Synthesis of 2-(5-carboxy-triazolylazo)-5-diethylamino benzoic acid and its color reaction with cobalt

The synthesis of reagent 2-(5-carboxy-triazolylazo)-5-diethylamino benzoic acid (abbreviated as CTZDBA) and the conditions of its reaction with Co~(2+) are reported.The structure of the reagent is determined by elemental analysis,UV spectrometry,IR spectrocopy and ~1HNMR spectroscopy.Its dissociation constants are pK_1=3.2,pK_2=10.5.The reagent reacts with Co~(2+) to form a stable red complex(1:3 by mole) in the medium of NH_3·H_2O-NH_4Cl at pH9.0.The maximum absorption wavelength and apparent molar absorptivity are 623nm and 8.11×10~4L·mol~(-1)·cm~(-1).Beer's law is obeyed in the range of 0-0.4mg/L for cobalt.The complex will not be decomposed by acidifying with some strong mineral acids,while complexes formed by other coexisting ions and CTZDBA will be decomposed,thus the selectivity is improved.The method has been applied to the direct determination of cobalt in VB_(12) and waste water with satisfactory results.The recovery of standard addition is 99.6%-101.1% with RSD of 0.5%-3.1%(n=6).