Spectrophotometric determination of cerium (M) with Chromazurol S.

Abstract

A small amount of cerium was determined spectrophotometrically with Chromazurol S(CAS).
Two milliliters of 0.25% CAS solution was added to 1015 ml of the acidic solution containing cerium, and pH was adjusted to 6.40 with 7% hexamine solution. After a dilution to 25 ml with water and allowing to stand for 10 min., the absorbance was measured at 510 mμ against the reagent blank. The absorbance obeyed Beer's law over 5120 μg Ce/25 ml, and the apparent molar absorptivity was 1.83×10⁴.
By a separation of cerium as fluoride from di-, tri- and tetra-valent cations with sulfuric acid and hydrofluoric acid, interfering cations were removed except for lanthanum and yttrium, which were colored intensely at pH 9.60 with CAS where cerium was colored very slightly.
Then 10200 μg of cerium, 7142 μg of lanthanum and up to 60 μg of yttrium were determined simultaneously by measuring the absorbances at 510 mμ (pH 6.4), 610 mμ and 560 mμ (pH 9.6), respectively.