General Test Procedure Limit Test Heavy Metals

Purpose
1. This procedure is applicable to perform limit test for heavy metals. (Perform the test by any one method as specified in the individual monograph)
Apparatus
1. None
Method A
1. Reagents
  1. Lead standard solution (20 ppm Pb)
  2. Dilute acetic acid
  3. Dilute ammonia solution
  4. Hydrogen Sulphide solution
2. Preparation of Reagents
3. 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 ml.
4. Lead standard solution (100 ppm Pb): Dilute 1 ml of lead standard solution (0.1% Pb) to 10 ml with purified water.
5. Lead standard solution (20 ppm Pb): Dilute 1 ml of lead standard solution (100 ppm Pb) to 5 ml with purified water.
6. Dilute acetic acid:Dilute 5.7 ml of glacial acetic acid to 100 ml with purified water.
7. Dilute ammonia solution: Dilute 42.5 ml of strong ammonia solution to 100 ml with purified water.
8. Hydrogen sulphide solution: A freshly prepared saturated solution of hydrogen sulphide in purified water.Prepare the gas by the action of hydrochloric acid, diluted with equal volumes of purified water, on iron sulphide and collected in water.
Procedure
1. Standard solution: Into a 50-ml Nessler cylinder pipette 1 ml of lead standard solution (20 ppm Pb) and dilute with purified water to 25 ml. Adjust with dilute acetic acid or dilute ammonia solution to a pH between 3.0 and 4.0, dilute with purified water to about 35 ml and mix.
2. 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 to produce 25 ml. Adjust with dilute acetic acid or dilute ammonia solution to a pH between 3.0 and 4.0, dilute with purified water to about 35 ml and mix.
3. 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, allow to stand for 5 minutes and view downwards over a white surface.
Method B
1. Reagents
  1. Lead standard solution (20 ppm Pb)
  2. Dilute acetic acid
  3. Dilute ammonia solution
  4. Sulphuric acid AR grade
  5. Nitric acid AR grade
  6. Hydrochloric acid AR grade
  7. Hydrogen sulphide solution
2. Preparation of reagents
  1. 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 ml
  2. Lead standard solution (100 ppm Pb): Dilute 1 ml of lead standard solution (0.1% Pb) to 10 ml with purified water.
  3. Lead standard solution (20 ppm Pb): Dilute 2 ml of lead standard solution (100 ppm Pb) to 10 ml with purified water.
  4. Dilute acetic acid: Dilute 5.7 ml of glacial acetic acid to 100 ml with purified water.
  5. Dilute ammonia solution: Dilute 42.5 ml of strong ammonia solution to 100 ml with purified water.
  6. Hydrogen sulphide solution: A freshly prepared saturated solution of hydrogen sulphide in purified water. Prepare the gas by the action of hydrochloric acid, diluted with an equal volumes of water, on iron sulphide and collected in purified water.

Procedure
1. Standard solution: Into a 50ml Nessler cylinder pipette 1ml of lead standard solution (20 ppm Pb) and dilute with purified water to 25 ml. Adjust with dilute acetic acid or dilute ammonia solution to a pH between 3.0 and 4.0, dilute with purified water to about 35 ml and mix.
2. Test solution: Weigh in a suitable crucible the quantity of the substance specified in the STP, add sufficient sulphuric acid to wet the sample, ignite carefully at a low temperature until thoroughly charred. Add to the charred mass 2 ml of nitric acid and 5 drops of sulphuric acid and heat cautiously until white fumes are no longer evolved. Ignite, preferably in a muffle furnace, at 500^oC to 600^oC, until the carbon is completely burnt off. Cool, add 4 ml of hydrochloric acid, cover, digest on a water-bath for 15 minutes, uncover and slowly evaporate to dryness on a water-bath. Moisten the residue with 1 drop of hydrochloric acid, add 10 ml of hot water and digest for 2 minutes. Add ammonia solution drop wise until the solution is just alkaline to litmus paper, dilute to 25 ml with purified water and adjust with dilute acetic acid to a pH between 3.0 and 4.0. Filter, if necessary, rinse the crucible and the filter with 10 ml of purified water, combine the filtrate and washings in a 50ml Nessler cylinder, dilute with purified water to about 35 ml and mix.
3. 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, allow to stand for 5 minutes and view downwards over a white surface.
Method C
1. Reagents
  1. Lead standard solution (20 ppm Pb)
  2. Dilute sodium hydroxide solution
  3. Sodium sulphide solution
2. Preparation of reagents
  1. 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 to produce 250ml.
  2. Lead standard solution (100 ppm Pb): Dilute 1 ml of lead standard solution (0.1% Pb) to 10 ml with purified water.
  3. Lead standard solution (20 ppm Pb): Dilute 2 ml of lead standard solution (100 ppm Pb) to 10 ml with purified water.
  4. Dilute sodium hydroxide solution: Dissolve 5.0 g of sodium hydroxide in 100 ml of purified water.
  5. Sodium sulphide solution: Dissolve 10.0 g of sodium sulphide in 100 ml of purified water.
Procedure
1. Standard solution: Into a 50ml Nessler cylinder pipette 1ml of lead standard solution (20 ppm

Pb), add 5 ml of dilute sodium hydroxide solution, dilute with purified water to 50 ml and mix.

1. Test solution: Into a 50ml Nessler cylinder place 25 ml of the solution prepared for the test as

directed in the STP, or dissolves the specified quantity of the substance being examined in a mixture

of 20 ml of purified water and 5 ml of dilute sodium hydroxide solution. Dilute with purified water to

50 ml and mix.

1. Procedure:To each of the cylinders containing the standard solution and the test solution respectively

add 5 drops of sodium sulphide solution, mix, allow standing for 5 minutes and viewing downwards

over a white surface.

Method D
1. Reagents
  1. Lead standard solution (1 ppm Pb)
  2. Lead standard solution (2ppm Pb)
  3. Acetate buffer pH 3.5
  4. Thioacetamide reagent
2. Preparation of reagents
  1. 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 to produce 250 ml.
  2. Lead standard solution (100 ppm Pb):Dilute 1 ml of lead standard solution (0.1% Pb) to 10 ml with purified water.
  3. Lead standard solution (10 ppm Pb):Dilute 1 ml of lead standard solution (100 ppm Pb) to 10 ml with purified water.
  4. Lead standard solution (2ppm Pb):Dilute 2 ml of lead standard solution (10 ppm Pb) to 10 ml with purified water.
  5. Lead standard solution (1 ppm Pb): Dilute 1 ml of lead standard solution (10 ppm Pb) to 10 ml with purified water.
  6. 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.
  7. 7M hydrochloric acid: Dilute 59.5 ml of concentrated hydrochloric acid to 100 ml with purified water.
  8. 6M ammonia solution: Dilute 45 ml of strong ammonia solution to 100 ml with purified water.
  9. 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 in a water bath for 20 seconds, cool and use immediately.
  10. 1M-sodium hydroxide: Dissolve 4.2 g of sodium hydroxide in 100 ml of purified water.
  11. Thioacetamide solution: Dissolve 2.0 g of thioacetamide in 50 ml of purified water.
Procedure
1. Standard solution: Into a small Nessler cylinder pipette 10ml of either lead standard solution (1