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What it is. This bromocresol purple indicator is a concentrated 1% (w/w) solution of the free-acid dye in methanol, supplied in a 120 mL size. It is a reddish-orange liquid prepared to ACS grade, intended for laboratories that need a strong indicator stock rather than a ready-to-use dilute solution.
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The bromocresol purple pH range. Bromocresol purple changes from yellow below pH 5.2 to purple above pH 6.8. Its transition sits in the weakly acidic to near-neutral zone, between the ranges of bromocresol green and bromothymol blue, which makes it useful wherever an endpoint or reading falls between about pH 5 and 7.
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Chemical identity. Bromocresol purple (5',5''-dibromo-o-cresolsulfonphthalein, CAS 115-40-2) is a sulfonephthalein dye with a molecular weight of 540.22 g/mol. In acidic solution, the dye exists mainly in its yellow form, absorbing near 420 to 430 nm; in neutral and alkaline solution it converts to the purple sulfonate form, which absorbs most strongly near 590 nm.
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Why a 1% methanol solution. The dye's free-acid form dissolves much better in alcohols than in water, so methanol allows a much higher dye concentration than an aqueous indicator. At 1% by weight, small volumes go a long way: you can dilute the stock for titration work, add it to culture media, or use it where a deeper color is needed. Because the solution is mostly methanol, it carries methanol's flammability and toxicity.
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Microbiology and culture media. Bromocresol purple is a classic pH indicator in microbiological media. Fermentation-produced acid turns the medium from purple to yellow, forming the basis of media such as bromocresol purple milk solids glucose agar, which distinguishes organisms by their metabolism.
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Clinical and cell-biology uses. The dye binds serum albumin, and the bromocresol purple method is used in clinical chemistry to measure albumin concentration. It has also been used as a fluorescent stain to count dead yeast cells, because it enters cells with damaged membranes and stains them while intact cells remain unstained.
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Shelf life and quality. Prepared to ACS grade with a stated shelf life of 24 months, this concentrated stock gives consistent color from batch to batch. Lab Pro also offers a ready-to-use aqueous Bromocresol Purple Indicator, 0.04% (w/v) for routine titrations that do not need a methanol-based stock.
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Handling at a glance. Treat this indicator as methanol: highly flammable, toxic if swallowed, inhaled, or absorbed through skin, and damaging to the optic nerve and other organs. Work in a fume hood away from ignition sources, wear chemical splash goggles and nitrile gloves, and store it in a flammables cabinet.
Technical Specifications
| Product |
Bromocresol purple indicator solution |
| Active Ingredient |
Bromocresol purple (free acid) |
| CAS Numbers |
115-40-2 (bromocresol purple); 67-56-1 (methanol) |
| EC Number (dye) |
204-087-8 |
| Synonyms |
5',5''-Dibromo-o-cresolsulfonphthalein, BCP |
| Formula (dye) |
C21H16Br2O5S |
| Molecular Weight (dye) |
540.22 g/mol |
| Concentration |
1% (w/w) in methanol |
| Grade |
ACS |
| Transition Range |
pH 5.2 (yellow) to pH 6.8 (purple) |
| Absorbance Maxima (dye) |
About 419 to 433 nm (acid form); about 590 nm (basic form) |
| Appearance |
Reddish-orange liquid |
| Melting Point |
-98 °C (methanol) |
| Boiling Point |
About 64.5 °C (methanol) |
| Flash Point |
11 °C (52 °F) (methanol) |
| Shelf Life |
24 months |
| Package Size |
120 mL |
Applications / Common Uses
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Acid-base titrations: Marks endpoints that fall in the pH 5.2 to 6.8 range.
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Culture media: Acts as the pH indicator that reveals acid production by fermenting microorganisms.
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Albumin determination: Serves as the dye in the bromocresol purple method for serum albumin.
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Indicator stock preparation: Dilutes into working indicator solutions or mixed indicators.
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Yeast viability staining: Stains dead yeast cells with damaged membranes for counting.
Storage, Handling & Shipping
Caution: This product is a methanol solution. It is highly flammable and toxic if swallowed, inhaled, or absorbed through the skin, and methanol exposure can cause blindness and organ damage. Handle in a fume hood away from heat, sparks, and flames, wearing splash goggles, nitrile gloves, and a lab coat.
Store tightly closed in a cool, well-ventilated flammables cabinet, away from heat, sparks, open flames, and oxidizers. Keep the solution protected from light to preserve the dye, and ground equipment when transferring larger volumes. Methanol evaporates readily, so close the container promptly to preserve the 1% concentration.
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Incompatible materials: Strong oxidizers, strong acids, alkali metals, and ignition sources.
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Exposure limits (methanol): OSHA PEL 200 ppm TWA; NIOSH REL 200 ppm TWA, 250 ppm STEL.
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Spill response: Remove ignition sources, ventilate, and absorb with a non-combustible absorbent; collect for disposal as flammable waste.
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First aid: Skin or eyes: rinse with water for 15 minutes. Ingestion or significant inhalation: seek medical attention immediately, even without symptoms.
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GHS signal word: Danger. Highly flammable liquid and vapor; toxic if swallowed, in contact with skin, or if inhaled; causes damage to organs.
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DOT / shipping: Ships as a hazardous material (flammable liquid).
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