Phenol Red   

Phenol Red (also known as phenolsulfonphthalein or PSP) is a pH indicator frequently used in cell biology laboratories. Most living tissues prosper at a near-neutral pH; that is, a pH close to 7. The pH of blood ranges from 7.35 to 7.45, for instance. When cells are grown in tissue culture, the medium in which they grow is held close to this physiological pH. A small amount of phenol red added to this growth medium will have a pink-red color under normal conditions. Typically, 15 mg/l are used for cell culture. 
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