Abstract: A colorimetric method using 2,4-dinitrophenylhydrazine(DNP)was developed to overcome the difficulties encountered in the determination of menadione sodium bisulfite in the presence of large amount of usual tablet excipients.Various reaction conditions particularly on the extraction of active principle and on phenyl- hydrazone formation were investigated.The method suggested is as follows: A sample representing 20 mg of menadione sodium bisulfite is suspended in water,well triturated and transferred into a separating funnel by the aid of a small amount of water.25 ml of benzene are added,then 0.1N NaOH solution added dropwise,and shaked gently.The benzene layer is seperated and the aquecus layer is further extracted with 20,15 and 10 ml of benzene.The benzene extracts are washed each time with the same 5 ml of water subsequently,and the aqueous washing liquid is washed with 10 ml of benzene.The combined benzene extracts and washings are filtered into an iodine flask,dried with anhydrous so- dium sulfate.The mixture is filtered into a 100 ml volumetric flask,and the filtrate made up to volume with benzene.0.6 ml of benzene extract containing about 60—80γ of menadione is pipetted into a small conical flask,3 ml of ab- solute alcohol and 1 ml of 0.25% alcoholic solution of DNP acidified with HCl are added.The reaction mixture is heated under reflux for 1 hour in water bath,keep- ing bath temperature at 74—76℃.Benzene is removed by distillation after add- ing 10 ml of absolute alcohol.To the remaining solution 5 ml of alcoholic am- monia solution(approximately 3N)are added and allowed to cool.The Solution is then transferred into a 50 ml volumetric flask,made up to volume with alcohol and mixed well.After standing for 15 minutes,3 ml of the solution are pipetted into a cell,diluted with alcohol to 5 ml.The transmittancy is determined at 640 mμ using alcohol as a blank. A standard curve was prepared in the same manner using menadione as stan- dard and the amount of menadione in the sample may be read off.