Paragraph 7 PROCEDURE

Preparation of the blank solution

7.1

See Method 25d (7.1). The blank solution must contain 10% by volume of the lanthanum salt solution used in 6.2.

Preparation of the calibration solutions

7.2

See Method 25d (7.2).

For an optimum interval of 0 to 5 mg/ml of zinc, place 0, 0.5, 1, 2, 3, 4 and 5 ml, respectively, of the working solution (4.4.2) in a series of 100 ml volumetric flasks. Where necessary, adjust the concentration of hydrochloric acid to bring it as close as possible to that of the test solution. Add 10 ml of the lanthanum salt solution used in (6.2) to each volumetric flask. Make up to 100 ml with the 0.5 M hydrochloric acid solution (4.2) and mix thoroughly. These solutions contain, respectively, 0, 0.5, 1, 2, 3, 4 and 5 mg/ml of zinc.

Determination

7.3

See Method 25d (7.3). Prepare the spectrometer (5) for measurements at a wavelength of 213.8 nm.