How to Make Bromocresol Green Indicator Solution

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From left to right solutions of 0.1 M HCl, 3 buffer solutions of pH 3.78, 3 of pH 4.00, 3 of pH 4.62 and NaOH 0.1 M after adding different amounts of bromocresol green.
From left to right solutions of 0.1 M HCl, 3 buffer solutions of pH 3.78, 3 of pH 4.00, 3 of pH 4.62 and NaOH 0.1 M after adding different amounts of bromocresol green. (Natan Consigli)

It’s easy to prepare bromocresol green indicator solution. Bromocresol green or BCG is a triphenylmethane dye used as a pH indicator for titration, microbial growth media, and DNA agarose gel electrophoresis. However, its most common use is to measure blood serum albumin levels in humans and other mammals when liver or kidney disease is suspected. Its chemical formula is C21H14Br4O5S. Aqueous bromocresol green indicator solution is yellow below pH 3.8 and blue above pH 5.4. Between pH values of 3.8 and 5.4 it appears green. The dye is only sparingly soluble in water, so it may be dissolved in ethanol or certain organic solvents. Here are two recipes for making bromocresol green indicator solution.

Bromocresol Green Ingredients

You need bromocresol green powder and a suitable solvent:

Two Ways to Prepare Bromocresol Green Indicator

0.1% in alcohol

Bromocresol Green Chemical Structure
Bromocresol Green Chemical Structure
  1. Dissolve 0.1 g of bromocresol green in 75 mL of ethyl alcohol.
  2. Dilute the solution with ethyl alcohol to make 100 ml.

Diethyl ether or benzene may be used in place of alcohol.

0.04% aqueous

  1. Dissolve 0.04 g of bromocresol green in 50 mL of deionized water.
  2. Dilute the solution with water to make 100 ml.

Safety Information

Avoid contact with bromocresol green powder or indicator, as it may irritate skin and mucous membranes.

In some situations, bromocresol purple is used instead of bromocresol green. Bromocresol purple displays color changes at pH 5.2 and 6.8.

References

  • Kolthoff, I.M. (1959). Treatise on Analytical Chemistry. Interscience Encyclopedia, Inc. New York.
  • Sabnis, R. W. (2008). Handbook of Acid-Base Indicators. Boca Raton, FL: CRC Press. pp. 43–44.