Does the supplementation of metal ions modify the intrinsic distribution of element species in food extracts?

Summary

A combination is presented of gel permeation chromatography for the separation of proteins with atomic absorption spectrometry for the detection of protein-bound metals. For the evaluation of the effects resulting from sample spiking with free metal ions, flame AAS in the direct coupling mode was used. Besides sample spiking we also evaluated the effects of adding traces of metals to the eluent. The separation material was TSK HW-55(S), the bed volume was 27 ml. The investigations were carried out on the example of an aqueous soybean flour extract that had been characterized before in view of its intrinsic metal distributions. The supplementation experiments were focused on zinc and nickel, both having essential as well as toxic properties. For both metals a selective enhancement of metal concentrations was observed after sample spiking in distinct fractions due to free binding capacities of certain proteins. It was also possible to detect hydrated (“free”) metal ions. Zinc is bound to the medium molecular weight (MMW) fraction and to the high molecular weight (HMW) fraction, nickel to the HMW fraction only. A depletion of metal ions from the mobile phase was observed in case of the elution of proteins with free binding capacities.