Assay & Identification of Acetaminophen Pharmacist Omar abdulrahman Pharmaceutical Chemistry Department College Of Pharmacy-HMU

Simple Definition Assay: to know the amount (quantity) of a given substance (drug) in a sample (any pharmaceutical dosage form). Identification: to characterize and identify the substance (a qualitative measure).

Principle of Assay The principle of paracetamol assay depends on hydrolysis (addition of water) of paracetamol to its primary ingredient (p-aminophenol). Then by redox reaction or titration, we can assay the amount of para aminophenol. This done by addition of ammonium ceric sulphate (oxidizing agent) that oxidize para amino phenol to aminoquinone.

Procedure for assay of paracetamol Dissolve the sample in a mixture of 10 ml of water & 50ml of 2N Sulphuric acid. Boil under reflux condition for 1hour. Cool and diluted to100ml with water. Add 40 ml of water in the form of ice to 20 ml of solution. Add 5 ml of 2N hydrochloric acid and 0.1 ml of ferroin solution. Titrate the solution with 0.1N ammonium ceric sulphate until a yellow colour appeared. Each ml of 0.1 N ammonium ceric sulphate is equivalent to 0.00756 g of C8H9NO2.

Identification Test 1: Dissolve 0.1 g of sample in 10 ml of D.W. in a test tube. Add 10 drops of ferric chloride , a violet-blue color will appear.

Test 2: Add 1 ml of hydrochloric acid ( conc.) to 0.1 g of paracetamol. Heat to boiling for 3 min. Add 1ml of water and cool in ice bath. Add 10 drops of potassium dichromate, a violet color develops.