Paragraph 7 PROCEDURE

Preparation of blank solution

7.1

See Method 25d (7.1). The test solution must contain 10% (v/v) of the lanthanum salt solution used in 6.2.

Preparation of calibration solutions

7.2

See Method 25d (7.2).

For an optimum determination range of 0 to 10 μg/ml of iron, place 0, 2, 4, 6, 8 and 10 ml respectively of working solution (4.5.2) in a series of 100 ml volumetric flasks. If necessary adjust the hydrochloric acid concentration as closely as possible to that of the test solution. Add 10 ml of the lanthanum salt solution used in 6.2. Make up to volume with 0.5 M hydrochloric acid solution (4.2) and mix thoroughly. These solutions contain 0, 2, 4, 6, 8 and 10 μg/ml respectively of iron.

Determination

7.3

See Method 25d (7.3). Prepare the spectrometer (5) for measurement at a wavelength of 248.3 nm.