Determination of Trace Amount of Phosphorus in Iron and Steel by Indirect Atomic Absorption Spectrometric Method Combined with Extraction of Phosphomolybdic Acid

Abstract

In order to improve the mechanical properties of steel, the low P-containing iron and steel are produced. Therefore, the determination of P in ppm order is required to know exactly 0.00n%, but the application of the conventional method, e. g., JIS G 1214-1969 is very difficult for the reason of its poor sensitivity. Consequently, an atomic-absorption spectrophotometry was studied to determine P in iron and steel by an indirect amplification procedure.
The present method comprised the process that phosphomolybdic acid, H₃PO₄ (MoO₃) ₁₂, was formed in nitric acid solution and selectively extracted away from other heteropoly acids and molybdate reagent into isobutyl acetate, and then the twelve molybdate ions associated with one phospnate ion were determined by direct atomic absorption spectrophotometry in the isobutyl acetate phase.
The interference with Nb, Ta, Ti, V, W and Zr could be avoided by the addition of hydrofluoric acid and adjustment of the nitric acid concentration above 6N.
The coefficients of variation as the reproducibilities of this method were 13.3%, 3.2%, and 1.7% for 0.05μg P/ml, 0.5μg P/ml and 1.0μg P/ml, respectively. Therefore, it was recognized that the diffreence of 0.001% in phosphorus content less than 0.01% could be judged certainly and phosphorus of ppm order in iron and steel could be exactly determined.