Extractive-photometric determination of cobalt(II) in steels using 4-(2-pyridylazo)resorcinol and xylometazoline hydrochloride

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 mu g of Co/ml with a molar absorptivity 42000 dm(3) 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.