PHOTOCHEMICAL DECOMPOSITION OF PHENOL RED (PHENOLSULPHONPHTHALEIN)

Commercially available Phenol Red, purified using adsorption chromatog raphy, was found to comprise two distinct compounds: pure Phenol Red a nd a contaminant, which in the solid state was very slightly pink in c olour. These two compounds alone and in combination underwent photodeg radation via a hydroxyl radical mediated reaction. Photolysis also occ urred when the compounds were incorporated into a lauryl sulphate brot h medium used in the membrane filtration method for the detection of c oliforms and 'faecal' E. coli in drinking water. These findings suppor t the contention that commercial preparations of Phenol Red should be purified prior to inclusion in growth media for bacteria.