Substoichiometric isotope dilution analysis of iron in biological materials by the 8-quinolinol-extraction

A highly precise and accurate method for the determination of minor amounts of iron by substoichiometric isotope dilution analysis is described. The constant amount of Fe(III) is substoichiometrically extracted with 2·10⁻⁴M oxine in chloroform from the aqueous phase of pH 9.2–10.0 containing 6·10⁻³M tartrate. The interfering ions such as Mn(II), Co(II), Ni(II), Cu(II), and Zn(II), can be removed by the preliminary extraction of Fe(III) from 7.5M hydrochloric acid solutions into isopropyl ether. The present method has been applied to the determination of iron in biological standard reference materials, i.e., the NBS Spinach (SRM-1570) and the NIES Pepperbush (SRM No. 1), and the results obtained are 548±9 ppm (NBS certified value: 550±20 ppm) and 193±4 ppm, respectively.