Phenol Red

CAS Number: 143-74-8
EC Index Number:205-609-7
Molecular Weight:354.38

General description

Phenol red (phenolsulfonphthalein, PH R) belongs to the class of triphenylmethane dyes. It is a waterͰsoluble anionic dye, mostly used as a pH indicator in cell biology laboratories. Also, in different protocols, it is used to detect H2O2(Hydrogen peroxide).


Phenol red can be used as a:

  • Dye in the preparation of phenol red/n-Si photodiode [phenol red/n-type silicon wafer] by spin coating technique. The device is appropriate for photo-detection applications.
  • Color-changing dye in the design of fiber optic pH sensor because as the acidity increases, the dye′s absorption properties shift from the green to the blue section of the spectrum.
  • Indicator in the determination of freshwater pH.

Features and Benefits

Phenol red is used to detect pH changes in cell culture,

  • pH is 6.4 or below yellow color
  • pH is 8.2 or above red color.

Analysis Note

  • Appearance of solution: passes test
  • 1st transition range: pH 1.2 - pH 3.0brownish orange - yellow
  • 2nd transition range: pH 6.5 - pH 8.0brownish yellow - red violet
  • Loss on drying (110 °C): ≤ 1
  • Transition range (according to ACS): passes test
  • ACS conforms
grade ACS reagent
Quality Level 200
form solid
loss ≤1% loss on drying, 110°C
visual transition interval 1.2-3.0, brown-orange to yellow(1st transition range)
6.5-8.0, brownish-yellow to red-violet(2nd transition range)
mp >300 °C
bulk density 200‑300 kg/m3
storage temp. 2-30°C
InChi 1S/C19H14O5S/c20-15-9-5-13(6-10-15)19(14-7-11-16(21)12-8-14)17-3-1-2-4-18(17)25(22,23)24-19/h1-12,20-21H