Paragraph 6 PREPARATION OF THE SOLUTION TO BE ANALYSED

Manganese extract solution

6.1

See Methods 26a and 26b. If it is not known whether chloride ions are present, perform a test on the solution with one drop of the silver nitrate solution (4.10).

6.2

In the absence of chloride ions, place an aliquot portion of the extract containing 10 to 20 mg of manganese in a tall form 400 ml beaker. Bring to a volume of about 25 ml either by evaporation or by adding water. Add 2 ml of concentrated sulfuric acid (4.1).

If chloride ions are present, it is necessary to remove them as follows:

6.3

Place an aliquot portion of the extract containing 10 to 20 mg of manganese in a tall form 400 ml beaker. Add 5 ml of 9 M sulfuric acid (4.2). Under a fume hood, bring to boiling on a hotplate and allow to boil until copious white fumes are released. Continue until the volume is reduced to about 2 ml (thin film of syrupy liquid at the bottom of the beaker). Allow to cool to ambient temperature.

Carefully add 25 ml of water and once again test for the presence of chlorides with one drop of the silver nitrate solution (4.10). If chlorides still remain, repeat the operation after adding 5 ml of 9 M sulfuric acid (4.2).