CI Phenolphthalein Indicator is a standardized 0.5% w/v solution in isopropanol used in acid-base titrations requiring a clean visual transition from colorless to pink in the pH 8.3 to 10.0 range. It is the endpoint indicator for alkalinity, hydroxide, and carbonate-bicarbonate determinations where a vague colour shift turns a routine test into operator guesswork. The isopropanol carrier promotes rapid dispersion and consistent endpoint visibility across laboratory and field sample matrices, making the reagent suitable for both burette titrations and drop-count methods used in water treatment and general industrial testing. Supplied in a 1-litre bottle for routine monitoring programs, CI Phenolphthalein Indicator is the analytical reagent that makes moderately basic titration endpoints readable, repeatable, and worth trusting.