Improved method for the simultaneous absorptiometric determination of cobalt and nickel with quinoxaline-2,3-dithiol.
A new, more stable reagent, S-2-(3-mercaptoquinoxalinyl)thiuronium chloride (MQT), is proposed for the simultaneous absorptiometric determination of cobalt and nickel. It is hydrolysed rapidly to quinoxaline-2,3-dithiol (QDT) in ammonia buffer at pH 10. In the presence of zinc(II), QDT is stabilized by complex formation and the reagent blanks are reduced. Samples containing cobalt(II) and nickel(II) react with the mixture on warming to give 1:3 cobalt and 1:2 nickel complexes, with maximum absorbances at 472 and 520 mmu respectively. The sensitivity of the method is high, 0.0017 and 0.0028 mug cm (2) for cobalt and nickel respectively, and there is a significant improvement in accuracy and precision, which is about +/-1 % over a 15-fold change in cobalt to nickel ratio. The selectivity is moderate; Ag(I), Cu(II), Pd(II), Cd(II), Hg(II), Sn(II), Pb(II), Bi(III) and Pt(IV) cause significant interference but most other common cations and anions can be tolerated.
Dalziel
J A
JA
Department of Chemistry, Chelsea College of Science and Technology, Manresa Road, London S.W. 3 U.S.A.
Slawinski
A K
AK