Analytical Sciences

Solid-Phase Spectrophotometric Determination of Cobalt(II) in Tap Water and Beverages Using 2-(5-Bromo-2-pyridylazo)-5-[N-propyl-N-(3-sulfopropyl)amino]phenol after Preconcentration as the 1-(2-Pyridylazo)-2-naphthol Complex

Chikako SHIMA, Isoshi NUKATUKA and Kunio OHZEKI *

Department of Materials Science and Technology, Faculty of Science and Technology, Hirosaki University, Hirosaki 036, Japan

A sensitive and selective method for the determination of trace amounts of cobalt(II) is described. The method is based on the combined use of 1-(2-pyridylazo)-2-naphthol (PAN) and 2-(5-bromo-2-pyridylazo)-5-[N-propyl-N-(3-sulfo-propyl) amino]phenol (5-Br-PAPS). Cobalt(II) is first extracted on a membrane filter as the cobalt(III)-PAN complex and the complex is decomposed with acid. The cobalt is then extracted on a membrane filter as the cobalt(III)-5-Br-PAPS complex in the presence of dodecylbenzenesulfonate and determined by densitometry. The proposed method has been applied to the determination of cobalt in tap water and beverages. (Keywords: Cobalt, membrane extraction, PAN, 5-Br-PAPS, solid phase spectrophotometry)

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