Separation of Fe from whole blood matrix for precise isotopic ratio measurements by MC-ICP-MS: a comparison of different approaches

Abstract

Anion-exchange and precipitation procedures for Fe separation from unspiked human whole blood after microwave digestion and ashing decomposition techniques were thoroughly evaluated in terms of Fe recoveries, decreases in matrix element concentrations and elimination of interfering species for subsequent Fe isotope ratio measurements by multi-collector ICP-MS. During isotope ratio measurements involving ⁵⁴Fe, ⁵⁶Fe and ⁵⁷Fe, on-line mass discrimination correction using Ni isotopes was applied, significantly reducing uncertainties both within and between Fe sample runs. Despite Fe recoveries below 100% for all separation procedures studied, no artificial isotope fractionation was detected. The degree of Fe fractionation in a commercially available, whole blood sample (Trace Elements in Whole Blood, Level 1, Sero AS), expressed as ⁵⁶δ (−2.83 ± 0.06‰) and ⁵⁷δ (−4.23 ± 0.08‰) values relative to IRMM-014 Fe isotopic reference material, agrees well with previously published data. Of the tested separation procedures, precipitation using NH₃ was found to be the most rapid and cost-effective method, yielding high Fe recovery and low levels of concomitant elements.