Extractive-photometric Determination of Cobalt(II) in Steels using 4-(2-Pyridylazo)resorcinol and Xylometazoline Hydrochloride

Department of Chemistry, Ranchi University, Ranchi-834 008

Analytical Chemistry Division, National Metallurgical Laboratory, Jamshedpur-831 007

Manuscript received 8 November 1995, revised 31 December 1996, accepted 12 June 1997

Cobalt(II) forms anionic chelates with 4-(2-pyridylazo)resorcinol (PAR) at pH 7.0-8.0, which can be quantitatively extracted into chloroform as an ion-pair with xylometazolonium cation (XMH). The ion-association system has an absorption maximum at 535 nm and obeys Beers law in the range 0-1.6 µg of Co/ml with a molar absorptivity 42000 dm³ mol^-1 cm^-1. The Job's method of continuous variations indicated a composition of 1 : 2: 2 for cobalt :PAR: XMH for the extracting species. Based on this extraction, a highly sensitive and selective spectrophotometric method for the determination of cobalt in various steels, after prior separation of iron, is described.