| Limit of Heavy Metal test |
| METHOD A for Heavy Metal test 1. Apparatus: • 50 ml Nessler’s cylinder • 1 ml pipette • 10 ml pipette • 1 ml graduated pipette • 25 ml measuring cylinder • Glass rods. 2. Reagent for heavy metal test: • Lead standard solution (20 ppm Pb) • Dilute acetic acid • Dilute ammonia solution • Hydrogen sulphide solution 3. Preparation of Reagents: Lead standard solution (20 ppm Pb): Dilute 1 ml of lead standard solution (100 ppm Pb) to 5 ml with purified water. Lead standard solution (100 ppm Pb): Dilute 1 ml of lead standard solution (0.1% Pb) to 10 ml with purified water. Lead standard solution (0.1% Pb): Dissolve 0.400 g of lead nitrate in water containing 2 ml of nitric acid and add sufficient purified water to produce 250.0 ml. Dilute acetic acid: Dilute 5.7 ml of glacial acetic acid to 100 ml with purified water/Distilled water Dilute ammonia solution: Dilute 42.5 ml of strong ammonia solution to 100 ml with purified water/Distilled water. Hydrogen sulphide solution: A freshly prepared saturated solution of hydrogen sulphide in purified water/Distilled water. Prepare the gas by the action of hydrochloric acid, diluted with equal volumes of purified water, on iron sulphide and collected in water. 4. Procedure: Standard solution: Into a 50-ml Nessler cylinder pipette 1.0 ml of lead standard solution (20 ppm Pb) and dilute with purified water/Distilled water to 25 ml. Adjust pH with the dilute acetic acid or dilute ammonia solution to pH between 3.0 and 4.0 & dilute with purified /Distilled water to about 35 ml and mix properly. Test solution: Into a 50-ml Nessler cylinder place 25 ml of the solution prepared for the test as directed in the STP or dissolve the specified quantity of the substance being examined in sufficient purified water/Distilled water to produce 25 ml. Adjust pH with dilute acetic acid or dilute ammonia solution to pH between 3.0 & 4.0, dilute with purified water/Distilled water to about 35 ml and mix properly. Procedure: To each of the cylinders containing the standard solution and test solution respectively add 10 ml of freshly prepared hydrogen sulphide solution, mix, dilute to 50 ml with purified water/Distilled water, allow to standing for 5 minutes and view downwards over a white surface. |
