Multi-element Speciation of Tea Infusion Using Cation-exchange Separation and Size-exclusion Chromatography in Combination with Inductively Coupled Plasma Mass Spectrometry

Abstract

The speciation of metals in tea infusion was studied using ICP-MS. Twenty-four elements were studied in tea leaves and tea infusion, and the extraction efficiency of the infusion process was calculated. Cation-exchange separation based on solid-phase extraction cartridges was used for studying the charge of the dissolved species. Size-exclusion chromatography was used to obtain information about the molecular size of the metal–organic complexes. The organic material eluted from the column was detected by UV spectrometry at 227 nm. The results indicate that Mg, Mn and Rb are present in tea infusion as cations, which are probably not associated with organic material. Also, Ca, Fe, Co, Ni, Cu, Zn, Sr and Ba appear to be present mainly in cationic form, but there is in addition a certain non-cationic fraction. For Fe, Ni, Cu and Zn, the non-cationic species may be metal–organic complexes in the size range 4000–6000 Da, whereas Sr, Ba and Pb are associated with even larger molecules. Al is the metal with the most marked non-cationic behaviour in tea infusion; it is associated with molecules in two size ranges, viz ., 4000–6000 and 6500–8500 Da, respectively.