Weigh accurately a portion of the sample expected to contain approximately 5 mg of chlortetracycline hydrochloride (see Note 2) into a 100 mL volumetric flask, add about 70 mL of water and 4 mL of 5M hydrochloric acid, shake the mixture for 10 min, dilute to the mark at 20 ๐C with water and mix thoroughly (see Note 3). Filter the mixture through Celite filter aid, discarding the first 20-30 mL of filtrate and then collect the clear filtrate