This is the recipe for bromocresol purple, which is a common pH indicator. The final solution will be 0.04% aqueous bromocresol purple.
Bromocresol Purple Ingredients
Bromocresol purple indicator is an aqueous solution of powdered dye. The solid is a dark violet powder, while the indicator solution is purple. It’s important to use deionized water rather than tap or distilled water. The most common indicator solution is 0.04%, as bromocresol purple has a solubility less than 0.1% in water.
- 0.04 g bromocresol purple
- deionized water
Prepare the Bromocresol Purple Indicator
- Dissolve 0.04 g of bromocresol purple in 50 mL deionized water.
- Dilute the solution to a final volume of 100 ml.
Color Change and Uses
Bromocresol purple changes color according to pH. The indicator is yellow below pH 5.2. It is purple above pH 6.8.
Bromocresol purple is used to measure albumin in medical laboratories, usually in situations where it performs better than bromocresol green. Another use of bromocresol purple is for staining dead cells and assaying lactic acid bacteria. Bromocresol purple is used to diagnose ringworm infestation by the fungus T. verrucosum in livestock and other animals. In photography, the indicator is used in acid stop baths to show when the bath has reached a neutral pH are requires replacement.
- Ito, Shigenori; Yamamoto, Daisuke (2010-02-02). “Mechanism for the color change in bromocresol purple bound to human serum albumin”. Clinica Chimica Acta. 411 (3): 294–295. doi:10.1016/j.cca.2009.11.019
- National Library of Medicine. “Bromocresol purple.” PubChem.
- O’Neil, M.J. (ed.) (2006). The Merck Index – An Encyclopedia of Chemicals, Drugs, and Biologicals. Whitehouse Station, NJ: Merck and Co., Inc.