Paragraph 4 REAGENTS

Hydrochloric acid solution, about 6 M

4.1

See Method 25d (4.1).

Hydrochloric acid solution, about 0.5 M

4.2

See Method 25d (4.2).

4.3

Hydrogen peroxide solution (30% H₂O₂ ρ = 1.11 g/ml) free from trace element.

Lanthanum salt solutions (10 g of La per litre)

4.4

See Method 25d (4.3).

Iron calibration solutions

4.5

Iron stock solution (1000 μg/ml)

4.5.1

In a 500 ml beaker, weigh to the nearest 0.1 mg, 1 g of pure iron wire, add 200 ml of 6 M hydrochloric acid (4.1) and 15 ml of hydrogen peroxide solution (4.3). Heat on a hotplate until the iron is completely dissolved. When cool, transfer quantitatively to a 1 litre volumetric flask. Make up to volume with water and mix thoroughly.

Iron working solution (100 μg/ml)

4.5.2

Place 20 ml of the stock solution (4.5.1) in a 200 ml volumetric flask. Make up to volume with the 0.5 M hydrochloric acid solution (4.2) and mix thoroughly.