Ionic Liquid-based Extraction of Heteropoly Molybdic Acids for the Sensitive Determination of Si, P, and As in High-purity Iron

Abstract

Traces of Si(IV), P(V), and As(V) in an iron sample solution were converted into heteropoly molybdic acids at 0.5 M acidity. They were extracted into a tiny amount of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([BMIM][NTf₂]), leaving the iron(III) matrix in the solution. The ionic liquid was diluted with methanol and analyzed by high-performance liquid chromatography with spectrophotometric detection at 310 nm. The distinct, well-separated peak was obtained for Si(IV), while the peaks of P(V) and As(V) were not separated from each other. To discriminate between P(V) and As(V), the extracted molybdoarsenic acid was decomposed with tetramethylammonium hydroxide before the HPLC analysis. The proposed method allowed the determination of Si, P, and As at low- to sub-μg g^–1 levels in high-purity iron metals.