueous solution with a hydronium ion concentration greater than 5.0 × 10−9 M (pH < 8.3). In more basic solutions where the hydronium ion concentration is less than 5.0 × 10−9 M (pH > 8.3), it is red or pink. Substances such as phenolphthalein, which can be used to determine the pH of a solution, are...

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Colorimetric Detection of Bacteria Using Litmus Test

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Paper-Based Colorimetric pH Test Strip Using Bio-Derived Dyes.

Aramis A Sánchez¹, Darwin Castillo^2,3, Grettel Riofrío-Cabrera²

¹PROSUR Construcción Sustentable del Sur, Puebla 72810, Mexico.

|December 24, 2025

Summary

This summary is machine-generated.

Natural dyes from cabbage, hibiscus, radish, and turmeric show promise as eco-friendly pH indicators. These sustainable alternatives offer cost-effective and easily distinguishable color changes for pH measurement.

Keywords:

cabbage dyes environment natural dyes pH pigments radish sensor testing strip turmeric

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Area of Science:

Green Chemistry
Analytical Chemistry
Natural Product Chemistry

Background:

Synthetic dyes raise environmental concerns in industrial applications.
Conventional pH measurement tools can be expensive and complex.
Natural dyes offer a sustainable and cost-effective alternative for various industrial needs.

Purpose of the Study:

To explore the pH-responsive properties of natural organic dyes.
To develop a novel pH indicator using natural dye pigments.
To evaluate the potential of natural dyes as alternatives to conventional pH measurement techniques.

Main Methods:

Extraction and analysis of pigments from forty vegetable species.
Utilized a solvent mixture of 70% methanol/30% water for pigment extraction.
Assessed the colorimetric response of dye extracts across a range of pH values.

Main Results:

Pigments from cabbage, hibiscus flower, radish, and turmeric demonstrated significant color changes over a broad pH range.
The color variations were easily distinguishable, correlating with specific pH levels.
Dry pigment states exhibited optimal reactivity and stability for pH indication.

Conclusions:

Natural dyes, particularly from cabbage, hibiscus, radish, and turmeric, are effective pH indicators.
These findings support the use of natural dyes as a sustainable and economical substitute for traditional pH measurement methods.
This research highlights a novel application for natural dyes in industrial pH verification.