Bromocresol purple (BCP) or5′,5″-dibromo-o-cresolsulfophthalein, is adye of thetriphenylmethane family (triarylmethane dyes) and apH indicator. It is colored yellow below pH 5.2, and violet above pH 6.8. In its cyclicsulfonate ester form, it has apKa value of 6.3, and is usually prepared as a 0.04% aqueous solution.[1]
Bromocresol purple is used in medical laboratories to measurealbumin. Use of BCP in this application may provide some advantage over older methods usingbromocresol green.[2][3] In microbiology, it is used for staining dead cells based on their acidity, and for the isolation andassaying oflactic acid bacteria.[4][5]
Inphotographic processing, it can be used as an additive to acidstop baths to indicate that the bath has reached neutral pH and needs to be replaced.[6]
Bromocresol purple milk solids glucose agar is used as a medium used to distinguishdermatophytes from bacteria and other organisms in cases ofringworm fungus (T. verrucosum) infestation in cattle and other animals.[7][8]
Similar tobromocresol green, the structure of bromocresol purple changes with pH. Changing the level of acidity causes a shift in theequilibrium between two different structures that have different colors. In near-neutral or alkaline solution, the chemical has asulfonate structure that gives the solution a purple color. As the pH decreases, it converts to asultone (cyclic sulfonic ester) that colors the solution yellow. In some microbiology tests, this change is used as an indicator of bacterial growth.[9][10]
^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.PMID19932090.
^Kurzweilová, H.; Sigler, K. (November 1993). "Fluorescent staining with bromocresol purple: a rapid method for determining yeast cell dead count developed as an assay of killer toxin activity".Yeast.9 (11):1207–1211.doi:10.1002/yea.320091107.PMID7509098.S2CID44782970.
^Kane, J.; Summerbell, R.; Sigler, L.; Krajden, S.; Land, G. (1997).Laboratory Handbook of Dermatophytes: A Clinical Guide and Laboratory Handbook of Dermatophytes and Other Filamentous Fungi from Skin, Hair, and Nails. Belmont, CA:Star Publishing Company.ISBN9780898631579.
^Li, Nan; Zhou, Siyu; Yang, Xingbin; Lin, Dehui (2022). "Applications of natural polysaccharide-based pH-sensitive films in food packaging: Current research and future trends".Innovative Food Science & Emerging Technologies.82.doi:10.1016/j.ifset.2022.103200.
