Paragraph 7 PROCEDURE

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

See Method 25d (7.2).

For an optimum determination range of 0 to 5 μg/ml of cobalt, place 0, 0.5, 1, 2, 3, 4 and 5 ml respectively of working solution (4.4.2) 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 to each flask 10 ml of the lanthanum salt solution used in 6.2. Make up to 100 ml with 0.5 M hydrochloric acid solution (4.2) and mix thoroughly. These solutions contain 0, 0.5, 1, 2, 3, 4 and 5 μg/ml respectively of cobalt.

See Method 25d (7.3). Prepare the spectrometer (5) for measurement at a wavelength of 240.7 nm.