Spectrophotometric determination of microamounts of chromium in pure iron

Abstract

An extraction procedure was introduced in order to eliminate the disturbance of iron in the photometric determination of microamounts of cobalt (010μg) in pure iron using β-nitroso-α-naphthol.One tenth gram of sample is dissolved in aqua regia, and the iron is extracted with methylisobutylketone from hydrochloric acid (10 : 6) solution. The water layer is separated, and heated to white fumes after adding 5 ml of perchloric acid. Twenty ml of water, 2 ml of citric acid solution (50%), and 3 drops of bromthymolblue alcohol solution (0.1%) are added, and ammonia water is added dropwise unitil the color of the solution becomes green. After 5 ml of β-nitroso-α-naphthol solution (0.04%) is added, the solution is shaken with 5.00 ml of a mixture of ethyl acetate and buthyl acetate (1 : 1) for about one minute. After the lower layer is rejected, the organic layer is washed with 5 ml of hydrochloric acid (1 : 10), and 5 ml of sodium hydroxide solution (4%), alternately, until the aqua layer is no longer colored. Cobalt is determined by measuring the absorbance of the organic layer at 430 mμ against a blank solution.Ten micrograms of each element of Al, As, B, Ca, Ce, Mg, Nb, P, Pb, Si, Sn, Ta, Ti, W, and Zn do not interfere.