Speciation of Cu, Fe and Mn in beer using ion exchange separation and size-exclusion chromatography in combination with electrothermal atomic absorption spectrometry

Methods were developed for studying the speciation of Cu, Fe and Mn in beer . The charge of the metal species was determined using cation and anion exc hange separation based on solid-phase extraction cartridges, and the molecu lar weight of the metal complexes was studied by size-exclusion chromatogra phy. Electrothermal atomic absorption spectrometry was used off-line for th e quantitative determination of the metals. It was found that the beer cont ained ligands that released Cu and Fe from the separation columns; therefor e, special procedures for cleaning the columns (with EDTA) had to be develo ped. The speciation analysis indicated that Mn was probably present as Mn2 in beer, whereas Fe was found as negatively charged complexes and Cu as bo th negative and positive species. Using globular proteins for calibration o f the size-exclusion column, the complexes were found to be of the order of 4-12 kDa. The ligands responsible for the complexation of Fe and Cu may be compounds such as polymeric phenols or phytic acid. When the beer was spik ed with Cu2+ and Fe3+, the added metal ions were recovered as negatively ch arged species, indicating that the beer contained free metal-complexing lig ands. It was found that the total metal concentrations in beer could be det ermined by direct analysis of 1 + 9 diluted beer; the results agreed with t hose obtained after decomposition of the beer with HNO3-H2O2.