Bromocresol purple

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Bromocresol purple
Skeletal formula of bromocresol purple in cyclic form
Ball-and-stick model of the bromocresol purple molecule in cyclic form
IUPAC name
Other names
Bromcresol purple
115-40-2 YesY
ChemSpider 7974 YesY
Jmol 3D model Interactive image
PubChem 8273
Molar mass 540.22 g·mol−1
Appearance Purple powder
Melting point 241 to 242 °C (466 to 468 °F; 514 to 515 K) (decomposition)
< 0.1 %
R-phrases R36/37/38
S-phrases S26, S36
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 1: Exposure would cause irritation but only minor residual injury. E.g., turpentine Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YesYN ?)
Infobox references

Bromocresol purple (BCP) or 5′,5″-dibromo-o-cresolsulfophthalein, is a dye of the triphenylmethane family (triarylmethane dyes) and a pH indicator. It is colored yellow below pH 5.2, and violet above pH 6.8. In its cyclic sulfonate ester form, it has a pKa value of 6.3, and is usually prepared as a 0.04% aqueous solution.[1]


A sample of bromocresol purple in its violet form
Bromocresol purple (pH indicator)
below pH 5.2 above pH 6.8
5.2 6.8

Bromocresol purple is used in medical laboratories to measure albumin, although it is no better in this role than the older method using bromocresol green.[2] In microbiology, it is used for staining dead cells based on their acidity, and for the isolation and assaying of lactic acid bacteria.[3][4]

In photographic processing, it can be used as an additive to acid stop baths to indicate that the bath has reached neutral pH and needs to be replaced.[5]

Bromocresol purple milk solids glucose agar is used as a medium used to distinguish dermatophytes from bacteria and other organisms in cases of ringworm fungus (T. verrucosum) infestation in cattle and other animals.[6][7]

pH Indicator[edit]

Similar to bromocresol green, the structure of bromocresol purple changes with pH. The low pH (acidic) form is yellow in solution and the high pH (basic) form is purple; the sultone (cyclic sulfonic ester) is the acidic form in the following equilibrium.

Bromkresolpurpur, Gleichgewicht.svg


  1. ^ "Bromocresol Purple". NCBI PubChem. National Center for Biotechnology Information. 
  2. ^ McGinlay, J.M.; Payne, R.B. (July 1988). "Serum albumin by dye-binding: bromocresol green or bromocresol purple? The case for conservatism." (PDF). Annals of Clinical Biochemistry 25 (4): 417–421. doi:10.1177/000456328802500417. PMID 3214125. 
  3. ^ 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. PMID 7509098. 
  4. ^ Lee, H.M.; Lee, Y. (June 2008). "A differential medium for lactic acid-producing bacteria in a mixed culture". Letters of Applied Microbiology 46 (6): 676–681. doi:10.1111/j.1472-765X.2008.02371.x. PMID 18444977.  open access publication - free to read
  5. ^ Anchell, Steve (2016). The Darkroom Cookbook (4 ed.). Routledge. ISBN 9781317337607 – via Google Books. 
  6. ^ 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. ISBN 9780898631579. 
  7. ^ Beneke, E. S.; Rogers, A. L. (1996). Medical Mycology and Human Mycoses (illustrated ed.). Belmont, CA: Star Publishing Company. pp. 85–90. ISBN 9780898631753. 

External links[edit]