Use of Azo Dyestuffs for the Polarographic Determination of the Lanthanides

Abstract

THE polarographic behaviour of some 2,2′-di-hydroxy azo dyes in the presence of the lanthanides has recently been a subject of study in this laboratory. The lanthanides were found to form coloured chelates in alkaline solution with erichrome violet B (5-sulpho-2-hydroxy benzene-azo-2-naphthol, C.I. No. 169), eriochrome black PV (5-sulpho-2-hydroxy benzene-azo-l,5-dihydroxy naphthalene, C.I. No. 170) and mordant blue 31 (5-sulpho-2-hydroxy benzene-azo-1,8-dihydroxy naphthalene 3,6-disulphonic acid, C.I. No. 16675). These dyes all exhibit well-defined single polarographic reduction waves. In ammonia, diethanolamine and piperidine buffers, the lanthanides cause a decrease in height of the dye step, and a second wave appears at a more negative potential. The height of the second wave is proportional to the concentration of lanthanide.