In this study, the total as well as the water-soluble and bioaccessible fractions of lithium in wheat, durum and barley flour were evaluated together with the isotope ratio. Lithium was determined by inductively coupled plasma – mass spectrometry (ICP-MS). The total lithium content was determined after an open-vessel digestion in HNO3. The water-soluble fraction was evaluated by extraction with deionized water. The bioaccessibility was determined in vitro under simulated stomach digestion conditions. The total lithium content in wheat ranged from 0.91 ng/g to 7.8 ng/g, in durum flour from 1.7 ng/g to 5.2 ng/g and for barley flour from 2.0 ng/g to 6.0 ng/g. For the water-soluble fraction, the ranges were for wheat flour 0.33 ng/g to 4.8 ng/g, for durum flour 0.83 ng/g to 2.5 ng/g and for barley flour 0.81 ng/g to 3.3 ng/g. The bioaccessible lithium content ranges in wheat flour from 0.38 ng/g to 5.3 ng/g, in durum flour from 0.98 ng/g to 1.9 ng/g and in barley flour from 1.3 ng/g to 3.1 ng/g. The water and bioaccessible fractions of the majority of the barley and durum flour samples had an isotope ratio differing statistically significantly from the natural ratio (p<0.05) which indicates enrichment of the heavier isotope.

Additionally, speciation of protein bound lithium in water and simulated stomach digestion extracts from respective flours were studied. Extracts from the respective flour types were chromatographically separated and fractionated with an ammonium nitrate buffer on a (size-exclusion-chromatography) SEC-column. Thirty fractions were collected, and their lithium contents were determined by ICP-MS. Lithium was mostly eluted in fraction 14, which indicates that most of the available lithium was protein-bound.