The reaction of lactose with anthrone and its application to the estimation of lactose in casein and other dairy products

Lactose was estimated accurately and rapidly in casein by use of anthrone reagent on the clear filtrate from precipitation of a sodium bicarbonate solution of the casein with 0·1 n-sulphuric acid. The reagent consists of 0·15% (w/v) anthrone in 70% (v/v) sulphuric acid. The ice-cold anthrone solution (10 ml.) was added, with cooling, to 1 ml. of the ice-cold solution containing 0–100 µg. of lactose. The mixture was heated at 100° C. for 6 min. and cooled for 30 min. The optical density of the coloured solution was then measured at 625 mµ