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A procedure is recommended for the spectrophotometric determination of niobium in steels using sulphochlorophenol S as a reagent. For the decomposition of the sample a new method has been worked out making use of solid tartaric acid after slow treatment with HC1 and H202. For the extraction of the complex formed several high-molecular amines have been studied, employing a concentration of 5 1 0 ~ o in butanol and a volume relation between aqueous and organic phases of 3:1. Best results were obtained with laurylamine and cetylamine, the latter being however more expensive. For 15 gg of Nb 2 ml of the reagent solution (0.03 ~ ) are required. Maximum permissible concentration of steel is 1 1.2 mg/ml. The standard deviation has been found to be 3 ~ . Beer's law is obeyed up to 15 gg of Nb in the aqueous phase. Mn, Cr, Ni, Co, W, Ti, Si and other foreign ions do not interfere. Opt imum conditions are incorporated in the following working direction.

Extraction-spectrophotometric determination of niobium in steels using sulphochlorophenol S and high-molecular amines