The Chemical Form of Nickel in Tea

Abstract

The chemical form of nickel in tea taken as a beverage was investigated in order to evaluate its toxicological and physiological effects.
1) About 89% of the nickel in tea leaves (Sencha) was extracted by boiling water. No nickel was detected in bound or complexed form in extracts from the tea with organic solvents such as n-hexane, benzene, chloroform and ethylacetate.
2) Sephadex G-25 gel filtration of the water-soluble nickel indicated that it forms complexes with ninhydrin- or phenol- sulfuric acid-reactive substances; however, nickel does not bind to proteins or pigments in tea, and is not present as unbound Ni.
3) Thin-layer chromatographic analyses demonstrated the presence of six distinct Ni complexes in the water-soluble nickel fraction obtained by gel filtration. A major constituent was positive to ninhydrin and to phenol-sulfuric acid staining.