Mass balance studies of iron without the need of subsampling using large sample neutron activation analysis

Accurate assessments of the iron (Fe) intake from food is mandatory for mass balance studies. The reliability of such assessments is strongly dependent on the representativeness of the analytical test portion and, as such, the quality of the homogenization of the double portions collected. Large sample Instrumental Neutron Activation Analysis (INAA) circumvents these problems as the entire double portions can be analysed without homogenization.
Fe was measured both in approximately 1 kg freeze-dried food as well as in moist products. A (commercially available) porridge fine wheat grain was used as a reference sample (assumed to be homogeneous in the Fe content). The amount of iron in the fine wheat grain was also measured using small sample INAA. The moisture content of the fresh food did not cause any problem during the irradiation such radiolysis and excessive gas formation due to low radiation dose during the irradiation. The results obtained for the moist sample were statistically equivalent to those found for the dried sample ( 73.1± 4, 74± 3 mg/kg respectively, zeta (ζ ) score = 0.18) . The applicability of LS-NAA was further illustrated by measurement of Fe in commercially available microwave meals which was found to be 30±2 mg/kg. Large Sample INAA is a novel and attractive approach for measurement of element content of the dietary intake by the double portion technique collected during 5-7 day in mass balance experiments. Similarly, it can be directly applied without sample preparation for the analysis of faeces collected in such studies.