| Limit of heavy metal test (Method C) |
| METHOD C 1. Apparatus: • 10 ml volumetric flask • 2 ml graduated pipette • 250 ml volumetric flask • 10 ml graduated pipette • 100 ml volumetric flask • Nessler cylinder • Dropper 2. Reagents: • Lead standard solution (20 ppm Pb) • Dilute sodium hydroxide solution • Sodium sulphide solution 3.0 Preparation of reagents for heavy metal test: Lead standard solution (20 ppm Pb): Dilute 2 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 Dilute sodium hydroxide solution: Dissolve 5.0 g of sodium hydroxide in 100 ml of purified water/water for injections. Sodium sulphide solution: Dissolve 10.0 g of sodium sulphide in 100 ml of purified water/ water for injections. 4.0 Method: Standard solution: Into a 50-ml Nessler cylinder pipette 1.0 ml of lead standard solution (20 ppm Pb), add 5 ml of dilute sodium hydroxide solution, dilute with purified water/water for injections to 50 ml and mix. Test solution: Into a 50-ml Nessler cylinder place 25 ml of the solution dissolve the specified quantity of the substance being examined in a mixture of 20 ml of purified water/water for injections and 5 ml of dilute sodium hydroxide solution. Dilute with purified water/water for injections to 50 ml and mix well. Procedure: To each of the cylinders containing the standard solution and the test solution respectively add 5 drops of sodium sulphide solution, mix properly, allow to stand for 5 minutes and view downwards over a white surface. |
