Industrial-grade 99% Bromocresol Purple 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. Its molecule undergoes protonation/deprotonation transitions under different pH conditions, resulting in changes in its absorption spectrum: it appears yellow below pH 5.2 and purple above pH 6.8 (maximum absorption wavelength approximately 590 nm)—this "pH-responsive color change" characteristic makes it a sensitive indicator for determining acidity and alkalinity in industrial water quality monitoring, process control, and quality testing, forming the functional basis for its application in the industrial field.

Chemically, bromocresol purple is stable, has a narrow color change range (pH 5.2~6.8), and exhibits a sharp color change, making it suitable as an acid-base indicator and a titration indicator for non-aqueous solutions. It is irritating, so dust inhalation and skin contact should be avoided. It should be stored in a sealed, light-protected, and dry place.

Industrial-grade bromocresol purple refers to products primarily intended for industrial testing and production process control, used as a basic raw material for industrial water quality monitoring, process pH control, and indicator production. Compared to indicator-grade (reagent-grade) products, industrial-grade products place greater emphasis on the following indicators:

Main content

Purity directly affects the sensitivity of the indicator and the accuracy of the detection. Industrial grade generally requires a main content of over 90% (indicator grade requires even higher purity).

Color change range

The core performance indicators are a color change range of pH 5.2~6.8 (yellow to purple) and a clear color change.

Moisture

Excessive moisture content can affect measurement accuracy and storage stability, and must be kept at a low level.

Ash

Ash content reflects the content of inorganic impurities, which affects the performance of indicators and the quality of downstream products, and must meet specifications.

Fineness

It is necessary to meet specifications for uniform particle size, which is good for dissolving and preparation of indicator solutions.

What are the applications of industrial-grade Bromocresol Purple?

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

Bromocresol purple is a chemical used as an acid-base indicator to test industrial water quality. 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 .

2. 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.

3. 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.

4. 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.

5. Microbial culture and detection (indirect contact)

Bromocresol purple is used as a pH indicator in microbial culture media It is used to measure acid formation in bacterial fermentation which leads to color changes. It is applicable in food microbiology testing and medical lab culturing processes.

6. Urine and body fluid testing (indirect contact)

Bromocresol purple is an indicator component in urine pH test strips that may contain it for a rapid determination of the acid–base status of body fluids.

7. Indicator Production and Supply (Basic Raw Materials)

Bromocresol purple is an industrial-grade basic raw material for manufacturing acid-base indicators, testing reagents and testing strips. It is provided to test reagent manufacturers for purification, solution preparation and formulation to support the whole indicator industry chain

8. Film processing (traditional application)

In traditional film processing, bromocresol violet is added to the stop solution to indicate the pH level of the stop bath (an acidic bath after development and before fixing), and is an integral part of traditional photographic processes.

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 processing, and educational experiments. In industry, industrial-grade bromocresol purple is widely used as an indicator for monitoring pH in industrial water and boiler water, a testing reagent in the swimming pool and water treatment industries, a quality inspection indicator in the food and beverage industry, and a pH control reagent in electroplating and surface treatment processes. It is an important acid-base indicator bridging "daily use" and "water treatment, food, and chemical testing."