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What it is. This bromocresol green indicator is a ready-to-use 0.1% (w/v) aqueous solution, containing 1 g of bromocresol green sodium salt per liter, supplied in a 500 mL size. The solution is dark blue as supplied and turns yellow, green, or blue depending on the sample's pH.
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Chemical identity. Bromocresol green (tetrabromo-m-cresolsulfonphthalein) belongs to the sulfonephthalein family of indicators, the same family as bromophenol blue and bromocresol purple. The sodium salt form dissolves readily in water, so this indicator is prepared without alcohol, keeping it stable, low-odor, and easy to dispense.
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The bromocresol green pH range. Bromocresol green is yellow below pH 3.8 and blue above pH 5.4, passing through green around pH 4.5. The color change comes from the dye converting between its yellow acid form and its blue base form, with a pKa of about 4.7. In the blue form, it absorbs most strongly near 616 nm.
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Why it suits alkalinity testing. Total alkalinity titrations of water end near pH 4.5, where carbonate and bicarbonate have been converted to carbonic acid. That endpoint sits at the center of bromocresol green's transition, which is why Standard Methods 2320 (alkalinity) and 2310 (acidity) list it, alone or as a mixed indicator with methyl red.
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Why 0.1%. At 1 g/L, a few drops give a sharp, easy-to-see color change without adding enough dye to shift the result. A ready-made solution avoids weighing milligram amounts of dye and provides consistent strength from lot to lot, making endpoint judgments repeatable across analysts.
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Water and environmental methods. Beyond alkalinity, bromocresol green appears in APHA methods for aluminum (Eriochrome cyanine R method) and radium determinations, and in ASTM electrometric or color-change titrations for acidity and alkalinity. Water, wastewater, and environmental labs keep it on hand for these routine tests.
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Other uses. The same dye binds serum albumin under acidic conditions, shifting its absorbance near 630 nm, which is the basis of the widely used BCG albumin assay in clinical chemistry. It also serves as a tracking dye in agarose gel electrophoresis and as a clear teaching indicator for weak-acid equilibria.
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Choosing between related indicators. For endpoints slightly lower or higher, compare Lab Pro's Bromophenol Blue Indicator, 0.04% (w/v), which changes between pH 3.0 and 4.6, and Bromocresol Purple Indicator, 0.04% (w/v), which changes between pH 5.2 and 6.8. Matching the indicator midpoint to the titration endpoint gives the sharpest, most accurate color change.
Technical Specifications
| Active Ingredient |
Bromocresol green, sodium salt |
| CAS Number |
62625-32-5 (dye, sodium salt); 7732-18-5 (water) |
| EC Number (dye) |
263-657-4 |
| Synonyms |
Bromcresol green, tetrabromo-m-cresolsulfonphthalein sodium salt |
| Formula (dye) |
C21H13Br4NaO5S |
| Molecular Weight (dye) |
720.00 g/mol |
| Concentration |
0.1% (w/v), 1 g/L in water |
| Transition Range |
pH 3.8 (yellow) to pH 5.4 (blue) |
| Midpoint Color |
Green near pH 4.5 |
| pKa |
About 4.7 |
| Absorbance Maximum (basic form) |
About 616 nm |
| Appearance |
Dark blue liquid |
| Method References |
Standard Methods 2320 and 2310 |
| Package Size |
500 mL |
Applications / Common Uses
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Total alkalinity titration: Marks the pH 4.5 endpoint in water and wastewater alkalinity testing.
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Acidity testing: Used in Standard Methods acidity procedures for natural and treated waters.
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Weak base titrations: Indicates endpoints when titrating weak bases with strong acids.
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APHA water methods: Supports aluminum and radium determinations in water analysis.
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Gel electrophoresis: Tracks sample migration as a loading dye in agarose gels.
Storage, Handling & Shipping
Store the indicator tightly closed at room temperature, away from direct light and strong oxidizers, which can fade the dye. The dilute aqueous solution carries low hazard, but the dye stains skin and surfaces, so wear gloves and eye protection. Avoid contaminating the stock solution with acids or bases, which shift its color; dispense only what you need for each run.
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Incompatible materials: Strong oxidizers.
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Shelf life: Keep closed and protected from light; check color and clarity before use.
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Personal protection: Safety glasses and nitrile gloves to prevent eye contact and staining.
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Spill response: Wipe up with absorbent material and rinse the area with water.
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