Methyl Red
C15H16ClN3O2 = 305.76
Dark red powder or violet crystals. Sparingly soluble in water; soluble in ethanol. Transition interval: from pH 4.2 to 6.3. Colour change: from red to yellow.
Methyl Red TS
Dissolve 10 mg of methyl red in 100 mL of ethanol, and filter if necessary.
Phenolphthalein
C20H14O4 = 318.33
White or faintly yellowish white, crystalline powder. Insoluble in water; soluble in ethanol.
Transition interval: from pH 8.3 to 10.0. Colour change: from colourless to red.
SENSITIVITY Dissolve 100 mg in 10 mL of neutralized ethanol, add 0.1 mL of this solution to 200 mL of carbon dioxide-free water, and then add 0.05 mL of 0.10 M sodium hydroxide: the solution is pink in colour when compared with an equal volume of water.
Phenolphthalein TS
Dissolve 1 g of phenolphthalein in 100 mL of ethanol (50 per cent).
Source/Reference
Thai Herbal Pharmacopoeia 2021 Page 854-856, Bureau of Drug and Narcotic, Department of Medical Sciences, Ministry of Public Health, Thailand.
FOR ACADEMIC PURPOSES ONLY
