Spectrophotometric determination of yttrium with Chromazurol S

Abstract

Chromazurol S reacts with yttrium to form a reddish violet complex in a nearly neutral medium (Barbital sodium-hydrochloric acid buffer) and it was applied to the determination of yttrium. Several conditions for the color development, the composition of the colored. complex and the influence of coexisting ions were in vestigated.
The maximum absorption wavelength of the complex against the reagent blank at about pH 7.0 or higher was 562 mμ. Absorption curves against water blank at pH 7.6 have an isosbestic point at about 487 mμ which depends on the amount of reagent.
The optimum pH for the color development is at about 7.6.
A linear relationship exists between the absorbance and the yttrium concentration (Beer's law). The optimum concentration range determined by Ringbom's plot is between 6 and 35μg. of yttrium in 10 ml. The molar extinction coefficient of the complex at 562 mμ is 22, 600.
The molar ratio of yttrium and chromazurol S in the complex is estimated to be 1 : 2 by a continuous variation method and by a mole ratio method. The complex has a formation constant of 1.5 × 10¹⁰ under the conditions studied.
Anions such as phosphate, EDTA, fluoride, oxalate, tartrate etc. inhibit the color development, and cations such as Be(II), UO₂(II) etc. give an overestimation of yttrium. Several heavy metals precipitate under the conditions and interfere with the determination.