The precipitation of hydrated cobalt 1-nitroso-2-naphtholate from homogeneous solution

Abstract

A method has been developed for determining cobalt by precipitating cobalt III 1-nitroso-2-naphtholate from homogeneous solution. The reagent is synthesised within the reaction mixture by treating 2-naphthol with nitrous acid in the presence of cobalt II ion. Thus nitrous acid serves the dual role as oxidant for the cobalt II ion and also as a reactant in the synthesis of the reagent. Excess reagent precipitates after the cobalt nitroso-naphtholate has settled. A washing procedure has been developed to eliminate the excess reagent without affecting the cobalt nitroso-naphtholate. After washing to remove excess reagent and filtration, the precipitate is dried at 115° and weighed as Co(C 10H 6O 2N) 3·H 2O. The presence offluoride prevents the interference of iron, tungsten and other elements which form strong fluoride complexes. The precision and accuracy is within 0-1 mg of cobalt at a 10-mg level and within 0-2 mg of cobalt at a 50-mg level.