Industrial grade 99% Bromocresol Purple Cas 115-40-2

What is Bromocresol Purple?

Bromocresol Purple (also known as bromocresol red, dibromo-o-cresol sulfonyl phthaloyl, or BCP) is a triphenylmethane dye and a classic acid-base indicator. Its chemical formula is usually written as:

C21H16Br2O5S (CAS No.: 115-40-2, molecular weight approximately 540.22)

At room temperature, it is a fine crystalline powder that is almost colorless to yellow or brick red, with a pungent odor. It has a melting point of about 245°C and a density of about 1.8 g/cm³. It is slightly soluble in ethanol (about 75 g/L at 20°C) and dilute alkaline solutions, almost insoluble in water, and turns reddish-purple when soluble in dilute alkali and ammonia solutions.

From a molecular structure perspective, bromocresol purple consists of a sulfonyl skeleton and two bromine-substituted o-cresol rings, belonging to the sulfonyl group of indicators.It is a molecule that undergoes transitions of protonation/deprotonation at different pH conditions that lead to changes in its absorption spectrum: it is yellow below pH 5.2 and purple above pH 6.8 (maximum absorption wavelength is approximately 590 nm), therefore this “pH-responsive color change” property makes it a sensitive indicator for the detection of acidity and alkalinity, which forms the basis for its widespread application in the fields of analytical chemistry, microbiology, and detection.

Chemically, bromocresol purple is stable, has a narrow range of color change (pH 5.2~6.8), and a sharp change of color so it can be used as an acid-base and titration indicator for non-aqueous solutions. It is irritating so avoid dust inhalation and skin contact. Store in a cool, dry place in a sealed container protected from light.

Bromocresol purple (excluding industrial grade) is for laboratory, testing and research use. These are mainly indicator grade (reagent grade) products with a purity of more than 95% usually. These products are more oriented toward the following indicators compared to industrial grade:

purity

Indicator-grade reagents require a main content of over 95% to ensure sensitive color change and accurate experimental results.

Color change range

The required color change range is pH 5.2~6.8 (yellow to purple), and the color change is sensitive and the boundary is clear, which are the core performance indicators.

Sensitivity

Sensitivity determines an indicator's ability to respond to minute changes in acidity or alkalinity and must meet indicator-grade specifications.

Solubility

It should be slightly soluble in ethanol, soluble in dilute alkali to produce a reddish-purple color, and have stable solution preparation properties.

What other uses does Bromocresol Purple have?

1. Laboratory acid-base indicators (reagent grade, core application)

Bromocresol purple is one of the most classic acid-base indicators in analytical chemistry. Its color change range is pH 5.2 to 6.8 (yellow to purple). It has a sharp color change and clear boundaries, and is widely used in acid-base titration analysis, pH determination and non-aqueous titration. It is an essential reagent in analytical laboratories.

2. Microbial culture medium indicators

Bromocresol purple is used as a pH indicator in media for microbial culture . It is a visual indicator for acid production by bacteria through a color change (yellow to purple) and is frequently employed in food microbiology, clinical microbiology, and bacterial culture within biological laboratories.

3. Test strips and rapid testing

Bromocresol purple is used in urine pH test strips and rapid test reagents to quickly determine the acid-base status of body fluids. It is an important part of indicator in health test products.

4. Film developing stop-motion indicator

In film processing, bromocresol violet is used by adding it to the stop solution to show the pH of the stop bath. This allows the photographer to control the acid neutralization process after development. It is an important part of traditional photographic chemistry.

5. Industrial water quality and boiler water monitoring (core application)

Bromocresol purple is an acid-base indicator used in the testing of the quality of industrial waters. It helps you monitor variations of pH of boiler water, circulating water and process water. It detects water quality anomalies in time and prevents equipment corrosion and scaling. It is an important test reagent for industrial water treatment and water quality control .

6. Testing in the swimming pool and water treatment industry

Swimming pool water pH testing and the public water treatment industry use test reagents containing bromocresol purple to quickly determine the acidity or alkalinity of water, ensuring that swimming pool water quality meets standards and protecting public health.

7. Food and beverage industry testing

Food and beverage manufacturers use bromocresol purple for quality testing and control of product acidity and alkalinity, helping to determine the pH status in processes such as fermentation and blending, and it is applied to quality inspection in industries such as beverages and dairy products.

8. Electroplating and Surface Treatment Process Control

In electroplating and metal surface treatment processes, bromocresol purple is used for rapid detection and process control of the pH of the plating solution, helping to maintain the stability of the acidity and alkalinity of the plating solution and ensure the quality of the coating.

9. Indicator Production and Supply (Basic Raw Materials)

Industrial-grade bromocresol purple is a basic raw material for the production of acid-base indicators, test reagents, and test strips. It is supplied to test reagent manufacturers for purification, solution preparation, and formulation, supporting the entire indicator industry chain.

It should be noted that indicator-grade specifications do not equate to "risk-free": bromocresol purple is irritating, and when using reagent-grade products in experiments, laboratory safety regulations should be followed, protective equipment should be worn, and dust inhalation and skin contact should be avoided.

Summarize

Bromocresol Purple (BCP) is a brick-red crystalline powder of triphenylmethane. It is a classic acid-base indicator, changing from yellow to purple within a pH range of 5.2 to 6.8, with a sharp and clear color change. In daily life, we indirectly encounter it through urine and body fluid test strips , microbial culture testing, swimming pool water quality testing, film developing, and educational experiments. Beyond industry, indicator-grade bromocresol purple is widely used in laboratory acid-base titration indicators, pH indicators for microbial culture media, test strips and rapid testing reagents, film developing stop-image indicators, and water quality monitoring. It is an important acid-base indicator bridging "daily use" and "analytical chemistry, microbiology, and health monitoring."