4-[(5-chloro-2-pyridyl)AZO]-1,3-diaminobenzene as a new sensitive and selective reagent for cobalt

Abstract

Cobalt (II) and 4-[(5-chloro-2-pyridyl)azo]-1,3-diaminobenzene (5-Cl-PADAB) in slightly acid, neutral or alkaline medium form a pink-coloured complex. This complex is very stable even in the presence of strong mineral acid. The complex has two absorption maxima at 530 and 570 nm in hydrochloric acid (2.4 M) solution. The colour is very stable and the system conforms to Beer's law; the optimal range for measurements in a 1 -cm cell is 0.02-0.5 p.p.m. cobalt. Common anions and cations do not interfere; only chromium (VI) interferes seriously. The molar absorptivity is 1.13·105 1 mol-1 cm-1 at 570 nm. The sensitivity is 0.00051 μg Co cm-2 at 570 nm for log I0/I= 0.001. © 1971.