Nagahiro, T. et al. 2010. Column Preconcentration of Cobalt Using 4-(5-Bromo-2-pyridylazo)-1,3-diaminobenzene and Ammonium Tetraphenyl-broate Supported on Naphthalene and Its Analysis Using Atomic Absorption Spectrometry . Asian Journal of Chemistry. 5, 3 (Mar. 2010), 743–748.