| Limit of Heavy metal test (Method D) |
| 1.0 Apparatus: • 10 ml volumetric flask • 2 ml graduated pipette • 250 ml volumetric flask • 10 ml graduated pipette • 100 ml volumetric flask • Nessler cylinder • 1 ml graduated pipette 2.0 Reagents: • Lead standard solution (1 ppm Pb) • Lead standard solution (2ppm Pb) • Acetate buffer pH 3.5 • Thioacetamide reagent 3.0 Preparation of reagents for heavy metal test : Lead standard solution (1 ppm Pb): Dilute 1 ml of lead standard solution (10 ppm Pb) to 10 ml with purified water/water for injections. Lead standard solution (2ppm Pb): Dilute 2 ml of lead standard solution (10 ppm Pb) to 10 ml with purified water/water for injections. Lead standard solution (10 ppm Pb): Dilute 1 ml of lead standard solution (100 ppm Pb) to 10 ml with purified water/water for injections. Lead standard solution (100 ppm Pb): Dilute 1 ml of lead standard solution (0.1% Pb) to 10 ml with purified water/water for injections. Lead standard solution (0.1% Pb): Dissolve 0.400 g of lead nitrate in purified water containing 2 ml of nitric acid and add sufficient purified water/water for injections to produce 250.0 ml Acetate buffer pH 3.5: Dissolve 25 g of ammonium acetate in 25 ml of purified water and add 38 ml of 7M hydrochloric acid. Adjust the pH to 3.5 with either 2M hydrochloric acid or 6M ammonia and dilute with purified water to 100 ml. 7M hydrochloric acid: Dilute 59.5 ml of concentrated hydrochloric acid to 100 ml with purified water/water for injections. 6M ammonia solution: Dilute 45 ml of strong ammonia solution to 100 ml with purified water/water for injections. Thioacetamide reagent: Add 1 ml of a mixture of 15 ml of 1M sodium hydroxide, 5ml of purified water and 20 ml of glycerin (85%) to 0.2 ml of thioacetamide solution. Heat with the help of a water bath for 20 seconds, cool and use immediately. 1M sodium hydroxide: Dissolve 4.0 g of sodium hydroxide in 100 ml of purified water/water for injections. Thioacetamide solution: Dissolve 2.0 g of thioacetamide in 50 ml of purified water/water for injections. 4.0 Method: Standard solution: Into a small Nessler cylinder pipette 10.0 ml of either lead standard solution (1 ppm Pb) or lead standard solution (2ppm Pb). Add 2.0 ml of the test solution and mix properly. Test solution: Prepare test solution as directed in the STP and pipette 12 ml into a small Nessler cylinder. Procedure: To each of the cylinders add 2 ml of acetate buffer pH 3.5, mix, add 1.2 ml of thioacetamide reagent, allow to stand for 2 minutes and view downwards over a white surface. |