Aluminium in tea: SEC-ICP-MS speciation studies of infusions and simulated gastrointestinal digests

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Abstract
The speciation of aluminium in tea infusions and in vitro gastrointestinal digests of tea infusions has been investigated using size exclusion chromatography coupled to inductively coupled plasma mass spectrometry (SEC-ICP-MS). At pH 2.5, following simulated gastric treatment, Al from tea eluted at a similar retention volume to that obtained for an aqueous Al standard. At pH 5.5, an aqueous Al standard was eluted from an SEC column in Tris buffer (Al recovery ≈ 100%) only in the presence of a complexing agent (NaF), and at a retention volume corresponding to a molecular mass greater than that expected for an ionic species. Aluminium associated with a tea infusion eluted in two fractions: a higher molecular weight fraction corresponding to Al strongly bound to ligands in the tea, and a lower molecular weight fraction probably comprised of labile Al eluting as Al-F complexes. Simulated gastrointestinal digestion produced three Al-bearing fractions, of which the two at higher molecular mass represented ligand-bound Al. The molarity of the Tris buffer strongly influenced the retention volume of the Al fractions, particularly for the ligand-bound Al. After simulated gastrointestinal digestion, the soluble labile fraction (15% of the Al from the tea infusion) was considered to be potentially available for absorption. The actual proportion of the fraction that might be absorbed would depend upon a number of physiological and nutritional factors.