Spectrophotometric determination of cobalt(II) based on the ion-pair of tetrathiocyanatocobaltate(II) with neotetrazolium chloride

The ion-pair formed between tetrathiocyanatocobaltate(II) and 3,3′-(4,4′- biphenylene)bis(2,5-diphenyl)]-2H-tetrazolium chloride (neotetrazolium chloride) can be extracted into 4-methylpentan-2-one and used for the spectrophotometric determination of cobalt (2.5–9.8 μg ml^?1) at pH 3.5–5.0. The Sandell sensitivity of the method is 0.02 μg Co cm^?2. With suitabte masking, the method is quite selective and is applicable to nickel wire alloys.