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.
